Threadworms - Clinical Pathology PDF

CLINICAL PATHOLOGY I – Lecture Threadworms Strongyloides spp.  Strongyloides spp. are another nematode of the small intestine  Aka “intestinal threadworm” Species  Strongyloides stercoralis**: Intestinal threadworm of dog and man, cats and n...

CLINICAL PATHOLOGY I – Lecture Threadworms Strongyloides spp.  Strongyloides spp. are another nematode of the small intestine  Aka “intestinal threadworm” Species  Strongyloides stercoralis**: Intestinal threadworm of dog and man, cats and non-human primates are also hosts  Strongyloides tumefaciens: Intestinal threadworm of cat (rare) **ZOONOTIC Unique Characteristics of Strongyloides stercoralis  Parasitic worms are all females  Female in DH reproduces via parthenogenesis  Ova hatch in GI tract of DH and larvae are passed in feces  Larvae can develop into free-living adult worms  Can undergo autoinfection in DH Distribution  Thrive in moist soil of warm climates; prefers swampy areas  Primarily in tropical climates, but can be found in temperate regions  In U.S., most often observed in southeastern states Location within the DH  Tiny adult worms embedded in mucosa of small intestine o 2 mm long o 0.035 mm wide  Eggs hatch in large intestine and larvae are passed in feces  Some larvae may develop into free-living adult worms Pathogenicity  Incidence is low, but spreads quickly, especially in kennel situations  Highly pathogenic to young puppies  Low morbidity, but mortality rate is high Life Cycle = Direct  First stage (rhabditiform / L1) larvae are passed in feces o Develop through two molts to infective stage larvae (filariform / L3) in 24 to 48 hours. OR (if no suitable host is available) o Develop through four molts to free-living adult worm  Free-living males and females mate to produce more rhabditiform larvae that o Usually become infective filariform larvae OR o Rarely become another generation of free-living adult worms 12/3/2024 1 Methods of Transmission  Oral ingestion: PP = one week  Skin penetration: PP = two weeks  Transmammary: PP = one week Transmission and Migrations of Threadworms  Oral ingestion: Larvae swallowed to small intestine, burrow into mucosa and mature to parasitic adult female (mucosal migration only)  Skin penetration o Tracheal migration: In juvenile dogs, larvae travel via circulatory system to lungs, up trachea, swallowed to small intestine where they penetrate mucosa and mature to parasitic adult female (tracheal migration followed by mucosal migration) o Somatic migration: In adult dogs, many if not most larvae encyst in tissues  Transmammary: Major route of transmission of Strongyloides spp. o As initial infestation is established in DH, many larvae migrate to deeper body tissues and become encysted (somatic migration) o Larvae are activated during pregnancy of female DH, and passed to offspring via milk o Larvae ingested with milk penetrate mucosa and mature into parasitic adult females (mucosal migration only) That’s Right: There are NO parasitic male threadworms Parasitic Females  Females produce eggs by parthenogenesis  Eggs hatch into rhabditiform larvae in large intestine  Rhabditiform larvae are passed in feces, and cycle repeats itself  Prepatent period = 1 to 2 weeks Clinical Signs  Skin penetration o Dermatitis with pruritus caused by migration of infective juveniles through skin o Mild to severe clinical signs of verminous pneumonia during migration through lungs; may be observed 7 to 10 days prior to diarrhea  GI o Inflammation of intestinal mucosa o Diarrhea accompanied by emaciation and exhaustion o In massive infestations, death may occur unless therapeutic measures are taken Diagnosis  Baermann apparatus to isolate larvae from fresh feces -- fecal flotation solutions distort larvae  Direct smear of fecal material -- may detect larvae  In animals with respiratory signs, tracheal wash may demonstrate migrating larvae  ELISA test may diagnose infestation by detecting Strongyloides spp. antibodies  Skin scraping of cutaneous lesions 12/3/2024 2 Treatment  Difficult to eliminate, especially in people and dogs because.... S. stercoralis has ability to “autoinfect” o Rhabditiform larvae can remain in GI tract long enough to develop to filariform larvae o Filariform larvae then penetrate intestinal mucosa, reinfecting DH after completing tracheal migration  Particularly in immunocompromised patients (including neonates)  Thiabendazole: Approved for use against Strongyloides stercoralis in dogs  Fenbendazole: Off-label use  Ivermectin: Off-label use Control  Good sanitation  Desiccation via sunlight Public Health Significance  Strongyloides stercoralis = Zoonotic o CLM o Patent intestinal infestation  Prevention via good hygiene – WASH YOUR HANDS 12/3/2024 3