Page 463 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART VI Parasitology
452
the typical oocysts in fecal specimens. Serologic tests are
not available. The treatment of choice is trimethoprim-
ache for the past 2 days. Pertinent history includes swimming in
a pond near their home in rural California in August. On exam,
sulfamethoxazole.
nuchal rigidity was observed and a lumbar puncture was per-
formed. The spinal fluid white blood cell count was 12,200 with
MICROSPORIDIA
80% neutrophils. Microscopic examination of a wet mount of spi-
nal fluid revealed motile trophozoites. Of the following, which one
Microsporidia are a group of protozoa characterized by
is the most likely cause?
obligate intracellular replication and spore formation. As
the name implies, the spores are quite small, approximately (A) Babesia microti
(B) Cryptosporidium parvum
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1 to 3 mm, about the size of Escherichia coli. One unique
(C) Naegleria fowleri
(D) Toxoplasma gondii
feature of these spores is a “polar tube,” which is coiled
(E) Trypanosoma cruzi
within the spore and extrudes to attach to the human cells
upon infection. The protoplasm of the spore then enters the
who had been vacationing 2 weeks ago on one of the islands off the
human cell via the polar tube.
coast of Massachusetts. Microscopic examination of a blood smear
Enterocytozoon bieneusi and Encephalitozoon intestinalis
reveals ring-shaped trophozoites in tetrads within red blood cells.
are two important microsporidial species that cause severe,
Of the following, which one is the most likely cause?
persistent, watery diarrhea in AIDS patients. The organ-
(A) Babesia microti
isms are transmitted from human to human by the fecal–
(B) Cryptosporidium parvum
oral route. Microsporidia are also implicated in infections
(C) Naegleria fowleri
of the central nervous system, the genitourinary tract, and
(D) Toxoplasma gondii
(E) Trypanosoma cruzi
the eye. It is uncertain whether an animal reservoir exists.
Diagnosis is made by visualization of spores in stool sam- ANSWERS
ples or intestinal biopsy samples. The treatment of choice is
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albendazole.
1. (A)
3. (C)
SELF-ASSESSMENT QUESTIONS
4. (A)
1. Regarding Acanthamoeba and Naegleria species, which one of the
following is most accurate?
SUMMARIES OF ORGANISMS
(A) They are free-living amebas that live in warm fresh water.
(B) Naegleria is a well-recognized cause of otitis media, primarily
in children.
begin on page 684. Please consult these summaries for a rapid
(C) The drug of choice for infections caused by these organisms is
review of the essential material.
chloroquine.
(D) Their main clinical presentation is pneumonia acquired when Brief summaries of the organisms described in this chapter
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water is aspirated into the lung.
PRACTICE QUESTIONS: USMLE &
2. Regarding B. microti, which one of the following is most accurate?
COURSE EXAMINATIONS
(A) It infects macrophages, causing them to lyse.
(B) Doxycycline is the drug of choice for babesiosis.
(C) It is transmitted by the bite of Culex mosquitoes.
in the Parasitology section of Part XIII: USMLE (National
(D) Seeing sporozoites within red cells supports the diagnosis of
Board) Practice Questions starting on page 731. Also see Part
babesiosis.
XIV: USMLE (National Board) Practice Examination starting
(E) Babesia microti causes disease primarily in the northeastern
on page 751.
region of the United States.
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