The leishmaniases are infections involving primarily the skin, mucous membranes, and certain internal organs. They are transmitted (in most situations) by biting sandflies from infected domestic and wild animals and humans. These parasitic diseases are mutilating and difficult to treat, and the disfigurement caused by cutaneous forms has a lifelong psychological impact. If left untreated, death may follow in some forms. Children are more vulnerable and is also the group in which the risk of failure of diagnosis is the highest. Control efforts are insufficient and hampered by the wide diversity of transmission situations, each of which may require different control approaches. Moreover, leishmaniasis control is usually hampered by ignorance of the true prevalence of the diseases and underestimation of the human suffering and invalidity they cause.
The disease is associated with considerable morbidity, debility, and mortality. In cutaneous leishmaniasis (Oriental sore, Baghdad boil) caused by Leishmania tropica, the parasites invade the skin and subcutaneous tissue provoking deep ulcers. The mucocutaneous form caused by Leishmania brazihensis, affects the mucous membranes of the nose and mouth causing severe ulceration and disfigurement. The more severe, generalized and often fatal form is visceral leishmanias; and organs rich in reticuloendethial cells are destroyed by Leishmania donovani.
The vector sandflies are abundant in the drier and deforested areas of the tropics and subtropics but may also be found in humid areas. The transmitting female sandfly (only female sandflies take blood) most frequently bites at night and shelters in dark corners during the day. The dog is the principal animal reservoir for leishmaniases but rodents, horses, cattle and sheep have also been found to play a role in transmitting the infection to man. Humans can act as a reservoir in some cases.
The parasites that cause leishmaniasis undergo profound changes during the course of infection. A sand-fly bite transmits the bug in a slender, swimming form called a "promastigote". Symptoms occur only after the organism invades cells and transforms into an oval "amastigote" stage.
With an estimated 12 million cases worldwide, leishmaniasis has been identified by the WHO as the least studied and least understood of the major parasitic diseases of the world. At least 350 million people are at risk. It is found in tropical and subtropical areas all over the world. The disease is widely disseminated in South America and spreading elsewhere, notably in Africa; serious outbreaks took place in India and Kenya in 1977. The disease is spreading to areas never affected before, sometimes causing epidemics of alarming proportions. Because of their zoonotic aspects, both the cutaneous and visceral forms are liable to increase with urbanization and with the reclamation of vast expanses of forest or desert, as in the Amazon basin or in the USSR. Herders and loggers have higher risks of contracting leishmaniasis. Sandflies are active during the day and are an occupational health risk to agricultural workers. Other high risk groups include workers in development projects (oil drilling, mining, road construction, and agriculture). Clearly, environmental changes brought about through human activity such as deforestation have exacerbated the public health risk of leishmaniasis. Movements of migrants, temporary labourers, and any large-scale population displacement may result in a high incidence of infection among such groups. Increasingly, tourists visiting endemic areas are reported to return infected. Among the population in endemic areas, the permanent risk of an epidemic creates constant and genuine fear. The World Health Organization estimates about 12 million cases of leishmaniasis in most parts of the world. More than 400,000 cases are reported each year. Some 350 million people in 80 countries are at risk of this disease.