CAPE TOWN, South Africa (AP) — Researchers in South Africa have discovered an outbreak of rabies in seals, marking the first known transmission of the virus among marine mammals. At least 24 Cape fur seals, found dead or euthanized along the west and south coasts of South Africa, tested positive for rabies, according to state veterinarian Dr. Lesley van Helden.
Rabies is a viral disease that affects mammals and can be transmitted to humans, almost always resulting in death once symptoms appear. The virus primarily spreads through saliva—typically via bites, but it can also transfer when animals lick or groom one another.
While rabies has been recognized in terrestrial animals like raccoons, coyotes, and domestic dogs, this is the first instance in which the virus has spread within seal populations. The only previous case involving a marine mammal was a ringed seal in Norway’s Svalbard islands in the early 1980s, which was believed to have contracted the virus from a rabid arctic fox.
The outbreak in South Africa was first brought to light in June after a dog was bitten by a seal on a beach in Cape Town. Following this incident, the dog was found to have rabies, prompting researchers to conduct tests on brain samples from 135 seal carcasses collected since 2021. Subsequent tests on around 20 additional samples yielded several more positive results.
Scientists are currently investigating how rabies may have infected the seals, if and how much it is spreading among their colonies, and what containment measures can be implemented. “It’s all very, very new,” said Greg Hofmeyr, a marine biologist focused on seal research in South Africa. “A lot of research is required… there are many unknowns here.”
There are approximately 2 million seals migrating along Africa’s south and west coasts, moving between South Africa, Namibia, and Angola. Dr. van Helden suggested that jackals in Namibia may be the initial source of the virus, as these animals hunt seal pups along the coast.
The genetic analysis of the rabies virus in seals closely matched that found in black-backed jackals in Namibia. This indicates that rabies is being transmitted among the seals, as most viral sequences were found to be closely related. “It’s essentially established itself in the seal population and is maintained through biting among them,” van Helden noted.
Living in proximity to human populations, especially on beaches near Cape Town, the seals have raised concerns among local authorities. Cape Town’s coastal and environmental management head, Gregg Oelofse, reported that the city has issued warnings to residents regarding the increased aggressiveness of seals, which has led to attacks on people, although no cases of rabies in humans have been confirmed as of yet.
In response to the situation, city authorities have begun vaccinating the small number of seals in two popular harbors, which attract tourists. Remarkably, one positive rabies test came from a seal carcass collected back in August 2022, indicating that the virus may have been present in the seal population for a longer period than previously recognized, according to Oelofse.
Experts have acknowledged the challenges that lie ahead. Dave Daigle, a spokesman for the U.S. Centers for Disease Control and Prevention, highlighted the unpredictability of rabies transmission dynamics. He noted that there have been instances where rabies viruses found new hosts but then died out quickly. For example, in 2021, gray foxes in the U.S. transmitted a variant of raccoon rabies for two years before the spread ceased.
Other uncertainties involve the efficacy of vaccines in seals, as such vaccinations have never been tested on marine mammals, though specialists remain optimistic. A major logistical challenge also exists: how to effectively vaccinate a significant number of seals that predominantly reside in the ocean and traverse a coastline exceeding 3,500 kilometers (about 2,170 miles). Unlike land animals, which can receive oral vaccines through bait, seals typically consume only live fish.
South African officials have been working closely with international experts. Hofmeyr raised further concerns about the potential for other seal species that interact with Cape fur seals to travel and spread the virus globally. “While the chances of this occurring are minimal, the implications of such an event would be significant,” he stated.
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