Bird flu

Summary

Until relatively recently, the bird flu virus co-existed in aquatic birds spreading from bird to bird in water without harming them. When people began taking birds to market, the virus was unable to spread and a new, more virulent virus emerged, one that could spread more easily in the faeces and secretions from the birds. Large-scale factory farms now provide the perfect environment for a mutating virus – closed, dimly lit (UV can harm viruses), crowded, stressful and unsanitary conditions – a perfect storm of our own making!

The virus has become able to jump species and has infected a range of animals including humans, in whom fatality rates can be very high. While it is still relatively difficult to catch, there have been reports of human-to-human infection and if it mutates further, becoming as easy to catch as a common cold virus, we will be in deep trouble. One way to take control of the situation would be for huge numbers of people to stop eating poultry, pigs and other animals and remove the viral reservoir of factory-farms. 

Bird flu – as avian influenza has become known – came to international attention in 1997 when it spread through live-poultry markets in Hong Kong and for the first time infected people, resulting in six deaths. The Hong Kong outbreak was controlled by slaughtering the entire poultry population. 

Avian influenza viruses occur naturally among wild aquatic birds and have done for millions of years – without making them ill. The virus infects the intestines of ducks, for example, and is then passed on in water from one bird to another, causing no problems. However since the 1950s, avian influenza viruses have caused illness and deaths in large numbers of land-birds, especially poultry (FAO, 2011). In the UK, a highly pathogenic strain of avian influenza virus called H5N1 caused serious disease among chickens in Scotland in 1959 and turkeys in England in 1991. The last reported case of H5N1 in the UK was in early 2008 (NHS Choices, 2015f).        

Various different strains of H5N1 have been identified – one particular strain is of huge international concern because it can infect people and has led to the deaths of several hundred. In June 2016, WHO confirmed that since 2003, there had been 851 cases of human infection with H5N1 and 450 deaths reported from 16 countries. Fatalities have been seen in Egypt, Indonesia and Vietnam as well as Cambodia, Thailand and China (WHO, 2016).

While there are low-pathogenic varieties of H5N1, high-pathogenic strains cause death in more than half (60 per cent) of the people they infect. So although it may be relatively hard for humans to become infected, when they are, the odds are not good. Case-fatality rates for past influenza pandemics have ranged from about 0.1-2.5 per cent (Li et al., 2008). Also, avian flu viruses aren’t usually transmitted from one human to another, but there have been a number of cases of human-to-human infection among families caring for infected relatives (Qi et al., 2013; Wang et al., 2008; Ungchusak et al., 2005). Imagine the death rate if a highly pathogenic avian influenza virus became able to spread like the common flu!  

In 2013, another pathogenic strain (H7N9) appeared, this time in China. Most of the cases of human infection with H7N9 followed recent exposure to live poultry or markets where live birds were sold. By May 2015, there had been 665 confirmed cases and 229 deaths. Most among middle-aged and elderly men but a number of cases were reported in travellers from Hong Kong, Taiwan, Malaysia and Canada.

Bird flu has gone from being a relatively rare occurrence to one that crops up frequently, every year and the UK has not escaped. In November 2014, a low-severity H5N8 virus was confirmed at a farm in Yorkshire, then in February 2015, a low-severity H7N7 virus was found at a farm in Hampshire. It seems that it just won’t go away and now H5N1 has infected migratory birds who are spreading it around the world. In 2015, a highly pathogenic H5N1 strain was identified at a chicken farm in the Dordogne in France (Defra, 2015b). It was subsequently detected in a number of other farms in southwestern France.      

But what caused bird flu to change into this much more sinister menace? The short answer is intensive factory-farming. Viruses are unlike other life-forms in that they are very simple packages of DNA that highjack the cellular machinery of plants and animals in order to replicate and multiply. They don’t breathe, drink, eat or excrete… they just replicate, almost like little machines. Their sole purpose is to infect animals or plants and make more copies of themselves. If a mutation occurs that makes this easier, the mutated version will thrive. Factory farms provide a perfect environment for the emergence of new ‘super-viruses’.  

