Page 456 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 52 Blood & Tissue Protozoa
stage. Serologic tests, especially the ELISA for IgM anti-
body, can be helpful.

Treatment
Treatment must be initiated before the development of
encephalitis, because suramin, the most effective drug,
does not pass the blood–brain barrier well. Suramin will
effect a cure if given early. Pentamidine is an alternative
mebooksfree.com mebooksfree.com Trypanosoma brucei—trypomastigotes. Arrow Prevention mebooksfree.com mebooksfree.com
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drug. If central nervous system symptoms are present,
suramin (to clear the parasitemia) followed by melarsoprol
should be given.

The most important preventive measure is protection
against the fly bite, using netting and protective clothing.
FIGURE 52–12
Clearing the forest around villages and using insecticides
points to a trypomastigote (the flagellated form) in the blood. (Source:
are helpful measures. No vaccine is available.
Dr. M. Schultz, Public Health Image Library, Centers for Disease Control and
Prevention.)
LEISHMANIA
The disease is endemic in sub-Saharan Africa, the natu-
ral habitat of the tsetse fly. Both sexes of fly take blood
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mebooksfree.com mebooksfree.com mebooksfree.com The genus Leishmania includes four major pathogens: mebooksfree.com
Leishmania donovani, Leishmania tropica, Leishmania
meals and can transmit the disease. The fly is infectious
mexicana, and Leishmania braziliensis.
throughout its 2- to 3-month lifetime. Trypanosoma gambiense
is the species that causes the disease along water courses in
west Africa, whereas T. rhodesiense is found in the arid
1. Leishmania donovani
regions of east Africa. Both species are found in central
Disease
Africa.
Leishmania donovani is the cause of kala-azar (visceral
Clinical Findings
leishmaniasis).
Although both species cause sleeping sickness, the progress
of the disease differs. Trypanosoma gambiense–induced
disease runs a low-grade chronic course over a few years,
The life cycle of L. donovani is shown in Figure 52–13. The
whereas T. rhodesiense causes a more acute, rapidly pro- Important Properties
3
life cycle involves the sandfly as the vector and a variety of
gressive disease that, if untreated, is usually fatal within
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mebooksfree.com mebooksfree.com mebooksfree.com sucks blood from an infected host, it ingests macrophages- mebooksfree.com
mammals such as dogs, foxes, and rodents as reservoirs.
several months.
Only female flies are vectors because only they take blood
The initial lesion is an indurated skin ulcer (“trypano-
meals (a requirement for egg maturation). When the sandfly
somal chancre”) at the site of the fly bite. After the organ-
isms enter the blood, intermittent weekly fever and
4
containing amastigotes (Figures 52–9E and 52–14).
lymphadenopathy develop. Enlargement of the posterior
After dissolution of the macrophages, the freed amasti-
cervical lymph nodes (Winterbottom’s sign) is commonly
gotes differentiate into promastigotes in the gut. They mul-
seen. The encephalitis is characterized initially by head-
tiply and then migrate to the pharynx and proboscis, where
ache, insomnia, and mood changes, followed by muscle
they can be transmitted during the next bite. The cycle in
tremors, slurred speech, and apathy that progress to som-
the sandfly takes approximately 10 days.
nolence and coma. Untreated disease is usually fatal as a
Shortly after an infected sandfly bites a human, the pro-
result of pneumonia.
mastigotes are engulfed by macrophages, where they trans-
form into amastigotes (Figure 52–9E). Amastigotes can
Laboratory Diagnosis
remain in the cytoplasm of macrophages because they can
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prevent fusion of the vacuole with lysosomes.
During the early stages, microscopic examination of the
blood (either wet films or thick or thin smears) reveals
trypomastigotes (see Figure 52–12). An aspirate of the
Phlebotomus species in the Old World; Lutzomyia species in South
chancre or enlarged lymph node can also demonstrate the
parasites. The presence of trypanosomes in the spinal fluid,
4
Amastigotes are nonflagellated, in contrast to promastigotes, which have
coupled with an elevated protein level and pleocytosis,
a flagellum with a characteristic anterior kinetoplast.
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