10 things you didn't know about bird flu

A dose of flu in winter is as inevitable as a broken boiler – and usually as harmless. But as public health expert Dr Michael Greger explains, intensive farming of animals around the globe may mean we are hatching out an influenza timebomb

1 Their bugs are worse than their bite

The biblical concept of ‘dominion over the fish of the sea and over the birds of heaven; and every living thing that moved upon the earth’ has populated a veritable Pandora’s Box full of humankind’s greatest killers. Scourges such as smallpox and measles, which have claimed hundreds of millions of lives in recent centuries, were birthed in the barnyard about 10,000 years ago.  

Smallpox likely came from camelpox and measles from the rinderpest virus of cattle. Before the domestication of ducks, there was likely no such thing as the human flu or influenza pandemics. Domesticated pigs probably gave us whooping cough, and water buffalo, leprosy. Horses likely gave us the common cold. How often did horses have chance to sneeze into humanity’s collective face until they were broken and bridled? Before then, the common cold was presumably only common to them.

2 All avian influenza viruses start out harmless to both birds and people

All bird flu viruses seem to arise innocuously out of the perpetual, benign reservoir of waterfowl influenza. Though they begin as so-called low pathogenicity [disease-causing] viruses, under extreme circumstances, some strains can mutate into a deadly, highly pathogenic form.

3 The deadliest outbreak in human history was caused by a bird flu virus

The 1918 flu pandemic killed more people in 25 weeks than AIDS has killed in 25 years. Half the world’s population was infected and 50 to 100 million people – about 2.5 per cent of the population most in the prime of life – died within a few months’ period. No war, plague, or famine has ever killed so many people so quickly. Brilliant medical detective work, which included digging up corpses of the pandemic’s victims found frozen in the Alaskan permafrost for tissue samples, revealed that humanity’s greatest killer appeared to come from bird flu.

4 The way we treat animals can have serious global public health implications

To support the tropical logging industry, the bushmeat trade shoots, butchers, smokes and sells as food dozens of species of primates, including thousands of gorillas, chimpanzees, and other endangered great apes. HIV/AIDS is considered to be a result of this trade. Someone butchered a chimp a few decades ago and now 20 million people are dead. At live markets, shoppers can not only pick up wild animals that are often confined in cramped, stressful, unhygienic conditions, but also SARS, the deadly disease traced back to these storefront and street-side shops.

The spread of monkeypox was a direct result of the exotic pet trade, a multibillionpound industry in which hundreds of thousands of different species of live animals are transported across national lines. And, the increasing industrialisation of animal agriculture has been blamed for a long list of deadly new pathogens, including the Nipah virus, E. coli O15:H7, antibiotic-resistant ‘superbugs,’ mad cow disease and the newest disease to threaten our global community, the hypervirulent strain of avian influenza, H5N1. Never before have so many diseases appeared in so short a time. According to the US Institute of Medicine of the National Academies, we may soon be facing a ‘catastrophic storm of microbial threats.’

5 H5N1 has 10 times the mortality rate than the deadliest flu virus on record

Millions of people come down with the flu every year. What if it suddenly turned deadly? The mortality rate of the seasonal fl u is 0.1 per cent. The 1918 pandemic was 25 times deadlier (2.5 per cent), and the Asian H5N1 strain appears 25 times deadlier still, having killed approximately 60 per cent of its known human victims. That means an H5N1 pandemic may have the potential to make the 1918 pandemic seem like the regular flu in comparison.

For instance, if H5N1 were to trigger a pandemic today, without losing any of its virulence, 50 per cent of the world could theoretically be infected but 60 per cent of those could die. No one knows when or how bad the next flu pandemic will be, but if a virus like H5N1 pulls the trigger, it could be like combining one of the most contagious diseases – flu – with one of the deadliest, akin to crossing Ebola with the common cold.

6 The next pandemic may be triggered by a virus of our own hatching

All three of the world's leading authorities–the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the World Organization for Animal Health (OIE) – blame in part the intensification of the global poultry industry for the emergence of H5N1. The United Nations specifically calls on governments to fight the role of ‘factory farming’ which, combined with live bird markets, provides what it refers to as ‘ideal conditions for the virus to spread and mutate into a more dangerous form.’

