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Koji su uslovi životne sredine za preživljavanje larve Haemonchus contortus?

Koji su uslovi životne sredine za preživljavanje larve Haemonchus contortus?


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Ono što se zna o ekološkim granicama za Haemonchus contortus preživjeti izvan organizma domaćina u stadijima larve?

zanima me da znam:

  • nivoi temperaturne tolerancije
  • željeni nivoi vlažnosti
  • pH tolerancija
  • koliko dugo može preživjeti izvan toleriranih raspona?

Najniža temperatura

Čaše od 2, 3, 4 i 5 sedmica koje sadrže jaja i neinfektivne larve u janjećim fekalijama nisu se razvile u infektivne larve (L3) kada su bile izložene fluktuirajućim temperaturama u rasponu od -1 do 15°C:

[… ] nije bilo značajnih razlika u broju sakupljenih larvi u različitim vremenskim tačkama za feces inkubiran na 15°C. Međutim, na 5°C i -1 do 15°C nije došlo do razvoja jaja, iako je utvrđeno da se mali dio razvio u infektivne larve kada se inkubira na 25°C dodatnih tjedan dana. (1)

Najviša temperatura

Temperatura od 40ºC negativno je korelirala sa stopom preživljavanja H. contortus L3. [… ] Smanjena pokretljivost je uočena 10. dana nakon zagrijavanja. [… ] Zagrevanje L3 na višim temperaturama (45ºC i 50ºC) izazvalo je 100% smrtnost već u 48. i 24. satu ekspozicije (2)

Isušivanje

Kada je u pitanju isušivanje, tri su glavne stvari koje treba uzeti u obzir:

  • Bitno je da li su larve u oplođenom ili obloženom stanju
  • mogu preživjeti nekoliko ciklusa isušivanja/rehidracije
  • najbolje je preživjeti ispod temperature smrzavanja

Eksperimenti o preživljavanju nakon isušivanja pokazali su da su, nakon nekoliko sati izlaganja 47% relativne vlažnosti, sve ličinke koje su bile izvučene u ovojnicu uginule, a sve larve preživjele. (3)

Isušivanje je štitilo larve od smrti prilikom skladištenja na temperaturama ispod nule, ali je bilo štetno na temperaturama iznad nule. (4)

Larve preživača su bile u stanju da prežive do 7 ciklusa isušivanja/rehidracije, a tokom anhidrobioze je smanjena metabolička aktivnost i produženo preživljavanje larvi kako u laboratoriji tako i na terenu. (5)

PH

Efekti temperature na preživljavanje i razvoj slobodnoživućih faza H. contortus proučavani su i fekalnim i agar-kulturnim metodama. [… ] sa pH rasponom od 6,5 do 8,5 (6)

Koliko dugo?

Kao i obično, zavisi od trenutnih varijabli životne sredine i trenutnog stanja organizma i tako dalje. Pročitajte gornje odeljke. Članak P. T. Ilieva, A. Ivanova, P. Prelezova ima nekoliko tabela koje vam mogu dati dobru predstavu o ovim vremenima (barem za temperaturu i vlažnost).


(1) Razvoj i prezimljavanje slobodnoživućih larvi Haemonchus contortus u Švedskoj, K. Troell, P. Waller i J. Höglund

(2) Utjecaj temperature i isušivanja na stopu preživljavanja Haemonchus contortus infektivnog stadija larve, P. T. Iliev, A. Ivanov, P. Prelezov

(3) Preživljavanje infektivne larve od isušivanja Haemonchus Contortus, C. ELLENBY

(4) Učinak isušivanja na preživljavanje infektivnog Haemonchus contortus larve u laboratorijskim uslovima, Kenneth S. Todd, Jr., Norman D. Levine i Paul A. Boatman

(5) Anhidrobioza povećava preživljavanje trihostrongilnih nematoda (samo sažetak), S E Lettini, Michael Sukhdeo

(6) Trendovi i perspektive u parazitologiji 2 (stranica 84), B. A. Newton


Koji su uslovi životne sredine za preživljavanje larve Haemonchus contortus? - Biologija

Nekoliko tačaka koje se tiču ​​prikupljanja fekalnih uzoraka zahtijevaju daljnje razmatranje.
1. Fekalne pelete se mogu uzeti iz rektuma ili pokupiti sa zemlje. Odlična prilika za uzimanje uzoraka je rano ujutro dok životinje napuštaju svoje leglo. Svježi uzorci se lako razlikuju od starijih, vremenskih izmeta.
2. Sakupite 8 do 10 toplih, vlažnih, mekih peleta po uzorku i stavite ih u plastičnu vrećicu koja se može zatvoriti (da zaštitite od dehidracije). Uzorke treba držati na hladnom (manje od 50 stepeni F) do analize. Ako analiza odmah ili istog dana nije moguća, uzorci se mogu čuvati u frižideru (ne zamrznuti) do 72 sata.
3. Prikupite najmanje 6 pojedinačnih uzoraka po jedinici za kontrolu parazita prije primjene anthelmintika. Jedinice upravljanja mogu biti pašnjaci, jata, zasebni rančevi, itd. Sakupljanje složenog uzorka, iako bolje nego bez broja fekalnih jaja, daje manje preciznu procjenu opterećenja parazitima.
4. Rano otkrivanje razvoja rezistencije i procjena anthelmintičke efikasnosti uključuje prikupljanje fekalija i analizu 7 do 10 dana nakon tretmana. Ponovo se predlaže najmanje 6 uzoraka.
Uzorci nakon tretmana potvrđuju efikasnost proizvoda.
Rezultate analize treba iskazati u jajima po gramu izmeta. Potreba za liječenjem može biti zasnovana na "pravilima" navedenim u Tabeli 2.

Tabela 2. Pragovi tretmana za unutrašnje parazite kod ovaca i koza

Doba godine Zrele životinje Godišnjaci i mlađi
Proljetno ozelenjavanje - 4. jul 1000 epg* 500 epg
4. jul - Prvi mraz 2000 epg 1000 epg
*epg = jaja po gramu izmeta
Broj jaja jednak ili iznad ovih nivoa opravdava davanje antihelmintika.

Ova osnovna pravila nisu urezana u kamen za svakog proizvođača ovaca i koza u Teksasu. Oni su samo mjerila koja proizvođači koriste u razvoju svog specifičnog IPM programa. Ova pravila se najviše primjenjuju na operacije jagnjenja/jarenja u proljeće. Obrazloženje iza ovih smjernica uključuje:
Tokom proleća i ranog leta, potrebe za hranljivim materijama za ovce i ovce su visoke zbog laktacije, tako da je tolerancija parazita manja nego kasnije u godini kada su potrebe za hranljivim materijama niže. Osim toga, otpornost ovaca ili srnjaka na Haemonchus contortus je oslabljena u vrijeme jarenja i tokom rane laktacije.
Mnogi potomci se odbiju i prodaju do sredine ljeta. Oni koji su ostali u jatu povećali su se u veličini i starosti tako da mogu tolerirati veći teret parazita.
Kao dodatak upravljanju životinjama, drugi cilj ovih smjernica je da se minimizira kontaminacija pašnjaka (taktički tretman) tokom ranog dijela sezone parazita. Donji pragovi od 500 i 1.000 pomažu da se smanji takva kontaminacija pašnjaka.
Što se tiče upravljanja parazitima, nema ničeg značajnog u vezi sa 4. julom osim što je to datum usred ljeta koji se lako pamti.

Sažetak
Razvoj efikasnog plana upravljanja za Haemonchus contortus uključuje tačan odgovor na tri jednostavna pitanja:

Pitanje: Kada liječim?
Odgovor: Apsolutno implementirajte strateški tretman usred zime. Ostale tretmane treba uskladiti sa upravljanjem pašnjacima i opravdati brojem fekalnih jaja.

