Page 458 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 52 Blood & Tissue Protozoa
447
the Middle East, southern Russia, and parts of China, the
reservoir hosts are primarily dogs and foxes. In sub-
Sandflies are the vectors for these three organisms, as they
Saharan Africa, rats and small carnivores (e.g., civets) are
are for L. donovani, and forest rodents are their main reser-
the main reservoirs. A third pattern is seen in India and
voirs. The life cycle of these parasites is essentially the same
neighboring countries (and Kenya), in which humans
as that of L. donovani.
appear to be the only reservoir.
Clinical Findings Pathogenesis & Epidemiology
The lesions are confined to the skin in cutaneous leish-
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maniasis and to the mucous membranes, cartilage, and
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Symptoms begin with intermittent fever, weakness, and
skin in mucocutaneous leishmaniasis. A granulomatous
weight loss. Massive enlargement of the spleen is character-
response occurs, and a necrotic ulcer forms at the bite site.
istic. Hyperpigmentation of the skin is seen in light-
skinned patients (kala-azar means black sickness). The
Old World cutaneous leishmaniasis (Oriental sore,
course of the disease runs for months to years. Initially,
Delhi boil), caused by L. tropica, is endemic in the Middle
patients feel reasonably well despite persistent fever. As
East, Africa, and India. New World cutaneous leishmania-
anemia, leukopenia, and thrombocytopenia become more
sis (chicle ulcer, bay sore), caused by L. mexicana, is found
profound, weakness, infection, and gastrointestinal bleed-
in Central and South America. Mucocutaneous leishmani-
ing occur. Untreated severe disease is nearly always fatal as
asis (espundia), caused by L. braziliensis, occurs mostly in
a result of secondary infection.
Brazil and Central America, primarily in forestry and con-
struction workers.
Laboratory Diagnosis
Diagnosis is usually made by detecting amastigotes in a
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bone marrow, spleen, or lymph node biopsy or “touch”
The initial lesion of cutaneous leishmaniasis is a red papule
preparation (see Figure 52–14). The organisms can also be
at the bite site, usually on an exposed extremity. This
cultured. Serologic (indirect immunofluorescence) tests are
enlarges slowly to form multiple satellite nodules that
positive in most patients. Although not diagnostic, a very
coalesce and ulcerate. There is usually a single lesion that
high concentration of IgG is indicative of infection. A skin
heals spontaneously in patients with a competent immune
test using a crude homogenate of promastigotes (leishma-
system. However, in certain individuals, if cell-mediated
nin) as the antigen is available. The skin test is negative
immunity does not develop, the lesions can spread to
during active disease but positive in patients who have
involve large areas of skin and contain enormous numbers
recovered.
Mucocutaneous leishmaniasis begins with a papule at
Treatment
the bite site, but then metastatic lesions form, usually at the
mucocutaneous junction of the nose and mouth. Disfigur-
The drug of choice is either liposomal amphotericin B or of organisms.
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ing granulomatous, ulcerating lesions destroy nasal carti-
sodium stibogluconate. With proper therapy, the mortality
lage but not adjacent bone. These lesions heal slowly, if at
rate is reduced to almost 5%. Recovery results in perma-
all. Death can occur from secondary infection.
nent immunity.
Prevention
Diagnosis is usually made microscopically by demonstrat-
Prevention involves protection from sandfly bites (use of
ing the presence of amastigotes in a smear taken from the
netting, protective clothing, and insect repellents) and
skin lesion. The leishmanin skin test becomes positive
insecticide spraying.
when the skin ulcer appears and can be used to diagnose
2. Leishmania tropica, Leishmania
Treatment
mexicana, & Leishmania braziliensis cases outside the area of endemic infection.
The drug of choice is sodium stibogluconate, but the results
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Disease
are frequently unsatisfactory.
Leishmania tropica and L. mexicana both cause cutaneous
leishmaniasis; the former organism is found in the Old
World, whereas the latter is found only in the Americas.
Prevention involves protection from sandfly bites by using
Leishmania braziliensis causes mucocutaneous leishmania-
netting, window screens, protective clothing, and insect
sis, which occurs only in Central and South America.
repellents.
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