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The destruction of natural habitats in the Amazon is increasingly forcing vampire bats into contact with people and even into cities, causing more outbreaks of the deadly rabies disease, say scientists.
In remote parts of the Amazon, rabies is usually controlled by vaccination of local populations in response to human deaths from the virus. But that has not succeeded in preventing further outbreaks, says Benjamin Stoner-Duncan from the University of Washington, who co-authored a recent review of the issue.
Stoner-Duncan’s paper, published in PLOS Neglected Tropical Disease in June, says that new ways to control outbreaks — such as vaccination of the bats themselves — urgently need research and development.
“We need a shift in management strategies for rabies,” says Stoner-Duncan. “The extremely difficult nature of mass vaccination underscores the need for preventative measures, rather than reactive vaccination campaigns after an outbreak.”
Bats are the most common natural reservoir for rabies in Latin America, says Stoner-Duncan. And for those communities struck by rabies outbreaks “the effect is absolutely devastating”, he adds.
According to the WHO, rabies kills 55,000 people a year, and is almost always fatal.
“The extremely difficult nature of mass vaccination underscores the need for preventative measures, rather than reactive vaccination campaigns after an outbreak.”
Benjamin Stoner-Duncan, University of Washington
In 2011 an outbreak caused by bats killed 21 children and two adults in the village of Yupicusa in the Peruvian Amazon. This is one of 32 recorded outbreaks in the greater Amazon Basin since 1975 — though Stoner-Duncan tells SciDev.Net that many are not reported.
The destruction of vampire bats’ habitat and the resulting displacement of their natural prey — mammals and other jungle wildlife — is increasingly driving them into contact with humans as an alternative source of blood, he says.
He adds that mass vaccination alone will not go far enough to reduce the risk of further outbreaks. To remote Amazonian communities rabies appears to be a devastating and mysterious disease, and it is sometimes ascribed to witchcraft. This, together with suspicion of vaccines, confounds public health efforts, he says.
To make matters more difficult, the pre-exposure rabies vaccination has a complicated schedule, requiring three doses over 28 days to be effective. In the remote Amazon people often travel for work at unpredictable times, and it is difficult to keep vaccines refrigerated, says Stoner-Duncan.
A 2013 WHO report on rabies says that despite the underreporting of cases in Latin America, evidence suggests that incidences of bat rabies are increasing and that “elimination of bat rabies is therefore not possible at the present time”.
Stoner-Duncan’s review proposes alternative control methods focused on bat behaviour that could be used alongside or as a replacement for pre-exposure vaccination campaigns in humans.
One option would be to capture vampire bats and apply an oral vaccine to their fur. In principle these animals could then be released and would inoculate wider bat populations during grooming.
Other possibilities include placing vaccinated cattle near human populations to lure vampire bats to the livestock rather than to people — and giving cattle a vaccine designed for bats that they would pick up as they feed on them.
Debbie Briggs, executive director of the charity Global Alliance for Rabies Control, agrees that a new approach is needed to prevent new outbreaks of rabies in the Amazon. “Most of the populations affected are unique and will require unique solutions,” she tells SciDev.Net.
But she still believes that incorporating pre-exposure vaccination into the WHO’s immunisation programmes for children living in the Amazon should be thoroughly investigated.
“It will take government approval and a coordinated effort to accomplish this, but it will begin to save lives immediately,” says Briggs.
Ron Behrens from the London School of Hygiene and Tropical Medicine agrees that novel methods to tackle the disease are needed. He notes that current vaccines and strategies aimed at the main global reservoirs of the disease, such as dogs and foxes, don’t work in bats because they are harder to access and vaccine-laden baiting doesn’t work.
> Link to full article in PLOS Neglected Tropical Diseases
> Link to WHO Expert Consulation on Rabies
PLOS Neglected Tropical Diseases doi:10.1371/journal.pntd.0002867 (2014)