A single disease-causing clone of the bacterium Leptospira interrogans was behind the recent sustained outbreak of leptospirosis in Thailand, according to a new collaborative investigation by researchers in Thailand, Australia, and the UK.
Human leptospirosis is usually acquired following exposure to Leptospira shed in the urine of an infected animal. A sustained leptospirosis outbreak occurred in northeast Thailand from 1999 to 2003, but the cause was unknown. Outbreaks in Thailand and elsewhere are often linked to climatic events such as flooding, which leads to an increase in exposure to environments contaminated by Leptospira. But the 1999--2003 outbreak could not be explained by such events.
To investigate the cause, Sharon Peacock (Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand) and colleagues identified patients with leptospirosis presenting to Udon Thani Hospital in northeast Thailand from 2000 to 2005, and they isolated the causative organisms from the blood.
The researchers used a special technique for identifying the organism--a form of bacterial genotyping known as multilocus sequence typing. This approach has advantages over existing typing schemes in that the data generated are amenable to detailed evolutionary analysis, and are readily comparable via the Internet.
Their study results provided evidence that the human outbreak was associated with a biologically successful clone of Leptospira interrogans, called ST34. It was also demonstrated that the bandicoot rat was an animal host for this pathogenic Leptospira interrogans clone.
"The existence of this strain collection," the authors say, "now provides the opportunity to study the basis for pathogenicity and disease acquisition."
Citation: Thaipadungpanit J, Wuthiekanun V, Chierakul W, Smythe LD, Petkanchanapong W, et al. (2007) A Dominant Clone of Leptospira interrogans Associated with an Outbreak of Human Leptospirosis in Thailand. PLoS Negl Trop Dis 1(1): e56. doi:10.1371/journal.pntd.0000056
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