The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has claimed the lives of over 5.1 million people since the World Health Organization declared COVID-19 a pandemic in March of last year.

There has been an increase in the number of COVID-19 cases worldwide since the appearance of SARS-CoV-2 Delta variants.

There are three ways in which SARS-CoV-2 can be transmitted: droplets, direct contact, and aerosols. Moreover, saliva contains infectious virions released from oral epithelia and salivary glands.

In this paper, the team hence says that a higher viral load of Delta variants in saliva than their parental wild-type strains contributes to their high transmissibility in the first place.

To compare the viral load, they utilized whole saliva specimens collected from individuals visiting a fever outpatient clinic at Nagoya, Japan, at different time points before and after the emergence of Delta variant (November and December, 2020 and August and September, 2021, respectively).

A prominent clinical laboratory, Bio Medical Laboratories Inc (BML) in Tokyo, Japan, studied virus-positive saliva samples with the L452R mutation.

To determine viral load as viral copy number, extraction of viral RNA and real-time quantitative polymerase chain reaction (qPCR) were conducted referring to a method provided by the National Institute of Infectious Diseases of Japan (4). Simultaneously, using synthetized standard viral RNA, RNA levels were measured using Poisson’s null distribution equation.

Mann–Whitney’s U-test or Wilcoxon’s signed-rank test was used to compare the viral copy number between the variants and wild-type strains. Viral localization in saliva, i.e., whether virions are associated with host cells or floating away from them, was investigated by comparing the viral load between whole saliva and supernatant samples after centrifugation (10000 × g, 5 min).

Additionally, the proportion of host cells isolated through the centrifugation was revealed with human chromosome-specific qPCR to be 99.5%, and it was not found in the supernatant.

Saliva samples from 22 wild-type strain-positive individuals (12 males, 39.5 ± 18.6 years of age and 2.6 ± 1.4 days since onset of symptoms) and 32 L452R mutation-positive individuals (20 males, 32.4 ± 14.8 years old and 3.6 ± 2.6 days since onset) were collected.

Average age (p = 0.12), gender (p = 0.57), or days since symptoms began (p = 0.096) did not differ significantly across groups.

The study found that Delta variants’ median copy number (1.86E+7, IQR: 3.16E+6~8.03E+7) was 15.1 times significantly higher than wild-type strains (1.23E+6, 1.76E+5~2.70E+7) per milliliter of whole saliva (Mann– Whitney’s U-test: p = 0.020).

The findings concluded that saliva from people who have been infected with DELTA covid variant contains 15 times more virions than saliva from people who have been infected with wild-type strains and this is what makes it more dangerous and infectious than other covid mutations.

Important note:

This study was published on preprint server medrxiv, and you should be aware that preprints are unconfirmed reports of work that hasn’t been peer-reviewed. They should not be used to guide clinical treatment or health-related behavior, and the news media should not present them as fact.

Source: medrxiv

Image Credit: Getty

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