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Questions and Answers

What is the primary method of transmission of Strongyloides spp. to offspring during pregnancy?

Environmental exposure in contaminated areas

Transmammary transmission (correct)

Direct skin penetration

Oral ingestion of larvae

What happens to larvae that migrate via the tracheal route in juvenile dogs?

They mature directly in the lungs

They encyst in the intestines

They are swallowed and penetrate the mucosa of the small intestine (correct)

They are excreted in feces immediately

What is the primary consequence of massive infestations of Strongyloides spp. in hosts?

Transmutation of larvae into free-living adults

Sudden weight gain and lethargy

Death if therapeutic measures are not taken (correct)

Permanent immunity to reinfection

In which phase of its life cycle does the female Strongyloides spp. reproduce by parthenogenesis?

Once it matures into a parasitic adult Signup and view all the answers

What is the defined prepatent period for Strongyloides spp. infestations?

1 to 2 weeks Signup and view all the answers

Which of the following clinical signs is associated with skin penetration of infective juveniles?

Dermatitis with pruritus Signup and view all the answers

Which diagnostic method is recommended for isolating larvae from fresh feces of infected animals?

Baermann apparatus Signup and view all the answers

What occurs to the larvae during somatic migration in adult dogs?

They encyst in deeper body tissues Signup and view all the answers

What is the primary indicator of respiratory signs in animals infected with Strongyloides spp.?

Migration of larvae through the lungs Signup and view all the answers

What is the role of rhabditiform larvae in the lifecycle of Strongyloides spp.?

They are released in feces to restart the cycle Signup and view all the answers

What is a unique reproductive characteristic of Strongyloides stercoralis?

Females reproduce via parthenogenesis Signup and view all the answers

Which animals are hosts for Strongyloides stercoralis?

Dogs, humans, and non-human primates Signup and view all the answers

Where is the typical habitat for Strongyloides spp.?

Moist soil of warm climates Signup and view all the answers

What happens to the larvae of Strongyloides stercoralis after they are passed in feces?

They undergo a process of autoinfection Signup and view all the answers

What is the mortality rate associated with Strongyloides stercoralis?

Low morbidity but high mortality rate, especially in young puppies Signup and view all the answers

What is the size of adult Strongyloides stercoralis?

2 mm in length and 0.035 mm in width Signup and view all the answers

In which regions of the U.S. is Strongyloides stercoralis most commonly found?

Southeastern states with warm climates Signup and view all the answers

What are the initial larvae of Strongyloides stercoralis called?

Rhabditiform larvae Signup and view all the answers

What is the life cycle type of Strongyloides stercoralis?

Direct lifecycle without intermediate hosts Signup and view all the answers

How long does it take for Strongyloides stercoralis larvae to develop into the infective stage?

24 to 48 hours Signup and view all the answers

Study Notes

Strongyloides spp.

Strongyloides spp. are nematodes of the small intestine, also known as intestinal threadworms.
Two species are common: Strongyloides stercoralis (found in dogs, humans, and other primates) and Strongyloides tumefaciens (rarely found in cats).
The species are zoonotic.

Unique Characteristics

Parasitic worms are all females.
Female worms reproduce asexually (parthenogenesis)
Eggs hatch in the GI tract and larvae are passed in feces.
Larvae can develop into free-living adult worms or reinfect the host (autoinfection).

Distribution

Thrive in moist soil of warm climates, primarily tropical regions.
In the U.S., frequently found in southeastern states.
Tiny adult worms are embedded in the mucosa of the small intestine (2 mm long, 0.035 mm wide).

Pathogenicity

Low incidence but rapidly spreads, especially in kennel settings.
Highly pathogenic to young animals (e.g., puppies).
Low morbidity but high mortality rate.

Life Cycle

Direct development through two molts to infective larvae (filariform) in 24-48 hours.
Alternatively, if no host is available, larvae may develop through four molts into free-living adults.
Free-living males and females mate to produce rhabditiform larvae.
These larvae usually become infective filariform larvae, to reinfect the host or become free-living adults.

Modes of Transmission

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

Transmission and Migrations

Oral ingestion causes larvae to burrow into the small intestine to mature into parasitic females. This happens through mucosal migration.
In juvenile dogs, larvae travel via the circulatory system, lungs, up the trachea, and into the esophagus, which ultimately gets swallowed.
This is known as tracheal migration followed by mucosal migration.
In adult dogs, many larvae encapsulate in tissues (somatic migration).

Parasitic Females

Produce eggs through parthenogenesis.
Eggs hatch into rhabditiform larvae in the large intestine and the cycle repeats itself.
Prepatent period is 1-2 weeks.

Clinical Signs

Skin penetration: dermatitis, itching.
Gastrointestinal: diarrhea, mild to severe pneumonia, inflammation of intestinal mucosa, exhaustion.

Diagnosis

Baermann apparatus to isolate larvae from feces.
Fecal flotation for detection of larval forms.
Direct fecal smears can sometimes detect larvae.
ELISA to test for antibodies in animals.
Tracheal wash or skin scrapings for animals with respiratory problems.

Treatment

Difficult to eliminate due to autoinfection.
Drugs like thiabendazole, fenbendazole, and ivermectin, though off-label uses are common, have shown varying degrees of effectiveness.