Pitanje: Koju životinju liječim?
Odgovor: Ako broj fekalnih jajašca ili vizualno promatranje ukazuju na značajno opterećenje parazitima kod nekih životinja, sve životinje u toj upravljačkoj grupi trebale bi biti tretirane. Neliječenje životinja nastavlja proces kontaminacije pašnjaka, reinfestira tretirane životinje i doprinosi razvoju otpornosti.

Pitanje: Šta koristim?
Odgovor: Efikasan proizvod. Rotaciju između proizvoda treba vršiti po grupama, a ne unutar grupe proizvoda (posebno benzimidazola). Strateški tretmani sredinom zime moraju uključivati ​​proizvod označen za inhibirane larve. Broj fekalnih jaja je jedini praktični alat za upravljanje za procjenu efikasnosti proizvoda.

Obrazovni programi Texas Agricultural Extension Service otvoreni su za sve ljude bez obzira na rasu, boju kože, spol, invaliditet, religiju, godine ili nacionalno porijeklo.

Izdat u cilju unapređenja zadruge u poljoprivredi i kućnoj ekonomiji, akti Kongresa od 8. maja 1914., sa izmjenama i dopunama, i 30. juna 1914., u saradnji sa Ministarstvom poljoprivrede Sjedinjenih Država. Edward A. Hiler, privremeni direktor, Texas Agricultural Extension Service, The Texas A&M University System.

Ovdje date informacije su samo u obrazovne svrhe. Pozivanje na komercijalne proizvode ili trgovačke nazive je napravljeno uz razumijevanje da nikakva diskriminacija nije namjerna i da se ne podrazumijeva nikakva podrška od strane Kooperativne savjetodavne službe.

Autori
Frank Craddock, profesor i specijalista za ovce i koze, San Angelo
Rick Machen, docent i specijalista za stočarstvo, Uvalde
Tom Craig, profesor, Odsjek za veterinarsku patobiologiju, College Station
Tom Fuchs, profesor i stručni entomolog, San Angelo
Teksaški A&M univerzitetski sistem.
Originalna .pdf verzija proizvedena od strane Agricultural Communications, The Texas A&M University System


Abstract

Ovdje smo otkrili endogenu dafahronsku kiselinu (DA) u socioekonomski važnoj parazitskoj nematodi Haemonchus contortus. Pokazali smo da DA potiče uklanjanje i razvoj larve u ovoj nematodi preko relativno očuvanog nuklearnog hormonskog receptora (DAF-12). Ovaj stimulativni učinak ovisi o dozi i vremenu, a odnosi se na modulaciju signalizacije nalik daueru i metabolizma glicerolipida i glicerofosfolipida, vjerojatno putem negativne povratne sprege. Pokazalo se da specifična hemijska inhibicija DAF-9 (citokrom P450) značajno smanjuje količinu endogenog DA u H. contortus kompromitiraju i izlučivanje larve i razvoj in vitro i moduliraju metabolizam lipida. Uzeti zajedno, ovi dokazi pokazuju da DA igra ključnu funkcionalnu ulogu u razvojnoj tranziciji sa slobodnog života na parazitsku fazu H. contortus modulacijom signalnog puta sličnog daueru i metabolizma lipida. Razumijevanje zamršenosti sistema DAF-12 i povezanih mreža u H. contortus i srodne parazitske nematode mogle bi utrti put novim tretmanima specifičnim za nematode.


Metode

Identifikacija C. elegans homolozi gena u H. contortus

Spisak svih gena (n = 102) i genskih proizvoda (n = 182) koji predstavlja cGMP, TGF-β i IGF-1 signalne puteve, kao i put steroidnih hormona u C. elegans ustanovljen je na osnovu objavljenih informacija [16, 39, 45] (Dodatni fajl 1: Tabela S1). Sekvencije gena i proteina, njihovi pristupni brojevi i transkriptomski podaci su dobijeni od WormBase (v.WS261). Homolozi ovih gena su identificirani pretraživanjem (tblastn e-vrijednost: ≤ 10 𢄥 ) C. elegans proteinske sekvence u odnosu na predviđanja gena iz najnovijeg objavljenog genoma i transkriptoma H. contortus [28�]. The C. elegans proteinske sekvence su takođe pretražene u odnosu na H. contortus genom koristeći BLAT v.34 [46] za identifikaciju homologa. Identifikovane sekvence gena su upoređene (blastx e-vrijednost: ≤ 10 𢄥 ) sa C. elegans proteina (PRJNA13758.WS261) kako bi se provjerio njihov identitet.

Kuriranje gena i strukturno modeliranje

Geni i transkripti su kurirani koristeći nedavno uspostavljenu metodu [47]. Ukratko, sekvence za koje se pretpostavlja da predstavljaju homologe mapirane su u skup genoma H. contortus pomoću programa BLAT v.34 mapiranje je prikazano pomoću Integrated Genome Viewer v.2.4.4 (IGV). Preslikani transkripti su ponovo sastavljeni pomoću programa CAP3 [48] za moguća proširenja. Ponovo sastavljene sekvence transkripta mapirane su u sklop genoma H. contortus [29], a odgovarajuće kodirajuće sekvence DNK (CDS) u genomu su rafinirane korištenjem 𠇌oding2genome” modela u programu Exonerate v.2.2.0 [49]. Sekvence odabranih gena su unakrsno provjerene sa sekvencama komplementarnih DNK (cDNK) za Hc-daf-16, Hc-daf-2 i Hc-pdk-1 [41, 43, 44]. Nakon toga, otvoreni okviri čitanja (ORF) su predviđeni pomoću programa ORF finder [50], a strukturni i funkcionalni domeni identificirani pomoću InterProScan v.61.0 [51, 52]. Poređenja u paru pretpostavljenih aminokiselinskih sekvenci vršena su pomoću programa MAFFT v.7.309 [53].

Strukturno modeliranje je provedeno za nuklearni hormonski receptor (DAF-12) korištenjem programa I-TASSER [54], nakon usklađivanja podataka o sekvenci aminokiselina u MAFFT v.7.309. Poravnanje je pregledano u MView v.1.62 [55]. Modeli su prikazani i upoređeni s dostupnim kristalnim strukturama [56] pomoću UCSF Chimera v.1.12 [57], a strukturne sličnosti između sekvenci upita i šablona mjerene su korištenjem TM-skora i srednjeg kvadratnog odstupanja (RMSD) [54]. Biološke funkcije (Gene Ontology, GO) modeliranog proteinskog domena su zaključene na osnovu strukturne sličnosti.

Analiza transkripcije

Čitanja RNA-seq (upareni kraj) iz pojedinačnih razvojnih faza/polova nematode su mapirana u individualne kurirane CDS u genomu koristeći Bowtie v.2.1.0 u okviru softverskog paketa RSEM v.1.2.11 [58, 59]. Najmanje 10 čitanja je potrebno za mapiranje na CDS da bi se transkripcija snimila. Nivoi transkripcije glasničkih RNK ​​(mRNA) zabilježeni su u fragmentima po kilobazi na milion mapiranih čitanja (FPKM). Za pojedinačne gene pojedinih razvojnih faza H. contortus, nivoi transkripcije su prikazani u toplotnoj mapi koristeći toplotnu mapu.2 u okruženju R-jezika (v.3.5.1).

