H5 pandemic in the making? Minks may become the bird flu vector for humans

Spain’s bird flu outbreak in minks hints at a mutating virus    

By Taran Deol
Published: Monday 30 January 2023
Photo: iStock

Bird flu, a virus not known to spread easily among mammals, led to the culling of 50,000 minks in Spain last October. The findings published January 19, 2023 indicated at least one mutation in the virus’ genome, which may make mammal-to-mammal infection easier. Typically, mammals catch the avian influenza directly from infected birds. 

The Spanish case study indicates the virus H5N1 is evolving and may be gaining pandemic potential as its mutation is the same mutation that was recorded in the gene of the 2009 pandemic swine-origin influenza A (H1N1) virus, according to the paper in the journal Eurosurveillance.

Of the 12 workers at the farm, 11 had come in contact with the minks. While asymptomatic, they were subjected to a nasopharyngeal test which revealed a negative result for the avian influenza. They were put under quarantine for 10 days thereafter as a precautionary measure. 

Read more: Largest bird flu outbreak in Europe, 50 million birds culled in the past one year: Report

In the first week of October last year, caretakers noted an unprecedented surge in the mortality rate of minks — up from the usual 0.2-0.3 per cent to 0.77 per cent. At this point, such mortality rates were restricted to certain ‘hotspots’ in two-four pens, where animals were dying within a day or two. 

This worrying trend continued to increase every week, reaching a peak between October 17-23, 2022 as the mortality rate increased to 4.3 per cent and spread across the premises. “The source of the outbreak remains unknown. No (avian influenza) cases were reported in poultry farms supplying the poultry by-products,” the authors of the Eurosurveillance paper noted. 

It is possible the minks were infected via seabirds in Galicia, a region in Spain, carrying the H5N1 virus since they were kept in an open cage and possibly interacted with the wild birds, they added.

“This species could serve as a potential mixing vessel for interspecies transmission among birds, mammals and humans,” the researchers wrote. “It is necessary to strengthen the culture of biosafety and biosecurity in this farming system and promote the implementation of ad hoc surveillance programs for influenza A viruses and other zoonotic pathogens.”

Bird flu is known to jump into mammals quite often, typically through the consumption of bird droppings or preying on infected animals. However, within-mammal transmission was uncharacteristic of the virus until now. 

Tom Peacock, a virologist at Imperial College London, was quoted by the journal Science as calling these findings “incredibly concerning”, while Isabella Monne, a veterinary researcher at the European Union’s Reference Laboratory for Avian Influenza in Italy, noted that “this is a clear mechanism for an H5 pandemic to start.”

While the threat of the evolving H5N1 virus to humans remains unknown for now, several bird flu outbreaks across the world are reason enough for concern. Poultry birds across Europe, Asia, Africa and North America have been victim to the highly infectious strain of the avian influenza virus. 

“Researchers say that the virus seems to be spreading in wild birds more easily than ever before, making outbreaks particularly hard to contain,” a piece in the journal Nature observed last May. This increase in circulation may also push up the chances of a spillover event.

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