April 6, 2010
Scientists Use Barcoding To Track Sand Flies Carrying Leishmania Strain
In the first survey of sand flies in Panama to use genetic barcoding, scientists at the Smithsonian Tropical Research Institute and Gorgas Memorial Laboratories identified 20 sand fly species from Barro Colorado Island. Two species carried Leishmania naiffi, a parasite that causes cutaneous leishmaniasis: persistent, itchy skin lesions. Three species carried Wolbachia, a bacterial parasite of insects that could contribute to a strategy to control the flies and limit disease transmission.
"We used DNA barcoding"”sequencing a particular gene of the blood-feeding flies we collected"”to identify the 20 fly species; two species could not be distinguished visually," said Don Windsor, a Smithsonian scientist, who collaborated with STRI interns Jorge Azpurua, Dianne de la Cruz and Anayansi Valderama. "By characterizing another gene fragment from the nucleus of Leishmania, we discovered which fly species carried this disease-causing trypanosome."Leishmaniasis is not new in central Panama"”it poses a long-standing health risk to residents and visitors in the region. L. naiffi, the species carried by the flies in this survey, was previously known only to be in the Caribbean and the Amazon. "Other species of Leishmania and the blood-feeding flies that transmit them are endemic in central Panama," said Windsor. "Either L. naiffi was here undetected, or it could be a recent introduction carried by animals or people coming into Panama. Another explanation is that it is gradually moving northward from South America into Central America."
Researchers hope that the presence of Wolbachia in the same species of flies that carry Leishmania may be useful in disease control. Wolbachia bacteria infect the flies and are passed readily from generation to generation. Wolbachia affects the flies' ability to reproduce and has been proposed as a possible biological control of other insect pests.
Windsor emphasized that common preventative measures such as wearing insect repellent and long-sleeved shirts and pants when going out at dawn or dusk should be standard practice for residents, researchers and tourists who visit lowland tropical forests where Leishmania is endemic.
The Leishmania study was published in the open access journal PLoS Neglected Tropical Diseases. Funding was provided by the U.S. National Science Foundation and Panama's Fundaci³n Gabriel Lewis Galindo.
First author Azpurua, former STRI intern and short-term fellow, now a graduate student at the University of Rochester, has gone on to co-author "Hypersensitivity to Contact Inhibition Provides a Clue to Cancer Resistance of Naked Mole-rat," which was selected from more than 3,700 research articles published in the journal Proceedings of the National Academy of Sciences to win the 2009 Cozzarelli Prize. The journal will present the award for papers that "reflect scientific excellence and originality" during the National Academy of Sciences Annual Meeting April 25 in National Harbor, Md.
Ref: Jorge Azpurua, Dianne de la Cruz, Anayansi Valderama, Donald Windsor. 2010. Lutzomyia Sand Fly Diversity and Rates of Infection by Wolbachia and an Exotic Leishmania Species on Barro Colorado Island, Panama. PLoS Neglected Tropical Diseases.
Image Caption: Traditionally, entomologists depended on characters like this male terminal segment to distinguish sand fly species. Because females (the vectoring sex) have less distinguishing morphological characters, this survey used the COI barcoding gene to confirm species identities. Credit: Don Windsor
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