Analize proteina

Proteomska analiza H. contortus provedeno je prema utvrđenom protokolu [31]. Ukratko, sekvence proteina predviđene iz pojedinačnih homolognih gena korištene su za pretraživanje podataka masene spektrometrije (MS) koji predstavljaju jaje, L3, L4 (žensko i muško) i odraslo (žensko i muško) stadijume H. contortus koristeći softver Proteome Discoverer v.2.0 (Thermo Fisher Scientific, San Jose, CA, SAD). Peptidi su identificirani korištenjem granične vrijednosti stope lažnog otkrića (FDR) od < 1% na nivoima peptida i proteina. Intenzitet peptida je izračunat korišćenjem Spectronaut softvera v.11 (Biognosys). Najmanje dva peptida potrebna su da odgovaraju odgovarajućoj sekvenci proteina za snimanje ekspresije. Intenzitet peptida je korišten da se zaključi nivo ekspresije pojedinačnih homologa proteina u različitim razvojnim fazama H. contortus. Fosfoproteomska analiza stadija jajeta, L3, L4 (žensko i muško) i odrasle (žensko i muško) H. contortus je proveden korištenjem utvrđenog TiO2 protokol obogaćivanja [60, 61]. Proteinske sekvence kodirane homolozima dauer signalnih gena korištene su za ispitivanje fosfoproteomskih podataka korištenjem softvera Proteome Discoverer. Fosfopeptidi su identifikovani korišćenjem FDR granične vrednosti od < 1% na nivoima peptida i proteina. Fosforilirani proteini su mapirani u dauer signalne puteve u H. contortus.


Patofiziologija, ekologija i epidemiologija infekcije Haemonchus contortus u malih preživača

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Haemonchus contortus i hemonchosis – prošlost, sadašnjost i budući trendovi. ed. / Robin Gasser Georg von Samson-Himmelstjerna. Academic Press, 2016. str. 95-143 (Napredak u parsitologiji, svezak 93).

Rezultat istraživanja: Poglavlje u knjizi/izvještaju/konferenciji › Poglavlje (recenzirano) › recenzija

T1 - Patofiziologija, ekologija i epidemiologija infekcije Haemonchus contortus u malih preživača

N2 - Parazitska nematoda Haemonchus contortus se često javlja kod malih preživara, a posebno je značajna prijetnja zdravlju i proizvodnji ovaca i koza u tropskim i toplim umjerenim zonama. Glavni znaci bolesti (hemonhoze) odnose se na njenu aktivnost hranjenja krvlju, što dovodi do anemije, slabosti i često smrti, osim ako se ne pruži liječenje. Zbog visokog biotičkog potencijala, veliki teret H. contortus može se brzo razviti kada uslovi okoline pogoduju fazama slobodnog života, a smrtni slučajevi mogu nastupiti uz malo prethodnog upozorenja. Kroničniji oblici hemonhoze, koji rezultiraju smanjenom proizvodnjom životinja i na kraju uginućem, javljaju se s manjim perzistentnim infekcijama, posebno u situacijama dugotrajne, loše ishrane. Globalna distribucija glavnih endemskih zona hemonhoze je u skladu s kritičnim zahtjevima stadija jajeta i larve H. contortus za vlagom i umjerenim do relativno toplim temperaturama, ali sezonska sklonost hipobiozi (inhibicija larvi četvrtog stupnja unutar domaćin) u velikoj mjeri objašnjava uobičajene, iako sporadične, pojave hemonhoze u sušnim i hladnijim sredinama. Široka klimatska distribucija također može odražavati prilagođavanje lokalnih izolata na nepovoljnije ekološke uvjete, dok se očigledno povećanje prevalencije epidemija u sredinama koje se ranije nisu smatrale endemskim za hemonhozu – posebno hladnim, umjerenim zonama – može pripisati klimatskim promjenama. Iako rizik od hemonhoze značajno varira na lokalnom nivou, čak i tamo gdje je H. contortus endemska, širok spektar ekoloških istraživanja pruža čvrstu osnovu za predviđanje relativnog geografskog i sezonskog rizika u odnosu na klimatske uslove.

AB - Parazitska nematoda Haemonchus contortus se često javlja kod malih preživara, a posebno je značajna prijetnja zdravlju i proizvodnji ovaca i koza u tropskim i toplim umjerenim zonama. Glavni znaci bolesti (hemonhoze) odnose se na njenu aktivnost hranjenja krvlju, što dovodi do anemije, slabosti i često smrti, osim ako se ne pruži liječenje. Zbog visokog biotičkog potencijala, veliki teret H. contortus može se brzo razviti kada uslovi okoline pogoduju fazama slobodnog života, a smrtni slučajevi mogu nastupiti uz malo prethodnog upozorenja. Kroničniji oblici hemonhoze, koji rezultiraju smanjenom proizvodnjom životinja i na kraju uginućem, javljaju se kod manjih perzistentnih infekcija, posebno u situacijama dugotrajne, loše ishrane. Globalna distribucija glavnih endemskih zona hemonhoze je u skladu s kritičnim zahtjevima stadija jajeta i larve H. contortus za vlagom i umjerenim do relativno toplim temperaturama, ali sezonska sklonost hipobiozi (inhibicija larvi četvrtog stupnja unutar domaćin) u velikoj mjeri objašnjava česte, iako sporadične, pojave hemonhoze u sušnim i hladnijim sredinama. Široka klimatska distribucija također može odražavati prilagođavanje lokalnih izolata na nepovoljnije ekološke uvjete, dok se očigledno povećanje prevalencije epidemija u sredinama koje se ranije nisu smatrale endemskim za hemonhozu – posebno hladnim, umjerenim zonama – može pripisati klimatskim promjenama. Iako rizik od hemonhoze značajno varira na lokalnom nivou, čak i tamo gdje je H. contortus endemska, širok spektar ekoloških istraživanja pruža čvrstu osnovu za predviđanje relativnog geografskog i sezonskog rizika u odnosu na klimatske uslove.

T3 - Napredak u parzitologiji

BT - Haemonchus contortus i hemonhoza – prošlost, sadašnjost i budući trendovi


Životni ciklus

H. contortus prolazi kroz šest životnih faza koje uključuju jaje, četiri stadija larve i odraslu osobu (El-Ashram i Suo 2017) (slika 2). Tipično za svoju porodicu, ženka parazita polaže brojna jaja sa prosjekom (±SE) od 1295,9 ± 280,4 po danu koja prolaze kroz fekalije na pašnjake (Saccareau et al. 2017). Jaja mogu umrijeti ili se razviti do slobodnog života larve 1. faze (L1), 2. faza (L2), i infektivni stadijum (L3) u roku od 1–7 (Schwarz et al. 2013) dana. Izlegljivost jaja i razvoj infektivnih larvi zavise od dostupnosti pogodnih uslova okoline (opseg temperature od 15-37 °C i relativna vlažnost od 85-100%) u fekalnim peletima i bilju (O'Connor et al. 2006). Faza L3 domaćin ga proguta gdje se podvrgava ovojnici u buragu i potrebno mu je 2-3 sedmice da se razvije u parazitski stadij L4. Nakon dva mitarenja i neposredno prije posljednjeg mitarenja, nezrela odrasla osoba L5 izbija u kojoj se razvija lanceta koja prodire u mukozne žile radi sisanja krvi. Sibuh je predilektivno mjesto gdje se odrasli crvi slobodno kreću. Parazit takođe može proći kroz zaustavljenu neaktivnu fazu razvoja kod životinje domaćina tokom zime koja se naziva hipobioza (Zajac i Garza 2020).

