Leishmaniasis is caused by 17 unique and different species of protozoan parasites. These parasites are able to be transmitted between
mammals (and namely humans) from a phlebotomine sandflies when they bite. It effects a fairly large number of people with an estimated 12 million humans infected. There are about .5 million cases of the visceral form and 1.5-2 million of the cutaneous form. It is predominately located in Central and south America, southern Europe, North and East Africa, the Middle East, and the Indian subcontinent.
The treatment situation thus far has been promising and the chemotherapy of Leishmaniasis is aided by new drugs and new formulations of older drugs. The immune systems of the patients themselves are vital in judging the probable efficacy of drug treatments. When people have human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), it is much less likely that commonly used drugs will be effective in treating their form of Leishmaniasis. Oftentimes, people who have HIV/AIDS lack an adequate T-cell mediated immune response which greatly limits their ability to fight infections such as Leishmaniasis. There are some Leishmaniasis drugs that are T cell dependent, such as pentamidine, but some are t cell independent, such as amphotericin B and miltefosine. In addition to people who express both HIV/AIDS, Idiopathic CD4+ lymphocytopenia patients are also more susceptible to prolonged Leishmaniasis. When people have too few CD4+ T lymphocytes, a specific type of white blood cell, they generally have a weakened immune system. Not only would it be weakened, and thus more susceptible to Leishmaniasis, but people with either of these conditions would be more susceptible to any type of infection.
There are over 17 known species of Leishmania that can infect humans, so, logically, each species has biochemical/molecular differences between each other. Because of these distinct differences, each species has a different level of sensitivity to several drugs and some may be more receptive to a certain drug over another. According to a number of previous studies, L. donovani and L. brasiliensis were found to be three to fivefold more sensitive to sodium stibogluconate (a common drug used to fight Leishmaniasis) than L. major, L. tropica, and L. mexicana. In addition to the species variation of certain Leishmaniasis causing agents, there has also been an increasing level of clinical resistance to Leishmaniasis fighting drugs.