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Sand Flies Spread Leishmaniasis Disease Worldwide - 2001-08-14

Spread by the bite of an infected sand fly, leishmaniasis is a parasitic disease found in 88 countries worldwide. Treatment is expensive and the availability of therapies is often scarce. So recent efforts to develop a potential vaccine may bring hope to those suffering.

The World Health Organization estimates that 12 million people worldwide are infected with a parasitic disease, known as leishmaniasis. The WHO says that the public health impact of this disease has been grossly underestimated. During the past 10 years, endemic areas have been spreading, with 350 million people thought to be at risk of infection.

Leishmaniasis is complex because there are many species of parasites and sand flies that cause it. "The two major forms are the visceral type, which effects internal organs of the body and can be life threatening if not appropriately and quickly treated," explains Dr. Barbara Herwaldt, an epidemiologist with the Centers for Disease Control in Atlanta, Georgia. "And then there is the cutaneous or skin type which causes skin sores that can be quite long lasting and sometimes quite disfiguring."

Symptoms of visceral leishmaniasis include fever, enlargement of the spleen and liver, and anemia, that typically develop within months, but sometimes years, after a person becomes infected.

Although the disease is found in close to 90 countries worldwide, endemic areas include only a handful of regions. The majority of new cases of the visceral type of this disease occur in five countries: Bangladesh, Brazil, India, Nepal and Sudan. Most of the skin-related cases are found in Afghanistan, Brazil, Iran, Peru, Saudi Arabia and Syria. Dr. Herwaldt says that even though disease and death are consequences of leishmaniasis, it often goes untreated. "The availability of health care appropriate for diagnosing and treating leishmaniasis is quite variable around the world and the tests that are needed to diagnose infection can be difficult to perform," she says.

A researcher from the Institute of Endemic Diseases in Sudan, Maowia Mukhtah, believes the reason leishmaniasis is so widespread is that there is a lack of funding for it. "I think leishmaniasis is one of the diseases that is not getting enough attention from the global community," he says. "It is a serious problem, and it is affecting the children mostly, and it is spreading. And the available treatment is not affordable."

Due to these difficulties, experts say developing a vaccine is of pressing importance. In the past, crude vaccines consisted of taking lesion material from one person and scratching it onto the skin of a healthy person. This produced a mild form of the disease, preventing re-infection at a later time. Since this is perhaps not the safest or the most effective method of vaccination, researchers have been experimenting with other approaches.

A recent study published in the Journal for Experimental Medicine discovered a unique method that may help advance vaccination research, explains the director of the study, Dr. Jose Ribeiro. "About 15 years ago we discovered that the saliva of sand flies, which transmits leishmania, would actually enhance leishmania transmission and at that time, we postulated that a vaccine against the saliva could prevent this enhancing effect of the saliva," he says.

Dr. Ribeiro and colleagues created a vaccine using the salivary glands from sand flies, which proved successful with laboratory mice. A researcher from the U.S. Infectious Disease Research Institute, Farroukh Modabber, calls this research encouraging. "Scientists are always optimistic," he says. "If they were not optimistic, they would not be in science. So I believe that we will have a vaccine within the next say five to seven years."

As the worldwide rate of HIV infection increases, the need for a leishmaniasis vaccine becomes even more pressing. Experts say the disease accelerates the onset and worsens the course for people infected with HIV. According to the WHO, as endemic areas of these two diseases continue to overlap, cases of co-infections will continue to rise.

Photos courtesy WHO/TDR.