Efekat životnog ciklusa H. contortus. Jaja se izlegu do L1 u izmetu, L1 mitari na L2 u izmetu, a jaja prelaze u izmet


Koji su uslovi životne sredine za preživljavanje larve Haemonchus contortus? - Biologija

Uzgoj malih preživača je tradicionalna aktivnost koju uglavnom praktikuje lokalno stanovništvo u zemljama u razvoju već nekoliko stoljeća. U današnje vrijeme, zbog brojnih biotičkih i klimatskih faktora, suočava se s raznim problemima koji oštećuju prihod malih posjednika, posebno onih koji se odnose na gastrointestinalne parazite. Za razliku od upotrebe kemijskih lijekova u suzbijanju ovih parazita, ispitivane su ljekovite biljke s manje nuspojava kako na kvalitet mesa tako i na okoliš. Ova trenutna studija imala je za cilj recenziju Haemonchus contortus rasprostranjenosti kod malih preživara širom svijeta i prisutnih ljekovitih biljaka koje se istražuju posljednjih decenija. H. contortus je identificiran kao najznačajniji parazit nematode kod malih preživača zbog njegove visoke prevalencije o kojoj su govorile mnoge studije. Njegovo prisustvo kod malih preživara dovodi do gubitka apsorpcije hrane i poremećaja metabolizma hranljivih materija, što dovodi do lošeg učinka i značajnog ekonomskog gubitka u stadu, posebno u ruralnim područjima zemalja u razvoju. Poslednjih decenija, njegova kontrola se uglavnom zasnivala na upotrebi hemijskih antihelmintika čija je upotreba bila ograničena zbog nekoliko faktora poput neracionalne i zloupotrebe. U posljednje vrijeme, primjena ljekovitog bilja identificirana je kao alternativna metoda njenog suzbijanja sa uvjerljivim rezultatima. Prijavljeno je da su dijelovi biljaka ili cijele biljke nekoliko biljnih vrsta relevantni za kontrolu H. contortus infekcija malih preživača kao što su: Bridelia ferruginea, Mitragyna inermis, Combretum glutinosum, Hagenia abyssinica, Chenopodium ambrosioides, Leucaena leucocephala, Phytolacca icosandra, Eucalyptus staigeriana, Carica papaya, Newbuldia laevis i Zanthoxylum zanthoxyloïdes.

Ključne riječi: Ekonomski gubici, gastrointestinalne nematode, hemijski antihelmintici, lekovito bilje, loš učinak.

Skraćenica: BW, Tjelesna težina FSA, Fakultet agronomskih nauka GIN, gastrointestinalne nematode/GIN: gastrointestinalne nematode LESA, Laboratorija za etnofarmakologiju i zdravlje životinja MP, metabolički protein UAC, Univerzitet Abomey-Calavi WAAPP, Projekat poljoprivredne produktivnosti zapadne Afrike.

UVOD

Mali preživari su neophodni u prirodnoj poljoprivredi zbog svoje izuzetne prilagodljivosti u teškim uslovima životne sredine. Oni obezbeđuju sirovine za agroindustriju, a njihov stajnjak se koristi kao izvor biogasa (Adua i Hassan, 2016) i đubrivo za promociju biljne proizvodnje. Osim toga, oni obavljaju ključne sociokulturne funkcije koje se teško mogu izmjeriti u novčanom smislu, na primjer, njihova upotreba za rituale i žrtve, za vrijeme ili za vrijeme svečanosti, te kao osiguranje od loše žetve (Hassan et al., 2013), a također se koriste za podučavanje i istraživanja. Uprkos svim ovim prednostima, sektoru se posvećuje malo pažnje i suočava se sa raznim izazovima, uglavnom problemima sa hranom i zdravstvenim problemima, posebno onima koji se odnose na gastrointestinalne nematode koje su veoma štetne za stoku (Hounzangbe-Adote et al., 2005.). Haemonchus contortus infekcije se obično identificiraju kao najznačajnije (Emery et al., 2016. Jamalm et al., 2016.) sa značajnim stopama rasta i smanjenja prinosa mlijeka kod sitnih preživača u tropskim sredinama što ih dovodi do gubitaka u proizvodnji u krdima, posebno malim hranjenim travom. preživače (Andrea et al., 2011). Nekoliko studija provedenih na sitnim preživarama otkrilo je postojanje poliparazitizma sa jakim i prevalencija probavnih strongila, posebno H. contortus (Salifou, 1996 Attindehou i sur., 2012 Adua i Hassan, 2016). Kao direktna posljedica, smanjuje se i prinos leševa ovih životinja i prihod malih farmera. U nekim područjima, posebno u tropima i suptropima gdje su uvjeti okoline idealni za razvoj i prijenos parazita nematoda, česta upotreba sintetičkih anthelmintika bila je uspješna u rješavanju problema nematoda (Knox et al., 2006 Torres-Acosta i Hoste, 2008). Paralelno sa sve većom i ne uvijek razumnom upotrebom ovih kemikalija, paraziti postaju sve otporniji na anthelmintike. Osim toga, visoka cijena, ograničena dostupnost ovih hemikalija i ostataka lijekova u finalnim proizvodima i okoliš nakon njihove upotrebe su drugi faktori koji obeshrabruju mnoge farmere da ih koriste u nekim zemljama u razvoju (Knox et al., 2006).

Suočeni sa svim ovim izazovima, postaje neophodno razviti nove metode za kontrolu parazitizma. Zaista, poboljšanje ishrane životinja putem dodataka hrani i upotreba lekovitog bilja identifikovani su kao alternative prilagođene finansijskim sredstvima i socio-kulturnom okruženju stanovništva (Wabo et al., 2012). Nedavna istraživanja su otkrila anthelmintičko djelovanje nekoliko ljekovitih biljaka u suzbijanju parazita gastrointestinalnih nematoda, posebno H. contortus kod malih preživača što se može uzeti u obzir pri izradi programa kontrole parazita. Stoga, ova trenutna studija ima za cilj da predstavi pregled rasprostranjenosti i efekata H. contortus o proizvodnji malih preživača (rast i proizvodnja mlijeka), zatim da sumiramo studije provedene na nekim ljekovitim biljkama s anthelmintičkim svojstvima testiranim na H. contortus.

MORFOLOGIJA I BIOLOŠKE KARAKTERISTIKE H. CONTORTUS

Također se naziva i Barber&rsquos pole crv (Brightling, 2006.), Haemonchus je rod gastrointestinalnog parazita koji pripada klasi Nematodae, porodici Trichostrongylidae i podfamiliji Haemonchinae. Rod broji tri vrste kao što su: H. contortus, Haemonchus placei i Haemonchus longistipes. Prijavljeno je da H. contortus (Slika 1) pogađa koze, ovce i goveda (Sutherland i Scott, 2010.), H. placei pogađa uglavnom goveda (Taylor et al., 2007. Sutherland i Scott, 2010.) i H. longistipes pogađa dromedara (Urquhart et al., 1996). H. contortus je glavna vrsta jaka koja se nalazi kod malih preživača u tropskim područjima Afrike, Centralne Amerike, jugoistočne Azije i suptropskih područja u Australiji i Južnoj Americi (Alowanou, 2016). Odrasli mužjak H. contortus je dužine oko 15 do 30 mm niži od ženke. Mužjak H. contortus karakterizira njegova kopulaciona bursa formirana od dva velika bočna režnja i malog asimetrično postavljenog dorzalnog režnja (Morales i Pino, 1987). Ženke parazita imaju crvenkastu probavnu cijev koja sadrži progutanu krv, spiralno okruženu s dvije bijele genitalne vrpce (Getachew et al., 2007). H. contortus je hematofag jaka lociran u sibuhu malih preživara. Ova karakteristika dovodi do veće patogenosti u odnosu na druge gastrointestinalne nematode (Penicaud, 2007). Zapravo, kao parazit koji siše krv, apsorbira krv iz finih kapilarnih žila probavne sluznice životinja, što može uzrokovati manje ili više teške anemije. Osim toga, ženka je izuzetno aktivna u pogledu mrijesta s izlučivanjem od oko 5000 do 7000 jaja/dan (Coyne i Smith, 1992).

H. contortus je izuzetno plodan parazit koji posjeduje različite strategije izbjegavanja nepovoljnih uslova okoline i imunoloških reakcija domaćina. Zbog svoje jedinstvene sposobnosti da tokom svog života proizvodi veliki broj jaja, H. contortus ima važnu prednost u odnosu na druge parazite. Pri tome lako može kontaminirati pašnjake i opstati u svojim domaćinima čestim i brzim ponovnim infekcijama. Osim toga, jer stepen infektivnosti značajno varira u zavisnosti od H. contortus izolati, studije su zaključile da je važno uzeti u obzir genetičku raznolikost parazita u različitim agroekološkim zonama (Aumont et al., 2003) u svim mjerama prevencije i kontrole. Ovi gore navedeni faktori opravdavaju njegovu visoku patogenost što je uslov za liječenje i kontrolu ovog parazita kod malih preživara (Can, 2015) (Slika 1).

