In experiments designed to learn more about the threat from the H5N1 avian flu virus spreading from cows to people, researchers found that an isolate from a sick dairy worker may be capable of replicating in human airway cells, is pathogenic in mice and ferrets, and can transmit among ferrets by respiratory droplets.
The team, based at the University of Wisconsin at Madison and Japan, reported its findings today in Nature. Working in a high-containment lab, the researchers used an H5N1 isolate grown from the eye of a dairy worker who had experienced conjunctivitis after exposure to infected cows.
They found that the virus has a PB2-E627K mutation that has been seen in H5N1 viruses that replicate in mammals.
In their multipart investigation, they found that the virus was sensitive to most antivirals, including favipiravir, baloxavir marboxil, and zanamivir, but was less sensitive to oseltamivir, according to a press release from the National Institute of Allergy and Infectious Diseases (NIAID), which funded much of the work.
Tests using human cornea and lung cells found that the virus was able to replicate. And, in mouse tissue experiments, the scientists found that the H5N1 virus was able to infect 15 different tissues, with the highest levels seen in respiratory tissues.
Lethal pattern in ferrets
Meanwhile, the team infected ferrets with a high dose of the virus from the dairy worker, and the infection pattern was more similar to human infections than mice infections. Ferrets are known as one of the best animal models for influenza in humans, because clinical signs of disease and transmission are similar.
All ferrets died within 5 days, and tissue sampling found the virus in all types, with the highest levels in the animals' respiratory tissues. In contrast, earlier research using a bovine H5N1 virus to infect ferrets found that the infections were severe, but not as lethal.
To gauge respiratory transmission, the team placed healthy ferrets in cages next to ferrets that were infected with different doses of the virus from the dairy worker. From 17% to 33% of ferrets in adjacent cages were infected by respiratory droplets, suggesting that the virus from humans can spread among mammals by that route, but with limited efficiency. All directly infected ferrets died within 6 days.
"Based in these observations, every effort should be made to contain HPAI [highly pathogenic avian influenza] H5N1 outbreaks in dairy cattle to limit the possibility of further human infections," they wrote.
California reports another suspected case
California today reported another suspected human H5N1 infection, which if confirmed by the US Centers for Disease Control and Prevention (CDC) would raise the state's total 16.
The CDC on October 25 confirmed 3 more infections in Washington poultry cullers, bringing the national total to 34. Once the California infection is confirmed by the CDC, the national total would rise to 35.
Virus strikes more cows, poultry
Meanwhile, the surge in outbreaks continues in California dairy cattle. The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) has confirmed 41 more outbreaks, raising the state's total to 178 and the national total to 380 from 14 states.
Also, APHIS confirmed more outbreaks in poultry in the West, this time in Oregon, including an egg-laying farm in Clackamas County that has 146,000 birds and a backyard facility in Crook County.
The agency also confirmed an outbreak at another broiler farm in Tulare County, California, and another in backyard poultry in Washington.
