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Small Ruminant Nematode Parasites

Small Ruminant Nematode Parasites. Southern Consortium for Small Ruminant Parasite Control. Parasites are Normal Disease is an Imbalance. Parasitic disease occurs when the number of parasites are in excess of what the host can tolerate

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Small Ruminant Nematode Parasites

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  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

  12. 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

  13. 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

  14. 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)

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

  16. 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

  17. Treatment Schemes

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. EIMERIAunsporulated oocysts (Calf 400X) artifact

  37. 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

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

  39. 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

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