ŽIVOTNI CIKLUS H. CONTORTUSA

Životni ciklus parazita, kao i svakog živog bića, opisuje cijeli razvojni proces njegovog života koji slijedi određeni obrazac označen pod pojmom životni ciklus. Što se tiče H. contortus, životni ciklus se smatra direktnim životnim ciklusom koji se sastoji od dvije faze: parazitske faze koja se odvija u domaćinu i faze slobodnog života koja se odvija u vanjskom okruženju (Walken-Brown et al., 2008 Solaiman, 2010) (Slika 2). Prema Ballweberu (2004.), H. contortus razvoj života generalno može potrajati 2 do 4 sedmice da se završi nakon infekcije. Walken-Brown et al. (2008) opisano H. contortus životni ciklus u sedam faza: stadij jaja, četiri stadijuma larve (L1, L2, L3 i L4) i dva odrasla stadijuma, iako se seksualno nezrele odrasle faze ponekad nazivaju L5. U procesu razvoja, odrasla ženka se pari sa mužjakom i polaže plodna jaja u probavni trakt domaćina. Kroz defekaciju, ta jaja domaćin slobodno ispušta u okolinu. Uz povoljne uslove okoline, jaja se izlegu do slobodnog života L1 (Bush et al., 2001 Brightling, 2006), koja se na svoju stranu mitare do faze L2. Ličinke i L1 i L2 stadijuma hrane se bakterijama u fecesu domaćina (Walken-Brown et al., 2008). Zatim se L2 stadijum djelomično mijenja u L3 stadijum, koji zbog svoje ovojnice nije u stanju da se hrani bakterijama (Bush et al., 2001). Dakle, količina energije koja je ostala nakon L2 faze određuje opstanak L3 larvi (Brightling, 2006). Unošenje L3 od strane domaćina je tada neophodno za završetak njihovog životnog ciklusa. Tako larve L3 napuštaju fekalije, migriraju po listovima trave na pašnjaku i ostaju suspendovane tokom jutarnje rose (Brightling, 2006). Nakon što je domaćin proguta, larve L3 se zatim pretvaraju u L4 koji zatim ulazi u sluz sibuha domaćina kako bi napredovao u L5 koji kasnije postaje spolno zrel u gastrointestinalnom traktu domaćina (Walken-Brown et al., 2008.). Kada odrasli od H. contortus dostigne zrelost, pare se i počinju da polažu jaja izazivajući novi ciklus.

FAKTORI KOJI UTIČU NA RAZVOJ H. CONTORTUS-a

Mnoga prijašnja istraživanja objavila su vanjske faktore koji utiču na obrasce H. contortus razvoj. Zaista, temperatura, padavine, vlažnost i vegetacijski pokrivač su faktori životne sredine koji utiču na razvoj gastrointestinalnih nematoda (GIN) (Selemon, 2018). El-Ašram i dr. (2017), rano, otkrio je direktnu korelaciju između ozbiljnosti problema sa gastrointestinalnim nematodama i padavina tokom vlažnih perioda godine u kojima se uzgaja stoka u zemljama u razvoju. Nadalje, Attindehou et al. (2012) je takođe izvestio, u Republici Benin, značajnu povezanost stope hemonhoze sa sezonom, minimalnu i maksimalnu stopu infekcije, odnosno 36,06% u januaru (sušni mesec) i 79,41% u julu (veoma vlažan mesec). Definitivno će ovaj sezonski trend prevalencije ovih parazitskih infekcija pomoći u pripremi odgovarajućih strategija kontrole, koje će biti korisne za uzgoj koza i industriju (Singh et al., 2015). Beside these environmental factors, many other factors have also been reported to influence parasitic infections in small ruminants: the nutrition (Bricarello et al., 2005 Knox et al., 2006), the management practices such as overcrowding, poor management and hygiene (Olanike et al., 2015), the differential management practices (Mandonnet et al., 2003), the drug treatments (Barnes et al., 2001), the genetic factors that provide natural resistance to the host like the breed of host (Chaudary et al., 2007 Saddiqi et al., 2011 Solomon-Wisdom and Matur, 2014 Singh et al., 2015), the age of the host (Solomon-Wisdom et al., 2014 Singh et al., 2015) and the sex of the host (Attindehou et al., 2012 Olanike et al., 2015 Poddar et al., 2017). Contrary to all the above factors, Attindehou et al. (2012) reported no significant difference in relation to animal&rsquos age, origin, sex or species, even if animals less than a year old and especially goats were mostly infected. Finally, both the body weight and reproductive status of the host, according to Tasawar et al. (2010), influence the parasitic infection development due to the development of acquired immunity with gradual increase in weight along with age of the animals.

PREVALENCE OF H. CONTORTUS IN SMALL RUMINANTS

H. contortus is a serious nematode in small ruminants and has been found as a dominant parasite of goat and sheep among the nematodes (Jamalm et al., 2016). Several parasitological surveys carried out in many regions of Africa have shown convincing results regarding the prevalence of gastrointestinal nematodes in small ruminants&rsquo herds. Indeed, in Benin Republic, 55.56% of the examined animals were infested by H. contortus and the monthly trend of infections showed that in all areas, haemonchosis is endemic with no significant differences in terms of origins or species (Attindehou et al., 2012). According to the same study, the minimum and maximum recorded H. contortus infection rate was respectively of 16.9% in January (a dry month) and 88.7% in July (a very wet month). In Nasarawa State (Nigeria), Adua and Hassan (2016) reported an overall nematodes infection rate of 32.40 and 17.01% in Red Sokoto goats and West African Dwarf goats respectively. According to the same study, the prevalence rate of nematodes infection was 22.45 and 17.82% in Red Sokoto goats while West African Dwarf goats had 14.58 and 8.33% in young and adults respectively. In addition, in the same country, Olanike et al. (2015) reported in Ibadan, 75.85% small ruminants positive for gastrointestinal parasites with the higher prevalence of 54.25% in Red Sokoto breed and the lower prevalence of 21.5% in West African Dwarf breed. According to the results of the same study, 22.75 and 10.5% Red Sokoto and West African Dwarf breeds respectively had mixed helminths (Strongyle spp, Strongyloides spp i Coccidia spp) and protozoa infections (Olanike et al., 2015). In the Plateau region of Togo, Bonfoh et al. (1995) reported a H. contortus prevalence up to 82%. Later, in peri-urban area of Sokodé, in Togo, approximatively the same prevalence rate of gastrointestinal nematodes in small ruminants was recorded (88% represented by Haemonchus sp. i Trichostrongylus sp.) with a negative effect of the season. In a similar way, in urban and peri-urban areas in Maroua, Far North of Cameroon, Ngambia Funkeu et al. (2000) have reported the presence of five species of parasitic nematodes: Haemonchus, Trichostrongylus, Cooperia, Oesophagostomum i Strongyloides papillosus with a predominance of Trichostrongylus i Haemonchus respectively in dry and rainy season. This same study revealed a prevalence of 27 to 31% for these two species depending on the age of the sheep without any significant influence of sex. An epidemiological investigation of small ruminants parasites in the southern forest zone of Ivory Coast carried out by Oka et al. (1999) has revealed a parasite fauna which consisted of nine species of nematodes with a predominance of Trichostrongylus colubriformis (89.7%) and H. contortus (84.1%) in terms of prevalence. Furthermore, in Eastern Ethiopia, Sissay et al. (2007), reported a prevalence of 60% in small ruminants. This is below the results of Mengist et al. (2014) who recorded an overall prevalence of H. contortus of 71.03% with prevalence in sheep and goat up to 67.57 and 71.39% respectively in and around Finoteselam, Ethiopia. According to the same study, the prevalence of haemonchosis was higher in males (73.22%) and adult animals (71.43%). The high rate of prevalence of infection among the goats could be attributed to poor management practices and lack of veterinary services in the area (Osakwe and Anyigor, 2007). A prevalence assessment of H. contortus infections in Goats in Nyagatare District (Rwanda) showed that 75.7% of the small ruminants had H. contortus eggs in faeces with a prevalence rate of 71.8% in goats (Mushonga et al., 2018). Moreover, a 12 months period of survey in the local abattoir of Nyala town, South Darfur State, Sudan revealed 85% of slaughtered goats harbored both adults and immature worms of H. contortus (Abakar, 2002) while an overall prevalence of H. contortus eggs of 12.1% with a 95% CI ranging from 7.97 to 16.23% has been reported in Khartoum State (Sudan) by Boukhari et al. (2016).

