Introduction
Coronaviruses are Nidovirales and belong to family of coronaviridae, and
subfamily orthrocoronavirinae (Shereen, Khan, Kazmi, Bashir, &
Siddique, 2020). Coronavirus shows crown-like spikes on their outer
surface; therefore, it was named as “Coronavirus”. The Coronaviridae
has the four subgroups Alpha, Beta, Gamma, and Delta (α, β, γ and δ)
coronaviruses(Zhong et al., 2003). The newly emerged SARS-CoV-2 belongs
to β-coronaviruses, which is a enveloped, positive (+) sensed RNA virus
(Su et al., 2016). SARS-CoV-2 causes a highly contagious disease called
Coronavirus Disease 2019 (COVID-19) (Adhikari et al., 2020). The
phylogenetic studies shows that SARS-CoV-2 has high resemblance with
Severe Acute Respiratory Syndrome virus (SARS-CoV) and the relatively
poor resemblance with Middle East Respiratory Syndrome virus (MERS-CoV)
(Shereen et al., 2020) (Wang et al., 2020). This is the
3rd zoonotic coronavirus outbreak in the
1st two decades of 21st century.
However, this time disease is rapidly transmitted from person to person
and have raised a global human concern (Xie & Chen, 2020). Human to
human transmission through close contact, air droplets and asymptomatic
incubation carriers within the families, friends and the community made
it extremely contagious (Guo et al., 2020). By following exponential
growth up to the end of January, 2020, outbreak reached to several
countries grabbing considerable attention in the entire globe (Cucinotta
& Vanelli, 2020). As of March 11, 2020, WHO announced the epidemic to a
global pandemic because of 13 folds increase in cases outside the China
and number of affected countries also increased 3 folds. A further
increase was is expected (Cucinotta & Vanelli, 2020).
Unfortunately, the Chinese New Year festival “Lunar” holidays, which
is celebrated on the beginning of new year, accord with the outbreak of
COVID-19, is a best celebratory event of the year in China during which
huge number of peoples’ migration occurred towards their home towns (Cai
et al., 2020). Approximately 3 billion people in China made close trips
over the 40 days’ travel period of “Chunyun”. About 5 million
individuals travelled from Wuhan, the epicentre of the COVID-19
outbreak, before the implementations of the travel ban on January 23,
2020 (Zu et al., 2020). Therefore, a rapid expansion and spread of
COVID-19 cases transmission observed within the China and outside the
China (Yang, Lu, et al., 2020). This review article highlights the
ongoing challenges of COVID-19, pathogenesis, diagnosis, current and
future treatment strategies, immune responses and future perspectives.