WHAT IS LEISHMANIASIS?
The leishmaniasis represent a diverse collection of diseases with over 20 Leishmania species. They affect approximately 150 million people in 98 countries and are recognised by WHO as major neglected diseases of poverty, and disproportionately affect populations in low and middle income countries.
There are three main forms of the disease:
Visceral leishmaniasis (VL), also known as kala-azar is caused by the protozoan parasites Leishmania donovani and Leishmania infantum. There is an estimated 50,000 to 90,000 new cases of VL occurring annually worldwide, and in approximately 95% of cases, it proves fatal if left untreated, with an estimated 20,000 to 30,000 deaths due to VL annually. VL is characterized by irregular bouts of fever, weight loss, enlargement of the spleen and liver, and anaemia.
Cutaneous leishmaniasis (CL) is the most common form of leishmaniasis. Figures state that over 600,000 to 1,000,000 new cases occur annually worldwide, with 95% of cases occurring in the Americas, the Mediterranean basin, the Middle East and Central Asia. CL presents as skin lesions, mainly ulcers, on exposed parts of the body, leaving life-long scars and serious disability.
Mucocutaneous leishmaniasis causes both skin and mucosal ulcers with damage primarily of the nose and mouth. Over 90% of mucocutaneous leishmaniasis cases occur in Bolivia, Brazil, Ethiopia and Peru.
Leishmania parasites are transmitted through the bites of infected female phlebotomine sand flies. There are approximately 500 known phlebotomine species, but only about 30 have been found to transmit leishmaniasis.
The sandflies inject the infective stage, metacyclic promastigotes, during blood meals. Metacyclic promastigotes that reach the puncture wound are phagocytized by macrophages and transform into amastigotes. Amastigotes multiply in infected cells and affect different tissues, depending on which Leishmania species is involved.
Sandflies become infected during blood meals on infected hosts when they ingest macrophages infected with amastigotes. In the sandfly’s midgut, the parasites differentiate into promastigotes, which multiply, differentiate into metacyclic promastigotes, and migrate to the proboscis.