Since 2022, a new, highly pathogenic strain of H5N1 influenza or “bird flu” has spread worldwide. In the U.S. it has affected over 100 million birds and for the first time, spread into dairy cows and a small, but growing, number of people. At UC Davis, experts in One Health — an approach that considers the health of people, animals and the environment together — are on high alert. 

Nothing but death

Dead silence met Marcela Uhart and her team when they arrived at the elephant seal colony at Punta Delgada, Patagonia on Oct. 10, 2023. 

“These beaches, at the peak of the breeding season, are bustling with life,” Uhart, director of the Latin American Program at the Karen C. Drayer Wildlife Health Center at the University of California, Davis, School of Veterinary Medicine, told a webinar in May. “The masters of the beach, the bull seals, interactions with mothers and their pups, that was not there. All we saw was carcass after carcass. … There was nothing but death.”

Uhart was speaking at an Emergency One Health Consultation on Combating H5N1 Influenza organized by UC Davis Grand Challenges and the School of Veterinary Medicine. The May 16 event was held in response to growing concern about the number of cases of H5N1 influenza, or “avian influenza,” worldwide. It included an international panel of experts on infectious diseases, influenza, veterinary medicine, food safety, disease diagnostics and public health.

Overlapping wild and domestic animals, human health and environmental health, H5N1 is a quintessential “One Health” problem. H5N1 influenza normally circulates in wild birds, especially waterfowl, sometimes spilling over to domestic poultry. The virus is always evolving and sometimes a new, more lethal variant — a highly pathogenic avian influenza, or HPAI — appears. 

Unprecedented scale

The current outbreak, which reached the U.S. in 2022, is unprecedented in its scope and scale, said Maurice Pitesky, associate professor of cooperative extension and an expert in poultry disease modeling at the School of Veterinary Medicine. The same strain has affected numerous bird and mammal species on all continents, even Antarctica, except Australia and Pacific islands. 

“We’ve never seen anything like this,” Pitesky said. “It’s orders of magnitude larger and more complex than previous outbreaks.”

For the first time, H5N1 has been found in dairy cattle, with outbreaks in at least 13 states. It has been detected in feral cats around dairies and in a few cases, dairy workers. Sick cows recover, but milk production decreases and milk from infected animals has to be discarded. 

H5N1 is a big challenge for dairies, Richard Pereira, associate professor of veterinary medicine, told the webinar. We just don’t know enough about how the virus is being spread between birds, cattle, cats and other mammals, said Pereira, who works with the dairy industry on livestock health. “We need more information to better target biosecurity measures.”

The tools available to control H5N1 on poultry farms are limited. Standard practice is to “depopulate,” or kill, the entire affected flock, because flu viruses do not grow in dead animals. That approach has succeeded in the past, but as the virus adapts to other animals, such as cows and cats, it has more places to hide, Pitesky said. 

Vaccination of poultry flocks is possible, but poses other problems, Pitesky said. 

“Vaccinated animals can still be infected. So unless you have really good surveillance you might end up having more disease transmission via birds that are vaccinated and infected without symptoms,” he said. Meat from vaccinated birds cannot be exported due to current trade restrictions. 

Pitesky favors a more focused, strategic approach. 

“Vaccinating 8 billion broilers and 300 million-plus layers would be challenging logistically. We should probably be vaccinating strategically when waterfowl are nearby,” he said. New tools such as The Waterfowl Alert Network can forecast the location and abundance of waterfowl around farms. This helps farmers make risk-based, informed decisions about implementing extra biosecurity precautions and vaccination. The tool has been commercialized as a subscription service by Pitesky and colleagues based on some of their recent research. 

Adapting to mammals

The deadly outbreaks among seals and sea lions in South America show that the new strain of H5N1 is adapting to spread among mammals. 

“This is increased evidence that we should be alert, especially for marine mammals,” Uhart told UC Davis in June. “The more it adapts to mammals the more important it becomes for humans.”

Could H5N1 start spreading among humans? There is no evidence yet of sustained human to human transmission, and it has been deemed of low risk to people, Angel Desai, assistant clinical professor of internal medicine at UC Davis Health, told the webinar. There have been 14 cases of H5 flu in humans in the U.S. since 2022, all in people exposed to poultry or dairy farms, most of them this year. 

Genetic analysis of an H5N1 virus from one of those patients showed mutations in one gene linked to adaptation to mammals, but not in another that would make it easier for the virus to infect the upper respiratory tract of humans. 

“All of this is to say that this could all change, which is why surveillance and having these genetic sequences to document mutations is important,” Desai said. 

The lessons of COVID-19

Many people would likely rather not think about another pandemic respiratory virus while COVID-19 is still causing outbreaks. But the coronavirus pandemic has provided some tools and lessons.

One is community surveillance through wastewater testing, an approach pioneered by Heather Bischel, associate professor in the UC Davis of Department of Civil and Environmental Engineering, as part of the Healthy Davis Together program (a partnership with the city of Davis) and now continuing as part of Healthy Central Valley Together. 

The National Wastewater Surveillance System, run by the Centers for Disease Control, collects wastewater test results for type A influenza (which includes H5N1 as well as influenza viruses that normally infect humans) from labs nationwide. Wastewater testing can alert communities to a surge of virus even before many people get sick. 

UC Davis Grand Challenges, working with Healthy Davis Together and the Bay Area Global Health Alliance, developed a pandemic preparedness roadmap based on the lessons of COVID-19. The roadmap emphasizes bridging gaps between sectors, enhancing public health communication, strengthening disease surveillance and ensuring equity.

“You have to put equity first. Equity and community engagement are key,” said Jonna Mazet, vice provost for Grand Challenges, a unit on campus seeking to bring together researchers to solve some of the most complex world problems. Accurate, useful information has to get into the hands of the most impacted communities, whether they are frontline workers during COVID or dairy farmers and workers in H5N1. 

A policy brief drawing together recommendations from the May webinar is in preparation. The document encourages lawmakers to consider new policies and funding that can strengthen our preparedness, prevention and response capacities for avian influenza and other health threats.

Read more about H5N1 from UC Davis Grand Challenges and the School of Veterinary Medicine.