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1. Introduction:

In human history, there are many cases of viral pandemic infections including polio [1], ebola [2], smallpox [3], chicken pox [4], HIV-AIDS [5], which had put human life on serious risk [3]. Nevertheless, owing to efforts taken by medical sectors across the globe, such diseases were controlled by either vaccine [6] or  treatments [7] or some of them are reduced by
prevention only [8]. The diseases mentioned above were life threatening and caused a potential biological loss in  the world [9,10,11]. Of them, airborne and contagious diseases [12] are more challenging to humankind since they are challenging to control. It is true, especially in those countries where the population is high, and awareness among people is less. Like other
biological species, viruses are capable of altering their
genetic makeup [13,14] and get chances of
reappearances [13,14,15], hence making them more
infectious than their parents [16]. The variation in
genes results in altered protein sequence leading to
changed functions of proteins [17]. The antiviral drugs
available against these infections are not as
productive as those were made to recognize only
specific target sites [18]. As a result, the infectious
particles go on infecting people continuously resulting
in international health concern and panic with
uncontrolled deaths.
According to Prajapat, M. et al. [19], there is only
one Protein Data Bank (PDB ID:6LU7) on the 2019-
nCoV, which forms a complex with the N3 inhibitor.
However, the genome sequence shows that there is
95% similarity with the bat -SL-CoVZC45 and 88% to SIRS CoV-ZSc [19]. This study suggests that the
changes have occurred in the amount of
recombination process in 2019-nCoV and the protein
structural and functional levels.
In this review, we analyzed the evolution of corona
virus family (Coronaviridae) [20] to know the genetic
similarity and variation patterns in relation with newly
arrived Severe Acute Respiratory Syndrome (SARSCoV2)virus, which infected 2,078,605 people from 213
areas, countries and territories with 139,515deaths
(table 1) till April 17,2020.Till date, there is no vaccine
or effective measure to stop its spread [16]. Apart
from analyzing the evolutionary aspect, the article
also discusses the probable genetic variation leading
to substantial uncontrolled health risk to human life
[13, 14] causing a higher uncontrolled health risk to
humans.
2. Evolution and future reappearance:
The viruses which contain RNA as their genetic
material have potential to get evolved [21] and
coronaviridae family has RNA as genetic material [22],
which can evolve. In sequence, the viral genetic
evolution has occurred in SARS-CoV that spreads
through human to human contact [12] and this idea
has been supported by [23]. They stated that SARSCoV and SARS-CoV2 belong to a beta group of corona
virus. They have 70% similarity at a genetic level
showing DNA level differences among them (figure 1).
This indicates that both viruses are 30% different in
their genetic structure that is a result of mutations
such as genetic recombination, gene deletion or
insertion creating the probability of outbreak in future
like its ancestors created in the past [16]. Likewise,
genome level gene exchange, recombination [24],
gene deletion or insertion may create a probability of
outbreak in future, like past incidences [25] (figure 1)
such as SARS CoV epidemics.
Additionally, SARS-CoV2 is considerably similar with
SARS-CoV helping for predictions on occurred
epidemic health disaster, and corona viruses may be
responsible for outbreaks with variant mutations like
previous one in upcoming years [13, 14, 25] (Figure 1).
This suggests that both types of corona viruses are
genetic variants. Besides, SARS-CoV and SARS-CoV2 are similar for
their severity. This idea was supported by Huang, C.,
et al., Chen, N., et al., Wang, D., et al., [27, 28, 29]
who proposed that SARS-CoV2 severity mimicked with
previously spread SARS-CoV and they also share same
clinical features [30]. Chaolin Huang et al. [31] supported our concept and
stated that corona viruses might lead to substantially
more novel as well as severe zoonotic incidences.
