DANIEL STREICKER
laboratories across the U.S. allowed us to assemble an unprecedented dataset for a wildlife disease. This dataset was comprised of hundreds of viruses from many different bat species from geographically widespread regions of the country across a 10-year period. We chose to focus the research on crossspecies transmission because it is the most important mechanism by which new diseases emerge in both humans and wildlife, but surprisingly little is known about how often it happens in nature, between which species it happens and whether transmission is likely to lead to a single isolated case or the next pandemic. In short, we saw the bat and rabies as a tractable system to address critical basic questions about how viruses emerge, while contributing to our understanding of an important zoonotic disease. Graduate School Magazine: Your database was enormous. What did the rabies study reveal about transmission? Streicker: First, we found that cross-species transmission is actually a surprisingly common event in the North American bat community, but one that from the virus’s perspective is almost always doomed to failure–most crossspecies transmissions fail to establish ongoing infections in the recipient species. Second, when we examined which species were most likely to infect each other, we found that the most important factor was not the ecological or geographic overlap of species, but rather how closely related the bat species were. In essence, the virus is much more likely to be transmitted between closely related bat species than distantly related bat species and
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once that initial transmission happens, permanent viral establishment is much more likely between close relatives. These results suggest that the biological or ecological similarity of closely related species effectively reduces the barriers that viruses must traverse in order to emerge in new species. At least for the bat rabies system, these results predict that the most likely source of a new virus for a bat is not its ecological neighbor, but its evolutionary relative. Graduate School Magazine: Can you tell us something about how you used gene sequencing? Streicker: Sequencing of both bat DNA and rabies virus RNA was absolutely critical to the success of this study. Bats can be difficult to identify to species based on morphology alone and we didn’t always have the complete specimen to verify that the initial species identification was correct. Obviously, if you don’t know what species you are dealing with, you can’t say much about cross-species transmission, so we sequenced the DNA of the bats to confirm their species identities. Our use of molecular sequence data from rabies virus was a totally novel way to quantify cross-species transmission. This represents a substantial advantage over historical methods to quantify cross-species transmission because of the declining cost of producing genetic sequence data and the growth of surveillance programs for wildlife diseases, which will produce more datasets like ours in the near future. My co-authors and I think that this framework holds great promise for describing the frequency of cross-species transmission in a variety of natural systems, many of which, like rabies, have important implications for human and animal health. Graduate School Magazine: You subsequently co-authored the paper on cross-species transmission of rabies that published in Science magazine last August. Were any of your fellow researchers doctoral students? Streicker: When the project was initiated, one of my co-authors, Amy Turmelle, was a graduate student at the University of Tennessee-Knoxville who was also doing her
In the case of rabies, the folklore is so surprisingly similar to the biology that it has been suggested that rabies was actually a driving factor in the development of the Eastern European vampire legends.
dissertation research in the CDC Rabies Laboratory; however, Amy graduated before the paper came out and is now a postdoctoral fellow in the CDC Rabies Laboratory. Graduate School Magazine: Exterminators warn that bats can gain entry to home attics via unsealed louvers. Should the general public be concerned about bats as a public safety issue? Streicker: Bats are reservoirs of rabies throughout the country, so contacts between bats and humans should be minimized. The rabies risk that bats pose to the general public is typically very low; however, if bats are entering the living space of a house this risk is heightened, particularly when the household includes young children or other people who might not recognize or report contact with a bat. If bat bites are detected and postexposure treatment is initiated in a timely manner, the risk of developing rabies is almost non-existent; however, rabies is a fatal disease when left untreated, either through ignorance of the risk associated with a bite or through failure to recognize a bite. Graduate School Magazine: Through a grant recently awarded by the National Science Foundation, your work continues with vampire bats in Peru in conjunction with the Peruvian Ministries of Health and Agriculture and the University of San Marcos. Does the old vampire and bat folklore only serve to trivialize a serious issue? Does this intrigue or irritate you? Streicker: Both rabies and folkloric vampires are associated with cycles of biting, aggression, hypersensitivity, disrupted sleeping patterns and other changes in behavior, so the symptoms of each mirrors the other. To me, these interactions between infectious disease and popular culture are much more a fascinating testament to the importance of infectious diseases in historical and modern