Putting aside the recent historical finding that it was not rats that carried the plague carrying fleas which triggered the medieval “Black Death“, but rather gerbils, there is a strng association between rats and fleas and fleas and plague.
In this context, researchers have found that some of New York City’s rats have Oriental rat fleas (Xenopsylla cheopis), which are known to carry plague bacteria (Yersinia pestis), as well as other pathogens.
With the new study, as The Verge reports, a group of entomologists, virologists, and immunologists trapped 133 Norway rats in Manhattan over a 10-month period and recorded the insects, arachnids, and pathogenic bacteria associated with the rodents. About 6,500 parasites were found on the rats, including several mite species, a louse species, and rat fleas. Xenopsylla cheopis was the only type of flea recovered. This was the first time that scientists have found the flea species known to carry plague bacteria in New York City rats.
The researchers also found a few different bacterial species from genus Bartonella, which can cause disease in humans. However, despite finding fleas associated with the plague they did not find plague bacterium.
Despite the absence of plague bacteria, Cornell University entomologist Matthew Frye sounded a note of warning in a research brief: “If these rats carry fleas that could transmit the plague to people, then the pathogen itself is the only piece missing from the transmission cycle.”
The study’s results have been published in the Journal of Medical Entomology. The research paper is headed “Preliminary Survey of Ectoparasites and Associated Pathogens from Norway Rats in New York City.”
In related news, in parts of Africa, the creation of maize fields has led to a 20-times increase in the population of the African rat (Mastomys natalensis.) This species of rat is renowned for being a carrier of the fleas that can be infected with the plague causing bacterium (Yersinia pestis.) There is also an association with the rats and Lassa fever.
