Dead seals are washing up along beaches in South Africa’s port city of Cape Town, a coastal management official told CNN Friday, amid an outbreak of rabies in the marine animals.

“We believe this to be the first spread of rabies within a marine mammal population and that is concerning for us,” said Cape Town’s coastal manager Gregg Oelofse.

Rabies in seals is rare and the only known case of the viral disease in a seal was detected in the Svalbard islands of Norway in 1980.

Cape Town, home to dozens of beaches and a coastline extending over 300 kilometers (186 miles), harbors thousands of Cape fur seals, a seal species native to southern Africa.

The city has recorded “11 positive rabies cases in seals so far,” with the last positive case detected in a seal tested 10 days ago, according to Oelofse. He urged calm, however, saying it is normal to find carcasses of Cape fur seals along the shoreline. While “lots” of dead seals have washed ashore this week, many of them have died naturally, he said.

He added that laboratory investigations were ongoing to determine how the seals were infected with the disease.

“We don’t know yet where it started. They are genetically sequencing the rabies virus found. We will know when they are done with that,” he said.

The Western Cape provincial health department alerted residents of a rabies risk last month, warning of “the potential for rabies cases along the entire coastline where seals are present.”

Authorities said in late June that they had confirmed seven cases of the disease in seals from seven beaches in Cape Town and elsewhere on the Western Cape, urging residents to avoid contact with the animals. The first case was detected in October 2023, they noted.

“There is no cause for panic,” Cape Town city authorities stated at the time, adding that “while rabies is new in Cape fur seals, it is endemic in many wildlife populations in South Africa.”

The area has witnessed many seal deaths in recent years. In November 2021, Western Cape provincial officials said they buried close to 200 dead seals in a single day after their carcasses washed ashore from suspected malnutrition.

Rabies, which is almost always fatal once symptoms appear, is an infectious viral disease that affects the brain and central nervous system.

According to the World Health Organization, dogs are the main source of rabies transmission to humans. The virus is transmitted to humans through animal bites or scratches and can take between three and 12 weeks to begin showing symptoms.

Oelofse said there was yet to be a seal-to-human transmission of rabies in Cape Town and the city’s authorities were working to prevent it.

“We have a lot of people that are coming into contact with seals daily such as surfers, kayakers, scuba divers, and others. So, one of the things that we want to avoid is the potential of transfer of rabies to a person and so far, that hasn’t happened.”