Small Ruminant Nematode Parasites

1. Small Ruminant Nematode Parasites Southern Consortium for Small Ruminant Parasite Control

2. Parasites are NormalDisease is an Imbalance • Parasitic disease occurs when the number of parasites are in excess of what the host can tolerate • The number of parasites is a function of exposure, host susceptibility and parasite response to control • Exposure to parasites varies with climate and management

3. Management Factors • Breed and use for the animals • Pasture or confinement • Interactions with other animal species • Quality and quantity of feedstuffs • Season of parturition • Age of weaning • Source of animals and parasites

4. Gastrointestinal Nematodes • Life cycle of most species similar outside of host • Different species will be of primary concern in different climates • Immunity can be established but takes repeated exposure and can be overcome • Immunity relaxes at time of parturition • Many nematodes have arrested development in host to evade unfavorable conditions

5. Gastrointestinal Nematodes (Worms) of Small Ruminants Abomasum: Haemonchus contortus* (southeast US) Teladorsagia (Ostertagia) circumcincta Trichostrongylus axei Small intestine: Trichostrongylus colubriformis Cooperia Nematodirus Large intestine: Oesophagostomum Trichuris

6. Life Cycle http://www.ext.vt.edu/pubs/sheep/410-027/figure1.html

7. Pasture Infectivity • Adult worms produce eggs which are disseminated on pasture • Larvae survive on pasture over winter or during drought • Young animals do not develop immunity until 4-6 months of age, if ever • Immunity acquired by exposure to infective larvae

8. Larval Development • Egg to infective larva • 1 to 4 weeks and is temperature dependent • Desiccation during development will kill larva • Infective larva covered by sheath • Protects from environment and cannot feed • Infective larva • Lives 1 to 8+ months and is temperature dependent • Requires moisture to exit fecal pellet • Migrates up forage

9. Infection • Larva exsheath in rumen • Enter organ of habitation (abomasum/SI) and molt to 4th stage • Larva either continue development to adults and begin laying eggs (approximately 15-21 days) or interrupt (arrest) development at early L4 • Larva in arrested development resume activity • Depressed immunity of host (parturition) or season change • Mature and begin producing eggs

10. Dynamics of Infection • Hypobiotic (arrested development) larvae develop at parturition or when climate changes • Winter to spring , dry to wet season • Larvae on pasture become active with warming of weather and sufficient moisture to free them from fecal pellet • Adults are source of eggs into environment which can become heavily laden with larvae • Young exposed to increasing numbers of larvae

11. Dynamics of Infection • Climate determines the species of parasites in a geographic area • Weatherdetermines when the parasites are transmitted • Management determines who and when hosts are going to be exposed to parasites

13. Focus of Control Programs • Warm humid season • Haemonchus transmission • Summer and early fall or rainy season • Cool moist season • Telodorsagia and Trichostrongylus transmission • Fall and winter

14. Haemonchus contortus • Most important parasite of small ruminants in Southeastern United States • Death losses, not weight losses, most important aspect of infection • Immunity largely acquired but not manifest until young are 4 to 6 months of age • Periparturient relaxation of resistance coincides with reactivation of hypobiotic larvae

18. Acute Haemonchosis • All ages, but usually young • Summer and fall • Flock problem and 10- 60% of flock may have clinical signs • Anemia • Hematocrit (PCV) <15 • Serum protein loss • Intermandubular edema (bottlejaw)

19. Anthelmintics • BENZIMIDAZOLES • Albendazole (Valbazen) • Fenbendazole (Safegard, Panacur) • Oxifendazole (Synanthic ) • IMIDAZOTHIAZOLES • Tramisol, Levasol, Rumatel • MACROCYCLIC LACTONES • Ivermectin (Ivomec) • Doramectin (Dectomax) • Moxidectin (Cydectin) • Eprinomectin (Eprinex)

20. Anthelmintic Use • Goats metabolize anthelmintics faster than other species • Bioavailability is lower and/or shorter than with other hosts • Goats require 1.5 to 2 X dose compared to sheep or cattle to achieve a therapeutic dose • Haemonchus contortus resistance to all 3 classes of anthelmintics

21. Treatment Schemes

22. Opportunistic Treatment • Treat when livestock are available and you think about it • Treat when money or labor are available • You feel better having done something but are unlikely to have affected parasite populations for more than a few weeks

23. Suppressive Treatment • Treat to remove parasitic worms from the environment • Treating at 3 week or monthly intervals • When anthelmintics work there are few parasites • Strong selection for anthelmintic resistance • Suppresses immune response

24. Strategic Treatment • Treatment when the highest proportion of the worm population is in the animal and not on the pasture • At parturition when arrested larvae are activated but not producing eggs • Moving animals onto safe pastures • But helps select for resistance

