• Friday, Mar 24, 2023
  • Last Update : 10:24 am

OP-ED: What happens when a person is simultaneously infected with two variants?

  • Published at 09:54 pm March 4th, 2021
Covid-19 virus coronavirus

The evidence does not suggest that co-infection leads to more disease

Scientists in Brazil recently reported that two people were simultaneously infected with two different variants of SARS-CoV-2, the virus that causes Covid-19. This co-infection seemed to have no effect on the severity of patients’ illness, and both recovered without needing to be hospitalized.

Although this is one of the few such cases recorded with SARS-CoV-2 -- and the study is yet to be published in a scientific journal -- scientists have observed infections with multiple strains with other respiratory viruses, such as influenza. This has raised questions about how these viruses may interact in an infected person, and what it could mean for generating new variants.

Viruses are masters of evolution, constantly mutating and creating new variants with every cycle of replication. Selective pressures in the host, such as our immune response, also drive these adaptations. Most of these mutations won’t have a significant effect on the virus. But ones that give an advantage to the virus -- for example, by increasing its ability to replicate or evade the immune system -- are cause for concern and need to be closely monitored.

The occurrence of these mutations is down to the error-prone replication machinery that viruses use. RNA viruses, such as influenza and hepatitis C, generate a relatively large number of errors each time they replicate. This creates a “quasi-species” of the virus population, rather like a swarm of viruses, each with related but non-identical sequences. 

Interactions with the host cells and immune system determines the relative frequencies of the individual variants, and these co-existing variants may affect how the disease progresses or how well treatments work.

Compared with other RNA viruses, coronaviruses have lower mutation rates. This is because they are equipped with a proof-reading mechanism that can correct some of the errors that occur during replication. Still, there is evidence of viral genetic diversity in patients infected with SARS-CoV-2.

The detection of multiple variants in a person could be the result of co-infection by the different variants, or the generation of mutations within the patient after the initial infection. One way to discriminate these two scenarios is by comparing the sequences of the variants circulating in the population with those in the patient. In the Brazilian study mentioned above, the variants identified corresponded to different lineages that had been previously detected in the population, implying co-infection by the two variants.

Mixing it all up

This co-infection has opened concerns of SARS-CoV-2 acquiring new mutations even more rapidly. This is because coronaviruses can also undergo large changes in their genetic sequence by a process called recombination. When two viruses infect the same cell, they can swap large parts of their genomes with each other and create completely new sequences.

This is a known phenomenon in RNA viruses. New variants of influenza are generated by a similar mechanism called “reassortment.” The genome of influenza virus, unlike coronavirus, comprises eight segments or strands of RNA. When two viruses infect the same cell, these segments mix and match to produce viruses with a new combination of genes. Interestingly, pigs can be infected with different strains of influenza viruses, and have been referred to as “mixing vessels” that shuffle them into new strains. The 2009 H1N1 pandemic virus emerged from a reassortment of a human, avian, and two swine influenza viruses.

With coronaviruses, which only contain one RNA strand in each virus particle, recombination can only occur between RNA strands 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, suggesting that this could drive the generation of new variants. In fact, the ability of SARS-CoV-2 to infect human cells is proposed to have developed via recombination of the spike protein between closely related animal coronaviruses.

It is important to note that this requires the two viruses to 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. Indeed, this was seen in patients, where different quasi-species of coronaviruses were found in the upper and lower respiratory tracts, suggesting that viruses in these sites were not directly mixing with each other. 

The evidence so far does not suggest that infection with more than one variant leads to more severe disease. And although possible, very few cases of co-infection have been reported. More than 90% of the infections in the UK currently are by B117 -- the so-called Kent variant. With such a high prevalence of one variant in the population, co-infections are not likely to occur. Still, monitoring this landscape allows scientists to track the emergence of these new variants of concern and understand and respond to any changes in their transmission or vaccine efficacy.

Maitreyi Shivkumar is Senior Lecturer in Molecular Biology, De Montfort University. This article was previously published by The Conversation, and has been reprinted by special arrangement.

Facebook 334
blogger sharing button blogger
buffer sharing button buffer
diaspora sharing button diaspora
digg sharing button digg
douban sharing button douban
email sharing button email
evernote sharing button evernote
flipboard sharing button flipboard
pocket sharing button getpocket
github sharing button github
gmail sharing button gmail
googlebookmarks sharing button googlebookmarks
hackernews sharing button hackernews
instapaper sharing button instapaper
line sharing button line
linkedin sharing button linkedin
livejournal sharing button livejournal
mailru sharing button mailru
medium sharing button medium
meneame sharing button meneame
messenger sharing button messenger
odnoklassniki sharing button odnoklassniki
pinterest sharing button pinterest
print sharing button print
qzone sharing button qzone
reddit sharing button reddit
refind sharing button refind
renren sharing button renren
skype sharing button skype
snapchat sharing button snapchat
surfingbird sharing button surfingbird
telegram sharing button telegram
tumblr sharing button tumblr
twitter sharing button twitter
vk sharing button vk
wechat sharing button wechat
weibo sharing button weibo
whatsapp sharing button whatsapp
wordpress sharing button wordpress
xing sharing button xing
yahoomail sharing button yahoomail