Scientists hunt for clues in mystery rabies outbreak

Along the western seaboard of Southern Africa, epidemiologists are trying to make sense of a rabies outbreak that has baffled scientists.

Just over a year ago rabies was detected in a seal off the Western Cape, the first time health officials had seen the disease spread between individuals of a sea mammal species. Since then academics have been piecing together how this happened, and how the outbreak is evolving.   

A genetic study of the rabies virus in seals has identified a suspect. Seal rabies was matched to rabies in black-backed jackals in Namibia. The jackals hunt baby seals along the beach. It’s likely that a jackal bite transferred the virus, and now the disease is spreading among Cape fur seals. On June 17, a case of rabies was confirmed in a Cape fur seal in Walvis Bay. 

Jacqueline Weyer, a principal medical scientist at the National Institute for Communicable Diseases (NICD), believes this particular rabies outbreak might extend into Angola, as Cape fur seals are known to travel that far north.

What scientists like Weyer want to find out is at what point the virus passed from jackals to seals.

Tests on brain samples from seal carcasses collected since 2021 have found evidence of rabies. “I think once we have more data, especially if data starts becoming available from Namibia, we will be better placed to do a specific type of analysis that will tell us, at least theoretically, when this started,” she says.

The discovery of rabies in sea mammals is a setback in the fight to meet a tight deadline set by the World Health Organisation (WHO). The Zero by 30 is a global campaign by the WHO to end human deaths from dog-mediated rabies by 2030.

Dog bites are the cause of most rabies cases in people in Africa and Asia. Jackals are the main culprits in passing the virus on to dogs, but already there has been at least one case in Cape Town where a dog contracted the disease after being bitten by a seal.

Prof Andrew Leisewitz, of the College of Veterinary Medicine at Auburn University in the US, says: “Rabies in developed countries is a problem of exposure, particularly in the US, to bats and other wild animals because domestic dog rabies vaccination is so fastidiously applied that they are no longer the main vector. It is an easy thing to get on top of, if you get good vaccine coverage in the dog population to prevent transmission. You need about 60% of domestic dogs vaccinated to prevent disease outbreaks.”

The presence of stray dogs and the price of vaccines make attaining this coverage difficult. About 59,000 people die of rabies globally every year after contracting the disease when they are exposed to saliva transmitted through bites and scratches.

Vaccines and immunoglobulins can prevent rabies, but once clinical symptoms of the disease appear, the fatality rate is 100%.

One way of monitoring the spread of rabies, says Weyer, is tracking dog bites. She is co-author of a recent NICD surveillance report that stresses the importance of monitoring bite incidents and human rabies cases to identify high-risk areas for targeted interventions in Limpopo.

Dog bites are not notifiable, but Weyer and her colleagues found that they are common, with 131 dog bites per 100,000 people in Limpopo between 2011 and 2023.

Unarine Makungo, lead author of the study, says in a statement: “This article provides vital evidence-based information on the risk of rabies in Limpopo, where outbreaks still occur and children are disproportionately affected. It highlights the importance of dog vaccination, public awareness and timely medical care after animal bites.

“The findings are directly relevant to health-care providers, policymakers and community members who play a role in rabies prevention and control.”

It is estimated that 40% of rabies fatalities in people are children. To effectively fight rabies, a multipronged approach is needed, says Weyer. This includes vaccinating dogs, monitoring dog bites and educating people about the disease.

But even with these interventions, it is unlikely that South Africa will meet the Zero by 30 deadline in five years. “Though we can maybe achieve elimination, it will come with terms and conditions that might be for a specific time, and it might involve just specific geographical areas, but certainly we must try,” says Weyer.