Previous research has shown that reverse transmission of various zoonotic pathogens from humans to animals is a global problem. Additionally, on July 6, 2022, the World Organization for Animal Health (OIE) stated that while occasional occurrences of COVID-19 in domestic or zoo animals have little long-term consequences, infections at the wildlife population level indicate the possibility of further evolution of the virus in animals and a future re-introduction of the virus into humans at a later date. Therefore, it is of crucial importance to identify the risk of establishment of SARS-CoV-2 in the wild mammal population.
Research Letter: Serological Surveillance of SARS-CoV-2 Infection in Wild Rodents, Europe. Photo credit: Rudmer Zwerver/Shutterstock
Wild rodents are suspected to be more susceptible to SARS-CoV-2 infection. In most cases, infection results in little or no detectable disease, although shedding of the virus occurs 4 to 7 days after infection and can be transmitted to naïve rodents. This could lead to widespread spread, retransmission and long-term establishment of SARS-CoV-2 in the rodent population. The joint advisory group of the Food and Agriculture Organization of the United Nations and the OIE (FAO-OIE) on the development of SARS-CoV-2 in animals suggested that a large surveillance study of rodent populations exposed to humans is needed to fill a significant gap in SARS-CoV- 2 research.
Experiments have shown that the detection of antibodies occurs several weeks or more after rodents have been infected with SARS-CoV-2. However, the virus is only excreted for a few days. In addition, a recent survey in Hong Kong found that Norwegian rats are seropositive for SARS-CoV-2. Therefore, more extensive surveillance studies are needed in other habitats, continents and non-commensal rodent species given their high ubiquity and biodiversity.
A new study, published in the journal Emerging Infectious Diseases, conducted a large-scale serological survey of SARS-CoV-2 in multiple rodent species to investigate the reverse transmission of SARS-Cov-2 and its establishment in wild rodents in different environments to determine.
About the study
The study collected samples of 1,202 rodents and 35 shrews from 8 city parks and 23 forest areas in 5 European countries (Poland, Germany, France, Belgium and Ireland). This was followed by an assessment of each rodent’s SARS-CoV-2 serological status using an infected cell-based immunofluorescence assay (IFA). Real-time quantitative reverse transcription PCR of SARS-CoV-2 was also used to confirm infection.
The results showed one IFA-positive rodent, which was a wood mouse, taken from a municipal park in Belgium. However, no neutralizing antibodies against SARS-CoV-2 were detected in the wood mouse. In addition, RT-qPCR results from 59 rodents from the same area were observed as negative.
Therefore, the current study shows no significant evidence for the spread of SARS-CoV-2 among rodents in northern Europe. A similar observation was also reported from Hong Kong, which has denser human and larger rodent populations. Therefore, no evidence of widespread circulation of SARS-CoV-2 among rodents has been reported to date.