Rabies causes aggressive Cape Fur Seal behaviour - scientists

Lester Kiewit speaks to Gregg Oelofse, the City of Cape Town’s Coastal Manager.

The City of Cape Town in partnership with the Department of Forestry, Fisheries and the Environment (DFFE), the Two Oceans Aquarium Foundation and Sea Search, convened an expert scientific workshop last week. 

The workshop investigated possible causes of the increase in unprovoked Cape Fur Seal bites and aggression on recreational users in the Western Cape.

With the recent confirmation of rabies in the Cape Fur Seal population, the workshop included discussions about the implications of and appropriate management responses to the rabies virus in the Cape Fur Seal population.

Marine mammal experts, veterinarians, marine scientists, various government departments and key stakeholders from South Africa and the world attended the two-day workshop held in Cape Town from 23 to 24 July 2024 at the Two Oceans Aquarium.

The key findings, outcomes, and agreements are as follows:

Causes of aggression:

Some levels of aggression in seals should be considered normal and may arise from various causes including territorial behaviour, maternal protectiveness, pain or distress, as well as from poor health conditions caused by diseases.

However, excessive aggression associated with unusual behaviour being documented in multiple cases is not normal and directly linked to the now-confirmed presence of the rabies virus in some individual Cape Fur Seals.

Eradication unlikely:

Rabies appears well-established in the Cape Fur Seal population and is unlikely to be eradicable and should now be considered endemic, requiring ongoing and long-term management by coastal authorities.  

"The number of positive cases of rabies in seals have gone up to 15 since May and it's now in the seal population and associated with aggressive behaviour, typically unusual for seals. From a public health point of view, we have to be careful."

- Gregg Oelofse, Coastal Manager - City of Cape Town

"It's difficult to eradicate from any animal population because it's a slow burn virus with a long incubation period, so there's no way we can tell which animals have the virus at any given time... with a population of over two million seals, there's no ability to knock this virus out."

- Gregg Oelofse, Coastal Manager - City of Cape Town

Source:

Initial indications are that rabies was transmitted to seals from another wildlife population and not from local domestic dogs.

What it means for seals:

The effect on the seal population remains unknown, but in other animals, rabies typically pursues a 'slow burn' course of flares and declines, rather than resulting in mass mortalities. Questions however remain about the differences between seals – highly gregarious animals living in large colonies – and other terrestrial animals in which rabies occurs.

Given that this is the first documented rabies infection in a marine mammal population there are many unknowns.

"We now have to accept from the experts' opinion that it's in the population and will flare up and die down as it does in other animal populations... it can also live in domestic animals, so the strategy around getting rabies out of domestic dogs is to vaccinate them."

- Gregg Oelofse, Coastal Manager - City of Cape Town

Proactive measures:

Coastal authorities in partnership with the State Vet, veterinary experts, researchers, marine mammal experts and animal welfare organisations will need to continue implementing ongoing proactive measures to manage the rabies outbreak responsibly.

Vaccination may be valuable in some seals:

Although the efficacy of rabies vaccines in seals is not yet known, there is no reason to expect adverse outcomes, and it was strongly recommended that vaccination be trialled with a focus on animals that come into regular contact with humans. This would include harbour-associated seals and rehabilitation centre seals. The Two Oceans Aquarium will develop a standard procedure for vaccinating seals, including dosage and injection options. Vaccinated seals should be tagged to allow repeat identification and follow-up vaccination.

Vagrant seals:

Visiting elephant seals and Sub-Antarctic fur seals will be vaccinated as a precautionary measure even while efforts are underway to establish the efficacy of the vaccine in seals as a responsible precautionary measure to reduce the small risk of rabies spreading to the Sub-Antarctic and the southern ocean regions. Vaccinated seals will be tagged where possible to allow repeat identification.

Rabies testing:

Only seals involved in a confirmed bite on a person or domestic dog will and must be euthanised immediately, and sent for testing for rabies by the State Vet.

Public Health Advisory:

The public health advisory remains that rabies vaccines are not recommended for the general public and that anyone bitten or scratched by a seal resulting in an open wound must seek immediate medical attention and receive post-exposure prophylaxis.

Domestic Dogs:

Dogs' rabies vaccines must be up to date at all times. The public is also reminded they must prevent their dogs from having contact with seals.

Public communication:

Ongoing updates on the rabies outbreak in Cape Fur Seals will be provided. Only results provided by the State Vet should be considered confirmed and factual.

Seal Feeders:

Seal feeding as done at Hout Bay harbour is illegal, as is the aiding and abetting of any seal feeders through paying or participating, which includes taking photos – these are offences and offenders may be arrested.

What to do:

The public is again advised to stay clear of all coastal wildlife including seals regardless of their rabies status. It is illegal to approach, touch, handle, harass or interfere with coastal wildlife.

Seals are a healthy and normal part of our coastline and you should expect to see and encounter seals along our beaches and in-shore areas.

Those who come across a seal that is behaving unusually or aggressively, are advised as follows:

Move away from the animal or leave the water if they are surfing, swimming or diving. Immediately inform the relevant authorities:

• Cape Town – City of Cape Town on 021 480 7700, Cape of Good Hope SPCA on 021 700 4140
• West Coast – CapeNature on 083 236 2924
• Overberg – CapeNature on 083 236 2924
• Southern Cape – Plett Stranding Hotline on 079 463 4837 and CapeNature on 044 5332125
• Eastern Cape - Bay World Stranding Hotline – 071 724 2122
• Table Mountain National Park on 021 783 0234       

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