Lockdowns are a horrible experience, but fortunately one that is in the past now. Unless, that is, you’re a domestic bird in Britain. Since 7 November, a UK directive has instructed all farmers to keep their birds indoors as part of a stringent measure to stop the spread of avian flu, or the H5N1 virus. This measure is intended to avoid infection of domestic birds from wild birds, and will result in tens of millions of chickens, ducks, geese and turkeys being brought inside for the foreseeable future. We’ve also seen island birds affected, resulting in the shutdown of human visitors to the Isle of May in Scotland for five weeks, among other measures.
Avian flu is known as one of the most infectious diseases: the R number, which was often discussed for the spread of Covid-19, can be as high as 100 for avian flu, meaning one bird can infect as many as 100 others. And the past few months have seen exponential spread of the virus, with Britain and Europe hit especially hard. A lab in Surrey that tests samples says it has seen a 600% increase in cases in the past three months.
Why is this outbreak causing concern not just among scientists but also poultry farmers and government officials? Currently, avian flu outbreaks have been limited in humans because the virus doesn’t spread easily between us. But this is a ticking timebomb. A mutation that makes this virus circulate more easily between humans is possible. This would be a gamechanger and raise the risk to humans considerably. And the more chances the virus has to jump into a human and mutate, the more likely it is a dangerous strain will emerge that could set off the next pandemic.
While humans have been infected by birds, they are usually workers on poultry farms and those in close contact with infected birds, and even these instances have been rare. For example, on 3 November, two farm workers in Spain tested positive; it was the second known infection of humans in Europe since 2003. Infection is usually through handling sick or dead birds.
Infected birds have the flu virus in their saliva, blood, mucus and faeces, and humans can get infected if they get this virus into the eyes, nose or mouth, or inhale droplets in close range (you can’t get infected with avian flu by eating fully cooked poultry or eggs). And this virus is not mild. The fatality rate is thought to be high in humans: the World Health Organization estimate is roughly 60% for H5N1. We currently have no vaccine to use in humans; nor does the seasonal flu vaccine work against avian flu.
But while the chance of human transmission is a future worry, right now the virus is affecting people’s livelihoods and farms, and putting hundreds of millions of domestic and wild birds in danger. Outbreaks in chickens can kill the entire local population; in other birds, such as ducks and geese, the disease is often mild or even asymptomatic. Ducks have even been called the “Trojan horses” for the virus, given their ability to carry it and infect others while remaining unaffected themselves.
Bird flu is highly infectious and poses a high risk to chickens and turkeys. As a result, if a farm tests positive for bird flu, the entire flock is culled. This can lead to hundreds of thousands to millions of pounds in lost income, and places enormous strain on poultry farms. It also has implications for the price and availability of turkeys and chickens going into Thanksgiving and Christmas. And, of course, it is a tremendous loss of bird life.
The heart of the issue is how we raise and treat animals, and their interactions with humans. Poultry are often kept in difficult conditions where they are packed into close quarters and diseases easily pass through them. Some experts think that this more infectious strain developed in an industrial factory environment, where animals are kept in close quarters and viruses have the chance to circulate and mutate.
And this is not just an issue with avian flu, but other infectious diseases as well. In places such as China and India, antibiotics are freely given to animals in order to prevent infection (especially in industrial farming) and to make them as large as possible. A survey of chicken farmers in China found that they all used antibiotics. The rationale here is cheap and fast meat to meet the growing demand in emerging economies.
But this creates its own problems. Feeding antibiotics to animals can lead to the emergence of resistant bacterial strains, and then humans such as farmers becoming infected with antibiotic-resistant infections. These then circulate in humans and reduce the effectiveness of one of the most powerful drugs in modern medicine. Chemotherapy, infections and surgeries of all kinds have become safer because of antibiotics. If the drugs don’t work, these procedures become high-risk and life-threatening, as they used to be in the pre-antibiotic era. And as we’ve learned, all it takes is for a person to get on a plane with a novel infectious disease for it soon to become a problem for everywhere else in the world.
The major infectious disease threats in humans tend to come from animals: think of Sars-CoV-2, Sars, Mers, Ebola … the list goes on. There are more than a million viruses circulating in the animal kingdom, and it would be a fool’s errand to try to stop that circulation. But we can limit the chances these have to jump into the human population, and limit their circulation in domestic animals. This requires taking the animal-human interface seriously, and knowing that while it’s a major economic, animal welfare and farming problem now, the situation becoming even worse is just a mutation away.
Prof Devi Sridhar is chair of global public health at the University of Edinburgh
