The World Health Organization warned on Thursday that the ongoing spread of the bird flu among both birds and mammals around the world is a "significant public health concern."
The H5N1 subvariant of bird flu has been increasingly reported in cattle in recent weeks, with 32 cases reported in eight states since March 25.
Earlier this month, a person who had exposure to infected cows in Texas was found to be infected with the H5N1 subtype, with conjunctivitis being their only symptom. The infected person was treated with a flu antiviral drug and recovered.
Dr. Jeremy Farrar, chief scientist at the WHO, explained on Thursday that the great concern is that as the bird flu has spread around the world in both birds and mammals in the past two years, it could eventually evolve and develop the ability to infect humans and eventually the ability to pass between humans.
“Do the milking structures of cows create aerosols? Is it the environment which they’re living in? Is it the transport system that is spreading this around the country?" said Farrar. "This is a huge concern and I think we have to…make sure that if H5N1 did come across to humans with human-to-human transmission that we were in a position to immediately respond with access equitably to vaccines, therapeutics, and diagnostics.”
Farrar expressed concerns that vaccine development for the bird flu was "not where we need to be."
The WHO scientist added that the virus "is just looking for new, novel hosts" and that its spread among mammals brings it closer to humans, according to The Guardian. Farrar called for increased monitoring, stressing that it's important to understand how many human infections are happening in order to keep track of potential adaptations by the virus.
Bird flu appears to be spreading between cows, from cows back to birds
The US Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) updated on Tuesday that while wild migratory birds are believed to be the original source of the outbreaks among cattle, there is evidence of some cases where it appears the virus spread between cows and from cows back to birds.
Analyses of viruses found in the cows have so far not found any changes affiliated with transmission between people. The USDA added that it remains unclear exactly how the virus is spreading between cows, although respiratory-related samples did not include significant concentrations of the virus, indicating that respiratory transmission is likely not the main way it's being spread.
The WHO reported on Friday that the bird flu had been detected in very high concentrations in raw milk from infected animals, although it remains unclear how long the virus can survive in milk.
WHO: Bird flu may be spreading in new ways
Wenqing Zhang, head of the global influenza program at the WHO, told reporters that the fact the virus was now spreading from cows to humans, between cows, and between cows and birds suggests that "the virus may have found other routes of transition than we previously understood."
The US Centers for Disease Control and Prevention (CDC) updated on Friday that tests had found that the H5N1 virus that infected a person in Texas earlier this month could be treated with antiviral medications used for seasonal flu.
Additionally, some preliminary analyses have shown that two candidate vaccines for the bird flu could offer protection against the virus found in the infected person.
CDC believes risk to humans still low
The CDC added that this is a "rapidly changing, emerging situation," but stressed that it still believes that the risk to humans is low.
Health officials from the CDC and the WHO have stressed the importance of not consuming raw milk. Pasteurization should kill any bird flu viruses present in dairy products.
Scientists concerned US not transparent enough about cattle flu outbreak
Some scientists have expressed concerns that US officials are not being transparent or clear enough about the outbreaks of bird flu.
Marion Koopmans, head of the department of viroscience at Erasmus Medical Center in Rotterdam, told STAT news that studying the spread of the virus in cattle has been difficult for scientists not in the US due to a lack of information being released by the US.
Koopmans stressed that health officials need to figure out if the outbreak among cattle and other related mammals is unique to the US or is a risk around the world.
Only a few genetic sequences from the outbreak have been uploaded to international databases, all of which are from early in the outbreak, making it difficult for scientists to monitor if the virus has changed as it spread further.
Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy, told STAT that the behavior of US officials concerning the outbreak has created "the perception that something is happening or not happening that would not meet with the public’s approval."
STAT also noted that the belief that pasteurization would kill bird flu viruses was based on work done on other viruses, not H5N1. When they asked the USDA and FDA if they were testing to see if the process also killed H5N1, they were told work on the matter had not yet been done.
The New York Times reported on Friday that officials in North Carolina found bird flu infections in a cattle herd with no symptoms, information the USDA has not shared publicly. The fact that cattle herds may be infected without expressing symptoms could mean that the outbreak is more widespread than previously thought.
The Times also noted that federal officials have shared only limited genetic information with scientists and officials in other countries. Federal officials are also not actively monitoring infections in pigs, which are considered to be central to evolving flu viruses and are often kept close to cattle.
Dr. Tom Inglesby, director of the Johns Hopkins Center for Health Security at the Bloomberg School of Public Health, told the Times that if more information was shared, scientists outside the government could help contain the virus already.
Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security, noted that widespread testing of animals with and without symptoms is important in order to understand the scale of outbreaks and how they're spreading. The USDA is not requiring widespread testing at this point.
Dr. Amy Swinford, director of the Texas A&M Veterinary Medical Diagnostic Laboratory, noted that some dairy farmers are afraid to test their herds due to concerns that fears about bird flu could hurt their business.
"I think there’s many more dairies that have had this going on than what we’ve gotten samples from," Swinford told the Times.
The USDA has stressed that it has been "timely and transparent" about the release of information, according to STAT.
Dr. Rosemary Sifford, the USDA’s chief veterinarian, stressed in an interview to the Times that over a dozen federal epidemiologists, and many laboratory employees, field staff members, and academic and state collaborators were working on monitoring the virus. Sifford noted that the agency has been engaged with the issue for less than a month and is working hard to generate more information."
Bird flu continues to spread around the globe
Outbreaks of avian influenza have been increasingly reported in mammals as the virus has continued to spread around the world in the past few years.
Since 2021, Europe and the Americas have been suffering from a nearly continuous outbreak of H5N1 avian influenza, which has been described as "the largest-ever" on the three continents. The virus has affected tens of millions of birds and thousands of mammals worldwide. Outbreaks of the virus have also become more common in Africa and Asia in the past year and have even spread to Antarctica in recent months.
The World Organization for Animal Health (WOAH) noted in March that, while estimates vary, about 485 bird species and 37 mammal species have been infected with avian influenza since 2021. Only the Pacific Islands, Australia, and New Zealand have been spared from the virus.
“The loss of wildlife at the current scale presents an unprecedented risk of wildlife population collapse, creating an ecological crisis,” noted WOAH.