Parasitology Quiz: Strongyloides stercoralis Questions and Flashcards

Study Notes

Life Cycle and Diagnosis of Strongyloides

Rhabditiform larva is the diagnostic stage, found in stool samples
The life cycle has three stages: cutaneous, pulmonary, and intestinal
Cutaneous stage involves initial skin penetration
Pulmonary stage involves larval migration in the lungs
Intestinal stage symptoms depend on worm load, with immunocompromised patients exhibiting leukocytosis and eosinophilia

Hyperinfection Syndrome and Autoinfection

Repeated reinfection with larvae can lead to death due to tissue damage
Occurs in immunosuppressed patients (AIDS, drugs)
Can be transferred through organ transplant
Transmammary transmission is possible
Autoinfection occurs when some rhabditiform larvae develop into filariform larvae in the bowel and reinfect the host

Eggs and Ova

Ova measures 50-60 micra by 20-30 micra, averaging 55 by 36 micra
Ova are D-shaped and asymmetrical, with one side flattened and one side convex
Ova have a translucent shell with triple albuminous covering and lipoidal membrane for protection
Eggs become infective (embryonated eggs) in 4-6 hours outside the host
Eggs are resistant to disinfectants, affected by dehydration, and remain viable for 0-13 days or more in moist conditions

Life Cycle and Habitat

Infective stage is the embryonated egg/ova
Diagnostic stage is the ova
Definitive host is humans
Habitat is the large intestine (adult worms) and small intestine (larvae)
No intermediate host is needed, and autoinfection is possible

Diagnosis and Symptoms

Perianal itching or pruritus ani is a common symptom
Autoinfection can lead to familial disease
Diagnosis involves the Scotch tape technique, which collects eggs and larvae stuck to the tape
Best time to collect sample is early morning or at dawn before taking a bath
High titers of filarial antibody (IgE) and formation of hydrocoele or chylocoele are also diagnostic indicators

Malayan Filariasis and Mosquito Vectors

Caused by Wuchereria malayi, which is transmitted by Mansonia mosquito vectors
Takes about 2 weeks to develop
Causes deformities, such as elephantiasis, restricted to the upper extremities

Loa loa (Eye Worm)

Resides in subcutaneous tissue
Exhibits diurnal periodicity (day and night)
Nuclei is continuous up to the tip of the tail
Causes Loiasis, which leads to Calabar swelling (allergic reaction due to worm migration in tissue and death in capillaries)
Also causes itchy and burning sensation in the eye
Mosquito vectors are of the fly genus Chrysops

Description

Test your knowledge on Strongyloides stercoralis, a parasite with a clear, thin shell and rhabditiform larva inside. Learn about its diagnostic stage, definitive hosts, clinical diseases, and the different stages based on its life cycle.