7 A quirk of nature makes chickens potential human pandemic stepping stones

The respiratory tracts of chickens bear a number of similarities on a molecular level to our own primate respiratory tracts, allowing chickens to bind human influenza viruses and vice versa. This could mean that as influenza viruses like H5N1 mutate to get better and better at infecting and killing chickens, they may be getting better and better at killing us. Chickens would seem the most threatening possible species to be exhibiting human virus binding attributes, as they are the one animal in the world we raise by the tens of billions every year. Spread wing-to-wing, the number of chickens killed every day for human consumption would wrap more than twice around the world’s equator.

8 A handful of breeding corporations controls the global genetic poultry stock

Because of selective breeding (and, to a lesser extent, growth-promoting drugs), the overwhelming majority of chickens raised for meat have been manipulated to grow so fast to reach slaughter weight in the shortest possible time that their cardiovascular and skeletal systems can collapse under their unnaturally heavy weight. Their abnormally rapid growth also outpaces their immune systems, leaving them susceptible to disease, particularly when raised in industrialized sheds, lying in their own excrement without the sanitising benefits of sunshine (the UV rays in sunlight have been shown to effectively destroy H5N1 in 30 minutes).

Combined with an array of virulent chicken immunodeficiency viruses, the emergence of which has also been blamed on intensive confinement systems, the industry’s continued focus on breeding for the fattest rather than fittest has resulted in a global monoculture of chickens with built-in immune dysfunction, convenient viral fodder for the initiation and spread of bird flu viruses with human pandemic potential.

9 An outbreak of bird flu in Europe in 2003 infected more than 1,000 people

In the 2003 Netherlands outbreak of a highly pathogenic bird flu virus, H7N7, symptomatic poultry workers passed the disease to 59 per cent of household family members, a human-to-human transmission efficiency comparable with seasonal flu.Thankfully, the virus only killed one person – one of the attending veterinarians. We learned from this outbreak that bird flu viruses are capable of evolving directly to jump from person to person, while H5N1 has shown us that the virus can evolve into an efficient human killer.

Since the global industrialisation of the poultry industry, highly pathogenic avian influenza has gone from an extremely rare disease to one that now crops up every year. The number of avian outbreaks in the first few years of the 21st century already exceeds the total number of outbreaks recorded for the entire 20th century. If this trend is allowed to continue, a pandemic strain could potentially arise that presents the worst of both worlds – contagious and deadly.

10 There have been calls from scientific authorities to deintensify animal agriculture

University of Hong Kong Professor Emeritus Kennedy Shortridge, credited for having first discovered the H5N1 virus in Asia, was among the first to blame the ‘crux of the problem’ on the emergence of chicken factories in China, some of which now confine 10 million birds at a single operation. Measures as simple as providing straw bedding for pigs so they don’t have the immunosuppressive stress of lying on bare concrete their whole lives can decrease swine influenza infection risk.

A 2007 editorial in the American Journal of Public Health entitled ‘Chickens Come Home to Roost’ went further, questioning the prudence of raising so many chickens in the first place: ‘It is curious… that changing the way humans treat animals… at the very least, radically limiting the quantity of them that are eaten, is largely off the radar as a significant preventive measure.

Such a change, if sufficiently adopted or imposed, could still reduce the chances of the much-feared influenza epidemic. It would be even more likely to prevent unknown future diseases that, in the absence of this change, may result from farming animals intensively… Yet humanity does not consider this option...’

The editorial concludes: ‘Those who consume animals not only harm those animals and endanger themselves, but they also threaten the well-being of [future generations]… To switch avian images, it is time for humans to remove their heads from the sand and recognize the risk to themselves that can arise from their maltreatment of other species.’

Michael Greger, MD, is director of public health and animal agriculture at The Humane Society of the United States. His latest book, Bird Flu: A Virus of Our Own Hatching, is now available free at: www.BirdFluBook.org. Article references at: http://tinyurl.com/BirdFluScience.

This article first appeared in the Ecologist February 2009