Viral reassortment

In virology, reassortment refers to the exchange or mixing or redistribution of genetic information between two similar viruses. In most cases, this involves variants or subtypes of a viral species or closely related species within a viral genus.

Reassortment is only possible under natural conditions when:

• the two virus types replicate in the same infected cell, and
• their genome consists of several segments (fragmented genome).

The exchange of fragmented genomes (multiple pieces of nucleic acid form the complete genome), in addition to the simple exchange of bases, leads to a high variability of genetic information. A typical example of this is provided by the influenza virus, which uses this type of mutation to create new types of virus.

Condition No. 1 can only be fulfilled if two virus types can also infect the same host, as only then can their genomes be located in the same cell. Viruses that are not fixed to a single host, i.e. have low host specificity or can frequently adapt to a new host through variants (host switching: bird/human; term avian influenza: mutant influenza viruses can infect both humans and birds), reassort more frequently because more hosts and thus more viruses are available to them for reassortment. The transmission of a new influenza strain (H5N1) from poultry to humans can be considered an example (Honkong 1997). 20 people were infected, 1/3 fatally. No human-to-human transmission.

Condition No. 2 is fulfilled only in some virus families characterized by a segmented genome.

A distinction is made between

• reassortment in viruses with a segmented genome (as in influenza viruses), in which the individual nucleic acid strands remain unchanged
• and
• homologous recombination within such a segment, which is also possible in viruses with an unsegmented genome (as in the coronaviruses).