The flu is nothing to sneeze at. Most years we see outbreaks of the flu that involve a number of fatalities. In a typical year as many as five million people will die from influenza worldwide, and up to 50,000 people here in the US will succumb to the disease. But every once in a while, a severe epidemic comes through, such as the Spanish Flu of 1918 which killed over 50 million people worldwide. While not nearly as severe as the Spanish Flu, influenza is again making its way across the country. As if the flu weren’t bad enough, the new strain H3N2 out this year has already caused 306 cases reported from 10 states, and typically infections with this strain tend to be more severe.
 
Many people are unaware of the connection between the flu and raising livestock, especially those livestock raised on large scale farming operations, known as factory farms. Influenza viruses start out in aquatic birds, but humans are not readily directly infected by these strains. Pigs, however, are highly susceptible to both avian and human influenza A viruses. They are commonly referred to as “mixing vessels” in which avian and human viruses commingle.

In pigs, viruses swap genes, and new influenza strains emerge with the potential to infect humans. Pigs may have been the intermediate hosts responsible for the birth of the last two flu pandemics in 1957 and 1968, and the so-called bird flu everyone was worried about a couple of years ago, H1N1, was a triple hybrid avian/pig/human virus.

In factory farms, thousands of animals are confined, often crowded into huge sheds. The crowding leads to stressful and extremely unhygienic conditions. The combination of reduced immunity due to prolonged stress in the pigs, and the high density confinement, makes these farms the perfect breeding grounds for new viruses. Under these conditions, new strains of swine flu are rapidly generated and transmitted from one pig to another, and then finally to humans who work with the animals. Once it gets into the community, the virus can spread very rapidly, as we have seen.

What’s true for pigs is largely true of chickens as well, which can also be mixers and propagators of influenza.  Large scale chicken farms can become both the mixing vessels and breeding grounds for more strains of the influenza.
 
In order to better avert the threat of epidemics, public health efforts need to address the conditions that allow pigs and chickens to become breeding grounds for infectious disease. More focus needs to be placed on preventing flu viruses from getting into the human population in the first place, and that means starting at the farm.

Of course, if everyone changed to a vegetarian diet, there would be no need for factory farms, the livestock farm link in the influenza chain would be broken, and influenza epidemics and pandemics could become a thing of the past, saving both humanity and farm animals much suffering and premature death.