Finding the Virus Vectors
During the first year of the pandemic, there was growing worldwide consensus that COVID-19 was spread primarily through respiratory means. It was also shown quite early in the pandemic that transmission from presymptomatic/asymptomatic carriers was a virus vector as well.
The reported respiratory studies drove the vast majority of research and focus to those areas, and reporting on the ways to prevent respiratory transmission quite effectively pushed states and governments into requesting and then mandating the use of face masks. New infections did show drops after masks became the rule and the subsequent development of mRNA-based vaccines showed to be extraordinarily effective at preventing patients from getting the virus.
However, a recent study published in Nature Medicine has shown that SARS-CoV-2 may be spread through saliva, as well. While the study was quite small, it may well show a way to limit the spread of SARS-CoV-2 by asymptomatic carriers. Researchers Kevin M. Bird, D.D.S., Ph.D., and Blake M. Warner, D.D.S., Ph.D., published the study in March 2021.
According to the model published in the JAMA Open Network, more than 50 percent of all infections were transmitted by those without symptoms. This puts public health officials into the quandary of dealing with a population that does not know that they are ill still moving about, transferring the infections they carry to others.
While there has been some disagreement of how effective it is to simply keep as many people as possible isolated and thus not spreading infections, in order to find out whether isolation is effective, there had to be a good estimate of how many people a) don’t have the virus, b) have the virus and haven’t started showing symptoms as yet, c) have the virus but have no symptoms or extremely mild ones, or d) have the virus and symptoms that vary from feeling ill to life-threatening. The same research notes that those who have the virus but no symptoms are apparently just as likely to transmit the disease as someone with symptoms. Unfortunately, they are probably the least likely to be tested.
Minor Symptoms Are Easy to Miss
The study by Bird and Warner notes that certain persons with COVID-19 have oral symptoms that include a loss of taste (often directly associated with a loss of smell) as well as oral lesions and xerostomia. As part of the study, these researchers were also working with asymptomatic carriers. They exposed saliva from eight individuals who were infected with the virus but without symptoms to cells known to be virus-free. One-fourth of the healthy cells became infected, showing a possible oral transmission route for the virus from asymptomatic carriers.
In another, 35 volunteers with COVID-19 and with either minor symptoms or asymptomatic, Bird and Ward also found a correlation between lack of both smell and taste if the infection was present in their saliva. The research is important in order to diagnose another vector for this virus as well as begin to develop a possible weapon against the virus for those who are unwilling or unable to obtain a vaccine.
In closing, the researchers state, “Our findings highlight how simultaneous testing of oral and NP (nasopharyngeal swab) sites might be required to fully understand SARS-CoV-2 spread. Moreover, our findings might partially explain some false-negative tests using only NP or saliva testing. However, these results raise new questions about COVID-19 pathogenesis, including 1) whether this is primarily a ‘nasal-first’ infection that spreads to the oral cavity, 2) the possibility of an ‘oral-first’ infection via droplet/aerosol inoculation or fomite ingestion, and/or 3) whether the pattern of infection affects disease severity and host immunological responses. To test whether oral transmission can precede nasal infection and/or occur in the absence of nasal infection, it will be necessary to design studies that include daily surveillance using NP and salivary tests in an at-risk cohort.”