Scientists have found that a relatively high proportion of two remote Peruvian Amazon populations, who have had a high level of contact with vampire bats, display some protection against bat-transmitted rabies.
These individuals appear to have survived exposure to the rabies virus, even without a prior vaccination, according to scientists at the US government's Centers for Disease Control and Prevention (CDC) who carried out the study in collaboration with the Peruvian Ministry of Health.
The findings could open up the possibility of developing new treatments for the disease, which is usually fatal if it is not treated in time.
The researchers travelled to the remote Loreto region of the Peruvian Amazon, where outbreaks of rabies caused by bites from vampire bats have occurred regularly over the last two decades.
The team interviewed 92 people in two communities exposed regularly to bat bites.
Blood samples were taken from two thirds of those interviewed. Of these, seven were found to have antibodies — which are only produced when the body is directly exposed either to rabies or to a vaccine for the virus — that neutralised the virus, according to the findings published in the August issue of the American Journal of Tropical Medicine.
One of the seven reported having received an anti-rabies vaccine. But there was no evidence that the other six had been vaccinated, or had sought medical attention for bat bites, suggesting that they had already been harbouring the rabies antibody.
This level of a population showing such antibodies "is relatively high," lead author Amy Gilbert, a postdoctoral fellow at CDC’s National Centre for Emerging and Zoonotic Infectious Diseases, told SciDev.Net.
She described the result as "remarkable", adding that scientists had long believed that hosts such as humans and cattle were unable to mount an immune response to rabies.
Children were also tested, but only adults showed the antibodies. "It is possible that what we are seeing is multiple low-dose exposure that accumulates over a lifetime," Gilbert said.
Bats are the most common natural reservoir for rabies in Latin America, and few people who get bitten survive exposure to the virus. "The virus gains access to the central nervous system, where it causes the almost entirely fatal disease," said Gilbert.
In the case of the Peruvian individuals found to have the antibodies, "one hypothesis is that the human body mounted an immune response when the virus was [inside it], but still outside the central nervous system," Gilbert said.
Another was that some isolated populations are genetically unique, she added.
In an editorial accompanying the study, Rodney E. Willoughby, a paediatric infectious disease specialist at the Children’s Hospital of Wisconsin, in the United States, said that if there are distinct populations with complete or relative resistance to rabies, "careful, respectful studies" could potentially help develop new, life-saving treatments.
According to the WHO, rabies kills 55,000 people a year — 95 per cent of these in Africa and Asia — and appears to be on the rise in China, the former Soviet republics, Southern Africa and Latin America.