So far, the virus has not caused outbreaks in livestock in other countries, perhaps because animals are not moved from farm to farm as frequently as in the United States.
Some genetic data suggest that the outbreak in the United States was due to a single jump of the virus from birds to livestock and that it then spread to other regions of the country.
“At that time, many wild birds had the virus, but that spread seems to have slowed down, so it’s possible that another jump won’t happen,” said Tom Peacock, a virus expert at the Pirbright Institute in the United Kingdom.
Scientists say there is a small chance the virus could infect susceptible cattle herds and then disappear, at least for a while. But if that happens, it could take months or even years.
The virus is more likely to become enzootic (endemic or specific to animals), much as has happened with other viruses in pigs. Pig farms are never free of a new virus because susceptible piglets are constantly being introduced into the population.
The same could be true for dairy cattle in the United States, Gray said: “What we’re seeing on hog farms is something we hope we never see on dairy farms, where you have multiple strains of influenza that can mix together and create new viruses.”
The outbreak in livestock is already endangering poultry, as well as people.
The virus detected on Colorado poultry farms appears to have originated in dairy cattle, leading to the culling of 1.8 million birds. Nine workers involved in the slaughter became infected.
“If this continues at the same rate, the dairy industry will kill off the poultry industry,” Peacock warned.
“They have been given all kinds of warnings about the potential for this virus to become a pandemic,” he added, referring to federal officials.
Several scientists have warned that without a sharp shift in state and federal policies, the bird flu virus that has plagued American dairy farms is likely to take hold among their livestock.
This means that bird flu could soon pose a permanent risk to other animals and humans.
So far, the virus, called H5N1, doesn’t easily infect humans, so the risk to the public remains low. But the longer the virus circulates among livestock, the more likely it is to acquire the mutations needed to cause a flu pandemic.
“I think the window of opportunity to contain the outbreak is closing,” said Krutika Kuppalli, an infectious disease doctor who worked for the World Health Organization until April.
“We immediately blamed China for what happened with SARS-CoV-2, but our actions are no better at the moment,” he added. “That’s how pandemics happen.”
Half a year after the initial outbreak, H5N1 shows no sign of losing ground among American dairy cattle or the workers who handle them. In recent weeks, the virus has spread to birds and workers.
As of Aug. 21, infections had been reported in 192 herds of cattle in 13 states and 13 people. Nine of those people were workers at poultry farms near dairy farms in Colorado.
Earlier this month, the state reported that H5N1 infections had also been diagnosed in six cats, two of which lived indoors and were not directly exposed to the virus.
However, some fundamental questions about the outbreak remain unanswered.
Investigators do not know how many farms are being investigated for the virus, how many cows are infected in each state, how and how often the virus jumps to people and other animals, what the course of the disease is in humans and animals, and whether it is possible for cows to be infected more than once.
“We need to know the area of circulation in dairy cattle in the United States, which we don’t have,” said Maria van Kerkhove, acting director of WHO’s Epidemic and Pandemic Prevention and Preparedness Department.
Van Kerkhove praised the Department of Agriculture’s financial incentives to encourage farmers to cooperate with research, but said “a lot more needs to be done.”
The government’s response to the outbreak may have been complicated by election-year politics and because the agency charged with overseeing these efforts is a federal department that is tasked with not only regulating but also promoting the agricultural industry.
Federal officials have downplayed the risks to animals, saying the virus causes only mild illness in cows. But a study published in late July showed that the percentage of cows dying on affected farms was twice the normal rate and that some of the infected cows were asymptomatic.
In theory, nothing about this outbreak makes it difficult to contain, Van Kerkhove and other experts said. Unlike other influenza viruses, this version of H5N1 does not appear to spread efficiently in livestock through the respiratory tract.
Rather, in most cases, transmissions appear to have occurred through contaminated milk or viral particles on milking machines, vehicles, or other objects, such as workers’ clothing.
“This is actually good news,” said Juergen Richt, a veterinarian and virus expert at Kansas State University who led the study.
“If we want to control or eradicate this disease, we only need to focus on mechanical or anthropogenic transmission,” he said.
Some federal officials have said findings like these reinforce their belief in their ability to stop the virus.
“I think the response is appropriate,” Agriculture Department official Eric Deeble told reporters on Aug. 13.
He also said that the outbreak is containable because there is no natural reservoir for the virus, meaning there is no species in which it lives and multiplies naturally.
But some experts not affiliated with the government disagree, saying current measures are not enough to quell the outbreak. The virus is prevalent in wild birds such as waterfowl, as well as a wide range of mammals, including house mice, cats and raccoons.
“Being positive is wonderful, but it’s not enough to get the results you need,” said Michael Osterholm, an infectious disease expert at the University of Minnesota. “We’re still in a state of complete confusion.”
It would be best if farms would do “bulk testing” of pooled milk from many cows and restrict movement of cattle and workers until the virus is eradicated.
Unfortunately, federal regulations only require testing when cattle are moved from one state to another. Additionally, many states only require testing if cows show visible signs of disease.
Colorado is the only affected state so far that requires bulk milk testing, a move that helped identify 10 more infected herds within two weeks of the order, which went into effect July 22.
The Agriculture Department has also tried to encourage testing through a voluntary program. Of about 24,000 farms that sell milk in the country, only 30 are participating.
CONTENT FOR SUBSCRIBERS
The program has identified herds with infected cows, “indicating that the system is working as designed,” a department spokesman said in an email.
Given the risk it poses to their business, few farm owners have taken up the offer of compensation in exchange for implementing testing or biosecurity measures. Many have migrant workers who fear deportation.
“Right now, these people feel very vulnerable, so very, very few are willing to cooperate,” said Gregory Gray, a public health researcher specializing in infectious diseases at the University of Texas Medical Center in Galveston. “Those who did decide to cooperate, in some cases, I think, regretted doing so.”
#avian #flu #pandemic #starting #American #farms
