Leishmania mexicana – Parasite
One of a Group of Parasites That Cause Leishmaniasis
Leishmania mexicana, a tissue parasite, causes large skin lesions that are slow to heal. It may be expanding its range northward in the United States.
The word leishmania refers to a genus of parasites that includes many different species, not all of which infect humans. Leishmaniasis, the disease caused by these tiny tissue parasites, also takes various forms, making the topic of leishmania and leishmaniasis somewhat confusing. Leishmania mexicana, one of the less dangerous species, occurs in Central and South America, and occasionally in the US state of Texas.
Leishmania spp. are often divided into two groups: Old World species (occurring in Europe, Africa, the Middle East, Asia, and Polynesia) and New World species (occurring primarily in Central and South America). Though the species are closely related, and may have diverged relatively recently, most Old World species do not occur in the New World, and vice versa.
What is leishmaniasis?
Leishmaniasis is actually a complex of diseases:
- Cutaneous leishmaniasis is a skin disease where the leishmania parasite multiplies in the skin causing a lesion or ulcer that does not heal or takes months to do so. Secondary bacterial infection is common. What appears to be cutaneous leishmaniasis sometimes progresses to more serious forms of the disease.
- Mucocutaneous leishmaniasis occurs when the parasite attacks mucous membranes such as the mouth, nasal passages, pharynx and, rarely, the genitals. Untreated, these lesions can result in terrible deformity and complications are sometimes fatal.
- Visceral leishmaniasis is the most serious form of the disease. Parasites proliferate in internal organs and tissues and severely damage the immune system. Typically, untreated victims die within about three years of the first symptoms.
Visceral leishmaniasis is most common in India, China, Bangladesh, Ethiopia and Sudan. In the Americas, the vast majority of leishmaniasis is cutaneous or mucocutaneous—Leishmania mexicana usually causes cutaneous lesions that heal in three or four months.
How do you catch leishmaniasis?
Leishmania spp. are transmitted to humans through the bite of a sand fly, a tiny blood-sucking fly of any of more than 600 species. Infecting the fly when it bites an infected host, the parasites multiply in the fly’s gut and are expelled into the bite site when the fly feeds again. Infected animals such as rodents, dogs, and cats can pass the parasite to sand flies, which may then infect humans.
Leishmania mexicana
Leishmania mexicana is found from Brazil north to the south-central United States and is thought to be endemic (naturally and regularly occurring) in all these places. Recent reports of human cases in north Texas suggest that the parasite may be expanding, probably the result of either infected rodents or sand fly vectors moving northward. Agricultural and forest workers have an increased risk of infection because of time spend in proximity to rodents.
Fortunately, skin lesions caused by L mexicana often heal on their own, cause little scarring except in certain locations. The infection is sometimes called chiclero ulcer, or bay sore. Reports referring to it as Baghdad boil are technically inaccurate: Baghdad boil refers to cutaneous leishmaniasis caused by Old World species (L. tropica or L. major), which do not occur in the Americas.
Read about other skin parasites:
Scabies mite – Sarcoptes scabiei
Dermatobia hominis – Warble Fly
Find other interesting topics in Microbiology
Sources:
Clinical Parasitology 9th ed. Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Philadelphia: Lea and Febiger, 1984.
Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.
Foundations of Parasitology 6th ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