Other recent studies conducted on goats in the rest of the world, particularly in Madhya Pradesh (India) concluded that H. contortus was the most predominant parasite followed by Trichostrongylus sp., Oesophagostomum sp., Strongyloides sp. and Bunostomum sp. Of the 960 faecal samples of goats examined, 94.48% were found positive for one or more gastrointestinal parasitism viz., coccidian (82.4%), strongyle (69.27%), amphistomes (22.71%), Strongyloides (9.17%), Trichuris (3.85%), Moniezia (3.02%), Schistosoma (2.29%) and Fasciola sp. 1.77% (Singh et al., 2015). Furthermore, various others studies had earlier reported the high prevalence rates of gastro-intestinal parasites in goats, especially H. contortus, from Indonesia (89.4%) (Widiarso et al., 2018) and different parts of India like 88.23% prevalence of helminthes in Nagpur (Maske et al., 1990), 90.05% from Jabalpur (Lalbiaknungi, 2002), 96% in Tarai region of Uttarakhand (Pant et al., 2009). In Markhor of Chitral Gol National Park, a prevalence rate of 40% of H. contortus has been recorded by Jamalm et al. (2016) against 56-61% prevalence that has been recorded for the parasite in goat in previous studies especially in the Potohar area of Pakistan (Chaudary et al., 2007) and 77.7% Jehangirabad District Khanewal, Punjab, Pakistan recorded by Tasawar et al. (2010). Furthermore, Adhikari et al. (2017) reported a polyparasitism with the higher prevalence for H. contortus of 13.89% in goats of Western Chitwan of Nepal. According to the same study, H. contortus was more prevalent in non-dewormed (40.32%) than in dewormed (5.26%). Finally and in agreement with the previous reports, H. contortus has been reported, in the region of Valle de Lerma (northwestern Argentina), by Suarez et al. (2013) to be the most prevalent nematode species.

EFFECTS OF H. CONTORTUS INFECTIONS ON SMALL RUMINANTS’ PRODUCTION

Information on the effects of H. contortus infections on small ruminant production mostly concern milk production (both the yield and quality). And even in this context, compared to dairy cows, effects of H. contortus infections on dairy goats and sheep are not well documented. However, several decades ago, while comparing milk yield in ewes orally infected with 2500 H. contortus larvae weekly during pregnancy and lactation, Thomas and Ali (1983) reported a striking weight loss and reduction of sheep milk yield by 23%. This result was then greater than 2.5% to 10% milk yield reduction that had been recorded by Hoste and Chartier (1993) from machine-milked goats infected three times with H. contortus L3 larvae at 50-day intervals. But recent studies have revealed greater reduction rates than these previous ones. Indeed, in Italy, a study involving untreated naturally infected and anthelminthic-treated animals has revealed significantly effect of GINs infections on milk production, with the highest milk yield recorded in the treated goats (Rinaldi et al., 2007). More recently, in Argentina, Suarez et al. (2017) reported a significant difference in the mean total milk production between treated (399.5 L ± 34.0 L) and untreated goats (281.6 L ± 37.5 L), amounting to 41.8% increase in total milk yield. The same study also revealed a post-partum peak in egg count and a negative effect of gastrointestinal nematodes (GINs) on milk yield, even with moderate infections. In addition, studies have gone further by assessing the effects of those GINs infections on the lactation length in small ruminants. Considering milk production of the whole period in naturally infected goats in France, Chartier et al. (2000) r eported a significant effect of GINs infections on the lactation period length with a longer duration of lactation in the high protein diet treated group compared to the group treated with normal protein diet (301.5 vs. 294.9 days) and a similar tendency for the total milk yield. According to Suarez et al. (2009), anthelmintic treatment positively affects the length of the milking period with regard to the length of the milking period of untreated dairy sheep. The same way, Suarez et al. (2017) revealed, in goats instead, a significant negative effect of the GIN infections on the milking period length of the goats after kidding (262.3±9.8 days and 223.3±10.8 days respectively for treated and untreated goats). These different results could explain the positive correlation between the GINs infections treatment and the persistence increase in milk yield in dairy goats, ranging from 7.4 to 18.5% with respect to control values observed by Rinaldi et al. (2007). The same study (Rinaldi et al., 2007) highlighted the deteriorating effect on milk quality caused by nematode infections, when they observed that 29.9% lower fat, 23.3% lower protein and 19.6% lower lactose contents in milk from the untreated goats than that from the control group. However, these finding were not in accordance with Hoste and Chartier (1993) who previously had reported no changes in fat and protein contents between infected and uninfected dairy goats. This might be due to the high level of resistance development in the GINs that occurred more recently in small ruminants herds and reported by several studies in small ruminants (Kaplan and Vidyashankar, 2012 Torres-Acosta et al., 2012b Geurden et al., 2014 Besier et al., 2016). Finally, in Pakistan, Muhammad et al. (2011) estimated the effect of haemonchosis on milk yield and goats weight respectively up to 29 and 27% reduction.

Losses due to H. contortus infections are related to productivity performances, particularly to decrease in body weight that can range from 20 to 60% (Kawano and Yamamura, 2001). These losses could be explained by the loss of appetite (reduction of voluntary feed intake), diarrhoea, anemia and reduced growth (Khan et al., 2008) and disturbance in the nutrient metabolism that cause young H. contortus. In overall, Muhammad et al. (2011) estimated losses due to haemonchosis in sheep and goats at 10-20% reduction of the production.

In disease pathogenesis, anorexia or depression of voluntary feed intake is properly recognized as a critical factor that is capable of revealing largely the response to imbalance of nutrition during gastrointestinal nematodes infection (Sahoo et al., 2011). Even in subclinical infections, anorexia is present (Sykes and Greer, 2003), and may account for around 40 to 90% production losses detected during intestinal parasitism (Greer, 2008). According to Sahoo et al. (2011), in a parasitized animal, anorexia occurrence is as a result of the different factors, viz: a) triggered by the parasite itself for its own advantage b) reduction of voluntary feed intake is aimed at starving the parasites c) in the host, it helps in promoting an effective immune response and d) anorexia affords the host an opportunity to chose diets that minimize infection risk. According to both the nutrient contents of feed offered to parasitized animals and the number of established parasites present, Petkevi?ius (2007) revealed voluntary feed intake reductions varying from 6 to 50% which, according to Greer (2008), could be understood to be the cost of the developing immune response. Feed intake of parasitized animals usually returns toward normality as animals acquire resistance to infection (Sahoo et al., 2011). More recently, on artificial infection with 15 000 third-stage larvae of H. contortus given as three divided doses, Tonin et al. (2014) concluded on progressive degradation of physiological condition weakness, lethargic and pale state and depressed feed intake of crossbred Corriedale lambs.

