Leishmaniasis: A forgotten disease among neglected people

摘要

Although leishmaniasis is almost unknown in North America, it is an endemic disease to more than 80 countries with a global incidence of 1.5 – 2 million cases each year. In the last decade there has been a significant increase in the number of cases of leishmaniasis in the few countries with previously high rates of infection. There were also hundreds of confirmed cases in the United States, most in military personnel whom had returned from Iraq. With more soldiers travelling to Afghanistan, increased cases will likely return to the United States bringing a need for domestic public health to better understand this disease. In this article we review the epidemiology, risk factors, clinical presentations, pschycosocial impact, and methods of treatment and prevention of the disease. Introduction Leishmaniasis is one of the most neglected tropical diseases with current high worldwide incidence. Caused by a group of protozoan parasites belonging to the genus Leishmania, an infection of the disease usually results with a variety of clinical syndromes, and can lead to death. In this review we discuss the pathophysiology, epidemiology, risk factors, clinical manifestation, diagnosis, treatment, and psychosocial impact of the disease, along with the existing prevention measures. Pathophysiology Humans become infected by the bite of the female sand fly (the vector). Humans may play a part in maintaining the transmission cycle. Sand flies do not live on or near the sand, as their name would imply. Their primary habitat is in forests, the cracks of stone or mud walls, or animal burrows. The sand fly usually bites at night, and typically flies close to the ground. When sandflies take blood meals from an infected host, they take up macrophages infected with Amastigotes. The Amastigotes transforms into Promastigotes in the midgut of the vector fly. They multiply and finally migrate to the fly's pharynx. The feeding sandfly then clears out its pharynx by expelling Promastigotes into the skin of the host, from where they pass into the blood and tissues of the human host (1). Rodents and/or canines (wild or domestic) serve as the reservoir for most Leishmania species. Infection due to leishmaniasis occurs as a consequence of the interaction between the mammalian reservoirs, the sandfly vectors and humans.Promastigotes are phagocytosed into macrophages of the human’s reticuloendothelial system, where they shed their flagella and become amastigotes again. Amastigtes multiply by binary fission. The infected cells then rupture, causing the infection to spread to other macrophages, and are then carried throughout the body (2). Leishmaniasis can cause a wide spectrum of diseases ranging from mild skin involvement to severe systematic disease. This probably relates to differing virulence in the various parasite species, and differing immune responses of the host. Temperature plays a role in determining the localization of leishmanial lesions. Species causing visceral leishmaniasis usually grow at core temperatures, while those causing cutaneous leishmaniasis grow best at lower temperatures ( See table 1).