Culling vampire bats to stop rabies can backfire

Culling vampire bat colonies to stem the transmission of rabies in Latin America does little to slow the spread of the virus and could even have the reverse effect, according to University of Michigan researchers and their colleagues.

Vampire bats transmit rabies virus throughout Latin America, causing thousands of livestock deaths each year, as well as occasional human fatalities. Poison and even explosives have been used since the 1960s in attempts to control vampire bat populations, but those culling efforts have generally failed.

Last year, a team of U-M researchers and their University of Georgia colleagues reported the results of a long-term vampire bat field study in Peru. Now, the same team has combined the field findings with new computer models of rabies transmission and data from infection studies using captive vampire bats to show that culling has minimal effect on containing the virus, and can, in some cases, actually increase its spread by driving infected bats into neighboring colonies.

The findings suggest that geographic coordination of vampire bat control efforts in Latin America—taking into account the interconnectedness of seemingly isolated colonies—might reduce transmission to humans and domestic animals. The team’s new paper, scheduled for online publication in the Proceedings of the National Academy of Sciences on Dec. 2, also establishes that rabies is usually not lethal among vampire bats.

“In the paper last year, we demonstrated that bat colony size wasn’t a predictor of rabies prevalence, which indicated that culling hadn’t reduced transmission,” said U-M population ecologist and epidemiologist Pejman Rohani, senior author of the PNAS paper (the first author is Julie Blackwood, a former postdoctoral research associate in Rohani’s lab who is now at Williams College).

“In the current paper, we do a number of things. First, we fit models that encompass alternative assumptions regarding this system and we identify an important role of movement between colonies. We then use the best-fitting model to examine what happens under culling, especially if the cull is indiscriminate, rather than targeting infected bats specifically. Again, culling is shown to be ineffective, but now the model helps us understand why that is.”

Developing effective control strategies for vampire bat-transmitted rabies virus in Latin America requires an understanding of the mechanisms that have allowed the highly virulent pathogen to persist despite control efforts. But understanding the persistence mechanisms has proved elusive, despite recognition of the virus and its health risks since the early 1900s.

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