On the other hand, one of the key features of GINs infection, such as H. contortus infection is an increased loss of endogenous protein into the gastrointestinal tract, partly due to plasma protein leakage and partly because of increased production of muco-protein and sloughing of epithelial cells into the alimentary tract (Petkevi?ius, 2007 Sahoo et al., 2011). A substantial amount of these proteins are redigested before absorbtion at sites distal to infection however, subsequent recycling of digested nutrients would result to additional energy expense by the small ruminants (Knox et al., 2006). The quantity of nutrients reabsorbed endogenously depends on the distal tract (whether there is adequate compensatory absorptive capacity or the lesions position (whether they are in the anterior) (Coop and Kyriazakis, 2001). A proportion that is not resorbed is either further digested in the large intestine or waits to be excreted in the faeces, absorbed as ammonia and excreted as urea in the urine and can therefore constitute a major drain to the infected animals&rsquo overall nitrogen economy (Knox et al., 2006). In parasitized animals, nutrients diversion from production towards specific proteins synthesis for replacement, repair, and reaction to the gut wall damage, to whole blood or plasma loss as well as to mucus production can inflict a significant drain on resources that otherwise would have contributed to fiber, bone, milk and muscle synthesis (Liu et al., 2003 Sahoo et al., 2011). For instance, according to Liu et al. (2003), an additional 17g/day Metabolisable Protein (MP), which is equivalent to 0.57, 0.71, and 0.14 of the MP requirement, is respectively needed for growth, late pregnancy, and early lactation as compensation for losses owing to GINs infection. According to Colditz (2003), GINs adult and larval stages incidence in the gastrointestinal tract leads to inflammation and activation of the acute phase response to infection and occurs locally and systemically. These responses may cause significant drain on the nutritional resources at the disposal of the animals along with protein redirection away from other body processes (Knox et al., 2006).

Finally, the analysis of the situation on the economic plan designates H. contortus as the most economically vital gastrointestinal nematode in its main endemic zones (Perry et al., 2002 Mcleod, 2004) ma inly owing to the common occurrence and potential for substantial rates of mortality in small ruminants. Animal losses vary significantly between seasons, years and regions, contingent on environmental conditions as well as control measures&rsquo effectiveness, including anthelmintic resistance impact (Besier et al., 2016). Although it is difficult to assess the impact of chronic H. contortus infection, and also critically significant in wide grazing situations where routine monitoring is seldom conducted, Muhammad et al. (2011) ascribed considerable loss to the reduced value of animal production. For example, in Australia, gastrointestinal nematodes cost the sheep industry $369 million annually or around 8.7% of its total value (Sackett et al., 2006). All these results revealed the negative interaction between small ruminants and nematode (Hoste et al., 2010), and could justify the fact that, even at moderate burdens, GIN control should not be neglected in small ruminants production.

CONTROL OF GASTROINTESTINAL NEMATODES PARASITES IN SMALL RUMINANTS

Use of chemical anthelmintics

Anthelmintics have continued to be the bedrock of many GIN control programmes in grazing animals owing to their ease of use, low cost, and lack of real alternative options (Kenyon and Jackson, 2012). However, in many countries, the resistance of gastrointestinal parasites to chemical anthelmintic is an increasing burden and poses real concern to numerous countries (Kaplan and Vidyashankar, 2012 Torres-Acosta et al., 2012b Geurden et al., 2014). Anthelmintics resistance is an increasing challenge not only in small ruminants (Kaplan and Vidyashankar, 2012) but also in cattle (Cotter et al., 2015) and horses (Nielsen et al., 2014). GINs resistance to the three classes of anthelmintics (macrolytic lactones, nicotinic agonists, and benzimidazoles) has become recurrent globally, since the foremost case of resistance was identified in the early 1960s (Fleming et al., 2006 Kaplan and Vidyashankar, 2012 Cotter et al., 2015). Moreover, in single nematode strains, multiple resistance remains a concern (Taylor et al., 2009 Geurden et al., 2014). Nevertheless, GINs resistance levels against anthelmintics may vary between areas (Torres-Acosta et al., 2012b).

As regards anthelmintic resistance of GIN in goats, since the very first reported cases in different areas of the world like New Zealand (Kettle et al., 1983), Australia (Barton et al., 1985), France (Kerboeuf and Hubert, 1985), this challenge has become globally prevalent as in sheep (Fleming et al., 2006 Jackson et al., 2012 Chandra et al., 2015). In Australia and South America, there is particularly high prevalence however, in Europe there are increasing reports of elevated prevalence (Váradi et al., 2011). Though both goats and sheep are infected with the same nematode species (Hoste et al., 2008), parasites in goats seem to be more resistant to chemical drugs, especially in large flocks characterized by high stocking rates, industrial schemes of production, and frequent treatment based on anthelmintics. Thus, resistance to chemical anthelminthic is assumed to be more frequent in goats&rsquo parasites than in sheep (Váradi et al., 2011). According to Jackson et al. (2012), this low sensitivity to anthelmintics in goats parasites primarily results from difficulties in ascertaining the precise dose of drugs in goats as compared to sheep. A number of anthelmintics are registered for use in sheep, but in goats, they are used off-licence. Thus, goats treatment at the recommended dose rates of sheep led to routine underdosing which reduces the efficacy of the drug used and partly explains the high prevalence of anthelmintic resistance of parasites in goats in comparison with sheep (Hoste et al., 2011).

To retain anthelmintics effectiveness for a prolonged period, a detailed comprehension of the factors that are likely to initiate anthelmintic resistance of GINs is necessary. As a result, there is need for appropriate approaches implementation and development that will slow or impede possible resistance (Leathwick et al., 2015). Resistance development in GINs against anthelmintic may be influenced by many factors, e.g those listed in Table 1.

Alternatives control methods

Elimination of the source of contamination of animals

The purpose of the depletion of the source of contamination is to block the biological cycle of gastrointestinal nematodes (GINs) by controlling the infestation of grazing and thus minimizing the risk of contact between sensitive hosts and L3s larvae (Paolini et al., 2004 Heckendorn, 2007). Various methods of grazing management exist to achieve this goal. These methods are based on three main principles: prevention, evasion and dilution (Pomroy, 2006). Prevention is to put healthy animals on clean pastures (free of L3s) while evasion involves transferring treated animals with anthelmintics from contaminated pastures to clean pastures. Finally, the last principle is to dilute the infestation of grazing.

Improvement of the host resistance

The improvement of the host resistance may be done by two ways: selection of genetically resistant animals and improvement of the host diet.

Selection of genetically resistant animals

The selection of animals resistant to gastrointestinal nematodes (GINs) is a long-standing approach to reduce the use of synthetic anthelmintics (Pomroy, 2006), as such selection would theoretically reduce host infestations and gradually decrease pasture contamination. Genetic variability in GINs resistance has been reported either between breeds or between individuals of the same breed (Bishop and Morris, 2007). Selection of resistant animals may also present some limitations such as the risk of increased host susceptibility to other pathogens (Gruner et al., 1998) or an adverse effect on productivity (Stear and Murray, 1994 Gray, 1997). In addition, these resistant animal selections remain long-term programmes that must take into account local breeding conditions, availability of breeds, and breeding objectives (Pomroy, 2006).

Improvement of the host diet

Gastrointestinal nematodes (GINs) cause severe disruption of digestive physiology and induce an increase in the host's dietary requirements to overcome the strong disturbances of protein and energy metabolism (Hoste et al., 2005). On the basis of this observation, it has been suggested that an improvement in the feed ration to cover the additional needs associated with the presence of nematodes would contribute to improving the host's response to parasitism, particularly when corrections are made. In general, it has been shown that protein metabolism is far more affected by gastrointestinal parasitism than energy metabolism (Coop and Kyriazakis, 1999). As a result, the studies have focused on the benefits of protein supplementation. The notion of

immuno-nutrition has been suggested because improving the diet leads to greater resilience by reducing the consequences of subclinical infestations and improved resistance (Hoste et al., 2008).

