Mekong Schistosomiasis Is Spreading

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Main Category: Tropical Diseases
Also Included In: Infectious Diseases / Bacteria / Viruses;  Public Health
Article Date: 02 Apr 2008 - 0:00 PDT

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A new genetic analysis suggests that the parasitic worm Schistosoma mekongi is more prevalent than previous research indicated. This study, published on March 19, 2008 in the open-access journal PLoS Neglected Tropical Diseases, estimates that population at risk of infection could be up to 10 times higher than previously estimated.

Schistosomiasis, a parasitic flatworm of the genus Schistosoma, can localize in several parts of the body but commonly affects the intestines. Symptoms include abdominal pain, fever, cough, diarrhea, abnormally high eosinophil count, and enlargement of the liver and spleen, and it is transmitted through certain species of snails. It primarily infects people in developing countries, infecting over 200 million people worldwide.

There are several species of the Schistosoma genus that affect humans -- this study focused on Schistosoma mekongi, which is found primarily in the Mekong River basin in South-East Asia. Treatment programs in the mid-1990s reduced the prevalence of the disease and increased optimism about contolling S. mekongi infections. That said, the results of this new study imply that there are issues that still must be addressed.

Stephen W. Attwood of China's Sichuan University, Farrah A. Fatih of London's Natural History Museum, and E. Suchart Upatham of Thailand's Mahidol University examined DNA sequences from samples collected from the Mekong river as well as its tributaries in Cambodia, Laos, and Malaysia. While it was previously believed that S. mekongi was largely limited to a small area in the lower Mekong River, this team found that organizms in tributaries across Cambodia were of the same species. Additionally, the range of snail intermediate hosts and the proper ecological conditions for transmission were also shown to be much broader than originally assumed.

Before this study, scientists also assumed that S. mekongi originally lived in Yunnan, China, then migrated south across Laos and into Cambodia. It was thought to have become extinct in Laos because conditions were unsuitable for its transmission. Attwood's team's results suggest a more recent and continuous migration northwards from Vietnam towards Cambodia and Laos. According to the authors, if there is indeed no barrier found in the ecological conditions of Laos, we may expect the future spread there.

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PLoS Neglected Tropical Diseases (http://www.plosntds.org/) is a peer-reviewed, open-access journal devoted to the pathology, epidemiology, prevention, treatment, and control of the neglected tropical diseases, as well as public policy relevant to this group of diseases. All works published in PLoS Neglected Tropical Diseases are open access, which means that everything is immediately and freely available subject only to the condition that the original authorship and source are properly attributed. The Public Library of Science uses the Creative Commons Attribution License, and copyright is retained by the authors.

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Among Schistosoma mekongi Populations and Related Taxa; Phylogeography and the Current Distribution of Asian Schistosomiasis.
Attwood SW, Fatih FA, Upatham ES
PLoS Negl Trop Dis 2(3): e200.
doi:10.1371/journal.pntd.0000200
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Written by Anna Sophia McKenney
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