Leishmaniasis

Leishmaniasis is a vector-borne parasitic disease caused by protozoa of the genus Leishmania and transmitted by the bite of infected sandflies. It presents in distinct clinical forms, most importantly cutaneous leishmaniasis, which causes chronic skin lesions, and visceral leishmaniasis (kala-azar), which affects internal organs and can be fatal if untreated. Cutaneous disease is the form most often seen in travelers.

Definition

Leishmaniasis is infection by protozoan parasites of the genus Leishmania, transmitted through the bite of phlebotomine sandflies, with clinical forms ranging from localised skin lesions to disseminated visceral disease.

Scope

This entry covers the Leishmania-sandfly transmission cycle, the main clinical syndromes (cutaneous, mucocutaneous, and visceral leishmaniasis), and the relevance of the disease to travelers visiting endemic regions. It is a reference and educational topic within travel and tropical medicine and does not provide individualised diagnostic or treatment guidance.

Core questions

• How does the Leishmania-sandfly life cycle transmit infection, and what determines whether disease is cutaneous or visceral?
• What distinguishes cutaneous, mucocutaneous, and visceral leishmaniasis clinically and geographically?
• Why is leishmaniasis, especially the cutaneous form, a relevant consideration in travelers with chronic skin lesions?

Key concepts

• Leishmania species (Old World and New World)
• Phlebotomine sandfly vector
• Promastigote and amastigote life-cycle stages
• Cutaneous leishmaniasis (chronic skin ulcer)
• Mucocutaneous leishmaniasis
• Visceral leishmaniasis (kala-azar)
• Reservoir hosts and zoonotic transmission

Mechanisms

Leishmania has a two-stage life cycle split between the insect vector and the mammalian host. Infected female sandflies inoculate the flagellated promastigote stage into the skin during a blood meal; the parasites are taken up by host macrophages, in which they transform into intracellular amastigotes and multiply, and further sandflies become infected when they feed on an infected host (Burza, 2018). The clinical outcome depends on the Leishmania species and the host immune response: some species remain localised in the skin to produce the chronic ulcer of cutaneous leishmaniasis, some can spread to the mucosa of the nose and mouth (mucocutaneous disease), and others disseminate through the reticuloendothelial system to the spleen, liver, and bone marrow, causing visceral leishmaniasis (Burza, 2018; de Vries, 2015). Transmission may be zoonotic, involving animal reservoirs, or anthroponotic, depending on the region and species.

Clinical relevance

Cutaneous leishmaniasis is a recognised cause of chronic, slow-healing skin lesions in travelers returning from endemic regions, and visceral leishmaniasis is an important consideration in travelers with prolonged fever, weight loss, and splenomegaly after relevant exposure. The entry explains these associations at a reference and educational level and does not direct individual diagnosis or treatment.

Epidemiology

Leishmaniasis is endemic across parts of the Middle East, North and East Africa, the Mediterranean basin, Central and South Asia, and Latin America, and is classed among the neglected tropical diseases; visceral leishmaniasis in particular causes substantial mortality in endemic foci (Burza, 2018). Among travelers, cutaneous leishmaniasis is the predominant imported form, and surveillance of ill returned travelers identifies leishmaniasis as a recognised cause of post-travel skin disease, varying by destination (Freedman, 2006; de Vries, 2015).

History

The causative parasites were identified at the turn of the twentieth century, with the genus named after William Leishman, who described the organisms in visceral disease, and the sandfly was subsequently established as the vector. Contemporary reviews integrate the parasitology, the spectrum of clinical forms, and the global burden of disease (Burza, 2018).

Seminal works

• burza-2018
• devries-2015

Frequently asked questions

How is leishmaniasis transmitted?

It is spread by the bite of infected female sandflies, small insects active mainly at dusk and night in endemic areas. It is not spread directly from person to person in ordinary contact; in some regions animals act as reservoir hosts.

What form of leishmaniasis do travelers most often get?

Travelers most commonly acquire cutaneous leishmaniasis, which causes one or more chronic, slow-healing skin sores at the site of sandfly bites. The more serious visceral form is less common in travelers but important to recognise after exposure in endemic areas. Diagnosis and treatment are clinical decisions beyond the scope of this educational entry.