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.