Herpesviruses Not as Host-specific as Once Thought

According to a recent study published online in the journal MBio, herpes viruses may not be as host-specific as scientists have previously thought they were.

“Cross-species transmissions have occurred much more frequently than previously estimated, and most of the transmissions were attributable to bats and primates,” write Dr. Marina Escalera-Zamudio, from the Leibniz Institute for Zoo and Wildlife Research (IZW), Berlin, Germany, and colleagues.

Although herpesviruses can infect humans and other animal species, these viruses have long been considered to be highly host specific and to share a long evolution in synchrony with their hosts. They comprise three groups: alpha-, beta-, and gamma-herpesviruses.

Gammaherpesviruses, in particular, cause latent infections that persist throughout the host animal’s life, but they typically cause disease only in naive or immunosuppressed individuals. Two gammaherpesviruses of interest are Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV), both of which infect lymphoid and epithelial cells and are implicated in the development of cancer.

Although gammaherpesviruses have been detected in different bat species, detailed investigation of the evolutionary history of these viruses has been lacking, the researchers explain.

With this in mind, they conducted a study to test the hypothesis of host-restricted virus coevolution within gammaherpesviruses. Using their own sequencing data as well as publicly available data—including those from viruses from many bat species—the researchers produced the largest dataset of gammaherpesvirus sequences to date. Next, they analyzed the data to investigate the relationships of the viruses with each other, as well as with their host animals.

Dr. Escalera-Zamudio and colleagues found that cross-species gammaherpesvirus transmissions have occurred frequently in the past—contrary to the traditionally held belief that these viruses are host specific. According to the researchers, bats were the most common source of the switches, and primates were the second most common source.

In particular, they found that gammaherpesviruses in hairy-legged vampire bats and common vampire bats and were similar to those in cattle. “Vampire bats have been selectively feeding on the blood of cattle since their introduction in the Americas, as they represent an easily accessible food source,” the authors say, adding that some of the cattle gammaherpesviruses in vampire bats might have been introduced into these bat species as a consequence of dietary specialization.

However, they also note that feeding ecology may not be an essential factor for cross-species transmission of gammaherpesviruses, suggesting that bat traits (such as flight, large population sizes, and a wide geographical range) might also have contributed to, or increased, switching of gammaherpesviruses from bats to other species.

“[F]uture analyses using other viral genomic regions and a greater sampling of viral diversity should help to clarify the full extent and timing of viral cross-species transmission at different evolutionary timescales,” the authors conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.