The new strain, called Bartonella rochalimae, was discovered in an American woman with an enlarged spleen who had recently traveled to Peru.

Professor Chao-Chin Chang, from the National Chung Hsing University in Taiwan, wrote in the Journal of Medical Microbiology that the discovered infection may be one of the first documented cases of an emerging zoonotic pathogen.

A zoonosis is any infectious disease capable of being transmitted from other animals to humans, or vice-versa.

The suspected culprit in spreading the new bacterial infection is the brown rat, which is the biggest and most common rat in Europe.

Rodents have been responsible for spreading the Black Death and other plagues in Europe and parts of Asia since the Middle Ages.

Professor Chang says his findings raise concerns about the existence of a 21st-century plague.

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