Tiny, tropical sand fly can spell big trouble

December 1, 2005

The parasitic disease is regarded by the World Health Organization as one of the most serious infectious diseases worldwide.

National report - Tiny sand flies halfway around the world can create quite a commotion.

According to Scott A. Norton, M.D., M.P.H., chief of dermatology at Walter Reed Army Medical Center in Washington, D.C., the medical staff there has treated close to one thousand returning military forces for leishmaniasis - an infectious disease transmitted by the bite of a sand fly.

While relatively unknown in the U.S. because of its prevalence in rural tropical regions such as the Middle East, the parasitic disease is regarded by the World Health Organization (WHO) as one of the most serious infectious diseases worldwide.

"The worldwide morbidity and mortality associated with leishmaniasis, particularly the visceral form of the disease, are among the greatest of any infectious diseases that we know of," Dr. Norton says. "And we're likely to see more and more of the disease."

U.S. implications

For U.S. dermatologists, the disease is becoming more important for a variety of reasons. First, increased world travel for both tourism and migration have increased the number of patients with leishmaniasis in the United States. Second, the disease is hyperendemic or epidemic in some parts of Southwest Asia, including Iraq and Afghanistan where many Americans are now working, both in the military and civilian sectors.

"Some of these people will return to the U.S. with either a clinically obvious or clinically inapparent infection with leishmaniasis," Dr. Norton tells Dermatology Times.

"I have seen many cases of leishmaniasis; first, when I was stationed with the military in the Middle East for a year in the late 1980s, and again in recent years since our military forces have been in the Middle East and Southwest Asia. Many of the soldiers are treated at Walter Reed and are evaluated by my dermatology staff."

Among the soldiers evaluated and treated at Walter Reed, the vast majority - about 750 - were diagnosed with the cutaneous form of the disease, which is the most benign and most common form worldwide.

The cutaneous type appears as one to many nodulo-ulcerative lesions on the skin at the sites of a sand fly bites. The lesions start out looking similar to an ordinary insect bite, or papular urticaria. The difference though is that the lesion does not resolve in a week the way one would expect. A small papule then arises at the site. It may resemble a common bacterial infection but it will not respond to typical antibacterial antibiotics. Within a few weeks to a few months, the lesion enlarges to several centimeters in size, become elevated into a nodule and then typically ulcerates in the middle, hence the name nodulo-ulcerative lesion. This type affects only the skin and is the form that most dermatologists will see.

"Fortunately, the cutaneous form - more specifically, the Old World cutaneous form - in most cases is self-healing within a year," says Dr. Norton. "A New World cutaneous form can be a bit tricky and may ultimately lead to death after a seeming cure or self-resolution. This can occur years after the original skin lesion appeared to resolve but the disorder then recurs in the mid-facial region, particularly in the oral pharynx and can cause inexorable destruction of the vital structures of the face."

Leishmaniasis has long intrigued immunologists because it is an intra-cellular pathogen, according to Dr. Norton, and in some ways, shares some of the immunologic attributes with other diseases such as tuberculosis or HIV.

The most serious form of the disease is the visceral form, which involves the skin only transiently. Eventually, the parasites go to the liver, spleen and other organs. Left untreated, this form is usually fatal.

"Scientists have learned a lot about human immunologic responses to intracellular organisms by studying leishmaniasis," he says, "and a lot of research is being conducted at institutions like NIH (National Institutes of Health) and CDC (Centers for Disease Control and Prevention) because there are so many lessons to be learned that can be extrapolated to other diseases."