Strongyloides stercoralis Parasitology Quiz

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