Strongyloides spp. Quiz

Strongyloides spp.

• Strongyloides spp. are intestinal nematodes.
• Also known as "intestinal threadworm".
• Strongyloides stercoralis affects dogs, humans, cats, and non-human primates.
• Strongyloides tumefaciens affects cats (rare).
• Considered zoonotic.

Unique Characteristics

• Parasitic worms are all female.
• Female worms reproduce asexually (parthenogenesis).
• Eggs hatch in the gut and larvae pass in feces.
• Larvae can develop into free-living adult worms.
• Can cause autoinfection in the host.

Distribution

• Thrive in moist, warm climates, especially swamps.
• Primarily found in tropical climates.
• Common in southeastern US.

Location in the Host

• Tiny adult worms embedded in the small intestine mucosa.
• Approximately 2 mm long and 0.035 mm wide.
• Eggs hatch in the large intestine and larvae are passed in feces.

Pathogenicity

• Low incidence but can spread quickly, especially in kennels.
• Highly pathogenic to young puppies.
• Low morbidity but high mortality rate.

Life Cycle (Direct)

• First-stage (rhabditiform/L1) larvae are passed in feces.
• Develop into two molts to infective larvae (filariform/L3) in 24-48 hours.
• OR, if no suitable host is available, develop through four molts into free-living adult worms.
• Free-living males and females mate to produce rhabditiform larvae.
• Usually become infective filariform larvae.
• Rarely, these become a new generation of free-living adult worms.

Mode of Transmission

• Oral ingestion (1 week).
• Skin penetration (2 weeks).
• Transmammary (1 week).

Transmission and Migration

• Oral ingestion: Larvae travel to the small intestine, burrow into the mucosa, and become adult females (mucosal migration).
• Skin penetration: Larvae travel to the lungs, then trachea, are swallowed, and migrate to the small intestine (tracheal migration followed by mucosal migration).
• Somatic migration: Larvae migrate to deeper tissues and become encysted.
• Transmammary: Larvae are transmitted to newborns via milk, which penetrates the mucosa and becomes parasitic adult females.

Parasitic Females

• Females reproduce asexually using parthenogenesis.
• Eggs hatch into rhabditiform larvae in the large intestine.
• Pre-patent period: 1-2 weeks.
• Rhabditiform larvae are passed in feces.

Clinical Signs

• Skin penetration: Dermatitis & pruritus.
• Gastrointestinal: Mild to severe verminous pneumonia, diarrhea, emaciation, and exhaustion.

Diagnosis

• Baermann apparatus (fecal material): Isolating larvae.
• Direct smear of fecal material: Detecting larvae.
• Tracheal wash: Respiratory issues.
• ELISA: detecting antibodies.
• Skin scrapes: Cutaneous lesions.

Treatment

• Difficult to eliminate, especially in humans and dogs due to ability to autoinfect.
• Rhabditiform larvae can remain in the GI tract.
• Filariform larvae penetrate the intestinal mucosa, reinfecting the host.
• Thiabendazole, Fenbendazole, and Ivermectin are approved or off-label for use in dogs.
• Ivermectin, used off-label, shows promise.

Control

• Good sanitation.
• Desiccation (sunlight).

Public Health Significance

• Strongyloides stercoralis is zoonotic.
• Clinically significant.
• Prevention via good hygiene (handwashing).

Test your knowledge about Strongyloides spp., intestinal nematodes that impact various species including humans and pets. This quiz covers their unique characteristics, distribution, and pathogenicity. Learn about their reproduction and how they thrive in warm climates.