Parasites Flashcards
How do internal parasites damage a host?
- competition for nutrients
- sucking blood
- tissue destruction
- physical obstruction
- immune mediated reactions
- abnormal migration
What does the degree of harm depend on?
- pathological potential of the parasite
- concentration of parasites
- immune status of host
- general health of host
What is the life cycle of cyathostomins or small strongyles?
eggs with morula are defecated out of infected horse onto the ground. -> reaches L3 on ground -> ingested by horse -> becomes an adult in the intestine of the horse -> process repeats
What is the time until infective of horse having ingested cyathostomins?
1 week in ideal conditions
What are cyathostomins? (characteristics)
- mild pathogens unless in large numbers
- larvae can undergo inhibited/encysted development in the gut mucosa, remaining as early third-stage larvae and emerging in spring
- requires access to pastures to spread effectively
- can cause GI disturbances
What are the clinical signs of a cyathostomin infection?
diarrhea, dehydration, inappetance, wasting, edema, and sometimes death
What is the life cycle of anoplocephala perfoliata? (tapeworm)
egg with hexacanth larvae pooped out (immediately infective) -> Mite ingests egg -> free living mite with cysticercoid -> ingested by horse -> become adults inside horse
repeats
What are the characteristics of anoplocephala perfoliata, or tapeworm?
- indirect life cycle
- infection is from ingesting infected mites
- requires access to pastures
- difficult to diagnose using common egg counting since eggs are passed only intermittently with shedding and proglottids disintegrate
What can a anoplocephala perfoliata cause?
- ileal impaction and spasmodic colic but no evidence in canada
What is the life cycle of Parascaris equorum?
egg with morula pooped out -> egg with L1 -> egg with L2 -> ingested by horse -> tracheal mucosa -> adults in intestine
repeats
What are the characteristics of Parascaris equorum?
- can infect horses who are in confinement and pasture
- deworming heavily parasitized foal can cause small acute impaction of intestine
What are the effects of parascaris equorum?
risk for small intestinal impactions, ill-thrift and poor growth and migrating larvae can cause signs of airway inflammation, cough and nasal discharge
What horses are most effected by parascaris equorum?
foals due to developing immune system
What is parasite control?
- minimize risk of parasitic disease
- to control parasite egg shedding
- to maintain efficacious drugs and avoid further development of anthelmintic resistance as much as possible
NOTE: goal is to LIMIT parasite infections so animals remain healthy and clinical illness does not develop, NOT to eliminate parasites from an individual
What are some new factors to consider with regards to parasite control?
- individuals differ in their innate susceptibility and therefore the amount of eggs shed
- Horses <3 years old are more susceptible and require different treatment strategies
3, increasing antihelmintic resistance - refugia important
What is resistance?
the ability of worms in a population to survive treatments that are generally effective against the same species and stage of infection
Is resistance inherited?
yes and resistant parasites never loose their resistance
What is resistance prevalence related to?
- selection
2. worms surviving treatment and breeding
What is refugia?
portion of a population of parasites (or stages of parasites) that escapes selection with the drug at the time of treatment
- larvae, encysted stages, free-living parasites on pasture, parasites that did not get treated
- NOT selected for resistance and dilute population of resistant worms
What is the only test/method used for detecting resistance?
Fecal Egg Count Reduction Test (FECRT
What test evaluates parasite loads in horses?
Fecal egg count (FEC)
What is the parasite control program?
- to minimize the risk of parasitic disease
- to control parasite egg shedding
- to maintain efficacious drugs and avoid further development of antithalmintic resistance as much as possible
What is the problem with drugs?
they kill adults in the lumen of the GIT but not all drugs kill larval stages which cause the most disease
How is the Larval stage problem fixed?
- kill worms before they start to pass large number of eggs into the environment
- treatments only necessary when environmental conditions are conductive to egg and larval development and survival (usually spring and summer)
