One Health is a complex area.

The interactions between human health, animal health and the environment are legion; as are the number of scientific disciplines, which must be considered, if the challenges presented by One Health problems are to be managed. Nestled within this intricate maze of One Health science lie virology and epidemiology, subjects which have enjoyed increasingly high profiles in recent years in the face of the COVID epidemic. And this prominence is far from receding. It is with considerable concern that VetSalus notes the transition of the highly pathogenic Avian flu strain, which has spread globally in recent years, into a virus capable of infecting cattle and also human beings.

The H5N1 lethal variety of bird flu has been spreading globally since 2020, reaching North America in 2021 and late last year the virus was identified in seabirds in Antarctica (1). The virus has previously been reported as infecting sea mammals (2) but a disturbing development was reported in the USA in late March 2024, when reports of the H5N1 virus infecting dairy cows in several states were confirmed (3). At that time the presence of dead birds on the affected properties was noted and it seemed most likely that cows were infected by direct or indirect contact with these sources; there was no evidence to support cow to cow transmission but the appearance of cases in six US states, as geographically widespread as Texas and Michigan was of concern. These reports were quickly followed by the report of a single human case, a mild infection of a person who had been in contact with infected cows in Texas. More worryingly, the evidence for spread between infected cattle was growing (4).




While experts are talking down concerns of a pandemic at this stage and the current human infection is mild, it is known that infections with the H5N1 strain of Avian Influenza are serious in humans: a mortality rate of 52% was reported by WHO in the 889 cases recorded in 23 countries since 2003. The WHO update on the US case can be found here.

It should be emphasised that there is no evidence that the current strain of the virus has developed the genetic changes necessary for human to human infection. The WHO advice on Avian influenza remains unchanged. Rosemary Sifford of the USDA recently confirmed that only one sample had shown some genetic change towards developing a mammalian infecting capability: “It very much remains an avian virus with no significant changes… In other words, it is not becoming a [cow] virus,” said Sifford (5).

However, concerns are growing in the USA, with work towards developing a vaccine being ramped up and affected farms are now receiving financial compensation for milk loss, to provide employees with PPE and equipment to facilitate local pasteurisation is being installed on farm (6). This proactive response is to be welcomed and is in contrast to some of the initial responses to the COVID outbreak. VetSalus welcomes this transparent and open response to a concerning infection, which will be of intense interest to all veterinarians engaged in One Health practice.

LMG May 2024


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