June 12, 2024


On a US dairy farm, working in the milking parlor can mean seven-day weeks, 12-hour shifts and intimate contact with cows and everything they expel.

“When you disconnect the machine from the udder, it can shoot milk in your face,” said José Martínez, a former dairy worker and United Farm Workers advocate based in Washington state. “And there’s no time or place to eat. So we ate our tacos in spare moments with cow shit on our hands.”

Conditions on US dairy farms are in the spotlight since the H5N1 influenza virus, which has decimated bird populations around the world, jumped species and adapted to spread between cows. That makes dairy farm workers the frontline for spillover infections into humans.

As of 24 May, there are 58 known infected herds across the US. Two human infections have been documented, in dairy farm workers in Texas and Michigan. But there are anecdotal reports of other farm workers with mild symptoms.

One-off spillover infections between species are not in themselves enough to cause a pandemic. That would require the virus to adapt to spread easily between humans, as it has to spread between cows.

The probability of the virus accumulating the right combination of mutations to do this is low. But influenza is known for its ability to evolve, and a sluggish public health response is giving this H5N1 an opportunity to become entrenched in cows – a species that has a lot of close contact with humans.

“Just because we had a coronavirus pandemic doesn’t mean we’re done,” said Michael Osterholm, an epidemiologist at the University of Minnesota. “The pandemic clock is ticking. We just don’t know what time it is.”

Since H5N1 was discovered in US cows, scientists have scrambled to define the situation.

Yet many unknowns remain, for example how many states and herds are affected, how it spreads between cows, how the two human cases were infected – and whether they are the only ones.

Genomic sequence data from infected cows suggests that the virus jumped from a bird to a cow probably late last year, meaning it circulated among cows for months before it was detected.

One theory is that a dead infected bird got into cow feed, then it began spreading cow to cow through milking machines, and the dairy farm workers were infected because of milk getting into their eyes, as Martínez described.

Wastewater testing has flagged several sites across the US where levels of influenza – but not specifically H5N1 – are unusually high for this time of year, though the source remains unclear.

Meanwhile, a nationwide survey of retail milk by the US Department of Agriculture found noninfectious remnants of H5N1 viruses in one in five samples tested, though those samples were still safe to drink.

But to really understand what is happening would require better access to dairy farms, say experts.

“Right now, I feel like we have both hands tied behind our back,” said Osterholm. “Largely, American agriculture interests have not wanted to know what’s going on. And they’ve made it difficult for public health workers to get to farms.”

Part of the problem is that producers have little incentive to cooperate with authorities.

Infected cows are only experiencing mild symptoms before recovering, meaning there is only a transient effect on milk production.

But if authorities found a positive cow on their farm, that could mean having to shut down operations. And cows would still need to be milked, so producers would have to pay for labor while dumping the product.

“If you find cows that are positive on your farm, your reward for that is potentially financial ruin,” said Angela Rasmussen, a virologist at the University of Saskatchewan in Canada.

On 10 May, the USDA announced a package of financial incentives – up to $28,000 per farm over the next four months – to encourage testing and biosecurity on dairy farms.

But it neglected perhaps the most important element: the workers.

“In my opinion, the focus should be on the dairy farm worker,” said Amy Liebman of the non-profit Migrant Clinicians Network. “And that worker – that immigrant worker – gets lost in this approach.”

There are perhaps 150,000 dairy farm workers in the US, according to Elizabeth Strater, from the United Farm Workers union. The great majority are probably undocumented.

These workers are the people most exposed to H5N1 – and the least protected.

“Dairy cattle are handled pretty intimately,” said Strater. “Workers in the milking parlor might spend 12 hours a day with their face about 6in away from udders.”

It varies from farm to farm, but in some cases workers live in communal housing, which makes self-isolation difficult and facilitates the spread of infectious disease.

Experts agree that there has probably been more than just the two human infections.

The Centers for Disease Control and Prevention are relying on passive surveillance: people showing up in emergency rooms of their own accord, and happening to be tested for influenza.

But the barriers for a dairy farm worker to seek out medical attention are immense.

“Very few have health insurance,” said Bethany Alcauter, from the National Center for Farmworker Health. “They make very low wages. Dairies are typically in pretty remote places. And then they work very long shifts.”

“They’re unlikely to go to the emergency room for anything that isn’t life-threatening,” said Strater. “In fact, they’re avoiding testing because they know they won’t get any compensation if they’re ordered to stop working.”

In its package of financial incentives, the USDA offered $75 to workers who get tested. “That’s not even a day’s lost work,” said Strater. “And that’s a very bad gamble for someone that might miss weeks.”

As it stands, no dairy worker has died from H5N1, nor have clusters of sick people appeared in emergency departments, which implies the virus has not adapted to spread between humans.

“If there were large outbreaks of a severe respiratory disease, we’d pick that up even without surveillance,” said Osterholm. “But that could all change overnight.”

In the short term, experts are asking for more appropriate protective equipment, such as face shields, fully paid sick leave for workers and widespread screening tests on dairy farms.

All of this needs to come with a multilingual communications strategy to help farm workers understand how they can protect themselves.

Right now, many dairy workers are not even aware there is an H5N1 outbreak among cattle.

“Here in Sunnyside, Washington, I haven’t heard any workers talking about it,” said Martínez.

In Vermont, another dairy farm worker, who asked to remain anonymous, said they had heard nothing about H5N1. “[Management] haven’t even mentioned it,” they said. “Now I’m finding out about it, I think I’m worried. But I have no idea what it means.”

“During Covid, government agencies supported the infrastructure to do outreach to [such groups],” said Liebman. “It just takes money. And it takes the support of community groups, [including] faith-based organizations, which have linkages to the workers.”

Putting such measures and outreach in place could be the difference between controlling a potentially dangerous virus like H5N1 and giving it the chance to become a pandemic.

“Farm workers are canaries in the coalmine [for pandemics],” said Alcauter. “But I think it’s important not to frame them as victims or vectors in this. Because they could be trained to be frontline public health defenders.”



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