Equine Nematodes Flashcards
Family Strongylidae
Includes Cyathostominae and Strongylinae
Cyathostominae
Small strongyles or small red worms
> 50 sp with high prevalence
Direct, non migratory life cycle (PPP 5-12 weeks)
Propensity for prolonged duration inhibited development
Variable, but low host immunity
Principle parasitic pathogens of equidae in developed world
Develop in LI wall
Inhibited Larval Development
Hypobiosis- can last months/years with 100 to 1000s of larvae
Reflect incomplete immunity- ages 1-3 yrs, size larval challenge, and neg feedback at luminal L4 and adult stage (Keeps arrested in mucosa, remove with drugs, takes away neg feedback and you get disease)
Inhibited larval stages aren’t affected by modern drugs- resumption of dev reflects decreasing immunity
Disease= cyathostominosis with protein loosing enteropathy and sometices happens post dosing. diagnosis fecal larvae. higher in later winter/spring
Host susceptibility to cyathostomins
Majority are present in the minority of the host population
Host susceptibility is variable, but most adults have low levels of infections, and there is no 100% immunity so need lifelong drugs
Strongylinae
Large strongyles
6 main sp with low prevalence in the developed world
Direct, migratory life cycle (6-10 months) and migratory stages are highly pathogenic
Adults are plug feeders- pathogenic, but not as much as migratory stages
There is variable, but reasonable host immunity and all host stages are susceptible to modern drugs
Strongylus vulagris
Can cause colic and infarction (usually multiple) bc block blood to SI (via mesentaric art)
Killed by wormers
Have mouse ears
Strongyle Epidemiology
All ages can potentially contaminate pastrue
Temperate regions have year round pasture larval infectivity, but in UK peak at mid/late summer
Prolonged, dry heat is lethal to pasture larvae
Issues with control
Variable host susceptibility
Frequent movement of horses
Body wt often not known, dosed wrong
Conventional Control
Intensive, interval dosing of all grazing horses regardless of age/infective status
Assumes one size fits all, simplified strategies for owner and aggressive marketing by manufacturer-> decrease in S. vulgaris but also widespread anhelmentic resistance
Dont follow this anymore
Problems with resistance
Widespread prevalence
Hard to detect
Low awareness of owners
Drugs and their Resistance level
3 classes
Bezimidazoles- cyathostomins are almost completely resistant
Pyrantil salts- cyathostomins
Ivremectin (some ascrids show apparent resistance) and moxidectin (cyathostomins, newer drug and more potent)
Refugium
The proportion of parasites not exposed to anthelmintic chemical compound at points when animal/s is dosed are said to be in this
May be bad from disease point of view, but could be good for resistance point of view
resistance
Irreversible, genetic feature in pop
Brazil and UK have multi drug resistance in cyathostomins to al 3 major classes
Detecting resistance
Fecal egg count reduction test, <90% reduction is positive for resistance
Check at day 0 and day 10-14- not really reliable bc test is made for sheep, sample numbers are usually small, and over dispersed worm in pop
Best practice of parasite control
Includes Cyathostomins, tapeworm, and ascrids (esp in young), and less importantly bots and large strongyles
Would like to see selective dosing for cyathostomins with monthly fecal check of all animals and dose by correct body weight is positive
Monitor resistance
Apply mixed co-grazing
Good pasture hygiene, but caution harrowing
Tapeworm-target dose on basis of serology or annual inclusion of praziquantel (narrow spectrum product)
Bots- Give ivermectin in winter combined with tapeworm dosing
When best practice fails
Poor owner compliance
Frequent movement of horse
Groups of young
Serial use of moxidectin
Parascaris equorum
Common in foals/yearlings worldwide- shows age resistance, where infection rates decrease from 6 mo onwards
Large worm (40 cm) found primarily in SI duodenum and prox jejumum
Migrating Larvae causes damage to liver via focal hemorrhage and fibrosis, and lungs with focal hemorrhage, lymphocyte infiltration, and nodules
Adults cause very little problems but in high burden can cause impaction
Generally presents as ill thrift bc of adult worms in small intestine and can develop to emaciation if untreated as well as resp signs from migrating larvae. Foals can cough +/- greyish nasal discharge and runny nose
Diagnosis via histoy and fecal egg count
Egg is brown with thick pitted shell, resistant
Adults aren’t major source of contamination, but can be carriers and eggs tend to build up on pasture towards the end of summer
Control follows small red worms, some resistance to ivremectin
PPP 10-15 weeks
Strongyloides westeri
Adult <1cm and only the females are parasitic
Reasonably common in foals (transmammary route), seen worldwide
Requires heavy worm burden to see diarrhea, anorexia, dullness, and reduced weight gain
Diagnosis via clinical signs and larvated eggs in feces
Free living L3 not sheathed, not very resistant but like warm wet conditions
Oxyuris equi
Pinworm
L3 in egg is infective and live in large intestine (can not get human pin worm form animals). Adults in LI rarely produce clinical signs, but egg laying activity can cause intense perineal irritation leading to rubbing alopecia/inflammation over rump and tail head
Diagnosis via clinical signs +/- eggs around perineal region (usually not in feces), scraping and look at eggs or adults in feces
Infective L3 can develop on skin and little immunity to reinfection
Susceptible to many broad spectrum antehelmintics (some may be resistant to ML compounds). Need to keep environment clean bc thats a source of infection
Havronema microstoma
host is horse and donkey, with intermediate host of Muscid flies.
L3 from fly usually swallowed by horse and can develop in stomach
Can cause summer sores
Summer sores
Cutaneous infestation by L3 of Habronema or related parasite, Draschia
L3 deposited on skin (breakout from mouthpars when temp is within 1-2 degrees of body temp), often around eye, but no further development
Associated with warm weather, often on dark coated horses
