Leishmaniasis is a disease caused by a protozoal parasite from over 20 Leishmania species distributed in different parts of the world. About 90 phlebotomine sandfly species are known to be vectors for Leishmania parasites. The parasites are transmitted through the bites of infected female sandflies, which feed on blood for egg production. About 70 animal species, including humans, can be the source of Leishmania parasites. Various mammalian reservoir hosts include dogs, rodents, opossums, bats, armadillos, hyraxes, and others. Leishmaniasis is classified, based on the systems affected and the spectrum of clinical disease, into the following forms: visceral leishmaniasis (VL), cutaneous leishmaniasis (CL), and mucocutaneous leishmaniasis (MCL).

This summary will focus on MCL.

Over 90% of MCL cases occur in Bolivia (the Plurinational State of), Brazil, Ethiopia, and Peru. The most common leishmanial species that cause MCL include those in the Leishmania subgenus (eg, Leishmania mexicana, Leishmania amazonensis) and the Viannia subgenus (eg, Leishmania [Vianna] braziliensis, Leishmania [Vianna] panamensis, Leishmania [Vianna] guyanensis), particularly L braziliensis, Leishmania aethiopica, and L panamensis. All species associated with MCL can cause localized cutaneous disease. MCL can be life-threatening.

The incubation period varies depending on the clinical form of the disease but generally is more than 2 years for MCL.

Mucosal involvement in leishmaniasis can occur concurrently with cutaneous involvement or even after the clearance of cutaneous lesions, sometimes occurring years later. In areas where the disease is endemic, up to 20% of patients may experience mucosal involvement. MCL leads to partial or total destruction of mucous membranes of the nose, mouth, and throat. Lesions in the oral cavity can extend to the oropharynx and larynx, potentially affecting cartilage and vocal cords. MCL lesions are characterized by ulceration and can cause significant disfigurement.

The appearance and evolution over time of the skin lesions of MCL can vary widely. Typically, the primary lesion starts as erythema at the site of a sandfly bite. Thereafter, it evolves, over weeks to months, from a papule to a nodule, which may then ulcerate. Some lesions persist as nodules or plaques. Lymphangitis that ascends the lymphatic chain (sporotrichoid spread) and lymphadenopathy (sometimes bubonic) can be seen; the latter may precede the presence of skin lesions. Pruritus, pain, and bacterial superinfection may also be present. Systemic symptoms are rarely seen.

Unlike localized cutaneous leishmaniasis, mucosal disease does not heal on its own and can be fatal.

About Leishmaniasis
Geographically, leishmaniasis occurs in tropical and temperate regions restricted to natural habitats of the sandfly. In the World Health Organization (WHO) 2018 report, 92 countries were considered endemic for, or had previously reported cases of, CL. In 2022, the WHO estimated that more than 1 billion people live in leishmaniasis endemic areas and are at risk of acquiring infection. Annually, there are an estimated 30 000 new cases of VL, and more than 1 million new cases of CL occur. Leishmaniasis is on the WHO's list of neglected tropical diseases (NTDs). Children are more at risk to be infected with CL.

Approximately 95% of all CL and MCL cases occur in South America, the Mediterranean Basin, the Middle East, or Central Asia. In contrast, VL is more prevalent in Brazil, East Africa, and India. In 2018, over 85% of new CL and MCL cases reported to the WHO originated from Afghanistan, Algeria, Bolivia, Brazil, Colombia, Iran, Iraq, Pakistan, Syria, and Tunisia, while over 95% of new VL cases were reported in Brazil, China, Ethiopia, India, Iraq, Kenya, Nepal, Somalia, and Sudan. And 4 countries – Brazil, Bolivia, Ethiopia, and Peru – accounted for over 90% of new MCL cases.

In economically developed countries, infection is commonly associated with travel and immigration patterns. In the United States, for example, most cases of leishmaniasis are acquired outside the country. Individuals such as US travelers, government workers and volunteers, students, and military personnel are at risk of contracting the disease while overseas. Although sandflies can be found as far north as upstate New York, and cases of visceral leishmaniasis have been identified in foxhounds across various regions of the country, it is believed that human transmission is extremely rare in most of the United States. Occasional isolated cases of localized and diffuse CL have been reported in areas bordering Mexico, such as southern Texas and Oklahoma. While endemic leishmaniasis is uncommon in the United States, climate change may be altering patterns of acquisition. In Texas, for example, endemic leishmaniasis may be more common than travel-acquired disease due to more favorable environmental conditions for leishmaniasis vectors and reservoirs.