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35-03: Leishmaniasis

Philip J. Rosenthal

ESSENTIALS OF DIAGNOSIS

  • Sand fly bite in an endemic area.

  • Visceral leishmaniasis: irregular fever, progressive hepatosplenomegaly, pancytopenia, wasting.

  • Cutaneous leishmaniasis: chronic, painless, moist ulcers or dry nodules.

  • Mucocutaneous leishmaniasis: destructive nasopharyngeal lesions.

  • Amastigotes in macrophages in aspirates, touch preparations, or biopsies.

  • Positive culture, serologic tests, PCR, or skin test.

GENERAL CONSIDERATIONS

Leishmaniasis is a zoonosis transmitted by bites of sand flies of the genus Lutzomyia in the Americas and Phlebotomus elsewhere. When sand flies feed on an infected host, the parasitized cells are ingested with the blood meal (eFigure 35–7). Leishmaniasis is caused by about 20 species of Leishmania; taxonomy is complex. Clinical syndromes are generally dictated by the infecting species, but some species can cause more than one syndrome.

eFigure 35–7.

Life cycle of leishmaniasis. Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies. The sandflies inject the infective stage (ie, promastigotes) from their proboscis during blood meals

image
. Promastigotes that reach the puncture wound are phagocytized by macrophages
image
and other types of mononuclear phagocytic cells. Promastigotes transform in these cells into the tissue stage of the parasite (ie, amastigotes)
image
, which multiply by simple division and proceed to infect other mononuclear phagocytic cells
image
. Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sandflies become infected by ingesting infected cells during blood meals (
image
,
image
). In sandflies, amastigotes transform into promastigotes, develop in the gut
image
(in the hindgut for leishmanial organisms in the Viannia subgenus; in the midgut for organisms in the Leishmania subgenus), and migrate to the proboscis
image
. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)

A flowchart of the life cycle of leishmaniasis parasite.
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A flowchart of the life cycle of leishmaniasis parasite.

The estimated annual incidence of disease has been decreasing, with current estimates of 700,000 to 1 million annual cases of cutaneous disease and 50,000–90,000 cases of visceral disease. Progress against visceral disease has been greatest on the Indian subcontinent.

Visceral leishmaniasis (kala azar) is caused mainly by Leishmania donovani in the Indian subcontinent and East Africa; Leishmania infantum in the Mediterranean, Middle East, China, parts of Asia, and Horn of Africa; and Leishmania chagasi in South and Central America. Other species may occasionally cause visceral disease. Over 90% of cases occur in six countries: India, Bangladesh, Nepal, Sudan, South Sudan, and Brazil. In each locale, the disease has particular clinical and epidemiologic features. The incubation period is usually 4–6 months (range: 10 days to 24 months). Without treatment, the fatality rate reaches 90%. Early diagnosis and treatment reduce mortality to 2–5%.

About 90% of cases of cutaneous leishmaniasis occur in Afghanistan, Pakistan, Syria, Saudi Arabia, Algeria, Iran, Brazil, and Peru. Old World cutaneous leishmaniasis is caused mainly by Leishmania tropica, Leishmania major, and Leishmania aethiopica in the Mediterranean, Middle East, Africa, Central Asia, and Indian subcontinent. New World ...

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