In aquatic birds, the virus had found an ideal environment in which it could co-exist without harming the host. However, when these birds were taken to market, the virus could no longer spread from bird to bird in water. This meant there was a new pressure on the virus to mutate or die. Mutations naturally occur but unless they offer some advantage, the original version of the virus will continue to dominate. In this new environment, mutations occurred and the virus was able to spread – via faeces, nasal secretions, or secretions from the mouth or eyes of infected birds.

Of course, intensive poultry production provides the perfect breeding ground for a mutating virus. Chickens and other commercial birds are raised in closed, crowded, stressful and unsanitary industrial facilities with little or no natural light, offering the bird flu virus a perfect opportunity for infection, mutation and spreading. The genetic profile of birds found in factory farms is often less diverse than those raised in backyards. Due to the industry’s reliance on breeding methods, commercially raised broilers are genetically very similar. Broilers and turkeys are bred to produce birds that grow quickly (300 per cent faster than birds raised in the 1960s) to produce as much breast meat as possible, to the point where some birds struggle to stand. This inevitably adds to the stress and lowers their immune function increasing the opportunity for viral infection. A perfect storm of our own making!

An aberrant host is a ‘dead-end’ host from which viral replication does not normally occur, humans for example. A spillover host is a novel (new) population susceptible to infection that may go on to transmit the virus, poultry for example. Humans are currently regarded as aberrant hosts as, at the moment, we do not spread infection. However, we are at risk of becoming spillover hosts due to viral evolution, which could result in a global influenza pandemic. Influenza viruses typically evolve much more rapidly in spillover hosts such as chickens and turkeys than they do in reservoir hosts such as wild water birds (Suarez et al., 2000).

Avian influenza viruses have infected many different animals, including ducks, chickens, pigs, whales, horses, seals and dogs (CDC, 2015a). In 2006, authorities in Germany announced detection of H5N1 in a domestic cat that was found dead on the northern island of Ruegen where more than 100 wild birds have died from H5N1 infection. In 2003-2004 a number of captive tigers and leopards in a zoo in Thailand who were fed fresh chicken carcases died of H5N1 infection. Subsequent investigation determined that at least some tiger-to-tiger transmission of the virus had occurred (WHO, 2006).

There is widespread agreement that the pattern of avian influenza infection which occurred during the 2003-2005 Asian epidemic represents a disturbing new evolutionary development in the behaviour of the virus, the full ramifications of which may not yet have unfolded. In his comprehensive book which provides a full and insightful account on the subject of bird flu, Dr Michael Greger warns that:

There are three essential conditions necessary to produce a pandemic. First, a new virus must arise from an animal reservoir, such that humans have no natural immunity to it. Second, the virus must evolve to be capable of killing human beings efficiently. Third, the virus must succeed in jumping efficiently from one human to the next. For the virus, it’s one small step to man, but one giant leap to mankind. So far, conditions one and two have been met in spades. Three strikes and we’re out. If the virus triggers a human pandemic, it will not be peasant farmers in Vietnam dying after handling dead birds or raw poultry – it will be New Yorkers, Parisians, Londoners, and people in every city, township, and village in the world dying after shaking someone’s hand, touching a doorknob, or simply inhaling in the wrong place at the wrong time” (Greger, 2006).

The poultry industry has responded to the bird flu crisis by playing down the risk to humans. The Food and Agriculture Organisation of the UN recommend an integrated programme of vaccination and enhanced biosecurity including separating reservoir and spillover species, introducing restrictions on marketing and movement of birds and separating high risk and lower risk species during marketing (FAO, 2005). However, WHO spokesman for the Western Pacific region, Peter Cordingly said: “It might be time, although this is none of WHO’s business really, but the bottom line is that humans have to think about how they treat their animals and how they farm them, how they market them – basically the whole relationship between the animal kingdom and the human kingdom is coming under stress.” (CNN, 2004).