Genome Studies Reveal Extensive Copy Number Variation in Leishmania Parasites

Two remarkable discoveries have been revealed by researchers analyzing the genomes of Leishmania parasites. The research results were published in two studies appearing online on October 28, 2011 in Genome Research. First, the scientists found that the DNA sequence of individual strains of each species populations is almost completely identical. It appears that only a small number of genes may cause different symptoms of infection. Second, the parasite's evolutionary development and success may be driven by a genetic abnormality leading to multiple copies of chromosomes that would kill most organisms. This process leads to multiple copies of chromosomes and genes known as copy number variation. These studies increase our understanding of the process of drug resistance in Leishmania. Leishmaniasis is a disfiguring and potentially fatal disease that affects two million people each year. There are four main forms of the disease; ranging from skin lesions (cutaneous leishmaniasis), caused by species that include Leishmania mexicana, to a deadly infection of internal organs (visceral leishmaniasis, also called “black fever”) caused by Leishmania donovani parasites. Leishmania parasites are transmitted by sand flies and are found in 88 countries around the world. Leishmaniasis is poverty-related and typically affects the poorest of the poor: it is associated with malnutrition and displacement. The World Health Organization is committed to eradicating the disease in endemic areas. In the first of the two current studies, the researchers generated a high-quality draft genome of L. donovani using a sample taken from an infected patient in Nepal. The team used this as a reference framework to analyse a further 16 isolates from Nepal and India that had different responses to antibiotic medications.
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