4. Discussion
As a large number of people have left Wuhan, the control of the epidemic situation is extremely urgent, and the treatments of COVID-19 are imminent. On Feb. 14th, 2020, there were more than 54,000 confirmed patients in Hubei province, China [55]. Due to the lack of effective antiviral drugs, the prognosis of patients solely depends on their age and physical condition [74]. Although it was reported that the clinically recovered patients exceed the number of dead, the majority of the patients are still not cured in hospital. In addition, the potential adaptive mutation of SARS-CoV-2 makes it difficult for vaccine development. Therefore, it is urgent for us to develop more sensitive inspection methods and effective drugs.
Seven type of CoVs have been identified to cause human disease [107]. The two highly pathogenic viruses, SARS-CoV and MERS-CoV, cause severe respiratory syndrome in humans. The other four human CoVs (HCoV-NL63, HCoV-229E, HCoV-OC43 and HKU1) induce only mild upper respiratory diseases, although some of them can cause severe infections in infants, young children, and elderly individuals [4,108]. The latest one is SARS-CoV-2. It has been reported that SARS-CoV-2 shared almost 80% of the genome with SARS-CoV [11]. Our results also showed that almost all encoded proteins of SARS-CoV-2 are homologous to SARS-CoV proteins (Table 2). Hence, clinical drugs and therapies for treating SARS may be used as a reference for COVID-19 treatment [74].
In addition to the well-known SARS-CoV, MERS-CoV, as one Merbecovirus subgenus of β-CoVs, is also extremely invasive. MERS-CoV is the pathogen of the Middle East Respiratory Syndrome, which can infect both humans and animals, and can be transmitted through camels [109]. It mainly occurs in Saudi Arabia and has a high mortality rate [66]. Studies had demonstrated that the clinical course of SARS and MERS was highly similar, and SARS and MERS may have similar pathogenesis [66]. The genome sequence of SARS-CoV-2 also shows some similarities to that of MERS-CoV. It will be very interesting to study the relationship among SARS-CoV, MERS-CoV, and SARS-CoV-2 that may be exploited for future developing broad-spectrum antiviral therapies.
Although more and more studies for SARS-CoV-2 have sprung up since the outbreak of this epidemic COVID-19, based on our comparison, we propose some key questions to be clarified in future studies (Table 3). In-depth understanding the underlying pathogenic mechanisms of SARS-CoV-2 will reveal more targets for better therapy of COVID-19.