City rats are not the deadly disease carriers we think they are

(ORDO NEWS) — Rats have been considered filthy carriers of disease since at least the time of the plague, but a new study shows that rodents and other urban animals are less likely to cause the next pandemic than previously thought.

Researchers at Georgetown University in Washington studied data on nearly 3,000 mammals, expecting to find that urban environments harbor more viruses that can be transmitted to humans because they are in such close contact.

They found that urban animals do indeed carry 10 times more disease, yet more than 100 times more research has been published on them.

When the researchers corrected for this huge margin of error – a longstanding scientific preference for studying animals crawling underfoot rather than hiding in the rainforest – they were surprised to find that rats were no more likely to be the source of a new human disease than other animals. .

However, “you still shouldn’t get too close and friendly to urban wildlife,” said Greg Alberi, a disease ecologist who led the study, published Monday in the journal Nature Ecology & Evolution.

“These urban animals are unlikely to be the source of the next ‘disease X’, but they are still often the source of known important diseases,” he told AFP, citing leptospirosis, a bacterial disease commonly spread by rats, as an example.

The threat from another common object of urban contempt – pigeons – is “almost certainly” also exaggerated due to research bias, he said.

Because we have studied urban animals for so long, “we know so much about their parasites that there are relatively few unknowns; rural wildlife is far more uncertain and more likely to present us with the next ‘big threat’.”

Jonathan Richardson, professor of urban ecology at the University of Richmond, said the study was important because the authors “rightly highlight the overrepresentation of evidence from urban mammal studies.”

However, he told AFP it’s still fair to call rats “disease sponges” because humans are in such regular contact with them.

Richardson says his research has shown that urban rats carry more than 200 pathogens and parasites that can pass to humans, and that nearly 80 percent of rats in some cities carry leptospirosis.

Last week, Albery and his co-author Colin Carlson published a study showing that climate change could increase the risk of new epidemics.

They found that when animals like bats flee to cooler areas, they mix with other species for the first time and create new opportunities for the spread of diseases that can later infect humans.

Albury believes that urban mammals may play a role in this process.

If a bat encounters a rat and infects it with a new disease, and then the rat gains greater access to human areas, that would provide an important entry route into the human body,” he said.

His research on global warming also showed that new opportunities for viruses to jump from one animal to another would now occur closer to human settlements rather than in forests.

“The host-pathogen network is about to change dramatically, so what we know now about urban parasites is likely to quickly become obsolete,” Albery said.

“We need to improve surveillance of both urban and wild animals so that we can determine when a pathogen is moving from one species to another – and if the host host is urban or in close proximity to a human, we should be particularly concerned.”

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