- Maitreyi Shivkumar
- The Conversation*
Scientists from Brazil recently reported that two people were simultaneously infected with two different variants of SARS-CoV-2, the virus that causes covid-19.
This coinfection appeared to have no effect on the severity of the patients’ disease and both recovered without the need to be hospitalized.
Although this is one of the few cases of this type registered with SARS-CoV-2, and the study has not yet been published in a specialized journal, scientists have confirmed infections with multiple strains of other virusesrespiratory, like the flu.
This has raised questions about how these viruses can interact in an infected person and what it could mean for the emergence of new variants.
Viruses are masters of evolutionThey constantly mutate and create new variants with each replication cycle.
Selective pressures on the host, such as our immune response, also drive these adaptations.
Most of these mutations will not have a significant effect about the virus.
But those that give the virus an advantage, for example, by increasing its ability to replicate or evade the immune system, are cause for concern and should be closely monitored.
The occurrence of these mutations is due to the replication machinery prone to mistakes used by viruses.
RNA viruses, such as influenza and hepatitis C, generate a relatively large number of errors each time they are replicated.
This creates a “quasispecies” of the virus population, something like a swarm of viruses, each with related but not identical sequences.
Interactions with host cells and the immune system determine the relative frequencies of individual variants, and these coexisting variants can affect how it progresses from the disease or how well the treatments.
Compared to other RNA viruses, coronaviruses have lower mutation rates. This is because they are equipped with a review mechanism that can correct some of the errors that occur during replication.
Even so, there is evidence of viral genetic diversity in patients infected with SARS-CoV-2.
The detection of multiple variants in a person could then be the result of the coinfección by different variants, or the generation of mutations in the patient after the initial infection.
One way to discern these two scenarios is by comparing the sequences of the variants circulating in the population with those of the patient.
In the Brazilian study mentioned above, the identified variants corresponded to different lineages that had previously been detected in the population, which implies co-infection by the two variants.
This co-infection has raised concerns that SARS-CoV-2 will acquire new mutations even faster.
This is because coronaviruses can also undergo major changes in their genetic sequence through a process called recombination.
When two viruses infect the same cell, they can exchange much of their genomes with each other and create entirely new sequences. This is a known phenomenon in RNA viruses.
New variants of influenza are generated by a similar mechanism called “reordering”.
The influenza virus genome, unlike the coronavirus, comprises eight segments or strands of RNA.
When two viruses infect the same cellThese segments mix and match to produce viruses with a new combination of genes.
Interestingly, the pigs can be infected with different strains of the virus flu and therefore have been called “mixing containers” that stir them into new strains.
The 2009 H1N1 pandemic virus arose from a rearrangement of one human influenza virus, one avian influenza virus, and two swine influenza viruses.
With coronaviruses, which only contain one strand of RNA in each virus particle, recombination can only occur between strands of RNA derived from one or more viruses in the same cell.
Evidence of recombination has been found both in the laboratory and in a patient infected with SARS-CoV-2, indicating that this could drive the formation of new variants.
In fact, it is believed that the ability of SARS-CoV-2 to infect human cells was developed through the spike protein recombination among closely related animal coronaviruses.
It is important to note that this requires that the two viruses infect the same cell. Even if a person is infected with several variants, if they replicate in different parts of the body, they will not interact with each other.
In fact, this was observed in patients, where different coronavirus quasispecies were found in the upper and lower respiratory tract, indicating that the viruses at these sites did not directly mix with each other.
It is not more serious
The evidence so far does not suggest that infection with more than one variant leads to a more serious disease. And although it is possible, they have been detected very few cases of coinfection.
Over 90% of infections in the UK are currently due to B117, la denominated variant of Kent.
With such a high prevalence of a variant in the population, co-infections are unlikely to occur.
Still, monitoring this landscape allows scientists to track the emergence of these new variants that cause concern and understand and respond to any changes in its transmission or regarding the efficacy of the vaccine.
*Maitreyi Shivkumar es profesora de biologMolecular Science at De Montfort University, in UK.
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Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.