Leishmania braziliensis is a single-celled protozoan parasite that causes a specific form of leishmaniasis, a disease affecting millions globally. Prominent in the New World, particularly Central and South America, it is recognized for its genomic variability, especially in isolates found in Brazil and Peru.
Transmission Pathways
Leishmania braziliensis is transmitted to humans primarily through the bite of infected female sandflies, specifically species from the Lutzomyia genus. When an infected sandfly takes a blood meal, it injects the infective stage of the parasite, called promastigotes, into the human skin. These promastigotes are then taken up by macrophages and other immune cells in the human body.
Inside these human cells, the promastigotes transform into amastigotes, the multiplying form of the parasite. These amastigotes then multiply by simple division, infecting new mononuclear phagocytic cells within the human host. The sandfly becomes infected by ingesting these amastigote-filled cells when it feeds on an infected human or animal reservoir host.
Within the sandfly, the amastigotes transform back into promastigotes, developing in the gut before migrating to the proboscis, ready for transmission to another host. Forest rodents, sloths, and anteaters are among the known reservoir hosts for Leishmania braziliensis. The ability of Leishmania species to bind to the sandfly midgut allows them to propagate and differentiate into infectious promastigotes.
Disease Manifestations
Infection with Leishmania braziliensis leads to specific clinical forms of leishmaniasis, predominantly cutaneous leishmaniasis (CL) and mucocutaneous leishmaniasis (MCL). Cutaneous leishmaniasis, the more common initial presentation, involves skin lesions at the site of the sandfly bite. These lesions begin as small red papules that gradually enlarge, often up to 2 centimeters in diameter.
The initial papule can progress to an open lesion with a raised border and a central ulcer, which may be moist or crusted. These sores commonly appear on exposed skin areas, such as the face and extremities. The time between the sandfly bite and the appearance of the lesion can range from approximately two weeks to six months.
Mucocutaneous leishmaniasis (MCL) is a more severe form, often occurring after the primary cutaneous lesion has healed, sometimes months or even years later. This form is characterized by the dissemination of the parasite to mucous membranes, most commonly affecting the nose, mouth, and throat. Lesions in these areas can lead to ulceration and destruction of underlying tissue, causing significant disfigurement.
Mucosal lesions are frequently painful and susceptible to secondary bacterial infections. Without appropriate treatment, the destruction of tissue in MCL can be extensive and, in severe cases, may be fatal. In endemic areas, mucosal involvement may be observed in up to 20% of patients.
Diagnosis and Treatment Approaches
Diagnosing Leishmania braziliensis infection involves several methods. Direct methods include microscopic examination of tissue smears or biopsies taken from lesions, where the characteristic amastigotes can be observed. Parasite isolation through in vitro culture from tissue samples is another direct diagnostic approach.
Molecular methods, such as polymerase chain reaction (PCR), are highly sensitive and employed to detect parasite DNA in clinical specimens. While serological tests can be helpful for diagnosing visceral leishmaniasis, their utility for active cutaneous leishmaniasis is limited. Species identification, often done by reference laboratories, is important, especially when there is a risk of mucocutaneous leishmaniasis.
Treatment for Leishmania braziliensis infections involves antiparasitic medications. Pentavalent antimonials have historically been mainstays of therapy, although resistance is increasing in some areas. These are often administered parenterally, and treatment duration can vary, sometimes requiring up to 28 days for mucosal lesions.
Amphotericin B is another effective treatment option and is often preferred in cases of antimony resistance. Miltefosine, an oral medication, is approved for cutaneous and mucocutaneous leishmaniasis caused by L. braziliensis in patients aged 12 or older and weighing at least 66 pounds, who are not pregnant or breastfeeding. The choice of medication, dosage, and duration is individualized, considering parasite and host factors, along with the clinical characteristics of the disease.
Prevention Strategies
Preventing Leishmania braziliensis infection primarily focuses on avoiding sandfly bites, particularly during peak biting hours, which occur from dusk to dawn. Staying in well-screened or air-conditioned indoor areas can help reduce exposure to sandflies. These insects are considerably smaller than mosquitoes, allowing them to pass through smaller openings.
When outdoors, wearing protective clothing minimizes exposed skin. Applying insect repellent containing DEET to exposed skin provides additional protection. Permethrin-treated clothing and bed nets can also be used, with bed nets needing to be of a fine mesh size.
Spraying living and sleeping areas with insecticide can help eliminate sandflies. Using fans or ventilators indoors can disrupt sandfly movement, as these insects are weak fliers. While no vaccine or chemoprophylaxis is currently available for humans, these personal protective measures are the most effective way to prevent infection in endemic areas.