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Infectious Disease and Microbiology - Leishmaniasis
Leishmaniasis is a parasitic disease caused by protozoa of the genus Leishmania and transmitted through the bite of infected sandflies. It presents in three main clinical forms: cutaneous, mucosal, and visceral, with manifestations depending largely on the host immune response and the infecting species. The disease is widespread, with millions of cases globally and hundreds of millions of people at risk, particularly in tropical and subtropical regions.
Transmission occurs when infected sandflies inoculate promastigotes into the skin. These are taken up by macrophages, where they transform into amastigotes and multiply intracellularly. The parasites preferentially infect cells of the reticuloendothelial system. Disease severity is influenced by parasite burden, species type, and the host’s immune status. Immunocompromised individuals, especially those with HIV, are at increased risk of severe disease.
Cutaneous leishmaniasis typically begins as a papule at the site of the bite, which gradually enlarges, crusts, and ulcerates. The ulcer is usually painless, with raised borders and a granulating base, and may persist for months or even years. Mucosal leishmaniasis, most commonly associated with Leishmania braziliensis, affects the mucous membranes of the nose, mouth, and throat, potentially causing destructive lesions such as nasal septum perforation and voice changes.
Visceral leishmaniasis, also known as kala-azar, is the most severe form and is commonly caused by Leishmania donovani and Leishmania infantum. It presents with prolonged fever, weight loss, hepatosplenomegaly, anemia, and pancytopenia. Without treatment, it carries a high mortality rate. In advanced cases, patients may develop cachexia, edema, and profound immune dysfunction.
Diagnosis is confirmed by demonstrating the parasite in tissue samples such as bone marrow, spleen, liver, or skin lesions. Bone marrow aspiration is commonly used for visceral disease. PCR and serologic tests can support the diagnosis, particularly in visceral leishmaniasis, while skin tests are more useful in epidemiologic studies or cutaneous forms.
Treatment depends on the form and severity of disease. Liposomal amphotericin B is the treatment of choice for visceral leishmaniasis. Other agents include pentavalent antimonials, pentamidine, and newer oral therapies such as miltefosine. Many cases of cutaneous leishmaniasis resolve spontaneously, although treatment may be required for cosmetic reasons or severe disease. Mucosal disease requires systemic therapy due to its destructive nature.
The prognosis varies by form. Cutaneous disease generally has a good outcome, although scarring may occur. Visceral leishmaniasis is life-threatening if untreated but responds well to appropriate therapy. Mucosal disease can lead to significant morbidity and, in some cases, mortality. Complications include relapse, particularly in immunocompromised patients, and adverse effects from treatment such as toxicity from antimonial drugs.
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