A first look at how rabies affects the social behavior of vampires

According to a new study, vampire bats infected with the rabies virus are less likely to behave in a stereotypical “rabid” manner — instead, infected male bats tend to withdraw socially, reducing the common habit of caring for each other before they die of disease.

The study was the first to observe how rabies affects the social behavior of vampire bats, and one of only a few research efforts to understand how rabies infection affects behavior in one of the species most responsible for causing rabies outbreaks in humans and livestock in Latin America. The virus is usually transmitted to other species by direct contact between the saliva of infected bats and the broken skin of livestock or other animals (and rarely bite humans) to feed on blood.

Gerald Carter, senior author of the study and assistant professor of Evolution, ecology, and organic biology at The Ohio State University.

“Despite this possibility, no previous studies have attempted to identify changes in the grooming habits of rabies-infected vampire bats,” Carter said. “This could be the tendency of vampire bats to Withdrawing from social activity when sick What we have seen in our previous work reduces the likelihood of transmitting rabies to group mates despite living in close quarters within the roost.”

The study was first led by co-authors Sebastian StockmeierOhio State University, Chair Postdoctoral Professor in the Carter Lab, Elsa Kardenas-Canales, then a doctoral student and now a postdoctoral researcher in pathological biosciences at the University of Wisconsin-Madison.

The research was recently published in the journal Biology Letters.

Previous research in a variety of animal and human species has shown that there are two observed responses to rabies infection: “angry” symptoms of increased aggression, or “paralytic” symptoms that lead to lethargy and paralysis. A severe response is expected to increase transmission to other hosts.

In this work, the researchers outfitted a lab with infrared surveillance cameras to monitor 40 male common vampire bats that were part of a larger sample of bats used to test a candidate rabies vaccine. Groups of bats that underwent three treatments — oral vaccination, topical vaccination or placebo — were put together in cages for four months before being challenged with a wolf type of rabies virus.

One day after the challenge, the team began measuring behaviors from three sample periods each night, recording the absence or presence of either grooming or aggression. The team analyzed 18,808 behavioral samples to estimate behavior rates.

“We were generally interested in how social behaviors that might be related to rabies transmission – allosteric grooming and aggressiveness – changed when vampire bats were infected,” Stockmeyer said.

All bats showed low rates of aggressiveness, and compared to their healthy mates, rabid vampire bats showed a decrease over time in giving and receiving grooming. The effect was first seen about 12 days after inoculation with the virus and increased in strength when the bats died.

Researchers cannot be sure what caused the drop in grooming—whether it came from a general immune response that made bats sick and lethargic, and thus less social, or from a central nervous system malfunction from rabies infection.

con merdenas-Canales noted that signs of aggressive or paralytic forms of rabies are the last to appear before the animal dies – suggesting that transmission of the disease can occur without any obvious changes in behaviour.

“In some cases, asymptomatic bats fly, feed and react normally while having contagious saliva — making every bite, by feeding or fighting, contagious,” she said. “We can learn more by measuring how often bats in their saliva excrete virus in their saliva and feed by others, and what that might mean for rabies transmission.”

The findings, in male vampire bats, which can be aggressive toward each other, actually raise a question about a common notion related to rabies infection — that the virus manipulates its host to become aggressive to improve the chances of transmission of the virus.

“Rabies may not have to manipulate its host’s behavior if the host is frequently aggressive anyway or if it is likely to bite other animals to feed it,” Stockmeyer said. “It has yet to be tested.”

Another possible explanation for not noticing increased aggressiveness is that the behavioral effects of rabies are highly variable and may vary by viral strain. The researchers noted that bats infected with variants from other populations or species did not show obvious “angry” rabies in six other cases, but three observational studies reported signs of increased aggressiveness, all of which were in vampire bats that were naturally exposed to rabies. dog in the wild

This work was supported by the National Science Foundation, the US Geological Survey, the Institute of Global Health and the Institute for Regional and International Studies at UW-Madison.

Carter is an affiliate of the Smithsonian Tropical Research Institute. Other co-authors include Eleanor Cronin of Ohio State, Tony Rock of the USGS-National Wildlife Health Center, and Jorge Osorio of the University of Washington-Madison.

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