Bird flu never went away, but now it is back in the limelight after the discovery of a rare mutation of the H5N1 virus that has caused the first mammal-to-mammal transmission under controlled conditions in a mink farm in Galicia (northwestern Spain). Another epidemic among mammals had already occurred in New England but among seals, a wild animal species difficult to study and control. The outbreak in minks dates back to October 2022, and now a complete study has been published in Eurosurveillance journal along with the analysis of the genetic sequence of the virus.
However, the data indicate that the virus has not acquired the ability to transmit to humans. "So far the H5N1 virus had made only sporadic species jump to the mammalian population", but that of mink breeding in Galicia "is a noteworthy case because, based on the data collected, the virus has spread within the farm, between mammal and mammal", Isabella Monne, of the Istituto Zooprofilattico delle Venezie, co-author of the article with colleagues Bianca Zecchin, Alice Fusaro, Francesco Bonfante, Edoardo Giussani and Calogero Terregino, tells ANSA. The first author of the research is Montserrat Agüero, of the Central Veterinary Laboratory of the Spanish Ministry of Agriculture.
The virus found in Galicia belongs to the family responsible for the current avian influenza epidemic in Europe, referred to as 2.3.4.4b, and the T271A mutation found in the PB2 gene of the virus has become the object of close monitoring. "In this case - continues the researcher - an intensive mammal farm came into contact with a virus after infection events in wild birds, and there was transmission within the farm". "It is an event that reminds us that bird flu should be treated as a problem that can spread to other species. From an ecological point of view too - she adds - it is extremely important because a lethal virus in wild birds implies a loss of biodiversity". This is indicated, for instance, by the Australian black swans decimated by bird flu, as reported in the article published recently in the journal Genome Biology. "It's just one of too many examples," she notes.
The difficulty is in blocking the virus circulating among wild species to prevent a species jump, that is the ability of the virus to infect new species to ensure its own survival, moving from birds to mammals, including humans. Other mutations of the virus have also been found in the Galician mink farm, "the meaning of which we do not know yet". The good news, Monne adds, is that "no mutations capable of transmitting the virus from one man to another have been spotted".
It is a different case from the one that in 2003 caused at least 83 passages of the virus from animals to humans in a chicken farm in the Netherlands, but no human-to-human transmission. The virus that circulated at that time was very different from the one detected in the Spanish farm. "So far there have been very rare sporadic cases in humans, all linked to direct contact with infected animals," notes the researcher. The most recent occurred in 2021 in Great Britain, while in early January a baby girl in Ecuador was infected with the H5N1 virus.
Surveillance is a must, the researchers write in the article. Reports are frequent and in France the avian influenza virus has forced to kill 4.6 million chickens since summer 2022. "The more the virus continues to circulate, the more it has a chance of finding new hosts. Type A influenza viruses - notes Monne - have a higher evolutionary frequency: they attempt to adapt to as many hosts as possible".
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