Factory farms of disease: how industrial chicken production is breeding the next pandemic | Global health

UN bodies, academics and epidemiologists recognise the link between the emergence of highly pathogenic avian influenza viruses and increasingly intensive poultry farming.

According to the UN’s Food and Agriculture Organization (FAO): “Avian influenza viruses are evolving into a large, diverse virus gene pool … A pathogen may turn into a hyper-virulent disease agent; in monocultures involving mass rearing of genetically identical animals that are selected for high feed conversion, an emerging hyper-virulent pathogen will rapidly spread within a flock or herd.”

Wild birds are routinely blamed by governments and industry for spreading avian flu along migratory routes, but evidence is mounting that intensive farms are potential “mixing pots” for new, deadly viruses.

“Blaming migratory waterfowl … is clearly no longer a tenable position,” says Rob Wallace, an American virologist who argues that the new strains of flu emerging are adapting to industrial poultry production. “Influenza’s infiltration into industrial livestock and poultry is so complete that these farms now act as their own reservoirs [of disease],” he says. “They are their own source.”

With more than 20 billion chickens and nearly 700 million pigs being farmed at any one time, Wallace says the chances of new flu strains and variants emerging and spilling over to humans are high.

He is backed by Sam Sheppard, a biologist at Bath University, who says overuse of antibiotics, overcrowding and the genetic similarity between animals provide ideal conditions for many bacteria, viruses and other pathogens to merge, mutate, spread and then jump into humans.

Sheppard researches how keeping animals penned together triggers genetic changes in common bugs such as campylobacter, which are now widespread in poultry, pigs and cattle. “These first emerged in the 20th century, coinciding with large increases in the number of farmed cattle. The bugs are now resistant to antibiotics as a result of overuse of medicine,” he says.

Nor is it just poultry and pigs. The emergence of respiratory diseases such as Mers in camels, coronaviruses in mink farms and BSE in cattle suggests that the intensive breeding of any animal increases the risks of infection.

The next pandemic

Marius Gilbert, an epidemiologist at the Université Libre de Bruxelles in Belgium, and others have shown how bird flu is linked to the rapid intensification of poultry farming, which is now making bird flu viruses more dangerous.

Public health experts have long warned about the dangers of industrial farming but since Covid the stakes have become higher as the full costs of a modern pandemic are seen, says medical doctor and historian Michael Greger, author of the book Bird Flu: A Virus of Our Own Hatching.

Greger argues that there have been three eras of human disease: first, when we started to domesticate animals about 10,000 years ago and were infected with their diseases, such as measles and chickenpox; then in the 18th and 19th centuries, when the Industrial Revolution led to epidemics of diabetes, obesity, heart disease and cancer; and now, because of the agricultural intensification that is leading to zoonotic, or animal-borne, diseases such as bird flu, salmonella, Mers, Nipah and Covid-19.

“In evolutionary terms, rearing poultry, cattle and pigs in high-intensity, crowded, confined, entirely unnatural conditions may be the most profound alteration of the human-animal relationship in 10,000 years,” he says

“We are seeing an unprecedented explosion in outbreaks of new bird flu viruses, which historically have presented the greatest pandemic risk and certainly have the potential to be worse than Covid.”