Tropical Diseases - Leishmaniasis
Leishmaniasis is similar to malaria in that the disease organisms are protozoa transmitted to humans by an insect bite, but the insect in this case is the sandfly. There are several forms that leishmaniasis can take. The kind considered most lethal, with a mortality rate of up to 95 percent of untreated adults, is known as kala-azar , a term derived from the Hindi language meaning “black disease”. Kala-azar also is known as black fever , dumdum fever , and visceral leishmaniasis . It occurs from China through Russia and India to North Africa, the Mediterranean countries of Europe, and in parts of Central and South America. Kala-azar has appeared in the United States in cases contracted overseas.
The symptoms may not appear for a period of from ten days to more than three months after the bite of a sandfly, although the disease organism may be found in blood tests before the first symptoms occur. Symptoms include a fever that reaches a peak twice a day for a period of perhaps several weeks, then recurs at irregular intervals while the patient experiences progressive weakness, loss of weight, loss of skin color, and a rapid heartbeat. In some cases, depending upon the type of infection, there may be gastrointestinal complaints and bleeding of the mucous membranes, particularly around the teeth. There also can be edema, an accumulation of fluid in the tissues that conceals the actual loss of body tissue. Physical examination shows an enlarged spleen and liver plus abnormal findings in blood and urine tests.
American Cutaneous Leishmaniasis
The American cutaneous form of leishmaniasis usually begins with one or more skin ulcers resulting from sandfly bites, with the skin of the ear the target site of the insect in many cases. The skin lesion may enlarge, with or without secondary infection by other disease organisms, and spread into the lymphatic system of the body. From the lymph system, the infecting protozoa may invade the mouth and nose, producing painful and mutilating skin ulcers and other destructive changes in the tissues. Bacterial infections and respiratory problems can lead to the death of the patient. In some areas of Central and South America, more than 10 percent of the population suffer from the disfiguring effects of leishmaniasis. Diagnosis usually is confirmed by medical tests that identify the leishmaniasis organism in the patient's tissues.
Old World Cutaneous Leishmaniasis
A milder form, sometimes known as Old World cutaneous leishmaniasis, occurs from India westward to the Mediterranean countries and North Africa. An ulcer appears at the site of a sandfly bite, usually several weeks after the bite, but it heals during a period of from three months to a year. A large pitted scar frequently remains to mark the site of the ulceration, but the invading organism does not spread deeply into the body tissues as in the severe types of leishmaniasis.
Therapy for leishmaniasis cases includes administration of various medications containing antimony, along with antibiotics for the control of secondary infections. Bed rest, proper diet, and, in severe cases, blood transfusions also are advised.
The leishmaniasis organisms injected into the human body by the sandfly bite multiply through parasitic invasion of the tissue cells, particularly blood cells that usually resist infection. They may invade the lymph nodes, spleen, liver, and bone marrow, causing anemia and other symptoms. In populated areas, sandflies can be eradicated by insecticides. Unfortunately, rodents and other wild and domestic animals serve as a reservoir for the leishmaniasis protozoa and tend to perpetuate the disease in rural and jungle areas of warm climates.