Equine Threadworm (Strongyloides westeri) PDF

# Equine Threadworm ## *Strongyloides westeri* - Another nematode - Location in DH: Small intestine (5 to 10 mm long) - Direct life cycle - Age-related immunity *does* develop - Prepatent period = 5 to 10 days - May have zoonotic potential ## *Strongyloides westeri* Life Cycle - Similar to *S. s...

# Equine Threadworm ## *Strongyloides westeri* - Another nematode - Location in DH: Small intestine (5 to 10 mm long) - Direct life cycle - Age-related immunity *does* develop - Prepatent period = 5 to 10 days - May have zoonotic potential ## *Strongyloides westeri* Life Cycle - Similar to *S. stercoralis*: Complex, but still direct - **Females** are parasitic form - Egg contains L1 that hatches *after* passing in feces - L1 molts to L3 in ~ two days and becomes *either* parasitic or free-living ## *S. westeri* Ova An image is shown of microscopic *S. westeri* ova. ## Transmission 1. Oral 2. Transmammary 3. Skin penetration ## *Strongyloides westeri* Life Cycle ### Oral ingestion of larvae in environment - Larvae swallowed to small intestine, burrow into mucosa, mature to parasitic female adult (mucosal migration only) - PP ~ 5 days ### Skin penetration of larvae in environment - **Tracheal migration:** In young horses, larvae travel via circulatory system to lungs, up trachea, swallowed to small intestine, penetrate mucosa and mature to parasitic females (tracheal migration followed by mucosal migration) - PP ~ 10 days - **Somatic migration:** In adult horses, larvae become encysted in tissues ### Transmammary: Common source of infestation in foals - Mares have larval stages encysted in tissues; activated at parturition - Larvae move to mammary glands; transmitted to foals via nursing - Larvae mature to parasitic females and set up patent infestation (mucosal migration only) - Typically cause diarrhea in foals at ~ 10 days of age - PP ~ 5 days ## "Foal-Heat Diarrhea" - Commonly believed to be due to - Changes in chemical composition of mare's milk during first estrous cycle post-partum - OR - Normal changes in bacterial flora and function of foal's GI tract - Actually may be caused by *S. westeri* infestation via transmammary transmission ## *Strongyloides westeri* Clinical Signs ### Migrating larvae (skin penetration) - Cutaneous irritation and dermatitis - Pulmonary hemorrage and respiratory distress ("verminous pneumonia") ### Adults (small intestine) - Interfere with digestion - Diarrhea - Weakness ## *Strongyloides westeri* (continued) ### Prevention - Treat broodmares with ivermectin or oxibendazole - During final month of gestation - OR - Within 24 hours of parturition - Patent infestations rare in adults except those not exposed to *S. westeri* as foals ### Diagnosis - Demonstration of ova in fresh feces via fecal flotation (larvae hatches in 24 to 48 hours) - With older feces (> 24 to 48 hours), Baermann apparatus to detect larvae - *S. westeri* ova approximately 1/3 length of strongyle ova ### Treatment - After deworming mare at parturition, deworm foal at 1 month of age with either - Ivermectin - Oxibendazole