16.6:
Viral Recombination
Some cells may be infected by two different strains of a virus at the same time causing a mix-up of both genetic sequences in a process called viral recombination. More specifically, after the virus has entered the cell's cytoplasm, they disassemble and begin to replicate their genomes.
Similar regions of each genome can pair together and exchange pieces, reconnecting the strands. Alternatively, the viruses can swap some of their segments in a process called reassortment, in which new viruses made inside the cell can have a mixture of the strains, such as half of their segments from strain one and the other half from strain two.
These newly formed viruses have now evolved from the two original viruses forming populations that may continue to change over time.
16.6:
Viral Recombination
Cells are sometimes infected by more than one virus at once. When two viruses disassemble to expose their genomes for replication in the same cell, similar regions of their genomes can pair together and exchange sequences in a process called recombination. Alternatively, viruses with segmented genomes can swap segments in a process called reassortment.
Viral Recombination Can Create New Diseases
Some diseases can infect multiple species. For example, pigs can be infected by some human and bird viruses, in addition to the viruses that usually infect pigs. Because viruses can recombine when they co-infect the same cell, pigs can act like “mixing vessels” that recombine viruses from other species to create new viruses that can sometimes infect humans. This worrisome phenomenon represents a route through which infectious material from other species can enter the human population. Diseases that move from animals to humans are known as zoonoses. Humans can be highly susceptible to such viruses because we have no history of exposure that would have generated immunity.
Influenza A is a prime example of the “mixing vessel” theory of viral disease. Research has demonstrated that pig, bird, and human influenza A viruses have reassorted inside pig hosts. These events yielded “double reassortant” viruses that contained genes from human and bird viruses and “triple-reassortant” viruses that contained genes from human, bird, and pig viruses. In the Netherlands, a reassortant virus composed of human and bird flu genes was transmitted from pigs to humans.
Suggested Reading
He, Ping, Guojun Wang, Yanning Mo, Qingxiong Yu, Xiong Xiao, Wenjuan Yang, Weifeng Zhao, et al. “Novel Triple-Reassortant Influenza Viruses in Pigs, Guangxi, China.” Emerging Microbes & Infections 7 (May 16, 2018). https://doi.org/10.1038/s41426-018-0088-z.