Leishmaniasis is caused by protozoan parasites belonging to the genus Leishmania.
These parasites are transmitted to humans and animals through the bite of infected female phlebotomine sandflies. Over 20 Leishmania species can cause leishmaniasis, and over 90 sandfly species are capable of transmitting the parasite.
How Transmission Works
- Sandfly Bites: The primary mode of transmission is through the bite of infected female sandflies. Male sandflies do not bite.
- Parasite Introduction: When an infected sandfly bites a human or animal host, it injects Leishmania parasites (in their promastigote form) into the skin.
- Macrophage Infection: These promastigotes are then engulfed by macrophages (a type of white blood cell) in the host's body.
- Amastigote Transformation: Inside the macrophages, the parasites transform into their amastigote form, which multiplies within the host cells.
- Sandfly Ingestion: When a sandfly bites an infected host, it ingests macrophages containing amastigotes.
- Life Cycle Completion: In the sandfly's gut, the amastigotes transform back into promastigotes, multiply, and migrate to the sandfly's proboscis, completing the life cycle and preparing the sandfly to infect a new host.
Types of Leishmaniasis
The clinical manifestations of leishmaniasis vary depending on the Leishmania species involved and the host's immune response. The three main forms of the disease are:
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Visceral Leishmaniasis (VL): Also known as kala-azar, this is the most severe form. It affects internal organs like the spleen, liver, and bone marrow. Untreated visceral leishmaniasis is fatal in over 95% of cases.
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Cutaneous Leishmaniasis (CL): The most common form, cutaneous leishmaniasis causes skin sores or ulcers at the bite site. These sores can heal on their own, but may take months or even years, and can leave permanent scars.
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Mucocutaneous Leishmaniasis (MCL): A less common form, mucocutaneous leishmaniasis occurs when the parasite spreads from the skin to the mucous membranes of the nose, mouth, and throat. This can lead to significant disfigurement.
In Summary
Leishmaniasis is a parasitic disease transmitted by sandflies, caused by various Leishmania species. The form of the disease and its severity depend on the specific parasite and the individual's immune response.
