The study – led by researchers at the Universities of Glasgow and Michigan, and published in Nature Ecology and Evolution – found that a low effort vaccination programme could substantially reduce rabies transmission in wild vampire bats, thereby reducing the risk of lethal infections in humans and livestock.
The fluorescent gel – called Rhodamine b – was applied topically to bats in three colonies in Peru, where it acted as a marker to simulate the bat-to-bat spread of an oral rabies vaccine. Such vaccines have already been shown to protect multiple bats against rabies for every individual vaccinated in the laboratory, but their levels of spread in wild bats was until now unknown.
When the gel was ingested by bats that groomed each other, it led to fluorescence in the bats’ hair follicles, which was then monitored by fluorescent microscopic analysis of hair samples collected by the scientists.
Where common vampire bats routinely feed on human blood, rabies is estimated to cause up to 960 deaths in every 100,000 people, while losses from livestock mortality exceed $50 million annually, disproportionately affecting impoverished, rural communities.
Existing management strategies have been unable to mitigate the burden of rabies, with uptake of protective vaccines for humans and livestock limited by high costs and inaccessibility to remote areas.
Another strategy, poisoning the bats to reduce their populations, is controversial and has had mixed results for rabies control.
Dr Daniel Streicker, Senior Research Fellow at the University of Glasgow’s Institute of Biodiversity, Animal Health & Comparative Medicine (IBAHCM) and the MRC-University of Glasgow Centre for Virus Research, said: “Vampire bat rabies still has severe medical and agricultural impacts across North, Central and South America despite decades of efforts to mitigate its burden.
“Our findings demonstrated that bat-to-bat transfer oral rabies vaccines could increase population-level immunity up to 2.6 times beyond the same effort using conventional, non-spreadable vaccines.
“Until recently, controlling diseases in reclusive animals like wild bats seemed unimaginable.
“Our findings reveal the exciting potential for using a new generation of spreadable vaccine technologies to protect human and animal health by fighting diseases within their wildlife hosts.”
The scientists used mathematical models to demonstrate that observed levels of vaccine transfer would reduce the probability, size and duration of rabies outbreaks, even at low, but realistically achievable levels of vaccine deployment.
Models further showed that spreadable vaccine would control rabies more effectively than the current policy of killing the bats with a poisonous gel that spreads by the same route of contact and grooming.
Kevin Bakker, National Institutes of Health Research Fellow at the University of Michigan and former postdoctoral scientist at IBAHCM said: “Because rabies relies on vampire bat movement between colonies, a strategic switch from poisoning to vaccination would increase immunity and may lead to a dramatic reduction in rabies across Latin America.
“Hopefully this is just the first step in evaluating spreadable vaccines to control disease transmission across a multitude of pathogens and hosts.”