A Viral Factory

In the past decade of intensive farming industrialization, a deluge of viral diseases has threatened public health, writes Zaria Gorvett.

AsianScientist (Oct. 27, 2013) – SHANDONG, China. The jarring cries of 50,000 birds and the stench of ammonia saturate the air in a large warehouse. A strip of dim lights illuminates the bald, swollen creatures squatting awkwardly on the wood chip floor. These are broilers, young chickens grown for their meat. With an estimated population of 19 billion, they are the world’s most numerous birds.

In an effort to feed an ever expanding human population and keep up with unprecedented demand for meat, farming has undergone a transformation from pastoral to industrial. It is not without risk. In the early weeks of 2003, the SARS virus emerged, spreading from Hong Kong to 37 countries. In the decade since, a deluge of viral diseases has threatened public health. In 2008, the H5N1 influenza virus swept around the globe.

In 2009, the H1N1 swine flu went pandemic, killing 300,000 people. This April, the deadly H7N9 danced across China. Across the Persian Gulf, a new virus lurks; the Middle East Respiratory Syndrome (MERS), which is expected to return this autumn, has killed 51 people so far and is a close relative of SARS.

The pursuit of meat is thoroughly entangled in our shared history with viruses. With the advent of agriculture 13,000 years ago, human plagues have become commonplace as our animal pathogens swiftly adapted to infect us. A second farming revolution is upon us and, combined with the increasing contact between livestock and wildlife, it appears to be fueling the emergence of new pandemics.

In the meantime, governments and charities have responded by pouring money into vaccines, treatments and attempts to anticipate the next pandemic-but with limited success. Is it time to address the source of the problem?

“Prediction is very difficult, especially about the future.” – Niels Bohr

Approximately 75 percent of new infectious diseases are zoonotic – meaning they can be transmitted from animals to humans – and their incidence appears to be rising. In fact, every major pandemic in the last century has been linked to animals. South and Southeast Asia and Central Africa are global hotspots for these infections, and in our virus-friendly world, the cost of maintaining up to date defenses is high. Failed efforts to anticipate pandemic threats have left scientists playing catch-up, developing vaccines and treatments once diseases are already a health problem. Since its discovery in the early 80’s, over 260,000 papers have been published on HIV, and eight billion dollars has been invested in vaccine research in the last decade.

The main culprits are a cast of elite players, which include the influenza, HIV, measles, polio, rabies, Ebola, Marburg, Lassa, West Nile, Nipah and SARS viruses. These are all RNA viruses, whose genetic material is encoded in RNA, instead of DNA like ours. This quirk is a formidable weapon, because RNA is unstable and prone to copying errors. Consequently, RNA viruses are diverse and can evolve rapidly to evade vaccines, antivirals and our immune responses.

Humanity’s banal and long-standing companions, the influenza viruses, have a second trick. The viral particles multiply in infected cells, where the host’s machinery is hijacked for the task. The influenza virus genome has eight segments of RNA, and during the assembly of new viruses, one copy of each is incorporated. A cell infected with two influenza viral strains may produce progeny with a mixture of viral segments. Occasionally, this re-assortment will be a particularly potent strain, perhaps even capable of infecting a new species. The 1918 flu pandemic, which dispatched 50-100 million people (at the time, approximately 3-5 percent of the global population), was probably a mixture of bird, pig and human flu strains.

The pioneers of farming endured poor sanitation, nutrition and the attentions of new and exotic pathogens. The civilizations they founded provided a high density of potential victims, and long-distance trade spread them around the Old World. This deadly cocktail of influences contributed to an era of early death and high infant mortality.

History repeats itself. Proverb

In the 21st century, 74 percent of the word’s poultry meat and 85 percent of pork is produced using intensive farming methods. China is second only to the US in poultry production, and is forecast to produce over 14 million tons of broiler chickens in 2013. Profit-driven and ruthlessly efficient, intensive enterprises are a brave new world.

Researchers at the International Livestock Research Institute (ILRI) and the Royal Veterinary College, University of London have studied the recent rise of zoonotic diseases. They found the intensive farming revolution and widespread environmental change to be responsible for the new wave of illness. “Intensive livestock farming, especially of pigs and poultry, increases the risk of disease transmission” according to the authors.

Indeed, tens of millions of birds have died from H5N1 influenza, a virus that has colonized 64 countries and seems to be ubiquitous. Although the virus causes severe illness in birds, it is not spread easily from person-to-person. Its only redeeming feature is its ability to kill domestic poultry, which has helped farmers and public health workers to spot cases and contain outbreaks with culls. Ominously, H7N9 influenza is more conservative and has undermined surveillance-based approaches. In Asia, where densities of domestic poultry are especially high, conditions are ideal for fast transmission of virulent strains. With so many birds potentially infected, the influenza virus could be simmering in the dark.

The situation has led experts to call for an end to high-risk farming practices and for increased biosecurity in the industry. Earlier this year, the campaign groups Compassion in World Farming and the World Society for the Protection of Animals published a report in which they criticized the industry as “an increasing hazard for human health.”

Globally, we now produce five times more meat than we did in 1950, and demand is escalating. In a climate of intensive agriculture and international trade, it is easier than ever for new pathogens to evolve and spread around the world. In view of the tempo of viral evolution and the slow processes of vaccine and drug development, this is alarming. The question is: will we suffer another epoch of illness, or use our modern knowledge to prevent it?


Copyright: Asian Scientist Magazine; Photo: welcometoalville/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Zaria Gorvett is a freelance science writer based in the UK. She graduated with a bachelors degree in biological science from the University of Exeter, UK and a masters degree in medical microbiology from the London School of Hygiene and Tropical Medicine, UK.

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