On 27 June 2023, the Polish authorities notified the World Health Organisation (WHO) of the death of 46 cats and one caracal. Most of the samples tested from the dead or slaughtered animals were positive for avian influenza subtype H5N1 and clade 2.3.4.4b, which has been responsible for multiple outbreaks of avian influenza in poultry farms in Europe. In addition, the animals developed symptoms compatible with avian influenza infection. 

The affected animals come from different geographical areas of the country. The source of exposure of the animals to the virus is currently unknown and investigations are ongoing to determine how the infections occurred, which could be through direct or indirect contact with infected birds, or through consumption of contaminated feed, among other causes. It is important to note that none of the people who had close contact with the animals have developed symptoms related to possible infection with the virus. 

Previously, sporadic cases of infection in domestic or wild felines with avian influenza subtype H5N1 have been described, and it was known that felines are susceptible to this virus. However, this time the high number of reported cases is striking. 

Given the increase in the number of mammalian cases that have been infected with avian influenza subtype H5N1, the situation should continue to be monitored through active surveillance systems. In addition, it is important to assess the evolution of the virus in order to predict possible adaptations to mammals, including humans. It should be recalled that avian influenza has been a key player in recent influenza pandemics.

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