Experts in South Africa have discovered an outbreak of rabies among seals. This is the first time the virus has spread among marine mammals. Rabies, which affects land mammals and can be transmitted to humans, is known to have a mortality rate of close to 100% when symptoms appear.

Rabies in seals

Rabies is usually spread through saliva, bites or simply by grooming. The most common hosts are raccoons, jackals, foxes, coyotes and domestic dogs. The discovery of this deadly virus among Cape fur seals off the coast of South Africa came as a shock.

A single case of rabies was recorded in a ringed seal on the Norwegian island of Svalbard in the early 1980s, but unlike the recent outbreak in South Africa, there was no evidence of further spread of the disease among these seals.

Unusual aggression of seals

At least 24 fur seals were found dead or euthanized due to rabies, state veterinarian Dr. Leslie van Helden said.

But the discovery couldn’t have happened without the help of a dog bitten by a seal on a Cape Town beach, which led to the testing of 135 seal carcasses collected since 2021. With 20 more samples collected and tested, more positive results emerged.

How did rabies infect seals?

Experts are still scratching their heads as they try to figure out how rabies got into seals and whether the disease has spread among large colonies. Marine biologist Greg Hofmeyr admits that “this is all very, very new” and that they are looking at a lot of unknowns. So where does this leave us?

Determining the origin of the epidemic

An estimated 2 million seals migrate along the African coast between South Africa, Namibia and Angola. Van Helden suspects the seals may have contracted rabies from jackals in Namibia.

Interestingly, the genetic makeup of the rabies virus found in seals was a close match to rabies in black-backed jackals in Namibia. The virus is not only fixed in seals, but is also transmitted between seals through bites. Therefore, the high density of seals, especially in Cape Town, is a concern.

Fighting seal rabies

The seals, which are famous in Cape Town’s harbours, have become increasingly aggressive over the last three years and have been responsible for more attacks on humans. Although no cases of rabies have been recorded in humans, the increasing number of seal attacks has led the city to launch a seal vaccination programme.

Although the US Centers for Disease Control and Prevention is closely monitoring the situation, it is impossible to predict the long-term dynamics of transmission. Needless to say, the success of the seal vaccination program is based on the assumption that it works, since it has never been tested. There are also logistical questions about how to vaccinate seals along a coastline that stretches more than 2,100 miles.

The way forward

Now that rabies has been detected in Cape fur seals, a comprehensive approach to monitoring and research is needed. Experts are calling for increased monitoring of seal populations and cross-border cooperation with Namibia and Angola to understand the wider geographic impact.

Research efforts are also focused on developing diagnostic tools that can quickly and accurately assess the presence of rabies in marine mammals. Scientists hope these studies will lead to adaptive management practices that will help create a system that ensures the safety of both seals and humans.

Rabies formation in seals

Although rabies cases in seals represent uncharted territory, they are a stark reminder of the complexity of the ecology of the disease at the intersection of wildlife and human environments.

Rabies movement in marine mammal populations demonstrates an urgent need for interdisciplinary research and reassessment of current wildlife disease systems. The scientific community now faces the challenge of unraveling the mystery of this epidemic and developing strategies to prevent future cases.

Broader effects of the pandemic

This unprecedented situation highlights the delicate balance of ecosystems and the unpredictable ways that human actions, environmental change, and wildlife health interact. As research continues, we hope that collaborative efforts will yield insights that will protect the health of both marine ecosystems and our own communities.

Hofmeyr noted that several other seal species have come into contact with Cape fur seals and then travelled to other parts of the world, raising concerns of further spread.

“The chances of this happening are very small, but if it did, the consequences would be very significant,” said Hofmeyr, the seal researcher.