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.