According to the US Centers for Disease Control, 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.
The claim of the conspiracy theorists is that this new combination could not have occurred naturally, but this is not true. Flu viruses consisting of a mixture of human, swine and bird strains have been found before. However, there is a sense in which the virus could be regarded as man-made.
Flu viruses contain 8 strands of RNA, which code for 10 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 – a phenomenon called reassortment. Recombination – “cutting and pasting” – can also produce mixing within RNA strands.
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 worldwide.
There was reassortment between bird and human flu viruses in pigs in Italy during the 1980s, for instance, while in the 1990s a H1N2 swine flu circulating in pigs in the UK was found to be a mixture of swine, human and bird flu strains resulting from multiple reassortments.
It is not yet clear exactly when and how Mexican swine flu strain evolved, but it could certainly have happened without the help of genetic engineers. Despite this, the swine flu could still be regarded as man-made.
There are now over 6 billion people on the planet, and each year we raise more than a billion pigs and perhaps as many as 70 billion chickens. The result is a paradise for influenza viruses.
As New Scientist‘s flu correspondent Debora MacKenzie has reported over the years, the problem is not just the sheer number of potential hosts. The conditions in which animals are kept can favour the evolution of new and deadlier strains.
For instance, in the wild nasty flu strains that make animals too ill to walk or fly are unlikely to spread far. On crowded factory farms, they can spread like wildfire, helped by the global trade in animals and animal products.
The interaction of farm workers with animals, especially on small-holdings where pigs, ducks, chickens and children all happily intermingle, also provides plenty of opportunities for viruses to jump species.
Animal vaccines might seem like the answer, but vaccines that do not provide 100% protection can actually make things worse. When there is widespread vaccination, viruses can spread without any visible disease. Ineffective vaccines also create strong selective pressure driving the evolution of new strains that can dodge the immune attack provoked by the vaccine.
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.
The fact is that we still know so little about flu, and what makes it capable of spreading from human to human, means that deliberately engineering a virus of this kind would be a huge challenge. Yes, it’s possible that this virus was created by a mistake at a research laboratory or a vaccine factory.
But by far the most plausible explanation is that this monster is the long-predicted product of our farming system.