It is starting to appear likely that there is a significant variation in susceptibility to Covid-19, with some infected individuals essentially asymptomatic, and with children, apparently, relatively unaffected by life-threatening infections.
This variation points to the importance of further investigation of mechanisms that might be involved in resistance and how these may vary from one person to another. It is virtually certain that there are other aspects of a body’s ability to fend off infection besides the ability to quickly produce antibodies. Could the environment on bodily surfaces where virus particles first land be important?
Several well publicized reports have indicated that virus survival on different types of surfaces varies significantly. For example, Covid-19 is reported to survive intact much longer on plastic surfaces than it does on copper surfaces. Could bodily surfaces vary in ways that also inhibit or enhance viral survival and penetration?
One readily measured aspect of body fluids and associated surfaces that is known to be associated with certain disease conditions is pH. Might pH and/or alkalinity of saliva, mucous, and related surfaces of the upper respiratory tract be involved in resistance to viral infection?
The infectiousness of another coronavirus, MHV-A59, has been found to be extremely sensitive to pH; at 37 degrees C that virus was stable at pH 6.0 with a half-life of 24 hours but it was rapidly and irreversibly inactivated by brief treatment at pH 8.0 (Sturman, Ricard & Holmes, 1990). Another study (Heleinius, 2013) found that for most viruses, a drop in pH serves as a trigger for host penetration, and infection of at least one virus (SFV) was prevented by weak bases such as ammonium chloride and chloroquine; this prevention involved inhibition of virus entry.
The pH of various tissues and bodily secretions appears to vary considerably not only within one’s body but from one person to another. For example, pH of saliva is reported to vary from 6.2 to 7.6, with adults tending to have more acidic saliva than children (Frothingham, 2018). The pH of nasal mucus is approximately 5.5 to 6.5 and increases in rhinitis to 7.2 to 8.3 (England, et al. 1999). Is an increase in nasal mucus pH in people suffering from rhinitis the result of disruption by the ailment’s causal agent such as pollen or a virus, or a deliberate change by the body in an effort to deactivate that causal agent?
As data on Covid-19 disease accumulates, it could be important to correlate physiological measurements with infection severity. The pH and alkalinity of key bodily surfaces and media should be relatively easy to measure and may be subject to modification. Might variations in these parameters play a role in resistance to Covid-19? It should not be difficult to gather data that would shed light on this question.
References
England, R.J., J.J Homer, L.C. Knight, and S.R. Ell, 1999, Nasal pH measurement: a reliable and repeatable parameter, Clin. Otolaryngol Allied Sci. 24, 67-8
Frothingham, Scott, 2018, What is the pH of saliva? Healthline, https://www.healthline.com/health/ph-of-saliva accessed 4-15-20.
Helenius, Ari, 2013, Virus entry: What has pH got to do with it? Nature Cell Biology 15, 125.
Sturman, L.S., C.S. Ricard, and K.V. Holmes, 1990, Conformational change of the coronavirus peplomer glycoprotein at pH 8.0 and 37 degrees C correlates with virus aggregations and virus-induced cell fusion, J. Virol. 64, 3042-50.
