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 mucosal leishmaniasis (ML, historically known as mucocutaneous leishmaniasis).

This summary will focus on ML, also known as espundia.

Over 90% of mucosal cases occur in Bolivia (the Plurinational State of), Brazil, Ethiopia, and Peru. The most common leishmanial species that cause ML include those in the Leishmania subgenus, such as Leishmania mexicana and Leishmania amazonensis, and the Viannia subgenus, such as Leishmania (Viannia) braziliensis (the most common organism in the Western hemisphere), L (V) panamensis, and L (V) guyanensis.

Mucosal involvement in leishmaniasis can occur due to dissemination of organisms to the mucosa. Mucosal involvement may develop concurrently with cutaneous involvement or after the clearance of cutaneous lesions, sometimes occurring years later. ML leads to partial or total destruction of mucous membranes of the nose, mouth, throat, and rarely, the genitals. Lesions in the oral cavity can extend to the oropharynx and larynx, potentially affecting cartilage and vocal cords. ML lesions are characterized by ulceration and can cause significant disfigurement.

The appearance and evolution over time of the skin lesions associated with ML 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. Multiple lesions can also occur in the disseminated cutaneous form, which occurs most commonly in Latin America, and which is defined as the presence of 10 or more lesions in 2 or more anatomic locations. Leishmania (V) braziliensis is the most common cause.

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. Leishmaniasis is on the WHO's list of neglected tropical diseases (NTDs).

Approximately 95% of all CL and ML 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 ML cases reported to the WHO originated from Afghanistan, Algeria, Bolivia, Brazil, Colombia, Iran, Iraq, Pakistan, Syria, and Tunisia. Four countries – Brazil, Bolivia, Ethiopia, and Peru – accounted for over 90% of new ML 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 VL 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.