The worst-ever outbreak of bird flu has led to the disease becoming endemic in some birds, inflicted huge costs on the poultry industry, spread into wild and captive mammals and, in some rare instances, infected humans.

The World Organisation for Animal Health this month said a rising number of cases had been reported in mammals, “causing morbidity and mortality” in species such as otters and seals. Reports of infections in farmed mink in Spain had increased concerns, WOAH said, because cases involving large numbers of animals kept close to one another exacerbated the risk of wider transmission.

If H5N1, the strain mainly responsible for the latest outbreak from late 2021, develops mutations that make it easier to transmit to humans, experts fear the emergence of a pandemic that carries more risks for global health than the Covid-19 outbreak. Though bird flu has infected relatively few humans, its fatality rate is about 50 per cent, according to the European Centre for Disease Prevention and Control.