Bird flu kills thousands of South American sea lions as outbreak continues | CPT PPP Coverage

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Bird flu in mammals

While bird flu has been a cause of concern among public health experts for some time, its ability to infect mammals has remained relatively low.

Most HPAI strains can’t infect humans, and the ones which can, such as H5N1, can currently only bind to receptors that are uncommon in the upper airways of mammals, making infections less likely.

This has meant that while the virus has spread rapidly among poultry and wild birds, it is not thought to have been spreading between mammals. However, experimental studies in ferrets have suggested that five mutations could allow this to happen more easily.

These mutations may not just be limited to the lab, however. The virus responsible for an outbreak of HPAI at a Spanish fur farm, in which over 50,000 American minks were culled, was found to have acquired a mutation that allowed it to replicate faster in mammals.

While it’s not certain if the virus was spreading between the minks, the same study could not rule it out.

In the wild, evidence of HPAI spreading between mammals is even less clear. While cases have been reported in animals including raccoons, bears and foxes, these tend to be sporadic.

Pinnipeds may be particularly at risk due to their lifestyle, as not only do many species live closely together in breeding colonies, but they also have plenty of contact with seabirds.

‘While it’s not entirely certain how seals and sea lions have contracted bird flu, the leading theory is that they’ve caught it by eating infected birds,’ James says. ‘Birds form part of their diet, meaning it’s more likely that these mammals will catch the disease than others.’

He adds that although the number of deaths is significant, the large number of different sea lion colonies should help to buffer the species against HPAI.

‘Provided that the virus doesn’t spread between different sea lion colonies, they should be able to tolerate the disease,’ James explains. ‘South American sea lions and fur seals have been known to catch tuberculosis, and though on a smaller scale, this does not appear to have severely impacted their populations.’