Scientists report that SARS-CoV-2 infects oral cells
SARS-CoV-2, the virus that causes COVID-19, infects cells in the mouth, according to a study published today in Nature Medicine. This could change perceptions on how the virus travels to the lungs or the digestive system as well as how it is transmitted from person to person, the researchers write.
The investigators created a map of the mouth’s tissues and found some salivary gland and gum cells were vulnerable to the virus because of their potential to create ACE2 and TMPRSS2 proteins, or the entry points of SARS-CoV-2 infection. To confirm their suspicions, they looked at 18 COVID-19 cadavers, of which 88.9% had the virus in their salivary glands. Infection was also found in two sets of tissues, affecting five of six mucosal sites.
In 39 living people with COVID-19, those who were asymptomatic (22%) were associated with a 1-week quicker average viral clearance time (range, 0.5 to 3.5 weeks) than that of symptomatic participants. In symptomatic patients, saliva infected with SARS-CoV-2 was associated with a 4.8-fold likelihood of altered taste and smell (95% confidence interval, 1.14 to 19.98).
After exposing saliva from eight people with asymptomatic COVID-19 to lab-grown cells, the researchers noted that infection occurred in 25%. Salivary glands appeared to have the ability to mount immune responses, though, as an analysis of the larger cohort showed immunoglobulin G antibodies against nucleocapsid antigens (73.3%, 22 of 30) and spike antigens (53.6%, 15 of 28), both of which were measured to 9 weeks post-COVID confirmation.
The researchers conclude, “Matched nasopharyngeal and saliva samples displayed distinct viral shedding dynamics, and salivary viral burden correlated with COVID-19 symptoms, including taste loss. Upon recovery, this asymptomatic cohort exhibited sustained salivary IgG antibodies against SARS-CoV-2.”
“Our study could open up new investigative avenues leading to a better understanding of the course of infection and disease,” lead author Blake M. Warner, DDS, PhD, MPH, said in a National Institutes of Health (NIH) and National Institute of Dental and Craniofacial Research (NIDCR) press release. “Such information could also inform interventions to combat the virus and alleviate oral symptoms of COVID-19.”
Mar 25 Nat Med study
Mar 25 NIH/NIDCR press release
B117 variant exhibits higher transmission rates
The B117 COVID-19 variant, which was first identified in the United Kingdom, may have a 50% to 100% higher reproduction rate, according to a study published in Nature today. This finding echoes recent studies such as a Science article published at the beginning of March.
The researchers looked at 31,390 B117 and 52,795 non-B117 whole-genome SARS-CoV-2 sequences with known time and location of collection from Oct 1, 2020, to Jan 16, 2021, as well as samples with S-gene target failure (SGTF) results from mid-November, when more than 97% of confirmed SGTFs indicated B117 lineage.
While the variant of concern (VOC) was originally concentrated in London (9,134), South East (5,609), and East England (4,413), the researchers say that, since Jan 16, it is widely distributed across the country and became the majority strain on Dec 3 The researchers also note that it affects a larger proportion of people under 20 than non-B117 strains do.
The additive growth rate differences between B117 and non-B117 strains was 0.69 per week (95% credible interval [CrI], 0.61 to 0.76), which peaked in November and then declined to 0.43 (95% CrI, 0.33 to 0.52) by the study’s end. Further modeling suggested that the reproduction ratio of B117 to non-B117 strains is 1.89 (95% CrI, 1.43 to 2.65), and the researchers add that even if B117’s generation time is actually half that of previous variants, the ratio lowers to only 1.53 (95% CrI, 1.27 to 1.79).
“Analysis of trends in SGTF and non-SGTF case numbers in local areas across England shows that the VOC has higher transmissibility than non-VOC lineages, even if the VOC has a different latent period or generation time,” the researchers conclude.
Mar 25 Nature study