SDAV, the Rat Coronavirus-How Much Do We Know about It in the Light of Potential Zoonoses

Monitoring SARS-CoV-2 infection in urban and peri-urban wildlife species from Catalonia (Spain)

BACKGROUND

Human activities including deforestation, urbanization, and wildlife exploitation increase the risk of transmission of zoonotic diseases. Urban and peri-urban wildlife species often flourish in human-altered environments, with their survival and behavior heavily influenced by human-generated food and waste. In Catalonia, Spain, and other Mediterranean regions, species of rodents, including the house mouse (Mus musculus), black rat (Rattus rattus), Norway rat (Rattus norvegicus), as well as wild boar (Sus scrofa) are common in urban and peri-urban areas. These species host numerous infectious agents, including coronaviruses (CoVs), posing potential human health risks. During the coronavirus disease 2019 (COVID-19) pandemic, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolved to infect previously non-susceptible species, with variants capable of infecting rodents, emphasizing their importance in surveillance studies.

METHODS

The present study assessed SARS-CoV-2 presence and/or exposure in 232 rodents, 313 wild boar, and 37 Vietnamese Pot-bellied pigs in Catalonia during the pandemic period (2020-2023).

RESULTS

All the animals tested for acute SARS-CoV-2 infection (232 rodents and 29 wild boar) were negative. For SARS-CoV-2 exposure, 3 out of 313 (0.96%) wild boar tested positive by ELISA, while the remaining 32 rodents, 310 wild boar, and 37 Vietnamese Pot-bellied pigs were all negative. Cross-reactivity with other CoVs was predicted for ELISA-positive samples, as the 3 wild boar tested negative by the virus neutralization assay, considered as the gold standard technique.

CONCLUSIONS

The absence of SARS-CoV-2 exposure or acute infection in wild boar and rodent species supports their negligible role in viral spread or transmission during the COVID-19 pandemic in Catalonia. However, their proximity to humans and the ongoing genetic evolution of SARS-CoV-2 underline the need for continued monitoring. Surveillance of SARS-CoV-2 infection in animal species can contribute to design measures to control the emergence of new animal reservoirs or intermediate hosts that could facilitate viral spillover events.

Cross-species transmission, evolution and zoonotic potential of coronaviruses

Coronaviruses (CoVs) continuously evolve, crossing species barriers and spreading across host ranges. Over the last two decades, several CoVs (HCoV-229E, HCoV-NL63, HCoV-HKU1, HCoV-OC43, SARS-CoV, MERS-CoV, and SARS-CoV-2) have emerged in animals and mammals, causing significant economic and human life losses. Due to CoV cross-species transmission and the evolution of novel viruses, it is critical to identify their natural reservoiurs and the circumstances under which their transmission occurs. In this review, we use genetic and ecological data to disentangle the evolution of various CoVs in wildlife, humans, and domestic mammals. We thoroughly investigate several host species and outline the epidemiology of CoVs toward specific hosts. We also discuss the cross-species transmission of CoVs at the interface of wildlife, animals, and humans. Clarifying the epidemiology and diversity of species reservoirs will significantly impact our ability to respond to the future emergence of CoVs in humans and domestic animals.

Monitoring Urban Zoonotic Virus Activity: Are City Rats a Promising Surveillance Tool for Emerging Viruses?

Urban environments represent unique ecosystems where dense human populations may come into contact with wildlife species, some of which are established or potential reservoirs for zoonotic pathogens that cause human diseases. Finding practical ways to monitor the presence and/or abundance of zoonotic pathogens is important to estimate the risk of spillover to humans in cities. As brown rats (Rattus norvegicus) are ubiquitous in urban habitats, and are hosts of several zoonotic viruses, we conducted longitudinal sampling of brown rats in Vienna, Austria, a large population center in Central Europe. We investigated rat tissues for the presence of several zoonotic viruses, including flaviviruses, hantaviruses, coronaviruses, poxviruses, hepatitis E virus, encephalomyocarditis virus, and influenza A virus. Although we found no evidence of active infections (all were negative for viral nucleic acids) among 96 rats captured between 2016 and 2018, our study supports the findings of others, suggesting that monitoring urban rats may be an efficient way to estimate the activity of zoonotic viruses in urban environments.