This PowerPoint presentation, "Parasites and their biology" is the first from a four-part webinar series on worms. The author is Susan Schoenian, University of Maryland Extension Sheep & Goat
This PowerPoint presentation, "Parasites and their biology" is the first from a four-part webinar series on worms. The author is Susan Schoenian, University of Maryland Extension Sheep & Goat Specialist.
I. Parasites and their biology species, life cycles, pathogenicity, interactions
Barber pole worms in abomasumImage source: ScienceWatch.com What is a parasite? A (generally undesirable) living organism that exists by stealing the resources produced or collected by another living organism.
There are two kinds of parasites. Internal (endo) – a parasite that lives inside another organism. External (ecto) – a parasite that lives on the blood of the host or lays eggs on their hide or in their nose. External parasite: sheep ked (tick)Image from Colorado State University
There are two general kinds of internal parasites. Helminthsmulti-cellular Nematodes Cestodes Trematodes Protozoasingle cell Coccidia Giardia Cryptosporidium Haemonchus contortus (barber pole worm) Image from University of Georgia
A. Nematodes (roundworms)Phylum Nematoda Approximately 1 million Over 28,000 described Over 16,000 parasitic Round Elongated Worm-like Have digestive systems Reproduce sexually Mostly host-specific Not all are pathogenic Most significant kind of internal parasites that affect sheep and goats.
ClassNematoda -> SuperfamilyStrongyloidea -> FamilyStrongylidae-> Genera StrongylePrimary parasites affecting sheep and goats: Strongyles
Haemonchus contortusBarber pole worm Most common in warm, moist climates with summer rainfalls. Adapting to cooler climates. Most deadly worm. Blood sucker. Prolific egg layer.
Western Maryland Pasture-Based Meat Goat Performance Test (2009)
Strongyle- type worms Direct life cycles Weather dependent 14 to 21 days Eggs cannot be differentiated in fecal analyses. 75 – 95 µ m Mixed infections common. Have developed varying levels of resistance to anthelmintics. L4, adult suck blood L3 L1 L2
Environmental-parasite interactions Optimal conditions for development of Haemonchus larvae are 82⁰F and humidity above 70%. Teladorsagia is better adapted to cooler, temperate climates. They fair poorly in very hot, dry summers. Trichostrongylus spp. are more resistant to cold and desiccation than Haemonchus.
Hypobiosisinhibited or arrested larval development Period of delayed development whereby 4th stage larvae stop development and remain in the mucosa for 3 to 4 months. Occurs when there is insufficient moisture or temperatures that are too cold for larval development. Occurs in winter or summer, depending upon parasite and geographic location. Probably involves some immune and environmental cues. Survival mechanism No host response
Lungworms Muelleriuscapillaris Dictyocaulusfilaria Direct or indirect life cycle Prefer cool conditions Diagnosis is difficult Clinical signsPersistent coughing, respiratory distress, reduced weight gains Recovery of 1st stage larvae from feces Identify at post-mortem Image source: UPENN Vet School
Meningeal worm White-tailed deer are the normal host. Infection typically causes no clinical disease in deer. Severe neurological disease occurs when infected snails or slugs are ingested by other cervids or ungulates. Gastropods serve as intermediate host. Parasite migrates to spinal cord and brain. 10 to 14 days after ingestion of infected snail or slug
TREAMENT CLINICAL SIGNS Variable Mimic other neurologic disease Weakness Lameness Circling Blindness Head tilt Abnormal behavior Paralysis Death High doses of anthelmintics Ivermectin for five days Fenbendazole for five days Anti-inflammatory drugs No controlled studies have confirmed or refuted the efficacy of various treatment recommendations.
Prevention Limit deer access to pasture. Eliminate deer via lethal means. Deer-proof fencing for small operations. Make pastures less appealing to deer. Feed in enclosed areas. Reduce exposure to infected snails and slugs. Do not allow access to pastures that contain thick vegetation or moist shaded areas that are favorable snail and slug habits.
Prophylactic treatment with anthelmintics (every 10-14 d).
B. Cestodes (tapeworms) Flat Segmented Hermaphrodites Indirect life cycle Some cause symptoms in intermediate host
Tapeworms affecting sheep and goatsGenus Moniezia Indirect life cycle Pasture mites serve as an intermediate host. 6 weeks Segments visible in feces.Only worm visible in feces Generally thought to be non-pathogenic and of little consequence. Usually no benefit to treatment Treat with albendazole (Valbazen®), fenbendazole (Safe-Guard®), or praziquantel.
Sheep measles (Ovine cysticercosis) Sheep tapeworm of dogs Transmitted to sheep eating forages contaminated with tapeworm eggs shed by canines. Sheep and goats host larval stage of parasite No clinical signs in sheep or goats. Causes development of cysts in skeletal and heart muscle. Cause of carcass condemnation.
Control point: dogs
Image source: Optimal Livestock Services, LLC
C. Trematodes (flukes) Flat Oval shape Indirect life cycle Hermaphrodites Image source: http://www.flickr.com/photos/peteredin/3386220058/
Liver flukes Fasciola hepatica(common liver fluke) Gastropods serve as intermediate host. In U.S., found mainly in Gulf states, California, and Pacific Northwest. Symptoms include pale mucous membranes, bottle jaw, and weight loss. Treat with albendazole (Valbazen®). Image source: Agricultural Research Council in South Africa
Eimeria spp. - Coccidia Single cell Life cycle Complicated Many stages Oocytes -> sporulation (hatching) Sexual and asexual reproduction 21 days 10 species known to infect sheep and goats Host specific Not all are pathogenic Damage cells of small intestines Subclinical Clinical (diarrhea)
Internal parasites of sheep and goats Barber pole worm Teladorsagia (Ostertagia)Trichostronyglus spp. Roundworms Tapeworms Helminths Other strongylesLungworms Meningeal worm Liver flukes Coccidia Protozoa