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Study explains how and why people get illnesses transmitted by rodents

by Pragati Singh

In a worldwide investigation, researchers found that the majority of rodent-borne disease reservoirs prefer to reside solely or sporadically in or close to human houses and exhibit significant population swings. The COVID-19 pandemic has highlighted the necessity for more research into the methods through which illnesses propagate among animals. The study shows how the interaction of naturally occurring and human-caused variables influences the likelihood of virus transfer from animals to people. The “fast life” of rodents, which includes sexual maturity at a young age, several litters per year, and many young per litter, is a key factor in why they are significant disease reservoirs. But why can humans get infections carried by rodents?

“Most rodents that spread zoonotic pathogens, meaning pathogens spreading between animals and humans, show large population fluctuations, move at least occasionally indoors, or are hunted for meat or fur. Our results were consistent among pathogen types i.e., virus, bacteria, fungi, and parasites. And with transmission modes, i.e., intermediate, involvement of vectors or non-close and close contact, with close contact including inhalation of contaminated aerosols,” says Frauke Ecke, project leader and Professor at University of Helsinki, Finland and senior lecturer at Swedish University of Agricultural Sciences (SLU).

Survey of 436 rodent species worldwide
Researchers from SLU, the University of Helsinki, and the Cary Institute of Ecosystem Studies in the United States conducted a global quantitative investigation based on information gathered from databases and academic publications for the study that was published in Nature Communications. There are 436 species of rodents included in the study, of which 282 are recognised as reservoirs for zoonotic diseases. The relationship between the rodents’ preferred environments, population fluctuations, human hunting of rodents, and their role as reservoirs was investigated by the researchers.

“It is remarkable how consistent the results are among continents, disease systems and rodent species,” says Rick Ostfeld, co-leader of the study.┬áIt’s riskier in some parts of the world to contract zoonoses from rodents. The researchers have also pinpointed areas where there is a significant danger of human-to-rodent illness transfer.

The risk extends throughout a large portion of Europe, particularly central and northern Europe, as well as eastern Asia, eastern China, sections of South America, south-east Australia, and eastern areas of North America.

“If people encounter a rodent in these regions, there is a high risk that this rodent carries zoonotic pathogens,” says Ecke. The bank vole in Europe, the deer mouse in North America, and the Azara’s Grass Mouse in South America are a few examples of these pathogen-carrying rodents. These animals may go inside and have significant population changes.

“It is especially the large population fluctuations together with the disturbance of the rodents’ natural habitat that can explain why rodents move nearby and into human dwellings. This movement behaviour is typical for so-called generalists, which are species that can cope with many different environments. These generalists are the most important reservoirs of pathogens,” explains Ecke.

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