Page 452 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com TRYPANOSOMA mebooksfree.com mebooksfree.com
CHAPTER 52 Blood & Tissue Protozoa
441
with AIDS and in premature or debilitated infants. Hospital
outbreaks do not occur, and patients with Pneumocystis
The genus Trypanosoma includes three major pathogens:
pneumonia are not isolated.
Trypanosoma cruzi, Trypanosoma gambiense, and Trypano-
Pneumocystis jiroveci is distributed worldwide. It is
2
soma rhodesiense.
estimated that 70% of people have been infected. Most
5-year-old children in the United States have antibodies
to this organism. Asymptomatic infection is therefore
quite common. Prior to the advent of immunosuppres-
Disease
sive therapy, Pneumocystis pneumonia was rarely seen in 1. Trypanosoma cruzi
Trypanosoma cruzi is the cause of Chagas’ disease (American
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the United States. Its incidence has paralleled the increase
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trypanosomiasis).
in immunosuppression and the rise in the number of
AIDS cases.
Most Pneumocystis infections in AIDS patients are new
rather than a reactivation of a prior latent infection. This
The life cycle of T. cruzi is shown in Figure 52–8. The life
conclusion is based on the finding that Pneumocystis recov-
cycle involves the reduviid bug (Triatoma, cone-nose or
ered from AIDS patients shows resistance to drugs that the
kissing bug) as the vector, and both humans and animals as
patients have not taken.
reservoir hosts. The animal reservoirs include domestic
cats and dogs and wild species such as the armadillo, rac-
Clinical Findings
ingestion of trypomastigotes in the blood of the reservoir
The sudden onset of fever, nonproductive cough, dyspnea,
host. In the insect gut, they multiply and differentiate first
and tachypnea is typical of Pneumocystis pneumonia. coon, and rat. The cycle in the reduviid bug begins with
into epimastigotes and then into trypomastigotes. When
Bilateral rales and rhonchi are heard, and the chest X-ray
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mebooksfree.com mebooksfree.com mebooksfree.com within host cells. Many cells can be affected, but myocar- mebooksfree.com
the bug bites again, the site is contaminated with feces con-
shows a diffuse interstitial pneumonia with “ground glass”
taining trypomastigotes, which enter the blood of the per-
infiltrates bilaterally. In infants, the disease usually has a
son (or other reservoir) and form nonflagellated amastigotes
more gradual onset. Extrapulmonary Pneumocystis infec-
tions occur in the late stages of AIDS and affect primarily
dial, glial, and reticuloendothelial cells are the most fre-
the liver, spleen, lymph nodes, and bone marrow. The
quent sites. To complete the cycle, amastigotes differentiate
mortality rate of untreated Pneumocystis pneumonia
into trypomastigotes, which enter the blood and are taken
approaches 100%.
up by the reduviid bug (Figures 52–9A to C and 52–10).
Laboratory Diagnosis
Diagnosis is made by finding the typical cysts by micro-
Chagas’ disease occurs primarily in rural Central and
scopic examination of lung tissue or fluids obtained by
South America. Acute Chagas’ disease occurs rarely in the
bronchoscopy, bronchial lavage, or open lung biopsy Pathogenesis & Epidemiology
United States, but the chronic form causing myocarditis
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mebooksfree.com mebooksfree.com mebooksfree.com lives in the walls of rural huts and feeds at night. It bites mebooksfree.com
(see Figure 52–7). Sputum is usually less suitable. The
and congestive heart failure is seen with increasing fre-
cysts can be visualized with methenamine silver, Giemsa,
quency in immigrants from Latin America. The disease is
or other tissue stains. Fluorescent-antibody staining is
seen primarily in rural areas because the reduviid bug
also commonly used for diagnosis. PCR-based tests
using respiratory tract specimens are also useful. The
preferentially around the mouth or eyes, hence the name
organism stains poorly with Gram stain. There is no
“kissing bug”.
serologic test, and the organism has not been grown in
The amastigotes can kill cells and cause inflammation,
culture.
consisting mainly of mononuclear cells. Cardiac muscle is
the most frequently and severely affected tissue. In addi-
Treatment
loss of tone in the colon (megacolon) and esophagus
The treatment of choice is a combination of trimethoprim
(megaesophagus). During the acute phase, there are both
and sulfamethoxazole (Bactrim, Septra). Pentamidine and tion, neuronal damage leads to cardiac arrhythmias and
trypomastigotes in the blood and amastigotes intracellu-
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mebooksfree.com mebooksfree.com mebooksfree.com 2 species called T. brucei gambiense and T. brucei rhodesiense, but the mebooksfree.com
atovaquone are alternative drugs.
larly in the tissues. In the chronic phase, the organism
persists in the amastigote form.
Prevention
Trimethoprim-sulfamethoxazole or aerosolized pentami-
Taxonomically, the last two organisms are morphologically identical
dine should be used as chemoprophylaxis in patients whose
CD4 counts are below 200.
shortened names are used here.
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