H5 bird flu has spread beyond birds in Australia, with the virus confirmed in three mammal species since last weekend, prompting warnings from scientists that seal and sea lion populations could face severe losses.

On Friday, Australia's chief veterinary officer, Beth Cookson, said H5 bird flu had been confirmed in a red fox found in metropolitan Adelaide, marking the first case in a land mammal in Australia. A dead dolphin found on South Australia's Fleurieu Peninsula also tested positive this week, days after a long-nosed fur seal found dead at Beachport became the country's first mainland mammal case.

The state government announced a second suspected case on Monday in a dead long-nosed fur seal found on the Pages Islands, off Kangaroo Island, with results from CSIRO testing pending.

Scientists warn of 'carnage'

John Woinarski, a mammal scientist at Charles Darwin University, said he feared the virus would quickly start affecting more seals and sea lions. "The carnage may be substantial and represent a serious conservation impact," he said. "I fear for Australian sea lions in particular because of their small population size." He added that it was likely the virus would spread more quickly into the sea lion population in South Australia in the coming weeks because of the proximity of sea lion colonies to breeding seabird colonies.

Experts say about 12,000 Australian sea lions remain, though one recent estimate put the figure at less than 10,000. Three types of pinnipeds breed in Australian waters: the long-nosed fur seal, the Australian fur seal and the endangered Australian sea lion.

H5 bird flu has already affected pinnipeds in South America and sub-Antarctica, where it has caused catastrophic losses in some species, particularly among pups. In 2023, H5N1 killed more than 17,000 southern elephant seal pups in Argentina, and drone surveys detected more than 13,000 dead southern elephant seal pups on Australia's Heard Island in 2025 and 2026.

Jane Younger, an Antarctic disease ecologist at the University of Tasmania, said, "In South America, we've seen huge infection rates in sea lions and fur seals. Then across the Southern Ocean we've seen really big mortality rates in southern elephant seals and Antarctic fur seals. In some places, the numbers are just astronomical."

Spread across species

Bird flu has quickly spread around Australia since it was first detected in mid-June, moving from Antarctica to offshore Australia and then from beaches to inland waterways. As of late August there were more than 350 confirmed events of bird flu, including several mass mortalities, affecting more than 20 distinct animal species.

Affected mammals include the long-nosed fur seal and the common dolphin. Australian birds confirmed by CSIRO to be infected include greater crested tern, silver gull, Pacific gull, black-faced cormorant, little penguin, Australasian gannet, magpie, ravens, peregrine falcon and southern boobook.

The first cases of H5 in Australia were detected in seabirds that migrated in winter from the subantarctic Australian territory of Heard Island and McDonald Islands. The virus has also been detected in species that travel between Australia and New Zealand, including brown skua, giant petrels, white-headed petrel, white-fronted tern, fluttering shearwater and Hutton's shearwater.

Rachael Gray, a veterinary pathology researcher at the University of Sydney who has worked with the seals for decades, described the global environmental picture as "quite frightening." "It's pretty overwhelming at the moment," she said. "These animals, who we very much love and admire and respect … these animals are getting sick, they are suffering and then they are dying."

Vaccination and advice

Victoria is currently vaccinating thousands of little penguins, which are a popular tourist attraction. Little penguins on Phillip Island and St Kilda are the only wild species targeted for vaccination, with aims to capture and jab 5,000 of the 40,000 penguins in the area.

Michelle Campbell-Ward, a wildlife veterinarian at the University of Sydney, said it was "nearly impossible" to vaccinate most wild birds, and that vaccination was "by no means a silver bullet," with surveillance the most important measure.

The South Australian government said last week it was investigating potential opportunities to vaccinate high-priority at-risk mammals, such as Australian sea lions at Seal Bay on Kangaroo Island. South Australian Environment Minister Emily Bourke said the state would assess the possibility of importing an experimental US vaccine for use among mammals in Australia, but warned that vaccines for mammals such as cattle and cats being developed overseas are yet to be approved by authorities. CSIRO said there were no specific plans yet to vaccinate pinniped animals such as sea lions and seals.

Concern for sea lions

The Australian Marine Conservation Society said the arrival of bird flu in South Australia followed significant environmental harm caused by the algal bloom. Campaigns director Alexia Wellbelove said some species, such as sea lions, were in poorer condition because their food sources had been affected, "meaning they are likely more vulnerable." She said the organisation had been calling for increased funding to target other threats to the species, such as fishing. "With reported mass mortality of terns and now the death of a long-nosed fur seal on the Pages it is now highly likely that this vital population of Australian sea lions has also been exposed to the virus," she said.

Advice for pet owners

Bird flu infections have been reported in domestic cats and dogs overseas, though the Australian government says such infections are uncommon and usually occur through contact with infected birds. Overseas, cats infected with the virus have experienced a high mortality rate.

Robyn Alders, an animal influenza expert and honorary professor at the Australian National University's Crawford School of Public Health, suggests keeping cats indoors, especially in areas where bird flu cases have been confirmed, and keeping dogs on a leash when walking.

Infected birds spread the virus through droppings, feathers and other bodily fluids. It can also be transmitted via contaminated clothing, footwear, equipment and vehicles. Under favourable conditions, the virus can survive in the environment for months, Australian government authorities have said.

While the virus primarily spreads from infected birds, there is evidence it can also spread between some mammals, including during outbreaks in seals and dairy cattle overseas. Among scavengers like foxes and cats, infections have been linked to eating or interacting with bird carcasses.

Cookson said there was no evidence of mammal-to-mammal transmission of the virus in Australia. "This detection in a fox is a good reminder that people and their pets [should] take precautions," she said.