NIAID Scientists Track Down Leishmaniasis in Mali
Leishmaniasis is a parasitic disease transmitted by certain species of sand fly. It is prevalent in tropical and subtropical regions of the world, including Africa. In Mali, incidence of the disease is poorly documented, but recent NIAID-supported studies at the Malaria Research and Training Center (MRTC) in the capital city of Bamako have shown that cutaneous leishmaniasis (the form of the disease that affects the skin) may be widespread, though usually undiagnosed.
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NIAID researchers traveled to the rural district of Baraoueli to learn more about the prevalence and distribution of cutaneous leishmaniasis in Mali, Africa.
Credit: NIAID |
Because little was known about the epidemiology of cutaneous leishmaniasis in Mali, scientists from the Vector Molecular Biology Unit of the NIAID Laboratory of Malaria and Vector Research (LMVR), in collaboration with their colleagues at the MRTC, embarked on a program to learn more about the prevalence and distribution of the disease, as well as the sand fly species responsible for its transmission. The ultimate goal of the program is to identify proteins in the sand fly’s saliva that generate immune responses in humans and to test whether these responses help protect humans from infection by Leishmania parasites.
The LMVR researchers began their studies in Baraoueli, a district more than 100 miles from Bamako, where preliminary visits had uncovered active cases of cutaneous leishmaniasis among villagers. The researchers found that 41 percent of the combined population of two Baraoueli villages, Kemena and Sougoula, had been exposed to the parasite that causes the disease. The risk of acquiring leishmaniasis in the two villages was found to be nearly 10 percent.
Studies at the two villages and at other Malian sites revealed the presence of different varieties of sand flies, including those that do not transmit Leishmania parasites. However, in and around houses where active leishmaniasis cases were present, researchers found substantial amounts of the Phlebotomus duboscqi sand fly, suggesting that this species may be the primary transmitter, or vector, of the disease.
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Leishmaniasis is transmitted to humans by certain species of sand fly. This photograph depicts a Phlebotomus papatasi sand fly ingesting a blood meal, which is visible through its transparent abdomen.
Credit: CDC |
Furthermore, the researchers trapped rodents near the sites, and preliminary studies found that the immune system of Mastomys natalensis, a species of African rat, recognized proteins from the saliva of P. duboscqi as well as proteins from the Leishmania major parasite itself. This finding suggests that M. natalensis or other Mastomys species could be a natural reservoir, or long-term host, for the parasite. Reservoirs are important because they enable researchers to study the full lifecycle of an infectious agent, which can inform the development of strategies for preventing and controlling the disease it causes.
After catching female P. dubosqci flies in the field, LMVR researchers removed the salivary glands by dissection and shipped the samples to their labs in Rockville, MD. Using these glands, researchers produced genetic transcripts of the molecules found in P. dubosqci saliva. Subsequent computer analyses isolated the most abundant secreted salivary proteins, which are now being used by LMVR scientists to develop and test experimental DNA vaccines for leishmaniasis in lab animals and to identify the salivary proteins in the sand fly that produce a protective cellular immune response in humans.
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