Moreover, clinical characters of 2019-nCoV showed
similarity with previously studied beta coronavirus
infections [31]. Features showed by 2019-nCoV
infections revealed some resemblance with SARS-CoV
as well as MERS-CoV infections [32, 33].This strongly
suggests that the novel coronavirus (SARS-V2) has
evolved from previously observed SARS-CoV, a
member of the betacorona virus group.
Additionally, there is a difference between SARS
and 2019-nCoV regarding immunogenicity as former
causes pulmonary inflammation with high level lung
damage whereas the second causes raised production
of Th2 cytokines retarding inflammation [34]. This
effect might be due to 17% genetic variation caused
by 2019-nCoV in PL pro sequences. As a result, the
international crisis has occurred and there is no
proper vaccine or drug against it till writing this
article.
In spite of 83% similarity in the PLpro sequences of
SARS-CoV and SARS-CoV-2, both of them share active
sites which are similar [35]. According to Huang, C. et
al. [27], infections by SARS-CoV-2 and earlier
betacoronavirus showed similarities in clinical
characteristics. To add, sequence identity between
SARS-CoV2 and betacoronavirus members regarding
domains of conserved replicase is lower than 90% [36]
suggesting the relationship between both entities.  SARS-CoV-2 is considerably homologous to CoV that
caused SARS (Severe Acute Respiratory Syndrome)
during 2003. Also, SARS-CoV2 pathogen is more
similar in relation with genetic makeup to SARS-CoV
as compared with MERS-CoV [37, 38, 39]. As well,
both have a common factor, i.e. human ACE2 receptor
[39], which indicated that the genetic modifications in
newly arrived pathogen do not affect human cell
receptor recognition. With the exception, the COVID19 pathogen binds human ACE2 more weakly with
help of its S protein than SARS-CoV, causing less
potential infection than SARS-CoV [37]. Furthermore,
it was observed that death rate due to COVID-19 was
found as 2% [40] while that of SARS spread in 2002, it
was 10% [41] and in case of MERS, it was 37% [42]. It
may be because of genetic modifications. Moreover,
SARS-CoV has same size as SARS-CoV-2 [43], and both
have high homology [44] supporting morphological
similarity among them. Interestingly, over 95% sequences show a similarity
between SARS-CoV2 3CLpro and RdRp protease with
that of SARS-CoV, and both viruses have 79% genetic
similarity in their sequences [39]. Besides, they share
potentially conserved Receptor Binding Domain (RBD)
along with S protein domain [35,37,45] which is due
to recombination/mutation acquisition in SARS-CoV-2
[16]. To add, novel viral host cell entry and replication
proteins are similar with that of SARS-CoV with
respect to their structure [46]. Additionally, it is found that SARS-CoV2 is one of
the seven coronaviruses that infect human beings and
others are MERS-CoV, SARS-CoV (cause severe
infection), 229E, OC43, NL63, HKU1 (cause mild
symptoms) [49]. In future, genetic variations may
occur in the last four types (figure 2). Since the COVID19 pathogen has similarity with SARS-CoV along with
some symptoms, there is sense of its upcoming arrival
[13, 14].
Out of six genera (ending with suffix ‘virus’) of
family coronaviridae, i.e. alpha, beta, gamma delta toro and bafini [20], betacoronaviruses include
SARS-CoV, MERS, SARS-CoV-2 [46] and SARS-CoV-2
is a novel coronavirus in the genus that is
belonging to MERS-CoV and SARS-CoV (figure 1).
Like MERS-CoV and SARS-CoV, SARS-CoV2 targets
lower part of the respiratory system leading to
pneumonia and it also infects heart, kidney,
gastrointenstinal system, liver as well as central
nervous system [47, 48] showing pathological
similarity. It means that the virus family
understudy is genetically changeable and in
upcoming decade, the same virus or other viruses
of the same family will reappear [13, 14] with their
genetic variants (figure 1).
3. Conclusion:
The coronavirus family is highly changing and its
genetic variants may appear. In this sequence,
genetic mutants of SARS-CoV2 may be detected in
future.