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After receiving a heart transplant and immunosuppressive
therapy, a 56-year-old Vietnam War veteran develops
fever and pulmonary infiltrates. Microscopic examination
of bronchoalveolar lavage fluid reveals a 1-mm
worm. Which of the following is the most likely means by
which this infection was acquired?
(A) Ingestion of eggs in contaminated water
(B) Ingestion of infected feces
© Ingestion of larvae in infected meat
(D) Mosquito inoculation of larvae
(E) Skin penetration by larvae
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(E) Skin penetration by larvae
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The correct answer is E. This patient is suffering from
hyperinfection syndrome with Strongyloides stercoralis.
The original helminth infection was probably acquired
during his tour in Vietnam, and now that he is
immunosuppressed, the infection has accelerated.
Strongyloides is acquired by skin penetration of larvae,
and it has an unusual life cycle in that it can persist by
reinfecting the same host for unlimited periods of time.
When immunosuppressed, the speed with which the
life cycle repeats can become life threatening.
Strongyloides is one of three parasites that have a period
of migration through the lung, but of the others, Ascaris
produces a much larger larva, and hookworms (which
would have a similar-sized larva to the one described
here) could not persist in the host without renewed
infection from the outside. Ascaris could not persist in
the patient or reinfect by autoinfection, as seems likely
to have happened in this vignette.
Ingestion of eggs in contaminated water (choice A) is
an unlikely way of acquiring an intestinal helminth. In
the life cycle of most organisms that infect a host
through the ingestion of eggs, infection occurs when
fecal material is used as fertilizer and contaminates
foodstuff.
Ingestion of infected feces (choice B) is not the typical
means of acquiring a helminth infection. Usually, the
fecal material contaminating a food source is unwittingly
consumed.
Ingestion of larvae in infected meat (choice C) is the
means by which parasites such as tapeworms and the
nematode Trichinella are acquired.
Mosquito inoculation of the larvae (choice D) is the
means by which the agents of lymphatic filariasis are
acquired.
