A mass outbreak of avian flu among sea lions in Peru has revived fears the virus could be passing between mammals.
Since the start of the year, more than 600 sea lions (Otaria flavescens and Arctocephalus australis) have been found dead or dying on Peruvian beaches.
Six animals were tested for influenza and all tested positive. PCR tests confirmed that the virus was the H5N1 bird flu subtype that has killed tens of millions of wild and farmed birds since the current outbreak began in 2021.
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It is the聽first mass mortality event of wild mammals from avian flu in South America, and likely to be the first mass death of its kind among sea lions.
In a paper posted online before peer review, at San Agustin National University in Arequipa, Peru, and his colleagues say the deaths were 鈥渨orrisome鈥�, in part because some of the animals were found dead together in large groups of up to 100.
The sea lions may have become infected after eating or encountering seabird carcasses infected with the virus, but the researchers warned they 鈥渃annot rule out鈥� the possibility that the virus spread between the sea lions.
鈥淲e cannot exclude [the possibility] that the virus has adapted to mammals and that sea lion [to] sea lion transmission has begun in Peru,鈥� says team member at the National University of Comahue, Argentina. 鈥淗owever, we must be cautious and this transmission pathway should be urgently investigated.鈥�
The next step is to carry out genomic sequencing of the virus, says Plaza. This could add evidence that sea lions have caught the virus from other sea lions, or reveal if the virus has any genetic changes that may help it adapt to a new host.
The case of the sea lions is the latest example of bird flu 鈥渟pilling over鈥� into mammals. In October 2022, , while 700 seal carcasses infected with avian flu .
If the H5N1 virus has mutated to spread between mammals, it could have serious consequences for public health, says at the University of Leeds, UK. 鈥淭hat leap into a group of species that we are closely related to means that the potential for a jump into humans is just that much more likely,鈥� he says. 鈥淓specially if it made the jump into mammal species that are abundant and kept at high density, such as livestock.鈥�
But Ward stresses there isn鈥檛 yet conclusive evidence to prove mammal-to-mammal transmission is occurring.
at the University of Reading, UK, said the 鈥渦ptick鈥� in cases of avian flu in mammals is 鈥渙f concern鈥�, but is probably due to the fact so many wild birds are now infected with the virus.
鈥淭here鈥檚 a lot more avian flu around鈥� so a much larger proportion of birds, including seabirds, will be infected and of course they will die and drop into the sea. And they will become carrion which is preyed on by mammals,鈥� he says. 鈥淭he issue is that there is so much of [the virus] around, more so than any genetic changes which are predisposing to transmission among mammals.鈥�
Reference: bioRxiv,
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