Horse Nematodes 1-2

STRONGYLIDAE

- Cyathostominae (small red worms) = resistant to anthelmintics

- Strongylinae (large red worms) = sensitive to anthelmintics

CYATHOSTOMINAE

CYATHOSTOMIN

Protein losing enteropathy

- Diagnosis: Fecal larvae, NOT eggs

- Seasonal: Late winter/spring

- Often occurs post anthelmintic dosing for control program because clearing away adult worms clears away negative feedback on the arrested larvae and triggers reemergence

TRUE

STRONGYLINAE (large strongyles)

STRONGYLUS VULGARIS

LARGE STRONGYLES (strongylus):

- Long (PPP ~6 months) migratory life cycle

- Larval stages pathogenic & extremely sensitive to modern anthelmintics

SMALL STRONGYLES (cyanthostomins):

- Short (PPP ~8 weeks), non-migratory life cycle

- Propensity for prolonged arrested development (>2 years)

- Arrested larval stages refractory (unaffected by) to anthelmintics

- All ages of horse potentially contaminate pasture

- Common in temperate regions

- UK Peak pasture infectivity mid/late Summer

- Prolonged dry heat lethal to pasture larvae

1. Frequent on-movements of horses

2. BW of individual horses often not known so not treated with proper dosage leading to resistance

1. Test animal pre-worming to ensure there's a burden worth treating, otherwise treating without reason can lead to resistance.

- Monthly FWEC (fecal worm egg count) all animals

2. If FWEC "positive" (>200epg) than dose; ensure dosing is appropriate for weight of horse

BENZIMIDAZOLES

1. Benzimidazoles --> Cyathostomins resistant

2. Pyrantel --> Cyathostomins resistant

3. Ivermectin --> ascarids possibly resistant

4. Moxidectin --> Cyathostomins resistant

REFUGIA

1. Eggs in feces (L1s)

2. Eggs in pasture (L2-L3s)

3. Arrested L3s within host

PARASITE

TRUE - so important to test for resistance of worms before worming (FEC Reduction Test)

1. Day 0 = Take FEC

2. Treat with anthelmintic

3. Day 10-14 = retake FEC

<90% reduction indicates resistant worms.

1. Cyanthostomins

2. Tapeworm

- Either target dose on basis of serology or annual inclusion of praziquantel dose (combo products)

3. Ascarids (foals & weanlings)

4. Bots

- Ivermectin during Winter

- Can combine with tapeworm dose

5. Strongyles (large)

1. Monitor anthelmintic resistance

2. Mixed species co-grazing (sheep/cattle with horses)

3. Harrowing

- Caution: only done during dry, hot conditions when parasites can't survive, otherwise you'll just spread the parasites around.

4. Practice pasture hygiene (e.g. mowing and gathering pasture clippings; poop scooping)

ASCARIDOIDEA

- Resemble typical ascarid = large (~40cm), white, round worms

- Predilection for duodenum & prox. jejunum

- Immunity develops with age so high burdens more common in foals and yearlings

- Infection rates decrease from 6 months onwards

- Clinical signs: unthriftiness

- Typical direct ascarid life cycle

MIGRATING LARVAE cause damage to:

- Liver = focal hemorrhages and fibrosis

- Liver = focal hemorrhages, lymphocyte infiltration, nodules

ADULT WORMS in intestines = little pathology

- Rarely, heavy worm burdens cause impaction, perforation, peritonitis

More commonly seen in foals & yearlings (adults show age immunity)

1. Unthriftiness - due to adult worms in LI

2. Coughing, +/- greyish nasal discharge & runny nose (foals)

1. Clinical signs/history

2. FEC (tens of thousands pg)

- Sensitive for ascarids (high fecundity)

3. Eosinophilia - transient in migratory phases of infection

PARASCARIS EQUORUM

- Typical ascarid appearance

- Foal -> Foal disease

- Adult horses can act as carriers, but not major source of contamination.

- Female worms extremely fecund

- Eggs very resistant (survive several years) & sticky

- Eggs build up on pasture towards end of Summer

Control measures aimed at small strongyles (Cyathostomins) should effectively control parascaris

- Check for worm burden before treating and dose to BW

- Adequate pasture management and hygiene important

- Still sensitive to benzimidazoles but reports of ivermectin and pyrantel resistance.

WORLDWIDE

- Adult worms <1 cm

- Only FEMALES are PARASITIC

- Reasonably common in foals (<6 months old)

- PPP = 8-14 days

- Routes of entry: skin penetration or ingestion (infection of foals via transmammary route)

* Only seen in very young animals (few weeks old) & requires heavy worm burden!

1. Unthriftiness

2. Diarrhea

3. Anorexia

4. Dullness

5. Reduced weight gain

1. Clinical signs

2. Larvated eggs in feces (smaller than strongyle egg)

* High egg counts can be seen in healthy animals...

Free-living L3s not very resistant (not sheathed like ascarids)

- Require warm, wet conditions

- Transmammary route important: successive progeny of same dam often show heavy infections.

PINWORMS

- Predilection for LI

- L3 in egg is infective

- PPP = 5 months

Adults in LI rarely produce clinical signs.

- Egg laying activity can cause intense perineal irritation resulting in:

- Rubbing

- Alpecia/inflammation over rump & tail head

1. Clinical signs

2. +/- eggs around the perineal (anal) region (usually not in feces)

3. Scraping plus microscopic examination of eggs

4. ADULT WORMS in feces

OXYURIS EQUI

- 80-95 um length

- yellow, ovoid

- One side flatted

- Mucus plug at one end

- Infective L3 in egg can develop on perineal skin

- Usually flakes of skin with eggs rubbed off

- Little immunity to reinfection

- Heavy burdens can build up in infected stables

Susceptible to many broad spectrum anthelmentics

- May be some resistance to ML compounds

- KEEP ENVIRONMENT CLEAN!

HOST: Horses, donkeys

IMH: Muscid flies

SITE: Adults in stomach

ROUTE OF INFECTION: L3 from fly usually swallowed by horse and adults develop in stomach

SUMMER SORES

- Cutaneous infestation by the L3 of Habronema or related parasite, draschia

- L3 deposited in skin, often around eyes by flies when stimulated by temps within 1-2C of body temp

- No further development via cutaneous cycle of infection.

* Associated with warm weather & often dark coated horses.

1. Parascaris equorum = foals & yearlings

2. Strongloides westeri = very young foals