COVID-19: a not so general introduction
AM Zakir Hussain
Viruses have predilection to mutate by nature. Some viruses mutate too fast and too frequently, the human immunodeficiency virus, or HIV, being one of them. Like HIV, the coronavirus is also a ribonucleic acid and is the biggest of all ribonucleic acid viruses. The virus, as is known by now, spreads from an infected person’s sneezing or coughing, which produces droplets or aerosols of more or less 10 micrometres in size. Droplets may travel a distance of 10 metres in the case of coughing and 50 metres in sneezing. The virus may also spread from an infected person’s saliva, discharge from the nose or even from faeces. Since droplets are heavier; so, some or all of them settle on the ground or any other nearby objects soon and remain active for varying periods — from a few hours to a few days — in case of failure to lodge in any living hosts at a given time or when a healthy person remains at a distance of six feet. If a healthy person touches such surfaces or objects and then touches the mouth, the nose or the eyes, the contaminated hand may deliver the virus to a human host through such entry sites. This is the reason hand-washing has been emphasised so earnestly. But if there is no chance of touching such objects or surfaces, as when people neither go out from their houses nor anybody or anything comes from outside, repeated hand-washing is unnecessary.
Infection starts first in the nose and the throat, especially if the source is a droplet. Virions, or virus particles, can lodge in the alveoli, or smaller units of the lungs, only when their size is less than 10 micrometres called aerosol. Two types of masks are said to be of some help in preventing infection of a new host. N95 masks can prevent aerosols up to 0.3 micrometres but surgical masks can prevent only droplets, bigger than 10 micrometres. ACE-2, a protein on the surface of a host cell, which provides a docking site to the virus, is abundant in the nose and in the mouth and very few in the lungs. As droplets have higher possibility to contain a critical number of viruses, surgical masks should be able to reduce the chance of infection. It is like half a loaf is better than no loaf. Aerosols might also contain fewer viruses and also would have fewer docking sites in the lungs.
In the nose and mouth, the virus replicates and after reaching a critical number, it causes the initial symptoms of fever, dry cough, muscle pain, singularly or in combination in 4-5 days — the asymptomatic period, also known as the incubation period, may span 2-14 days but may even extend up to 27 days. During the asymptomatic days, infected people may infect the highest number of people because of their mobility while being unaware of the infection. This is further complicated by the fact that someone infected might, in fact, not even show any clinical features. Around this time, many patients lose the senses of smell and taste. It then spreads to the windpipes and to the lungs. In the windpipes, it causes excessive secretion of mucus, which blocks the airways and, hence, the respiratory distress. When the infection goes to the alveoli, pneumonia sets in and the lungs are fibrosed in 5-6 days. Death usually occurs around this time. Death, as has been noted, is the usual prognosis among the elderly, especially if there are co-existing diseases — eg diabetes, hypertension, cancer etc — which compromise immunity in a person. In others, who are not usually inflicted dangerously and show mild clinical features, there would be recovery in 7-8 days. Some patients may develop diarrhoea during the recovery or in terminal stages. There is no treatment against any virus except Hepatitis B although most of the vaccines have, in fact, been invented against virus. But despite all frantic efforts, no vaccine could be produced against HIV. The reason is the frequent mutation of the virus. The same is true about the coronavirus. This is, perhaps, the reason that some people become ill for a second time with the virus.
The real-time polymerase chain reaction in use to increase the number of the virions to ensure the success of the test to find infection is dependent on the sources of the sample. A recent paper, based on Chinese experiences, suggests that the test is 93 per cent sensitive in identifying the virus when the sample is taken from the bronchoalveoli, close to the lungs; sputum gives a 72 per cent positivity while samples taken from the nose give a positivity of 63 per cent and taken from the oropharyng, the back of the throat, the sample is likely to be positive only 32 per cent of the time. Even stool may give positive results albeit to a small percentage. A negative finding may, therefore, not be negative. In another paper, Chinese pathologists found patients to be negative repeatedly and some people were found positive in the seventh test. This fact has practical and important implication. The message is that laboratory test should be corroborated with the clinical features and necessary precautions should be taken not only based on laboratory test alone but also based on the clinical features.
A tacit approval of the use of hydroxyquinine and azithromycine was given for COVID-19. Hydroxyquinine reduces the excessive immunogenicity of the body to the virus which, otherwise, produces copious mucus and blocks the windpipes, and azithromycine acts against secondary bacterial infections leading to pneumonia. Hydroxyquinine may have deleterious effects on the heart and has been reported to kill people from its injudicious use. Information from China also suggests that breathing in hot steam and hot drinks each taken four times a day may kill the virus.