Why is South Africa vaccinating seals and issuing warning against them?

Scientists in South Africa have detected an outbreak of rabies among Cape fur seals, marking the first time the virus has been identified spreading in marine mammals. At least 24 seals found dead or euthanized along the country’s west and south coasts tested positive for rabies, according to state veterinarian Dr. Lesley van Helden.

Rabies Spread Among Seals

Rabies, a virus that affects mammals and is almost always fatal once symptoms appear, has traditionally been seen in land animals such as raccoons, coyotes, and dogs. The virus typically spreads through saliva, often via bites, but can also be transmitted when animals lick or groom each other. Until now, the virus had not been recorded spreading among sea mammals.

The only other known case of rabies in a sea mammal occurred in the early 1980s when a ringed seal in Norway was believed to have been infected by a rabid arctic fox. However, there was no evidence of further spread among seals in that instance.

Discovery and Testing

The outbreak was first identified in June when a dog was bitten by a rabid seal on a Cape Town beach. This incident led to tests on brain samples from 135 seal carcasses collected since 2021, along with 20 new samples. Several of these tests returned positive results, confirming the presence of rabies among the seals.

Scientists are now investigating how the virus spread to the seals, whether it is circulating widely among their large colonies, and what measures can be implemented to control it. “It’s all very, very new,” said Greg Hofmeyr, a marine biologist studying seals in South Africa. “A lot of research is required… there are a lot of unknowns here.”

Possible Transmission from Jackals

There are approximately two million seals migrating between South Africa, Namibia, and Angola. According to van Helden, the rabies virus found in the seals matches the strain present in black-backed jackals in Namibia, suggesting that jackals might have passed the virus to seal pups along the coastline. Genetic analysis also indicated that the virus is being transmitted among seals.”So, it’s basically established itself in the seal population and it’s being maintained by them biting each other,” van Helden said.

Public Safety Concerns

In response to the outbreak, authorities in Cape Town have issued warnings to locals, as seals frequently inhabit areas close to humans, particularly around the city’s beaches. Over the past three years, there has been an increase in reports of aggressive seal behavior and attacks on people, although no human rabies cases have been recorded.

Authorities have begun vaccinating seals at two popular harbors in Cape Town. One seal carcass collected in August 2022 tested positive for rabies, indicating the virus had been present for at least two years.

Challenges in Containment

Efforts to contain the virus face significant challenges. The US Centers for Disease Control and Prevention (CDC) is monitoring the situation but has yet to see clear evidence that this outbreak will be a long-term issue. Dave Daigle, a spokesman for the CDC, noted that similar instances, such as raccoon rabies spreading to gray foxes in the US, had eventually died out.

There are uncertainties regarding the effectiveness of the rabies vaccine in seals, as it has never been tested on marine mammals. Additionally, logistical issues complicate vaccination efforts, as seals mainly eat live fish and cannot be easily baited with oral vaccines.

Potential for Wider Spread

Researchers are also concerned that other seal species in contact with Cape fur seals could facilitate the spread of the virus to other regions. Hofmeyr noted, “The chances of that happening are very low, but the implications of that if it does happen are very important.”

Authorities continue to collaborate with international experts to manage the outbreak and explore ways to protect both the seal population and public health.

(Inputs from AP)