I have written before about our country’s lethargic public health response (with notable exceptions for the states of California, Colorado and Michigan) to the A(H5N1) avian influenza outbreak among U.S. poultry and dairy farms, and some of the developments that should be increasing our concern for the potential of this epizootic (epidemic in animals) to develop into an epidemic or pandemic among humans. In brief summary of these concerning developments, we start with the fact that we are dealing with a novel influenza virus for which there is little to no existing population immunity and that avian influenzas have already demonstrated their ability to contribute to the development of human pandemics (1918, 1957, and 1968) and have been recognized by public health authorities to be viruses with pandemic potential for decades. The outbreak of H5N1 among many animal (both land and marine mammals) species over the past two years is unprecedented, whereas in the past, few mammalian species have been known to be infected and those infections were sporadic and incidental in nature. Then, this year, for the first time, we have an outbreak occurring in dairy cattle, and that outbreak has been sustained, growing and unable to be contained with the current measures put in place by the USDA and CDC. Of even greater concern is that there have been an unprecedented number of infections in dairy and poultry workers in the U.S. Finally, the concerns heightened even more when a person in Missouri was diagnosed as infected with H5N1 who had no occupational work exposure to likely animals, no ingestion of raw milk or dairy products and no other risk factors for exposure, raising the concerning potential that there might be community spread.
New developments are again increasing concern that this virus is changing in concerning ways.
For much of the past six months, there were no known dairy herd infections in California. They were only recently discovered and the number of herds infected in California has now grown to 56. However, reports coming out of California describe a far more virulent infection in the cattle. Until now, we have had few details about the percentage of cattle in herds infected (according to the article it has previously been estimated to be about 10 percent of the herd), and we have been led to believe that most cattle were recovering from the infection with few deaths among the cattle. The LA Times is now reporting that although farmers were told to expect less than 2 percent mortality for infected cattle, preliminary reports suggest that 10 – 15 percent of the infected cows in the California outbreaks are dying. A veterinarian described the infected cows as appearing much more clinically ill than the descriptions we have been provided with in the past outbreaks, though he qualified that the abnormally high temperatures may be playing a role. He also indicated that many of the deaths were due to complications such as pneumonia or bloat. He also described that many of the cattle stop eating during the illness. As a consequence, the digestive tract doesn’t empty well, and in turn, the cattle can suffocate form the increased pressure on their diaphragm.
Another change appears to be in the duration of illness. We were previously led to believe that the infections in other states resulted in a week-long, or perhaps two, of mild illness. Now cattle are often sick for several weeks. This veterinarian estimates that as much as 50 – 60 percent of the cattle in the herds with these outbreaks are clinically ill. And, while we were led to believe that recovered cattle seemed to be completely recovered in other states, this veterinarian stated that the recovered cattle seemed to only recover about 60 – 70 percent of their milk production. https://www.latimes.com/environment/story/2024-10-04/bird-flu-deaths-increasing-among-california-dairy-cows.
To add to the concerns, three new human infections of H5N1 (suspected, but awaiting confirmatory testing) were detected this past week in California (the first two were reported on Friday and the third was reported today) – all in dairy workers with direct contact with cattle. None of these three had any contact with each other, so these were three separate spillovers. All thee had conjunctivitis (pink eye), with one worker having reported splashing of milk in his or her eye.
These developments could be in part explained by the fact that California has seemed to be much more aggressive and transparent in their response to these outbreaks, but many of us have an unsettledness that something has changed with the virus given that 3 human infections have been detected in just the past week (prior to this, there have only been 14 human cases detected this year across the entire country) and that the clinical severity in cattle appears to have changed significantly. Our main concern is whether the virus is adopting through mutations and reassortments an increased ability to infect humans and ultimately, the biggest concern would be for the virus to acquire increased efficiency in human-to-human transmission, which until the Missouri case, has seemed to be a remote possibility. And, a number of us are concerned for the upcoming human influenza season and the potential that dairy workers could transmit human seasonal influenza virus (H1 or H3) to cattle while there already appears to be such high levels of H5N1 infection in cattle that could result in co-infections that could facilitate reassortments (swapping of one or more of the eight genetic segments in influenza viruses) allowing the H5 virus to acquire genetic material from the human seasonal virus that would in turn give the H5 virus increased efficiency in human transmission.
We need much more testing, we need testing that does not have to be sent to the CDC in Atlanta and can be done with a faster turnaround time, we need genetic sequences for comparison to see if the virus has picked up mutations associated with enhanced mammalian spread, we need a reliable serological test so that we can assess the degree of spread among cattle and among workers and their close contacts, we need studies that help us understand the transmission modes of the virus, we need research to be done on vaccines against H5N1 and a we need more antiviral options for treatment, especially in the event of the development of oseltamivir resistance. In a nutshell, we need to shake off the sense of complacency, develop some greater sense of urgency, increase the transparency from USDA and CDC, engage academic and commercial laboratories in the development of faster and cheaper tests that can be more accessible, devote funding for research, make more serious and intensified efforts at containment of the spread of the virus, and we need a plan to minimize the risks of human-to-cattle spread of the upcoming seasonal influenza viruses.
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