Genetic forecasting of male-driven invasions of vampire bat rabies
Pathogen invasions across landscapes are increasingly common. From Zika and Ebola viruses in humans to White nose syndrome and Chytrid fungus in wildlife, these invasions have profound importance, but are notoriously difficult to predict. We recently showed that rabies virus – long considered an endemic virus of vampire bats – is actually an emerging virus, spreading across landscapes in highly predictable wavefronts and causing major losses to livestock and human health as the virus hits large, historically rabies-free bat populations. In our current paper, now out in PNAS, we use genetic data from vampire bats and rabies viruses to show that these invasions are likely driven by the dispersal of highly mobile male bats, not by more sedentary females. Moreover, genetic inferences of bat population structure provided a roadmap of how rabies could spread across the landscape through patterns of bat movement. This viral invasion forecast was validated by an independent dataset on livestock rabies mortality. If invasions continue at the rates and trajectories that we predict, vampire bat rabies could invade the Pacific coast of South America for the first time in recorded history as soon as 2020, which would have serious implications for livestock management practices across several countries. Now work is needed to assess the value of rabies control strategies that target male bats and to figure out what triggers invasions to new populations in the first place. Stay tuned.
Vampire bat rabies free areas on the Pacific coast of Peru might soon become infected as bat populations become more connected, allowing rabies to spread. Photo: Streicker
Some nice press on this paper from:
NPR, NSF, University of Georgia & University of Glasgow
Streicker, D.G., Winternitz, J., Satterfield, D., Condori-Condori, R.E., Broos, A., Tello, C., Recuenco, S., Velasco-Villa, A., Altizer, S., Valderrama, W. Host-pathogen evolutionary signatures reveal dynamics and future invasions of vampire bat rabies (2016) Proceedings of the National Academy of Sciences of the USA DOI: 10.1073/pnas.1606587113
Predicting advancing wavefronts of vampire bat rabies
Our latest set of analyses of data from the Ministry of Agriculture of Peru, together with our own questionnaire data, show that rabies continues to spread to the fringes of the vampire bat distribution in surprisingly constant and predictable wave-like expansions. The ability to forecast when and where rabies will appear next provides a tantalizing opportunity to develop interventions like vaccination of humans and livestock (or perhaps even the bats themselves) before rabies arrives to new regions. Hopefully this puts us one step closer to preventative rather than reactive management of vampire bat rabies.
Forecasting traveling waves of vampire bat rabies using simple landscape-adjusted linear regression models. Pie charts show the percentages of farms reporting bat bites (green), indicating the presence of vampire bats ahead of wavefronts. Blue and red points are the locations of rabies outbreaks in livestock.
The paper is published free online at Proceedings of the Royal Society B.
Julio and I also wrote a short piece in The Conversation describing the results of this analysis against a broader context of vampire bat rabies in Latin America.
Benavides, J., Valderrama, W., & Streicker, D.G. Spatial expansions and travelling waves of rabies in vampire bats (2016) Proceedings of the Royal Society B. DOI: 10.1098/rspb.2016.0328
Land use, vampire bat feeding and rabies
A stable isotope analysis of bat hair, stomach contents and possible prey species showed some expected things, like that bats specialize on livestock prey when they don’t have any other options. But there were also some surprises. For example, on the coast of Peru vampire bats in the same colonies fed on very food resources spanning primary consumers to top predators. Similarly, in the Amazon rainforest, we found evidence of individuals that fed mostly or exclusively on livestock living next to individuals that fed mostly on wildlife. This led to some of the largest within-population variability in carbon and nitrogen stable isotopes ever recorded in animals, suggesting that when it comes to feeding, these bats have personality and stick to what they know. Another surprise was that the diversity of dietary strategies tended to decline with the local availability of livestock, diets were most diverse in places where there were some livestock and some wildlife available – these were also the kind of places where we found bats feeding on people. But, once livestock became abundant, bats seemed to switched entirely to this relatively easy prey source. In the Amazon, this seemed to be a good thing for human health: bat bites on people were common in places without livestock but totally absent where bats were specializing on domestic prey. All of this is interesting from a disease transmission standpoint because as land use change and human behavior alter bat feeding behavior, they also alter which species are at risk for rabies infection. Next up, we will conduct genetic analysis of bat blood meals to find out exactly which species are bitten and Dan will investigate whether dietary differences among bat colonies affects bat immunity and infection.
The paper is published free online at Journal of Applied Ecology.
Streicker, D.G. & Allgeier, J.E. From food web to disease ecology: foraging choices of vampire bats in diverse landscapes (2016) Journal of Applied Ecology. DOI: 10.1111/1365-2664.12690