Scientists in South Africa have detected the first known outbreak of rabies in seals

CAPE TOWN, South Africa — Scientists in South Africa say they have detected an outbreak of rabies in seals. This is believed to be the first time that the virus has spread among marine mammals.

At least 24 South African fur seals found dead or euthanized at various locations on South Africa's west and south coasts were suffering from rabies, said state veterinarian Dr. Lesley van Helden.

Rabies, which affects mammals and can be transmitted to humans, is almost always fatal once symptoms appear. Rabies is transmitted through saliva, usually through bites but sometimes when animals lick and groom each other.

The virus has long been known to occur in wild animals such as raccoons, coyotes, foxes, jackals and domestic dogs, but spread among marine mammals has never been observed, van Helden and other experts said this week.

The only other known case of rabies in a marine mammal involved a ringed seal on Norway's Svalbard Islands in the early 1980s. That seal was likely infected by a rabid Arctic fox, researchers said, and there was no evidence that rabies was spreading among seals there.

Authorities in South Africa first detected rabies in Cape fur seals in June after a dog was bitten by a seal on a beach in Cape Town. The dog became infected with rabies, which triggered rabies tests on brain samples from 135 seal carcasses that researchers had already collected since 2021. About 20 new samples were also collected and more positive results were obtained in subsequent tests.

Scientists are trying to find out how rabies was transmitted to the seals, whether the disease is spreading widely in their large colonies and what can be done to contain it.

“This is all very, very new,” says Greg Hofmeyr, a marine biologist who studies seals in South Africa. “There's a lot of research that needs to be done… there's a lot that's still unknown.”

About two million seals migrate between South Africa, Namibia and Angola along the south and west coasts of Africa. The most likely possibility, says van Helden, is that rabies was first transmitted to the seals by jackals in Namibia, where the wolf-like animals hunt seal pups on the coast.

The rabies virus genes found in the seals matched those of rabies in black-backed jackals in Namibia. It also showed that rabies was transmitted between seals because most of the virus sequences were closely related, she said.

“So it has essentially become established in the seal population and is maintained by them biting each other,” van Helden said.

The seals live in close proximity to people in South Africa, particularly on beaches around Cape Town. The city has issued warnings to locals, said Gregg Oelofse, Cape Town's head of coastal and environmental management.

Authorities have been baffled over the past three years by reports of overly aggressive seals and an increase in seal attacks on humans, some of which have resulted in bites. As a result, no cases of rabies in humans have been recorded.

Oelofse said city authorities had begun vaccinating the few seals in two popular Cape Town ports, where they are considered an attraction.

One of the positive rabies tests was from a seal carcass collected in August 2022. This means that the seal population has been affected by rabies for at least two years, Oelofse said.

“It’s been here longer than we know about it,” he said.

According to experts, there are still many unknowns.

It's difficult to predict long-term transmission dynamics, said Dave Daigle, spokesman for the U.S. Centers for Disease Control and Prevention. He pointed to previous cases in which rabies viruses landed in new hosts and then died out. In 2021, for example, in the U.S., gray foxes spread the raccoon rabies virus variant for two years, then transmission stopped.

The US health authority is monitoring the situation in South Africa, but has not yet seen “clear evidence that this will be a long-term problem,” Daigle said.

Another unknown is whether the vaccine will be effective in seals. It has never been tested, but experts believe it should work.

There is also a logistical question, van Helden said: How do you vaccinate large numbers of seals, most of which live at sea and migrate back and forth along a coastline of more than 3,500 kilometers? Land animals can be vaccinated by laying out bait that releases the oral vaccine when they eat, but seals generally only eat live fish, she noted.

South African officials have been working with international experts.

Seal researcher Hofmeyr said some other seal species come into contact with South African fur seals and then migrate to other parts of the world, raising concerns about further spread.

“The likelihood of this happening is very low, but the consequences if it does happen are very serious,” he said.

___

AP Africa News: