For Strongyloides stercoralis, true: (DNB June 2011)
|A||Intermediate host is snail|
|B||Infecting stage is filariform larva|
|C||Both are true|
|D||Both are false|
a. The infective stage for S. stercoralis is filariform larva. There is only one host in its life cycle.
b. Mode of infection is penetration of skin by filariform larvae.
c. The life cycle of Strongyloides stercoralis is complex and unique among the intestinal nematodes. This worm has 2 types of life cycles—a free-living life cycle (rhabditiform larvae) and a parasitic life cycle (filariform infective larvae)—with 3 developmental stages: adult, rhabditiform larva, and filariform larva.
d. The first type of life cycle allows development of nonparasitic adults, both males and females, in the soil, which can indefinitely maintain infestation of the soil. This free-living phase is occasionally termed the heterogonic life cycle.
e. The second type of life cycle allows noninfective new larvae to molt in the human host into infective filariform larvae. Infective larvae can penetrate the intestine and set up a new cycle, commonly termed the hyperinfective or autoinfective cycle.
f. In this setting, unlike in other intestinal nematodes of humans, the larvae can increase in numbers without reinfection from outside. This life-cycle variation is responsible for the decades-long persistence of infection in untreated hosts.
g. Human infection is acquired by penetration of the skin or mucous membranes by infective filariform larvae, either from autoinfection or from contact with infected soil or other material contaminated with human feces.
h. The larvae migrate into the pulmonary circulation via the lymphatic system and venules. Larvae migrate up the pulmonary tree, where they are swallowed, and reach the GI system.
i. In the intestine, S stercoralis adults develop after two moultings can produce an inflammatory reaction and induce a malabsorption syndrome when it attaches to the mucosal folds.
j. The female lays eggs which hatch immediately. This is the only nematode infection in which larvae are seen in the stools.