The highly contagious H5N1 bird flu virus may be spreading through the air under certain conditions, according to a new study from the Czech Republic.
Government veterinarians made the discovery while investigating a mysterious outbreak at a highly secured chicken farm last February.
The farm had strict biosecurity measures — filtered well water, one-way airflow fans and fencing to keep wild animals out. Yet, the virus still infected the flock, causing thousands of bird deaths.
The likely culprit? Wind.
Dr. Kamil Sedlak, senior study author and director of the State Veterinary Institute in Prague, said that after all the possibilities were explored, windborne spread was most likely cause in this case, CNN reported.
Experts traced the virus back to a duck farm nearly 5 miles west of the chicken facility.
The duck farm, near a lake that hosted wildlife, had far less biosecurity and had been hit by a massive outbreak days earlier.
Bird flu swept through the duck farm rapidly — 800 ducks died on the first day. Within two days, 5,000 had died. A few days later, the entire 50,000-bird flock was culled to contain the outbreak.
Meanwhile, the chickens at the breeding facility became sick slowly. Birds near air intake vents were the first to die, suggesting they were exposed to virus particles carried by the wind.
Researchers checked the weather data from that week, which revealed perfect conditions for windborne spread.
There was a steady breeze from west to east (from the duck farm to the chicken farm). There was also a lot of cloud cover, which blocked UV light that usually kills viruses.
What's more, there were cooler temperatures —between 40 and 50 degrees Fahrenheit, which is ideal for virus survival.
“I think that under certain specific conditions, the spread of the avian influenza virus by wind can occur,” Sedlak told CNN.
The findings, which were published on the preprint server bioRxiv, should be considered preliminary until they are peer-reviewed.
Dr. Richard Webby, director of the World Health Organization's Collaborating Center for Influenza Ecology, said windborne spread has been suspected before but is hard to prove.
“The whole idea of potentially being sort of wind-driven has been out there for a while,” Webby, who was not involved in the study, told CNN.
He noted that the current strains of bird flu circulating in animals don’t easily infect people and would likely need to mutate more to become a serious human threat.
“I think it’s very low-risk for humans to be infected with the virus like that, but I think it happens,” Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said.
However, Osterholm also warned that wind-driven spread might explain unusual cases, such as the three veterinarians who tested positive for H5N1 antibodies after attending a conference, despite having no direct contact with sick animals.
It’s not only how much virus is blowing out into the air but also where it lands, said Dr. Montserrat Torremorell, professor and chair of Veterinary Population Medicine at the University of Minnesota, who reviewed the findings.
Torremorell recommended farms consider filtering the air in barns, in addition to following current precautions such as personal protective equipment and restricted access.
“I think the airborne transmission should be on the table,” she said.