North American deermice catch COVID-19 and feel absolutely fine despite having no history with the virus.
Infection tolerance is usually a specialized trait that develops over thousands of years as a species lives alongside a specific pathogen. These mice demonstrate a generalized biological superpower that lets them harbor the SARS-CoV-2 virus without any significant loss of health or fitness. Even though they are not natural reservoirs for the disease, their immune systems simply ignore the virus instead of mounting a damaging inflammatory response. This finding shows that some animals possess a universal shield against sickness that does not depend on past exposure. Understanding this innate tolerance could lead to new human therapies that focus on coexisting with viruses rather than fighting losing battles against them.
SARS-CoV-2 virus infection of Peromyscus leucopus demonstrates that infection tolerance is not limited to agents for which deermice are reservoirs
bioRxiv · 10.64898/2026.03.13.711660
The North American deermouse Peromyscus leucopus is reservoir for several zoonotic agents, including bacterial, protozoan, and viral. It is remarkable for indiscernible or limited fitness consequences of these infections, a trait known as infection tolerance. But experimental infections have largely been of pathogens that P. leucopus naturally harbors. We asked whether infection tolerance extended to an agent, like SARS-CoV-2 virus, it had presumably not encountered before. Following protocols f