June 30, 2008 Researchers at the University of Bath have discovered that a bacterium that causes Lyme disease originated in Europe, rather than in North America as previously thought.
The bacterium responsible for Lyme disease, Borrelia burgdorferi, originated in America, or so researchers thought. Now, however, a team from the University of Bath has shown that this bug in fact came from Europe, originating from before the Ice Age.
By understanding the origins of the bacterium and how it has evolved so far researchers hope to be able to predict how it will continue to develop, and so find ways to prevent its spread.
In the study, researchers from the University of Bath and colleagues from the UK and USA studied the evolutionary history of the bacteria by looking at the sequences of eight so-called 'housekeeping genes', which evolve very slowly. They analysed 64 different samples taken from infected humans and ticks in Europe and America.
In all, 33 different combinations of the housekeeping genes were found. The study's findings appear to show that Borrelia burgdorferi originated in Europe but that the species has been present in North America for a long time. The researchers suggest its re-emergence there in the 1970s occurred after the geographic territory of the tick that carries the bacteria expanded, for example through the restoration of woodland.
Lyme disease is a growing problem in Europe, Asia and - in particular - North America, where it is now the most common vector-borne disease. The disease was named after Old Lyme, Connecticut, the site of a number of cases in the 1970s. There is no vaccine for the infection, which can cause arthritis and problems with the nervous system and heart if left untreated.
Image: The blacklegged tick Ixodes pacificus, a known vector for Borrelia burgdorferi, the pathogen responsible for Lyme disease; CDC/ James Gathany; William Nicholson
Margos G et al. MLST of housekeeping genes captures geographic population structure and suggests a European origin of Borrelia burgdorferi. Proc Natl Acad Sci U S A 2008;105(25):8730-8735
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