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Scientists Investigate New Pathogen Carried by Rats

Is there a new plague for the 21st century?

Research published in the December issue of the Journal of Medical Microbiology suggests that brown rats, the most common and largest in Europe, may be carrying bacteria — spread by fleas — that can cause serious heart disease in humans.

"A new species called Bartonella rochalimae was recently discovered in a patient with an enlarged spleen who had travelled to South America," said professor Chao-Chin Chang from the National Chung Hsing University in Taiwan, in a press release. "This event raised concern that it could be a newly emerged zoonotic pathogen. Therefore, we decided to investigate further to understand if rodents living close to human environments could carry this bacteria."

More than 20 species of Bartonella bacteria have been discovered since the early 1990s. They are considered to be emerging zoonotic pathogens, because they can cause serious illness in humans around the world, ranging from heart disease to infection of the spleen and nervous system.

Scientists have found that rodents carry several pathogenic species of Bartonella; one can cause endocarditis (heart disease) and another neuroretinitis (eye inflammation) in humans. Although researchers haven't pinpointed the exact route of transmission, they speculate that fleas are the most likely carriers. Ctenophthalmus nobilis, a flea that lives on bank voles, has been observed transmitting different species of Bartonella bacteria. These pathogens have also been found in fleas that live on gerbils, cotton rats and brown rats.

"We analysed bacteria found in Rattus norvegicus in Taiwan. The brown rat is also the most common rat in Europe," said Chang. "By analysing the DNA of the bacteria, we discovered a strain that is most closely related to B. rochalimae, which has been isolated recently from a human infection in the United States."

The researchers took samples from 58 rodents, including 53 brown rats, two mice and three black rats. Six of the rodents were found to be carrying Bartonella bacteria, five of which were brown rats. Four of the rodents were harboring B. elizabethae, which can cause heart disease in humans, and one of the black rats was found to be carrying B. tribocorum. However, the scientists noticed one strain that had not been seen previously in rodents. Eventually, the strain was shown to be similar to B. rochalimae.

"Because of the small sample size used in this study, we cannot say for sure that the common brown rat is spreading B. rochalimae," said Chang. "However, several different Bartonella bacteria are surely transmitted by rodents. These results raise concerns about the existence of other reservoirs and vectors for this emerging infection. This certainly warrants further investigation."