# Comparison of Selected Characteristics of SARS-CoV-2, SARS-CoV, and HCoV-NL63
### Animal Origin of SARS-CoV
#### 1.4.2 Severe Acute Respiratory Syndrome SARS-CoV and Its Natural Hosts  
A highly infectious and fatal coronavirus disease was reported in 2003. The virus crossed the species barrier of the zoonotic reservoir to infect the human population [51]. It is assumed that the main source of the pathogen was found in local markets of Guangdong province [52], China. Cases of severe atypical pneumonia with subsequent respiratory failure were observed in Guangdong. The disease spread rapidly mainly due to a lack of population immunity to the new pathogen [53]. Human-to-human transmission occurred in close contact. Medical and nursing staff were mainly at risk and the virus spread further among family members. Transmission also occurred indirectly through infected respiratory secretions [23]. The virus was identified by researchers in March 2003 [54]; it was isolated on tissue cultures by electron microscopy and PCR sequencing of the virus genome [30]. The isolated virus was named SARS-CoV. The WHO defined clinical symptoms for the detection of suspected cases: Temperatures above 38 \({}^{\circ}\)C, a confirmed positive X-ray finding of pneumonia, RNA detection of the presence of the virus, and confirmed antibodies against SARS-CoV virus. The incubation period of the disease was established as 6-10 days. Lymphopenia and occasionally thrombocytopenia were reported based on hematological parameters. Elevated lactate dehydrogenase and creatine kinase levels were observed from biochemical values, often associated with a worse prognosis [55]. Zoonotic transmission was confirmed as the source of the disease. The primary natural reservoir is most likely the bat genus _Rhinolplus_. _Rhinolplus sinicus_ was analyzed in the Chinese provinces of Hubei and Guangdong; coronavirus genetically similar to SARS-CoV were detected in 22 out of 59 individuals. In addition, serum from _Rhinolplus sinicus_ contained antibodies specific to the human SARS-CoV N protein, antibodies identical to the SARS-CoV N protein, were also present. Genome sequencing showed that the genome of bat CoVs is genetically nearly identical to SARS-CoV isolated in humans and local civet species. Therefore, the most likely secondary vector was the palm civet. About 80% of civets (_Paguma larvaata_) from animal markets in _Guangzhou_ contained significant levels of antibodies to SARS-like-CoV [56]. The isolated coronavirus is genetically identical to SARS-CoV by up to 99%. In rare cases, genetic relatedness has been demonstrated to coronaviruses in the racon dog (_Nytereutes procyanoides_). Antibodies were detected in the Chinese ferret-badger _Melogale moschata_. The sequences were similar at 88-92%. Most of the variable regions were located at the 5' end of the S gene, which encodes the S1 domain responsible for the receptor binding region. Many SARS-CoV samples from humans isolated during the later stages of the epidemic in 2002-2003 had a 29 nt deletion in this region; this deletion is absent in civet isolates or human isolates from the early phase of foci. Bat viruses do not contain a deletion of 29, suggesting that SARS-CoV and animal SARS-like-CoV share a common ancestor. The SARS-CoV uses the ACE2 receptor to enter the cell [57]. The ability to effectively use the ACE2 receptor in humans and civets appears to be a major difference from other zoonotic CoVs. This is also the difference between SARS-CoV in humans and SARS-like-CoV virus in bats. This explains the limitation of the spread of the virus between individual species [58].