Researchers, including those at the Center for DNA Fingerprinting and Diagnostic (CDFD) in Hyderabad, advise testing of asymptomatic primary and secondary contacts followed by surveillance.
“It is important to consider the possibility that infection from asymptomatic patients, who presumably harbor good immunity, spreads to individuals who possess less robust immunity, leading to increased morbidity and mortality,” Murali Dharan Bashyam told PTI. , from the CDFD Molecular Oncology Laboratory.
Reacting to the study’s findings, immunologist Satyajit Rath said he is quite surprised by the finding of higher viral loads in asymptomatic individuals.
“Other studies, as the authors point out, report an upside-down association, if at all,” Rath of the National Institute of Immunology (NII) in New Delhi told PTI.
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The primary goal of the yet to be peer-reviewed study, published on the medRxiv preprint repository, was to identify the dominant viral lineages circulating among the Telangana population, especially in Hyderabad.
The researchers noted that Telangana has seen an unusually high infection rate with a sharp increase seen in the number of cases starting in the second half of April, with 2,734 new cases and nine deaths reported on Tuesday alone, leading the number of cases in the state at 1.27 lakh.
The study analyzed whole genome sequence data from virus samples from 210 patients in and around Hyderabad, and determined the very common mutations in the viral genome.
“We observed that the majority of the study population (more than 95 percent) was infected with clade (or strain) 20B, while some samples belonged to other clades and subclades,” Bashyam told PTI.
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“More importantly, 100 percent of the virus from May to July belongs to clade 20B,” he said.
The scientist pointed out that although the initial entry of the virus into the state came from 2-3 different viral clades, 20B was able to establish itself as the majority strain as of May.
“We also observed a very high prevalence of the D614G spike protein mutation, which has now been shown to be associated with higher rates of virus infection,” Bashyam noted.
The researchers were also able to identify some unique mutations not identified in other studies in India, in a functionally critical region of the virus’ non-structural protein 3 (nsp3), which is responsible for the replication of the viral genome.
According to the scientists, samples collected from late May to July accounted for a higher proportion of asymptomatic cases compared to samples collected earlier.
Most of the samples belonged to the age group between 15 and 62 years, and men (61 percent) dominated the distribution of the profile over women (39 percent), they said.
The scientists compared the distribution of cases with respect to the cycle threshold (Ct) values, which is a proxy for viral load.
Symptomatic cases appeared to be associated with higher Ct values, thus lower viral load, compared to asymptomatic cases, which was unexpected, the study found.
In a real-time PCR test, a positive reaction is detected by the accumulation of a fluorescent signal, and the Ct value is the number of cycles required for the fluorescent signal to cross the threshold or exceed the background level.
There was a reduction in Ct values in the samples tested near the end of June, implying that the newer samples appeared to have a higher viral load than previous samples, according to the scientists.
“We have seen a relatively higher association between asymptomatic cases and viral load. However, this association is highly dependent on multiple factors, including sample demographics, as well as the overall immune health of the patient during collection. shows, “said Bashyam.
He noted that the data correspond to samples collected up to the first week of July, adding that it will be interesting to verify if the trend continued in August-September.
“Viral transmission is based on several factors, but based on our results, it is now important to initiate studies on possible transmission of the virus from asymptomatic patients,” noted Bashyam.
He said that another interesting finding from the study was that most of the samples belonged to the age group 20 to 50 years, and one would expect this age group to have strong immunity.
Bashyam noted that scientists and physicians around the world are continually learning and advising respective governments on the basis of which they can make informed public health decisions.
“In this context, it is important to continue work similar to the one we have done so that the state government can be better informed about the spread of the infection,” Bashyam said.
“We will definitely recommend testing of asymptomatic primary and secondary contacts followed by surveillance,” he said.
Given the wide range of genetic heterogeneity in the Indian population, the scientists said it is difficult to extrapolate the findings to other states in India.
“I think everything it tells us for public policy regarding Covid-19 is what we should already know, that is, that all infections have some potential for transmission,” Rath added.
On video: higher viral load in asymptomatic patients with Covid-19, Indian scientists find
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