Rodent study backs claim that D614G mutation makes Covid-19 spread faster
COVID-19 | A new study published yesterday has offered some of the first concrete evidence of the D614G mutation’s ability to enhance Covid-19 infectivity.
A team of researchers reported when comparing hamsters infected with Covid-19 with or without the mutation, the infection in the former group appeared to spread faster.
In the experiment, the researchers set up ...
COVID-19 | A new study published yesterday has offered some of the first concrete evidence of the D614G mutation’s ability to enhance Covid-19 infectivity.
A team of researchers reported when comparing hamsters infected with Covid-19 with or without the mutation, the infection in the former group appeared to spread faster.
In the experiment, the researchers set up eight pairs of hamsters for each variant of the virus. Each pair comprised one hamster that was inoculated with the virus a day before, and the other is still susceptible to infection.
They were kept in separate cages with a barrier between them, such that they could not touch but breath the same air.
Researchers checked on the hamsters on days two, four, and six of the experiment and found differences in the timing of the disease’s onset.
On day two, five of the eight hamsters in the group exposed to the D614G variant of the virus were infected, whereas none of the hamsters exposed to the ancestral “wild-type” variant had no infection.
By day four, all hamsters in both groups of the experiment were infected.
“We demonstrate that the D614G variant transmits significantly faster between hamsters through aerosol and droplets,” the researchers wrote.
The study was conducted by researchers based at the University of North Carolina at Chapel Hill, University of Wisconsin, Japan’s National Institute of Infectious Diseases, and the University of Tokyo, and was published in the journal Science yesterday.
It is among the earliest experiments to report animal tests directly comparing the transmissibility of Covid-19 with and without the D614G mutation.
The scientists nevertheless urge caution in interpreting the findings of their study and its real-world implications, particularly in humans.
“The relationship between increased transmission and virulence remains complex and could be impacted by age, sex, and other comorbidities, and it is unclear whether the minimum infectious dose may be lower for D614G in humans.
“It is clearly important to monitor and identify the emergence of new variants of SARS-CoV-2 with increased transmission and pathogenesis and/or altered antigenicity, especially as levels of human herd immunity and active interventions alter the selective forces that operate on the genome,” they said.
The D614G strain is currently the dominant Covid-19 strain around the world and has been detected in at least some Covid-19 clusters in Malaysia, including those in Sabah.
READ MORE: KiniGuide: D614G: The mutation that’s causing Covid-19 to spread even faster
However, scientists have debated for months over whether the mutation itself is responsible for the spread, or whether this is a chance event where the virus was simply in the right time and place to be propelled by the large outbreaks in Europe in March.
The latest study helps build the case that the former is more likely to be true.
The study also differed from previous experiments by using a matched pair of authentic virus lines - one with and one without the D614G mutation - that are otherwise genetically identical.
Many previous experiments had used “pseudoviruses”, such as HIV engineered to produce a key protein involved in Covid-19 transmission. These can be safely handled in laboratories that are ill-equipped to deal with live Covid-19 samples and is a common technique in virology research.
Meanwhile, the researchers also conducted a battery of other tests using the matched pair of viruses.
They confirmed the findings of previous pseudovirus studies that the D614G variant more readily infects and replicates in cells on a petri dish.
When the cells are simultaneously exposed to both the wild-type and D614G variants, the D614G variant eventually becomes the dominant strain on the petri dish. This remained the case even if the initial amount of the wild-type virus outnumbered the D614G variant ten-to-one.
More reassuringly, however, the researchers found that the mutation did not significantly alter the severity of the disease.
It also backed the findings of previous pseudovirus studies that the D614G variant is readily neutralised by antibodies, which suggests that the current crop of vaccines in development would also be effective.
This helps allay the initial fears of some experts that the mutation would render the vaccine candidates ineffective before it is even ready for release.
