Julia Shi

According to new research from Yale, viruses may be able to better adapt to new types of host cells when those new host cells are introduced to the environment gradually, rather than suddenly.

Researchers studied two situations in which a virus was exposed to a new type of host, said Valerie Morley GRD ’16, a postdoctoral researcher at Penn State University and study co-author. In the first situation, the researchers rapidly shifted the virus’s environment so that the only available hosts were a cell type the virus had not previously encountered. In the second scenario, the researchers gradually increased the prevalence of new host cells in the virus’s environment, Morley added. The researchers looked at how the virus evolved in the two different environments, discovering that viruses adapted better when the new host cells were introduced slowly, according to the study.

“We found that a gradual change more often resulted in viruses that were well adapted to the new host,” said Morley. “Both types of environmental change can result in viruses that adapt to a new host, but this study suggests that there is greater opportunity when the composition of the host community changes gradually.”

The researchers used whole-genome next-generation sequencing to investigate how the virus populations were evolving in each situation, according to the study. Morley observed that the “patterns of evolution at the genetic level were different when the new host was introduced suddenly versus gradually.”

Morley noted that an example of sudden change within a real-life context might be a person who contracts a virus from an animal market and then returns home to a densely populated city. From the virus’s perspective, Morley explained, it is abruptly transferred to an environment in which the only available hosts are humans — a previously unknown species.

In contrast, a real-life scenario of gradual change could be when a new animal species invades a new environment.

“At first, local viruses might only be exposed to the new species very occasionally, but over time, the virus will encounter the new species more and more frequently,” she added.

According to Morley, there is growing public health concern about emerging viral diseases like SARS, Zika and Ebola. Noting that these viruses often originate in animal populations, Morley said viruses that spill over from animal into human populations can evolve to spread more effectively.

Morley said she would like to explore what is happening at the genetic level when these viruses adapt to the new host, adding that the evolutionary path a virus takes may be constrained by the first mutational steps the virus takes. Understanding these constraints could help researchers better predict how viruses are likely to evolve, she added.

According to the Centers for Disease Control and Prevention, viruses that have spread from animal populations to human populations include bird flu, SARS and HIV.