Leishmaniasis

Leishmaniasis is one of the most important parasitic diseases of humans. The cutaneous (skin) and mucocutaneous (skin and membranes) types cause over 2 million new cases and the visceral (organ) types leads to over 500,000 new cases every year. Many tens of millions of individuals suffer from its effects and over 60,000 die every year. There are hundreds of millions of people who live in the poorest parts of the world who are at risk of infection.

Leishmaniasis is caused by an intracellular protozoan parasite that is transmitted by the bite of infected sand flies of the phlebotomous (old world) and lutzomyia (new world) species. Reservoirs of these zoonotic parasites include dogs, rodents, and opossums, among others. There are more than a dozen species of leishmania that cause different clinical manifestations and are found in different parts of the world.

Cutaneous leishmaniasis is known in different parts of the world as Allepo evil, Delhi boil, Espundia, and Uta. It is caused most commonly by organisms of the Leishmania brazilensis complex (group of related species) in South America, and L. major/L. tropica complexes in Africa and Asia. The disease occurs from days to months after a bite by an infected insect and usually begins with a small nodule at the site of infection. Depending on the species and the individual patient, these lesions may remain small nodules or may form dry or wet well—demarcated painless ulcers with raised borders on exposed body parts. The lesions may vary from small single nodules to multiple diffuse disfiguring ulcerations, and last for variable durations. The mucocutaneous type can be particularly destructive in the oral and nasal mucosa and cause a great deal of discomfort and dysfunction. Diagnosis of cutaneous leishmaniasis may be made by touch smears, scrapings, or culture of exudates of lesions. Serological and polymerase chain reaction (PCR) techniques also exist, but cost limits their use.

Depending on the species, most cutaneous lesions heal spontaneously within three to 18 months and treatment may or may not be undertaken. Drugs that are effective for cutaneous and mucocutaneous leishmaniasis include a variety of antimony (Sb) compounds, amphotericin (particularly liposomal), and now miltefosine. There are also several novel topical regimens using paromomycin and imiquomod, among others.

Visceral leishmaniasis, also known as Kala-Azar and DumDum fever, is most often caused by L. donovani complex (including L. chagasi in the New World, and L. donovani and infantum in the Old World). Classically, the pentad of fever, cachexia, splenomegally, pancytopenia, and hypergammaglobulinemia follows the bite of an infected sand fly and an inconspicuous cutaneous lesion. While there are asymptomatic variants, in untreated patients, emaciation and death occur in up to 90 percent of cases within one to two years. Diagnosis of visceral leishmaniasis is made by tissue smear of splenic, marrow, or node aspirate, or by a variety of tests including rapid commercial, direct agglutination, and urine antigen tests. PCR is the most sensitive and specific but is not always available. Treatment of visceral leishmaniasis, like its severity and resistance pattern, varies with species and geography. Antimony compounds and amphotericin B are first-line treatments with miltefosine, azoles, and others gaining in popularity.

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