62 million.
That’s the number seared in Prasert Auewarakul’s memory. It is the number of birds – mostly chickens – that were dead by the end of Thailand’s avian flu outbreak that started in late 2003. Some died of the disease, others were culled to prevent the virus from spreading.
“It was very bad. Most of the farmers lost everything,” says Dr. Auewarakul, a virologist at Mahidol University in Thailand.
Now, two decades later, the U.S. is grappling with its own avian flu outbreak. And this time the virus has taken a new twist.
In late March, the U.S. Department of Agriculture announced the H5N1 virus, which is periodically found in farmed poultry, had been identified in dairy cows in two states – the first time scientists have detected a spillover to cattle.
Now, 92 herds spread across a dozen states have been infected, according to the World Health Organization. And the virus has spread to humans as well. Three farm workers have contracted the virus this year, according to the Centers for Disease Control and Prevention. So far, the virus has not shown the ability to spread easily between humans.
This outbreak has led some scientists and public health experts to look at past avian flu outbreaks.
“There are so many lessons that we have learned,” says Dr. Maria Van Kerkhove, interim director for epidemic and pandemic preparedness and prevention at the World Health Organization.
And the stakes are high. While there have been relatively few human cases of H5N1 – roughly 900 – more than half of them have been fatal.
What did Thailand do?
In December 2003 in Thailand, flocks of chickens were mysteriously dying. This was particularly problematic because Thailand was one of the world’s main poultry exporters, producing about a billion chickens a year. About 400,000 people were employed in the industry.
By January 2004, the authorities had the answer: avian flu.
While nobody knows for sure, Auewarakul says, the virus likely jumped from wild waterfowl to domesticated chickens. The effect was devastating. The virus can easily wipe out a flock of chickens in a matter of days. About 20 people in Thailand also fell sick and 13 of them died from 2003 to 2005.
Officials sprang into action to save Thailand’s poultry industry and prevent more spread to humans. Infected flocks – and nearby flocks as well – were culled (the government paid farmers for the loss).
And then Thailand reinvented its poultry industry. The movement of live poultry — to market, for example — was severely restricted. Farm hygiene was dramatically improved. A nationwide surveillance system was launched, including a network of village health volunteers who reported sick birds.
Perhaps the biggest and most lasting change, Auewarakul says, is that this outbreak abruptly accelerated the transition from backyard chicken farmers to large-scale industrialized poultry farms. He says this was a big cultural transition since chickens had been part of everyday life for many Thai families.
“They were raised like pets, like you would raise your dog,” he says. “But small farms disappeared and big companies with biosecurity systems stayed.” More recently, he notes, some backyard farms have returned. But the big farms still “dominate the market.”
In these big farms chickens often spend their lives entirely indoors. This lifestyle means there’s almost no intermingling with wild waterfowl and contact between flocks. Plus, the farms have instituted lots of protocols for who gets to go in and how.
“People don't go in and out that much,” Auewarakul says. “When people go in, they have to disinfect themselves” before and after visiting the poultry areas.
The shift to these industrialized farms has not fully eliminated avian flu in chickens, but the disease has been largely contained. With ongoing monitoring, cases are often identified early and dealt with before the virus can gain a foothold.
Other countries grappled with avian flu at the same time and managed to control their outbreaks: Cambodia, Indonesia, Japan, Malaysia, South Korea and Vietnam in Asia and the Netherlands, for example. Auewarakul says a similar approach to Thailand’s — a combo of culling, surveillance and limits on the movement of animals — has been a success.
“I remember in 2003, literally, countries were saying, ‘We killed a million birds today.’ And you don't hear that happening anymore because of the responses that were put in place,” says Andrew Pekosz, professor of microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health.
Does what works for the hen also work for the cow?
The answer is yes and no – and it’s not just because chickens cluck and cows moo.
Certain strategies — like widespread culling when an outbreak is detected — are unlikely to apply to cows.
“What has to be remembered here – and I think this is very important – is that cattle are worth huge amounts of money,” says Dr. Mike Ryan, executive director of the health emergencies program at WHO.
An individual chicken is valued at less than $10 while a lone lactating cow sells for close to $2,000, says veterinary doctor Pamula Ruegg, a professor at Michigan State University and editor of the Journal of Dairy Science Communications. So the bar for culling cattle is much higher. And a cattle cull would have a more severe economic impact on farmers, since cows don’t produce milk until they are about two years old while chickens lay eggs in a matter of months.
What’s more, H5N1 can decimate a flock of chickens – another pro-cull argument back in 2004. That’s not so for cows, whose symptoms are far milder, including a drop in milk production and loss of appetite.
“We're not killing cattle. We don't have to. Everything we've seen and all the preliminary data suggests they recover pretty rapidly,” says Ruegg.
As for keeping cows indoors, Ruegg says that while there are some indoor facilities for dairy herds, they tend to fare better when there's access to the outdoors.
Still both Pekosz and Auewarakul say a lot can be learned from how clean poultry farms have become.
“In countries around the world, a lot of their poultry workers have significant amounts of protective gear. Sometimes it’s a face shield, a pair of gloves that you change frequently, a pair of boots that you can disinfect periodically,” explains Pekosz. Some of the workers shower upon entering the chicken area and leaving it. The goal is simple: Don’t bring any viruses in or out.
These strategies “have all been shown to be incredibly effective in limiting human infections but also limiting the spread of a pathogen from one farm to another, from one flock to another, from one herd to another,” he says, noting that farm workers, delivery drivers, veterinarians and others may visit multiple farms.
The CDC has recommended protective gear for U.S. dairy farmers in the wake of the current outbreak to but, Pekosz says, there’s not been widespread compliance. He says that could be because of a lack of training, because it’s hard to change habits or because cow farms are run differently than chicken farms.
Ruegg says practices have to be specifically adapted to dairy farms. For example, she suggests glasses instead of face shields. “It'd be really easy for those full [face] shields to fog up when you're working [in a milking parlor],” she says.
Jamie Jonker, chief science officer for the National Milk Producers Federation, adds that one of his priorities is making sure to sanitize milking machines between cows because the virus has been found in high concentrations in raw milk.
The other lesson that can be learned from the poultry industry’s history with avian flu is the importance of farmer buy-in.
One way Thailand did it was to ensure reasonable compensation for farmers who lost their flocks to disease or culling – 100% of the animal’s value early on, then later 75%.
Pekosz would like to see the U.S. reassure farmers they don't lose financially if their cows are tested and found to be infected. “That’s really important to making sure we get more access to these farms so we can get a better understanding of the extent and magnitude of this outbreak,” he says.
New strategies are needed
While Maurice Pitesky isn’t opposed to borrowing from the past’s avian flu playbook, he says, it’s also necessary to write a new chapter.
Pitesky — who studies avian flu at the UC Davis School of Veterinary Medicine — says that two decades ago when Thailand was developing its strategy, there was one main threat: Wild waterfowl introducing the virus. “Now, we're dealing with an entire ecosystem issue,” he says.
That’s because in the past few years, H5N1 outbreaks have traveled far beyond chickens and cows. The virus has shown up on six continents and in a slew of wild and domestic mammals, from tigers and mink to cats and dogs. All in all, H5N1 has been reported in more than 48 mammal species across 26 different countries, according to a peer-reviewed journal published by the CDC. In South America, it’s caused the death of more than 17,000 elephant seals. Earlier this month, house mice in New Mexico tested positive for the virus.
“It's hard to see how this will ever not be an endemic disease at this point,” says Pitesky.
He says this will mandate new strategies that go far beyond the farm gates.
“We've never had anything like this before,” Pitesky says.
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