GAINESVILLE, Fla. — Two emerging pathogens with animal origins — influenza D virus and canine coronavirus — have so far been quietly flying under the radar, but researchers warn conditions are ripe for the viruses to spread more widely among humans.
If surveillance and diagnostics continue to lag, influenza D virus and canine coronavirus have real potential to trigger outbreaks, a team of infectious disease experts and authors write in an article in the January issue of Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention.
"Our review of the literature indicates these two viruses pose respiratory disease threats to humans, yet little has been done to respond to or prevent infection from these viruses," said co-author John Lednicky, Ph.D., a research professor in the Department of Environmental and Global Health at the University of Florida's College of Public Health and Health Professions . "If these viruses evolve the capacity to easily transmit person to person, they may be able to cause epidemics or pandemics since most people won't have immunity to them."
Since its discovery in 2011, influenza D virus has been associated with infections in pigs and cows, but it has also been found in many other livestock and wildlife species, including poultry, deer, giraffes and kangaroos. Influenza D virus is believed to contribute to bovine respiratory disease, estimated to cost the U.S. cattle industry $1 billion a year.
The authors' previous studies of cattle workers in Colorado and Florida found that up to 97% of people working with herds carry influenza D virus antibodies, suggesting the workers had been exposed to the virus. So far, these infections are known to be subclinical, meaning they have not caused symptoms of illness. However, scientists say influenza D virus bears the hallmarks of a virus primed to rapidly evolve. Indeed, a strain of influenza D recently isolated in China has developed the capacity for human-to-human transmission.
"So far, influenza D virus has not been associated with serious infections in humans," said Lednicky, a member of UF's Emerging Pathogens Institute . "However, canine coronavirus has, but diagnostic tests are not routinely performed for the virus so the extent at which the virus affects the population at large is not known."
Canine coronavirus, or CCoV, can cause gastrointestinal illness in dogs, and is not the same virus as SARS-CoV-2, the virus that causes COVID-19. Documented canine coronavirus infections in humans, while still rare, have been linked to pneumonia hospitalizations in Southeast Asia.
In a study led by Lednicky, a UF team isolated a canine coronavirus from a medical team member who had traveled from Florida to Haiti in 2017 and later experienced mild fever and malaise. The team named the strain HuCCoV_Z19Haiti.
Scientists led by Gregory Gray, M.D., director of the One Health Research and Training Laboratory at the University of Texas Medical Branch, reported the discovery of a new canine coronavirus strain, CCoV-HuPn-2018, in 2021. The strain had been isolated from a child hospitalized in Malaysia and was nearly identical to the coronavirus discovered by the UF team.
Since then, CCoV-HuPn-2018 has been found in people with respiratory illness living in Thailand, Vietnam and in the state of Arkansas, demonstrating this strain of canine coronavirus is already circulating across continents.
These recent influenza D virus and canine coronavirus discoveries underscore a familiar lesson from recent pandemics: Without proper preparation, a virus that quickly gains efficient human-to-human transmissibility can easily turn into a large-scale human epidemic. To prevent such a scenario, the scientists say better virus monitoring, more reliable tests, treatments and possible vaccines are needed.
"Our knowledge about the viruses' epidemiology and clinical manifestations are limited to a modest number of research studies," the authors wrote. "Even so, the limited data regarding these novel, newly detected viruses indicate that that they are a major threat to public health."
