Introduction
Coronavirus disease 2019 (COVID-19) is caused by severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2) which is a novel
single-stranded RNA virus that causes pneumonia and was first reported
in Wuhan, China. Now, COVID-19 is an unprecedented challenge for the
healthcare community and the World Health Organization has declared it
as a global emergency on March 11, 2020
(Valencia, 2020). SARS-CoV-2 outbursts
originated via zoonotic transmission related to the seafood market and
later known to the person to person transmission that leads to the
spreading of disease worldwide (Rothan &
Byrareddy, 2020). The most common symptoms include lower respiratory
tract infection, fever, dry cough, breathing problem, headache, vomiting
and diarrhea (Huang et al., 2020;
Jin et al., 2020). The symptoms of
COVID-19 disease appears at around 5.1 days of median incubation period
but in the 99% cases, the period from the beginning of COVID-19 signs
to demise fluctuated from 6 to 41 days with a median of 14 days.
However, this incubation period may differ from individual to individual
due to the age of the patients and immune status; older the age shorter
would be incubation period (Lauer et al.,
2020; Rothan & Byrareddy, 2020).
Epidemiological evidence reveals that mortality rates and
hospitalization cases are higher among the older COVID-19 patients
(Yuki, Fujiogi & Koutsogiannaki, 2020).
There is a similarity in the symptoms of COVID-19 and other
betacoronavirus such as severe acute respiratory syndrome (SARS) and the
Middle East respiratory syndrome (MERS). However, COVID-19 present other
clinical features that it specifically targets lower respiratory tract;
more intense gastrointestinal symptoms such as diarrhea; and chest
radiograph shows infiltration in the upper lobe of the left lung which
causes dyspnea (Assiri et al., 2013;
Phan et al., 2020). Reports also showed
that COVID-19 patients are asymptomatic and not presenting any clinical
features (Bai et al., 2020;
Hu et al., 2020). SARS-CoV-2 infection
induces a two-phase immune response, the first phase of immune response
is protective and seen during the incubation period in which adaptive
immune response tries to eradicate the virus and prevents the disease
progression at sever stages. The second phase is initiated when the
first phase of immune response gets weakened and induces activation of
pro-inflammatory macrophages, increased leucocytes, massive release of
cytokines and ultimately leading to lung injury
(Shi, Wang & Shao, 2020). Further,
COVID-19 does not only infect lungs, but it also affects other vital
organs where angiotensin-converting enzyme 2 (ACE 2) is highly expressed
and may facilitate the virus penetration that ultimately leads to organ
failure with heavy viral load and cytokine storm. Hence, this review
will shed a light on a path of increased co-morbidity and mortality rate
in COVID-19 patients with possible mechanism of multi-organ failure.