Use of medicinal plants

For centuries, medicinal plants and their extracts have been employed in treatment of diseases in man as well as animals (Akhtara et al., 2000 Hounzangbe-Adote et al., 2005 Athanasiadou et al., 2007). Worldwide, anthelmintic resistance occurrence in GIN populations has inspired investigation pertaining to plants and their extracts&rsquo usage as a substitute approach for controlling GINs in ruminants. These medical plants are reasonably inexpensive, generally accepted by small landholders and available locally (Athanasiadou et al., 2007 Hoste et al., 2011). Thus, several review works have already been conducted on use of medicinal plants as a substitutive means for controlling GINs in ruminants (Akhtara et al., 2000 Athanasiadou et al., 2007 Hoste et al., 2011). Table 2 summarizes information on some of these plants that have been used in the recent studies for controlling H. contortus infection in small ruminants.

This current study attempted to provide an overall view about the prevalence and the methods of control of gastrointestinal nematodes parasites, particularly H. contortus. Several previous studies have revealed a high prevalence of H. contortus in small ruminants, and in goats in particular all over the world. Its development is favored by many external factors mainly the climatic factors (temperature, humidity, etc.), management practices. Prisustvo H. contortus in small ruminants is associated to many problems (weight losses and milk yield reduction) that lead to significant economic losses. Conventional control methods used by farmers during decades are no more adequate to address parasite infections in small ruminants considering their negative impacts on cattle and farmers&rsquo benefits. Medicinal plants with anthelmintic properties have been investigated and can be used as alternatives to chemicals especially for small scale farmers. Knowing, understanding and mastering these alternatives methods might help the small ruminants&rsquo value chain actors to design appropriate control programmes adapted to the financial conditions and geographical area of small scale farmers.


Sources of resistance

The variety of anthelmintic products available to Texas sheep and goat producers is limited. In the US, new product development, relative to the size of its market, is cost prohibitive for pharmaceutical companies. The commercially available dewormers have been used for decades. As such, Haemonchus contortus has developed resistance to all major anthelmintics classes. Most Texas sheep and goat ranches have used a variety of dewormers and methods, so the resistance of Haemonchus to dewormers within these flocks and herds are different.

Several scenarios can result in resistance development. To uključuje:

  1. Insufficient dose: The margin of safety for all approved products is at least twice the recommended dose. Levamisole is the product with the narrowest margin of safety. The dosage selected for all animals should be appropriate for the heaviest animal in that group (grouped by weight). Underdosing might save a few cents in the short term but can be quite costly should resistance develop.
  2. Inappropriate route of administration: Anthelmintics available to livestock producers may be delivered in many forms—oral dose, subcutaneous injection, pour-on, or feed additives. The appropriate method for sheep and goats is oral administration of products designed for oral delivery. In general, injectable and pour-on treatments remain in the system longer but at lower levels. This allows for partially resistant worms to survive that would not have survived a treatment at higher levels.
  3. Ineffective compound: Anthelmintics available to U.S. producers can be divided into three groups according to active ingredient (Table 1). Using an ineffective product is a waste of money and could lead to resistance development. If the efficacy of a product drops below 98 percent, it should no longer be used. If you continue to use a product until efficacy is 50 percent or below, the product will not have value in future product rotations or combination treatments.

Rotations of anthelmintics should not be done during a grazing season unless you are trying to control another parasite or a product is no longer effective. Rotation during a grazing season selects for resistance to all of the drugs in the rotation more rapidly. When rotating products, the appropriate rotation is across classes of compounds (not within a class of compound). For example, rotate from Valbazen to Cydectin to Prohibit, not from Valbazen to Safe-Guard to Panacur.

Combination drenchers (two or more active ingredients) are commercially available in other countries. Mixing 2 drenches together is not recommended, rather, administer two treatments back-to-back. Research indicates that resistance develops slower when two or more active ingredients are used in a single treatment. However, if not used properly, resistance will develop to both products.

  1. Massive reexposure: Deworming animals and returning them to a heavily infested pasture is an exercise in futility. Animals will immediately begin the reinfection process. Animals that were anemic due to a heavy parasite load are not able to fight off new infection, until they have replenished their blood supply and body condition. Grazing management (pasture rotation) is an integral part of an internal parasite management plan. Animals with significant worm burdens can continue to shed viable eggs for several hours or days after you administer an anthelmintic. If possible, hold treated animals in the pen for 48 hours posttreatment and then release them to an uncontaminated pasture. However, this practice selects for a population of parasites that is solely resistant to the product used.
  2. Lack of refugia: Refugia is a population of worms from untreated livestock or wildlife. These worms have a much lower chance of having the genes for resistance. They mate with resistant worms in the abomasum resulting in offspring who have both resistance and susceptibility to anthelmintics. The anthelmintic will only kill the susceptible worms but the numbers removed may prevent disease.

Frequent deworming of all animals rapidly selects for a parasite population that is resistant to the dewormer. It is recommended to intentionally allow sheep and goats to be exposed to parasites that have not had a chance to develop resistance to a dewormer. Most often, this is accomplished by not treating some animals that are low risk for parasitism. These would include animals that do not show signs of parasitism, have a good body condition score, and/or are nonlactating mature animals.


ANHYDROBIOSIS INCREASES SURVIVAL OF TRICHOSTRONGYLE NEMATODES

This study demonstrates that infective-stage larvae of 2 trichostrongyle ruminant gastrointestinal nematodes, Haemonchus contortus i Trichostrongylus colubriformis, can enter into anhydrobiotic states when completely desiccated. Larvae of control trichostrongyle species, Heligmosomoides polygyrus i Nippostrongylus brasiliensis, that infect mice were unable to survive desiccation or to enter into anhydrobiosis. Ruminant larvae were able to survive up to 7 desiccation/rehydration cycles, and, during anhydrobiosis, metabolic activity was decreased and survival of the larvae was prolonged both in the laboratory and in the field. Relative humidity had no effect on ruminant larval survival after anhydrobiosis compared with controls. Temperature had a significant effect, 85.8 ± 2.3% of larvae in anhydrobiosis could survive low temperatures (0 C) that killed all control larvae. Metabolic activity, measured by changes in lipid content and CO2 respiration, was significantly lower in larvae that entered anhydrobiosis compared with controls (P < 0.05). In field experiments using open-meshed chambers under ambient environmental conditions, larvae in anhydrobiosis had significantly higher survival rates in the field compared with controls (P < 0.05) during summer and winter trials. These data suggest that anhydrobiosis in ruminant larvae promotes survival at freezing temperatures, decreases metabolic activity, and prolongs survival under natural field conditions.


Analysis of genome-wide SNPs based on 2b-RAD sequencing of pooled samples reveals signature of selection in different populations of Haemonchus contortus

The parasitic nematode Haemonchus contortus is one of the world’s most important parasites of small ruminants that causes significant economic losses to the livestock sector. The population structure and selection in its various strains are poorly understood. No study so far compared its different populations using genome-wide data. Here, we focused on different geographic populations of H. contours from China (Tibet, TB Hubei, HB Inner Mongolia, IM Sichuan, SC), UK and Australia (AS), using genome-wide population-genomic approaches, to explore genetic diversity, population structure and selection. We first performed next-generation high-throughput 2b RAD pool sequencing using Illumina technology, and identified single-nucleotide polymorphisms (SNPs) in all the strains. We identified 75,187 SNPs for TB, 82,271 for HB, 82,420 for IM, 79,803 for SC, 83,504 for AS and 78,747 for UK strain. The SNPs revealed low-nucleotide diversity (π = 0.0092–0.0133) within each strain, and a significant differentiation level (average Fst = 0.34264) among them. Chinese populations TB and SC, along with the UK strain, were more divergent populations. Chinese populations IM and HB showed affinities to the Australian strain. We then analysed signature of selection and detected 44 (UK) and 03 (AS) private selective sweeps containing 49 and 05 genes, respectively. Finally, we performed the functional annotation of selective sweeps and proposed biological significance to signature of selection. Our data suggest that 2b-RAD pool sequencing can be used to assess the signature of selection in H. contortus.

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