Following group of factors are responsible for increase in cases and deaths in India:
The agents factors mainly responsible are different strains variations, mutations (double/triple) see table 2. Different strains vary in virulence, infectivity, pathogenecity, reproduction resulting in different case fatality, mortality & morbidity rates. The prevalence rate and incidence rate is also dependent on above factors. The TCID 50 and cycle threshold values are equally important to assess the severity of infection. The attack rate, secondary attack rate and reproduction number should be taken into account while doing assessment of agent factors. Without having sound knowledge of above mentioned agent factors it’s just impossible to effectively control this pandemic.
The pathogenesis of the strains causing common cold e.g. HCoV-229E and HCoV-OC43 says that they infect ciliated epithelial cells in the nasopharynx via the aminopeptidase 1 receptor (group 1) or a sialic acid receptor. Viral replication leads to a cascade of events manifested externally as common cold symptoms similar to other virus group called rhinoviruses. 11Harrisons principles of internal medicine https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public
SARS-CoV infects the respiratory tract via ACE 2 receptors. The systemic illness is manifested more or less depending upon immune status as well as associated morbidity conditions. The systemic manifestations include variety of signs and symptoms and sometime it’s symptomless. The study of pulmonary pathology will reveal more findings in coming days. One key finding is that earlier 2002-2003 outbreaks have many similarities with ncovid-19. The disease is milder in children and ARDS is also found in ncovid-19 severe cases. Besides this symptoms of common cold etc are very much similar. The incubation period is 1-14 days range. In earlier cases 2002-2003 laboratory findings have shown in SARS lymphopenia present in approx 50 % cases resulting in decreased immunity. Mostly T cells CD4+ (helper t cells) were affected and also CD8+T cell as well as natural killer to some extent.
The detailed information about ncovid-19 is yet to be finalised as several strains have been found and the trends shows that these variations will keep going. The global market has several accredited vaccines duly recognised by World Health Organisation. The final analysis and results can be declared only after a large population of world get vaccinated and with the development of herd immunity the predictions can be clearer.
The main problem in understanding morphology and other important determinants to know more about this virus is that it’s difficult to cultivate it in vitro added with continuous variations. We can grow some strains in human tracheal organ cultures but quite difficult to grow in tissue culture. SARS-CoV is exceptional as it can be grown in African green monkey kidney (Vero –E6) cells facilitating to know more about this virus.
Generally human coronavirus infections present globally. Seroprevalence studies have demonstrated this fact. The seasonal trends in India shows that infection is more common in late fall, summer, and early spring times March to September). The huge population needs several other modifications which are discussed in conclusion which are responsible for spread and increase in number of death in India recently.
Host factors - As we are aware of the fact that corona viruses infects a variety of hosts we must have a proper plan to avoid contacts with other animals etc known to be reservoir of covid-19. The human beings are infected from covid-19 through droplets and many other modes. Here the infection can be dealt through clinical approach, public health or preventive approach. Best is a combination of both approaches. See figure 1. The public health approach as well as clinical approach should work in co-ordination to achieve the desired results. The governance should have a clear data regarding health workforce, finance, available no. of beds and several other parameters illustrated in figure 1 to act in effective way to provide healthcare to persons who need it most.