The Barcode Blog

A mostly scientific blog about short DNA sequences for species identification and discovery. I encourage your commentary. -- Mark Stoeckle

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Leishmaniasis: DNA helps ID vectors, parasite, control agent

Leishmaniasis is a chronic parasitic infection caused by various Leishmania species, kinetoplast protozoans related to Trypanosoma (the latter includes agents of African sleeping sickness and Chagas disease, suggested as a cause of Charles Darwin’s ill health in late life).  Depending on the species involved, leishmaniasis manifests as illness ranging from non-healing cutaneous or mouth ulcers (CL) to sometimes fatal visceral infection (VL). In the Neotropics, 12 species infecting humans have been identified, all associated with CL.  Neotropical leishmaniasis is mostly zoonotic  (ie originates from animal reservoirs as opposed to human-to-human transmission), and the vectors are tiny phlebotomine sand flies, particularly Lutzomyia sp.

Lutzomyia_longipalpis-sandflyIn March 2010 PloS Neglected Trop Diseases investigators from Smithsonian Tropical Research Institute (STRI) and Instituto Conmemorativo Gorgas de Estúdios para la Salud, Panamá, apply DNA testing to Lutzomyia sandflies collected on Barro Colorado Island, STRI’s island home in the Panama Canal. Aiming to analyze as many species as possible, Azpurua and colleagues selected 435 individuals, which they morphologically identified as representing 16 Lutzomyia and 2 Brumptomyia sandfly species, for further analysis. Over 95% of specimens in the original collection were from one species, L. panamensis, so this was not a completely representative sample; nonetheless, “the relative abundances of species collected in this study were significantly correlated to those found in a previous intensive study of sand fly community composition on the [Panama] mainland…that collected over 30,000 Lutzomyia individuals in 35 species.”

To skip to the end, COI barcodes unambiguously assigned all 49 individuals to 18 distinct lineages corresponding to named species, plus highlighted 2 genetically-divergent individuals that might represent cryptic species.  Using  primers for ITS-1 (a nuclear gene) and mini-circle DNA (part of mitochondrial genome), Leishmania were detected in 2 of 5 human-biting species, Lu. trapidoi (13/30 individuals tested, 43.3%) and Lu. gomezi (5/19 individuals tested, 26.3%). By my estimate, taking into account relative abundances of Lutzomyia sp., about 1% of Barro Colorado Island sand flies carry Leishmania. Surprisingly, DNA sequencing identified the parasite as Le. naiffi, a South American species not previously reported in Panama. Finally, using the same set of DNA extracts, the researchers tested for Wolbachia, a rickettsial intracellular insect parasite and candidate biological control agent. Wolbachia were found in 3 of 18 species, including 50% of Lu. trapidoi, the main vector of CL in Panama. As an aside, I note that the presence of Wolbachia apparently did not interfere with discriminating among sand fly species; hypothesized interference from Wolbachia was one of the early worries some expressed about DNA barcoding (e.g Whitworth Proc Biol Sci 2007).

Standardized DNA testing enables many more persons to identify insects, regardless of life stage, including those that serve as vectors for human diseases. In this report by Azpurua and colleagues, the discovery of a new species of Leishmania for Panama, and possible undescribed Lutzomyia vectors, suggests that wide application of standardized DNA testing will lead to further discoveries relevant to control of human and animal infectious diseases.

This entry was posted on Sunday, April 25th, 2010 at 10:51 pm and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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About this site

This web site is an outgrowth of the Taxonomy, DNA, and Barcode of Life meeting held at Banbury Center, Cold Spring Harbor Laboratory, September 9-12, 2003. It is designed and managed by Mark Stoeckle, Perrin Meyer, and Jason Yung at the Program for the Human Environment (PHE) at The Rockefeller University.

About the Program for the Human Environment

The involvement of the Program for the Human Environment in DNA barcoding dates to Jesse Ausubel's attendance in February 2002 at a conference in Nova Scotia organized by the Canadian Center for Marine Biodiversity. At the conference, Paul Hebert presented for the first time his concept of large-scale DNA barcoding for species identification. Impressed by the potential for this technology to address difficult challenges in the Census of Marine Life, Jesse agreed with Paul on encouraging a conference to explore the contribution taxonomy and DNA could make to the Census as well as other large-scale terrestrial efforts. In his capacity as a Program Director of the Sloan Foundation, Jesse turned to the Banbury Conference Center of Cold Spring Harbor Laboratory, whose leader Jan Witkowski prepared a strong proposal to explore both the scientific reliability of barcoding and the processes that might bring it to broad application. Concurrently, PHE researcher Mark Stoeckle began to work with the Hebert lab on analytic studies of barcoding in birds. Our involvement in barcoding now takes 3 forms: assisting the organizational development of the Consortium for the Barcode of Life and the Barcode of Life Initiative; contributing to the scientific development of the field, especially by studies in birds, and contributing to public understanding of the science and technology of barcoding and its applications through improved visualization techniques and preparation of brochures and other broadly accessible means, including this website. While the Sloan Foundation continues to support CBOL through a grant to the Smithsonian Institution, it does not provide financial support for barcoding research itself or support to the PHE for its research in this field.