Tropical Diseases: Leishmaniasis: The Sand Fly's Bug

Leishmaniasis: The Sand Fly's Bug

Leishmaniasis is a parasitic disease caused by a protozoan that initially lives in the sand fly and is transmitted to people through sand fly bites. The organism develops and multiplies in the gut of the fly and is introduced into the bloodstream of humans after a bite. It can cause a skin infection or a more serious systemic infection. The skin infection, which consists of sores, develops weeks or months after a sand fly bite. The more serious infection, which consists of fever, enlargement of the liver and spleen, and anemia, can take months or even years to develop.

The disease is found in 90 tropical and subtropical countries around the world. More than 90 percent of the systemic cases occur in Bangladesh, Brazil, India, Nepal, and Sudan. The disease is rare, but not unheard of, in the United States.

Skin Leishmaniasis

The incubation period after a sand fly bite ranges from a couple of weeks to several months, with no symptoms to indicate the presence of the disease. A cut or some other trauma to the skin can result in activation of a skin infection a long time after the initial bite. The skin lesions, which can be painful, usually evolve over time. They are usually found on exposed areas of the skin, especially the arms, legs, and face. When the lesions heal, they leave scars. The healing process can take months.

Systemic Leishmaniasis: The Black Fever

Malnutrition has been shown to contribute to this more serious form of the disease. The fever that develops may be continuous, or it may come and go at irregular intervals. Symptoms include weight loss, diarrhea, and weakness. Darkening of the skin is also a characteristic of the disease, which explains why it is sometimes called “black fever.”

The disease can be diagnosed in a variety of ways, including a skin test, which is simple and sensitive, but can't distinguish between active, inactive, new, or old infections. The disease-causing organism can be identified by examining a stool sample under a microscope, and cultures can be grown and antibody tests can be done as well.

The skin lesions caused in the mild form of the disease usually heal by themselves in 2 to 10 months; however, they may leave scars. Good wound care (use of local heat and keeping wounds clean) is important to reduce the chance of permanent scarring.

Antiparasitic drugs can be given as therapy once someone is infected, but they don't prevent the disease. Unfortunately, these drugs are not readily available in the developing countries where the disease is most common. Antibiotics and antifungal drugs have been used to treat the disease with some success as well.

Risk for Travelers and Prevention

Anyone who lives in or travels to places where the organism is found is at risk for contracting leishmaniasis. The highest risk is to those who are outside between dusk and dawn, which is when the sand fly is most active.

There are no vaccines or drugs that prevent the disease; the most effective preventive measures are to reduce contact with sand flies. Although sand flies mostly bite at night, they will bite during the day if they are disturbed. Travelers should wear protective clothing and use insect repellent. Bed nets and screen doors and windows should be used as well. The netting must be very fine in order to be effective, as sand flies are about one third the size of mosquitoes.

After treatment for infection, approximately 98 percent of people have immunity against reinfection with the same strain.

Disfiguring Complications

Complications for leishmaniasis can include secondary bacterial infection; disfiguring of the nose, lips, and palate; bleeding, ruptured spleen; edema (swelling); and lesions in the nose and throat, with destruction of tissue.

The prognosis for those who get leishmaniasis depends on their immune status as well as whether they are getting proper nutrition. People with weakened immune systems or who suffer from malnutrition are at greater risk of severe leishmaniasis or developing complications. With early treatment, 90 percent of people are cured. The death rate is 15 to 25 percent in untreated cases, with death occurring in 3 to 20 months.

Excerpted from The Complete Idiot's Guide to Dangerous Diseases and Epidemics © 2002 by David Perlin, Ph.D., and Ann Cohen. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.