The outbreak may be the first ever documented in marine mammals.
For the last three years, scientists in South Africa have been trying to unravel a grim marine mystery: What was happening to the Cape fur seals?
The boisterous marine mammals, which are common along the nation’s shores, began washing up dead in enormous numbers. Pregnant females delivered dead premature pups. And some seals began displaying unusually aggressive behavior, attacking humans, dogs and each other.
Some scientists suspected that a neurotoxin produced by algae might be to blame. In recent weeks, however, another specter has come into focus: rabies.
So far, 17 seals have tested positive for the virus, said Tess Gridley, a founding director of Sea Search Research and Conservation, who has been investigating the seal deaths. The cases, which date back to at least August 2022 and span hundreds of miles of coastline, may be the first sustained rabies outbreak ever documented in marine mammals.
“What I’m doing here is sitting here and putting together all the reports of aggressive interactions between seals and dogs and seals and people in the past few years,” Dr. Gridley said. “And it’s telling quite a scary story.”
Rabies, which is nearly always fatal once symptoms occur, spreads through the saliva of infected animals. So far, no human cases have been reported, but, according to Dr. Gridley’s tally, at least 72 people in South Africa have been bitten or scratched by Cape fur seals since 2021; eight have been bitten by seals since confirmed to have rabies.