Leishmaniasis (cont.)

The major risk factor for leishmaniasis is being exposed to infected sand flies. The sand flies are most active after dusk and are more common in rural areas. Casual travelers do not usually visit these areas at night, so infection is more common in adventure travelers, Peace Corps workers, missionaries, soldiers, and those with occupational activities that require them to live in rural areas. In healthy people, the degree of immune response to leishmaniasis appears to be genetically determined. In visceral leishmaniasis, a weak immune response is associated with more severe disease. Factors that weaken the immune system include malnutrition and infection with the human immunodeficiency virus (HIV). However, in mucocutaneous leishmaniasis, the symptoms appear to be caused in part by an overactive immune response. Interestingly, the Leishmania parasite itself can be infected with a virus that may cause the parasite to be more dangerous by overstimulating the inflammatory response from the human immune system.

Leishmania may live quietly for years in the body and then begin to multiply (reactivate) if the person's immune system becomes suppressed. Thus, people who were born in a country with leishmaniasis and those who have had travel-related exposure are at risk if they become immunosuppressed by conditions such as chemotherapy, use of steroids, or infection with HIV. Patients who have previously had cutaneous leishmaniasis acquired in certain parts of the New World are at risk for mucocutaneous leishmaniasis.

Source: MedicineNet.com
http://www.medicinenet.com/leishmaniasis/article.htm