Swine flu scareCurrent swine flu is the inevitable result of modern farming methods

The swine flu eruption is but two weeks old, but conspiracy theorists already claim that the swine flu virus now spreading around the world was genetically engineered by bioterrorists. Michael Le Page, the biology feature editor of New Scientist, points out that the truth is more prosaic: the virus is far more likely to be a product of mankind desire for bacon.

According to the U.S. Centers for Disease Control and Prevention (CDC),  the new virus is a mixture of four different viruses: North American swine flu, North American avian flu, human H1N1 flu, and a swine flu strain found in Asia and Europe. Now, the propagators of the conspiracy theory argue that this new combination could not have occurred naturally. La Page responds that this is not true. Flu viruses consisting of a mixture of human, swine, and bird strains have been found before.

There is a sense, though, in which the virus could be regarded as man-made (the following will require you brush up on Bio 101): Flu viruses contain eight strands of RNA, which code for ten proteins. If two flu viruses infect a cell at the same time, new viruses budding from that cell can contain a mixture of RNA strands from the two original viruses. This phenomenon is called reassortment, and it was responsible for the 1957 and 1968 pandemic flu strains (in both years, the flu strains were caused by reassortment between an avian virus and a human virus).

In addition to reassortment, scientists also use the term antigenic shift because the process in which at least two different strains of a virus, or different viruses, combine to form a new subtype, the new subtype features a mixture of the surface antigens of the two original strains. Note that recombination — of “cutting and pasting” — can also produce mixing within RNA strands.

Le Page notes that it is unusual to be infected by two flu viruses at the same time, and even rarer for one of those viruses to come from another species, but it does happen, especially in pigs, which are susceptible to both human and bird flu viruses. Repeated reassortments can produce mixtures like that found in the swine flu virus now spreading around the world.

It is not yet clear exactly when and how Mexican swine flu strain evolved, but there was need for genetic engineering for it to happen. Genetic engineering, though, is not the only way by which humans could have contributed to the creation — and spread — of the disease.

There are more than six billion people on the planet. Framers raise more than a billion pigs, and about 70 billion chickens, every year. As New Scientist’s writer, Debora MacKenzie, has reported in detailed articles over the years, the problem is not just the sheer number of potential hosts, but the conditions in which animals are kept, conditions which favor the evolution of new and deadlier strains.

On an open range, an animal sick and weakened by a flu virus may not be able to walk or fly far, limiting its ability to infect other animals. In industrial-farming businesses, in which thousands of animals are densely crowded in pens, infections spread like wild fire. Indeed, already attention is turning to the big pig farms in Mexico, and the role they may have played in creating this new strain of swine flu (see Tom Philpott’s report).

It is very unlikely that the swine flu outbreak is a result of bioterrorism. Accidents in medical research labs occur — see story elsewhere in this issue — but “by far the most plausible explanation is that this monster is the long-predicted product of our farming system,” Le Page concludes. The real question, then, is not why this particular incident of reassortment is unfolding — the question, rather, is why it has taken so long to occur.