25. Tactical Treatment • Treatment when the potential for parasitic disease is increasing but not yet there • Treat two weeks after rainfall which exposes animals to worm larvae but before the newly acquired worms reproduce • Treat when the average worm count is increasing but not yet critical • In south >1000 eggs/gram in spring /summer 2000 • Treat when moving to safe pastures • Lowers pasture contamination and removes worms which could cause problems

26. Targeted Treatment • Treat individual animals with signs of parasitism • Anemia, diarrhea, ill thrift, high egg counts • Treat animals at risk • Young, heavily exposed, stress (i.e. parturition, moving) • Treat high producing animals • Highest producers have longer periparturient relaxation of resistance, those with multiple offspring

27. Salvage Treatment • Save lives if timely • Will have to be repeated if management is not changed • Does not select for anthelmintic resistance

28. Rotation of Anthelmintics • RAPID ROTATION • Rotation within a grazing season and selects for resistance to other anthelmintics in the rotation • SLOW ROTATION • Rotation between years with different classes of drugs and may slow the onset of resistance • NO ROTATION • Use drug until it no longer works then change, similar to slow rotation

29. Anthelmintic Resistance • Resistant worms accompany hosts • Anthelmintics remove competition • Worms resistant to benzimidazoles are larger and lay more eggs • Do not revert to susceptibility • Levamisole resistance is sex linked • May revert to susceptible in several generations

30. Purchasing Resistant Worms • Buy livestock without knowledge of parasite status • Place purchased animals on pasture without checking the parasite status • Administer an anthelmintic on arrival then put in pasture • Buy livestock from a geographic area where problems occur

31. Selecting Resistant Worms • Remove the susceptible worm population by excessive deworming • Do not stimulate the immune system by preventing exposure to moderate exposure • Select animals that do best under optimum conditions, then raise them under normal conditions

32. Evasion of Resistance • Treat only heavily parasitized animals • Remove susceptible hosts from population • Use combinations 2 or more drugs from different classes simultaneously • Infect with susceptible worms to cross mate with resistant worms • Management of pastures to evade

33. FEC - Evaluation of Worm Numbers • Direct relationship between level of infection by adult worms and fecal egg count • Aid in deciding when to tactically treat • Determine efficacy of anthelmintics • Evaluate management schemes

34. Fecal Egg Reduction Test • FEC on 12-15 animals/flock prior to use of anthelmintic • FEC on same animals 7 to 14 days later to determine the percent reduction in FEC • (Pre – Post)/Pre x 100

35. Other Aids to Worm Control • Botanical anthelmintics may be either ineffective, unsafe or only locally effective • Condensed tannins in forages decrease worm fecudity (fewer eggs laid) and can kill some worms • Copper wire particles kill Haemonchus • Can be toxic in sheep, goats (??) • Nematophagous fungi kill larvae in feces • FAMACHA • Eye chart to reflect level of anemia - Haemonchus • Diatomaceous earth in feed may lessen establishment of larvae

36. Pasture Rotation • Short duration pasture rest • Results in high quality palatable forage • Results in greater exposure to nematode larvae • In humid tropics • 30 days pasture rest may be sufficient to kill off many larvae • In cool moist areas • 6-8 months or more is required for larval death

37. Pasture Rotation • Rotate between classes of livestock • Leader follower systems • Susceptible animals graze followed by resistant animals harvesting larvae from pasture • Fewer larvae available when susceptible animals return to pasture • Shared grazing • Each species of grazing animal has its own preferred forage and parasite fauna • More pounds of livestock can share a pasture without putting undue pressure on the environment and dilute the exposure to parasites

38. Control Parasites by Determining • Which parasites are present • When they are being transmitted • How they survive • Which anthelminthics are effective • What dose is required for host species • When is the most appropriate time to administer anthelminthics or use other alternative control methods

39. Coccidiosis - Eimeria • All animals are infected by Eimeria spp • Disease • Stress; parturition, weaning, moving, change in feed or water • Exposure to large numbers of virulent species of Eimeria in a short time frame • Largely a disease of confinement • Stimulates protective immune response • Temporary loss of protection if not re-exposed

41. EIMERIAunsporulated oocysts (Calf 400X) artifact

42. Eimeria • Sanitation key to control • Shaded areas that retain moisture are ideal environment for the development and survival of oocysts • Oocysts sporulate (become infective) in one to three weeks and can survive a year or more if protected • Coccidiostats are drugs which inhibit development of parasites in host cells

43. Control • Sanitation • Use coccidiostats only at time of risk • Parturition, in confinement, weaning, shipping, periods of inclement weather

44. Coccidiostats • Sulfonamides • Sulfamethazine, sulfaquinoxaline • Amprolium • Decoquinate • Monensin • Lasalocid • Do not kill Eimeria but slows asexual reproduction and reduces damage while immunity is established • Eimeria become resistant to coccidiostats