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Lifestyle options dwindle for bovine bacteria
The bacterium that causes leptospirosis, one of the most widespread infections transmitted between animals and humans, appears to be changing in ways that could limit its ability to survive and thrive. Research suggests that Leptospira borgpetersenii serovar Hardjo, which commonly infects cattle, is losing its capacity to live in water and is evolving towards a strict host-to-host transmission cycle. This finding is from Agricultural Research Service microbiologist Richard L. Zuerner, who works at the agency's National Animal Disease Center in Ames, Iowa, and scientists at Monash University in Australia. People and animals can be infected with Leptospira when exposed to water contaminated with urine from infected animals, or by direct contact with bodily fluids or tissue from infected animals. Pregnant cows infected with serovar Hardjo may experience abortion or stillbirth, or give birth to weakened offspring. Infected humans can develop flulike symptoms or--in more severe cases--may die. Worldwide, most cases of bovine leptospirosis are due to infection by L. borgpetersenii, but both L. borgpetersenii and L. interrogans transmit leptospirosis among cattle in North America. Many Leptospira strains, including L. interrogans, can be transmitted through surface water. Genomic sequencing studies conducted by Zuerner and his Australian colleagues Ben Adler and Dieter Bulach indicate that the L. borgpetersenii genome is decaying, which is impairing its ability to sense environmental changes, acquire nutrients and survive outside of a mammalian host. These changes have also significantly reduced or eliminated the ability of L. borgpetersenii to survive in water, which in turn restricts its effectiveness at spreading disease. It appears that L. borgpetersenii is now contracted mainly, if not solely, through close contact with infected animals. This research provides a foundation for comparing the disease-transmission processes of L. borgpetersenii and L. interrogans, and for developing increasingly effective vaccines and other disease control strategies for bovine leptospirosis. Read more about this research in the August 2007 issue of Agricultural Research magazine, available online at www.ars.usda.gov/is/AR/archive/aug07/disease0807.htm.
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