by New research into ongoing outbreaks of bird flu on dairy farms describes in unprecedented detail how efficiently the virus spreads among cows, and from cows to other mammals, including cats and raccoons.
It’s a sign that the virus is developing new abilities that have bird flu experts worried.
Avian influenza has affected more than 100 million wild waterfowl, commercial flocks and backyard poultry in the US over the past several years. Its spread has alerted scientists to the possibility that the evolved virus could one day spread from person to person, igniting the next pandemic.
No human-to-human transmission has yet occurred, as far as researchers know. But the total number of human cases continues to grow: Colorado state health officials confirmed three new cases of bird flu in humans on Thursday, bringing the national total to 14.
All of the human cases among farm workers have been infected after exposure to sick animals, and all but one have been diagnosed in the past four months. While little is yet known about the three newest infections, the rest were mild.
The new study shows that the virus is spreading from one mammal species to another – a relatively new phenomenon that could make it more difficult for authorities to control.
The longer the virus remains uncontrolled, the more potential it has to evolve and adapt to pose a threat to humans, according to the authors of the new study, published in the journal Nature on Tuesday.
“The virus is not very efficient at infecting humans and transmitting between humans, but if the virus continues to spread in and from dairy cows into other mammal species, that could change,” said Diego Diel, the author of the study and Dr. director of the Virology Laboratory at the Animal Health Diagnostic Center at Cornell University. “It’s a matter of concern.”
The new study assessed the first outbreaks of bird flu among cows at nine farms in Texas, New Mexico, Kansas and Ohio, sampling the animals and then comparing the genetic similarity of the virus between them.
The researchers found that the virus, a particular strain of bird flu known as H5N1, spread quickly among farms. When infected cows were moved from Texas to another farm in Ohio, the virus was soon discovered in cows in Ohio. And genetic sequencing suggests that cats and raccoons got the virus, and died, probably after drinking raw milk.
Sick cows began to eat less feed, regurgitated less, experienced reduced milk production and produced discolored milk, the study says. On some affected farms, cows died at twice the normal rate.
Andrew Bowman, a professor of veterinary preventive medicine at Ohio State University who was not involved in the new study, said the research reflects the experience of veterinarians on many US farms.
“It matches the clinical picture,” Bowman said. “That’s 100% what we’ve seen on dairy farms. This is only the first serious published documentation.”
The study reinforces evidence that handling or drinking unpasteurized milk is dangerous.
Diel said infected cows shed incredible amounts of virus through their mammary glands when they are infected – at higher concentrations than the virus can easily be cultured in a laboratory setting.
“Drinking raw milk is extremely dangerous,” Diel said.
Several studies have detected live H5N1 virus in raw milk, while others have shown that pasteurization inactivates the virus, making commercially produced milk safe to consume.
Farmers are not supposed to send any milk with a chance of contamination for production.
“Milk from a sick cow should not be entering the milk supply,” Bowman said.
As scientists continue to study the bird flu outbreak, Bowman said he would be interested in finding out whether cows can shed the virus before they get sick, as well as whether the virus continues to spread from the mammals that get infections from cows.
This is the third episode in which the virus has spread relatively quickly among a group of mammals, said Anice Lowen, a virologist and professor at the Emory University School of Medicine who was also not involved in the new study. Previously, the virus spread on mink farms and among sea lions and fur seals last summer.
There have been severe cases in some mammals and the virus has caused massive deaths among sea lions and seals, among other species.
Lowen said health officials should also consider the risk that people could be infected with H5N1 and the seasonal flu at the same time this winter. When a person is infected with multiple flu viruses, those viruses can go through a process called reassortment, in which they trade genetic information.
This process can give viruses a shortcut to evolve, which can change the way they spread.
“The virus we currently have in cows is a relatively low risk to humans. CDC has said that and they are right,” Lowen said. “But where the risk lies in my mind is viral evolution. They change when they adapt to a new host. They change when they go through reassortment and exchange genes.”
The Centers for Disease Control and Prevention declined to comment on the new research.
This article was originally published on NBCNews.com
