The world is suffering from corona, however, this will not be the last threat by a zoonotic virus. “The next flu pandemic virus is slumbering in pigs”, says the Freiburg virologist Martin Schwemmle (C01). Bird flu easily spreads in avian species and poultry but human cases are rare. According to the working group, the difference in susceptibility depends heavily on a single protein: Mx1. “It blocks virus infections in human cells, including flu viruses”, says Laura Graf (C01). “In a recent study, we could show a strong association between H7N9 infection and rare mutations in the MX1 gene by comparing IAV H7N9-infected patients with healthy poultry worker“.
Unfortunately, in swine, Influenza A viruses can acquire MxA resistance! In more than every second pig breeding farm, flu viruses circulate throughout the year, which differ considerably in terms of their genetic make-up. In the case of influenza viruses, the genome consists of eight segments that are remotely comparable to chromosomes. “If two different flu viruses infect the same cell, they can exchange entire segments,” explains Timm Harder from the Friedrich Loeffler Institute, the Federal Research Institute for Animal Health. “We call this reassortment.” Sometimes entire blocks of properties change viral owners. Not only does global trade bring together many virus variants in pigs, pigs are also continuously infected with human variants. In addition, the Mx1 hurdle in pigs – unlike the human one – hardly causes any problems even for avian influenza viruses thereby allowing the gradual adaptation towards Mx resistance.
Harder advocates that pig farmers and veterinarians regularly get vaccinated against seasonal flu, but also for a broader and better vaccination of pigs against viruses that circulate in the herd. He would also like to see better controls for flu infections here. In this way, the pandemic risk could be contained. It is only a matter of time before reassortment – the explosive exchange of flu viruses from birds, pigs and humans – randomly discards critical variants.
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