A new study suggests that brown rats, the biggest and most common rats in Europe, may be carrying the bacteria that can cause serious heart disease in humans.
Reported in the Journal of Medical Microbiology, the study report highlights the fact that over 20 species of Bartonella bacteria have been discovered since the early Nineties.
It further states that these bacteria are considered to be emerging zoonotic pathogens, as they can cause serious illness in humans worldwide from heart disease to infection of the spleen and nervous system.
"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.
"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 environment could carry this bacteria," the researcher added.
The authors of the study say that the research team found rodents to carry several pathogenic species of Bartonella, such as B. elizabethae, which can cause endocarditis, and B. grahamii, which was found to cause neuroretinitis in humans.
They admit that the research group is still uncertain as to the main route of transmission, but believe that it is most likely to be spread by fleas.
The authors write that Ctenophthalmus nobilis, a flea that lives on bank voles, was shown to transmit different species of Bartonella bacteria. According to them, such 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. 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," said Professor Chang.
For their study, the researchers studied samples taken from 58 rodents, including 53 brown rats, 2 mice (Mus musculus) and 3 black rats (Rattus rattus).
They observed that six of the rodents were carrying Bartonella bacteria, and five of them were brown rats.
The researchers also revealed that four of the rodents were carrying B. elizabethae, which can cause heart disease in humans, and one of the black rats was found to be harbouring B. tribocorum.
They even noticed one previously unidentified strain in rodents, which was finally found to be close 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. 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," said Professor Chang.