Juvenile and subadult bats may be the most likely to spread new coronaviruses to other species, according to a Cornell study published July 17 in Nature Communications.
Dr. Raina Plowright, the Rudolf J. and Katharine L. Steffen Professor of Veterinary Medicine in the College of Veterinary Medicine, and colleagues unveiled new insights into the natural dynamics of coronaviruses circulating in wild bats, which are their reservoir hosts. When young bats are weaned, they're more prone to viral infections, and more likely to shed those viruses into the environment. "We found that multiple coronaviruses circulate simultaneously within each bat population, with strains peaking synchronously across populations at the time when young bats may lose maternal immunity," Plowright said.
Genomic studies have established that most human coronaviruses originated from viruses in bats, including SARS-CoV2, which triggered the COVID-19 pandemic. However, it remained unclear exactly where and when such transmission happens.
Plowright aimed to pin down those details. "Preventing initial spillover events can stop pandemics at their source, saving lives and preventing disruption of the global economy," she said.
To do this, the scientists conducted a three-year study of five flying fox roosting sites in eastern Australia. They collected fecal samples for viral screening directly from individual bats captured via mist nets, as well as from population-level sampling by collecting bat scat on plastic sheets under the roosts. Sampling sessions occurred five times per year.
They applied a novel statistical modeling technique to integrate data from both types of samples. "Our approach was unprecedented in its scale and transdisciplinary integration," Plowright said. The models enabled her team to determine the drivers of viral shedding from the individual samples, and the population-level samples helped determine overall prevalence.
The results showed a consistent pattern of viral shedding, with a seasonal peak across multiple strains of viruses within the bat populations. During that peak, young bats had the highest prevalence of infection of both single and multiple strains of coronaviruses, and had the most viral shedding. This peak shedding period coincides with the weaning period for juvenile bats, when, without their mothers' milk, the young bats no longer have maternal antibodies in their system to protect them from new pathogens. Without this protection, the young bats can become co-infected with multiple strains of viruses, which enables recombination and evolution of new strains. "This represents a high-risk scenario for the emergence of novel viruses," Plowright said.
The study strengthens the idea that zoonotic spillover might be more predictable than previously thought. "Viral shedding from wildlife reservoir hosts is one of the first steps in the chain of events that can lead to a pandemic," she said.
"Understanding the ecological and host-viral drivers of seasonally dynamic infections, co-infections and recombinations, we can begin to build future predictive frameworks for coronavirus emergence - both in humans and other animals."
Lauren Cahoon Roberts is director of communications at the College of Veterinary Medicine.
