Public Health's Strategy to Protect Against Bird Flu

A form of avian flu that has been devastating to the nation's poultry industry in recent years has now spread to cattle. Although one dairy worker in Texas has been infected, public health officials believe the risk of contagion to humans remains low, but they are on alert nonetheless.

On April 1, the federal Centers for Disease Control and Prevention (CDC) reported that a worker on a Texas dairy farm had tested positive for an avian flu strain that has decimated poultry and wild bird populations. The U.S. Department of Agriculture (USDA) subsequently found that cattle in six states have been infected with it.

The dairy worker’s only symptom was eye redness. He was treated and has recovered. But it was the first time this virus had passed from an infected mammal to a human, and the first time it had been found in cattle.

The viral strain in question, H5N1, was first detected in China in 1996. Since 2021, it has killed hundreds of millions of wild and domesticated birds. Fewer than 900 cases of human illness caused by the virus have been documented worldwide, the result of exposure to infected birds. Half of those who became ill did not survive.

Scientists who monitor the transmission of disease from animals to humans have long worried that a mutation of the virus could spark a dangerous pandemic. At present, there are no signs that this has occurred, and also no evidence of human-to-human spread of the virus. The risk to those who work with poultry and cattle is greater, but still “low-to-moderate,” according to health authorities. The CDC has issued recommendations for minimizing their exposure.

State and local health officials are now working alongside the federal government and academic researchers to build the data collection and communications infrastructure necessary to monitor and understand an unprecedented situation that is unfolding in real time.

The threat to the population is low right now, says Adriane Casalotti, who heads government and public affairs for the National Association of County and City Health Officials (NACCHO). Public health officials are actively working behind the scenes to keep it that way — or identify new threats if they emerge.

Known and Unknown

The first challenge is to understand what’s causing dairy cattle to become infected. The virus isn’t showing up in nasal swabs of cattle, but it is present in their milk. At an international virtual meeting, representatives of the USDA said it’s possible that it is being spread by milking equipment or the people doing the milking.

So far, USDA scientists haven't found that cows are actively shedding virus and exposing other animals. Even if milking is to blame for spread, it doesn’t answer the question of how the virus came to be present in the first place.

The fate of the cows is another matter. So far, the USDA hasn’t issued orders to quarantine cattle, but it recommends minimizing their movement. Some states are restricting the import of cattle from states with infected herds.

The USDA has required poultry farmers to cull flocks infected with H5N1, leading to the loss of 85 million birds to date. Nothing this severe is being suggested for cows, but there are big concerns about what could happen if the virus in them spreads to poultry and leads to new infections in flocks.

There’s already a safeguard against exposure to the virus in milk. “One of the reasons we don't think that this will get to the general population is because milk is pasteurized,” Casalotti says. States have a patchwork of guidelines regarding the sale of raw milk, however. Two of the states where infected cows have been found, New Mexico and Idaho, allow the sale of raw milk in retail outlets. Only one, New Jersey forbids its sale under any circumstances.

As the origins of cattle infections and their potential impact on dairy workers are investigated, the CDC has urged health departments to tighten relationships with agricultural agencies and veterinarians. "It is very, very important that state or local agricultural government agencies and workers are being very, very collaborative and keeping the public health side up to date,” says Marcus Plescia, chief medical officer for the Association of State and Territorial Health Officials (ASTHO). “That's the big ask here.”


Marcus Plescia talks about the importance of collaborative communication between agriculture and public health.

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Casalotti also urges physicians who treat workers exposed to livestock to be alert to symptoms of possible H5N1 infection and alert local health departments when they see something. (The CDC has published guidelines for diagnostic testing and specimen collection.) Protective measures advised for those who work with livestock also apply to veterinarians, and public health officials need to know what they are seeing with animals, livestock workers and veterinary staff.

The Real Risk?

Unlike COVID-19, H5N1 isn't a new or novel virus. It has been known to epidemiologists for decades. Treatment exists, as do candidates for a vaccine if there should be the need for one. “Right before coronavirus showed up, the baseline assumption for a respiratory pandemic was an avian influenza,” says JP Lieder, director of the Center for Public Health Systems at the University of Minnesota.

Most fatalities from this strain of bird flu have occurred in developing countries. It’s hard to know what the fatality rate might be in a country with higher levels of medical and supportive care if cases become more common, Plescia says. Only one other person in the U.S. is known to have been affected by bird flu, in 2022. They were exposed to an infected flock, and their only symptom was fatigue.

Even if the current risk is low, it’s enough to prompt urgent conversations about “what ifs” within the public health community. Our dependence on industrialized factory farms for our food supply increases the likelihood of such a public health emergency, Lieder says. Bills currently before Congress that would limit states' ability to set standards for such operations, combined with limitations on public authority enacted in the wake of the pandemic, would weaken both protections and regulators' ability to respond.

There needs to be a hard look at the public health system’s continuing ability to act when serious threats emerge, says Brian Castrucci, CEO of the de Beaumont Foundation, which supports health efforts. Even if more transmission from cattle to humans occurs, tools exist to contain it, but may be effective only if public health departments are adequately staffed with trained workers. The foundation estimates that public health departments need 80,000 more full-time employees just to deliver basic services.

The country’s pandemic response capability is only as strong as the state that is least prepared, Castrucci says. This is an opportune time for every state to make a comprehensive pandemic preparedness plan that incorporates learnings from COVID-19, and for states and the federal government to look for ways to work together against diseases that pose national, not state-level, threats.

“We spend a lot of time worried about China and Iran,” Castrucci says. “We need to be much more concerned about viruses that we haven’t even named.”