3. Pathogenic Characteristics of Coronavirus
Coronavirus is a single strand positive RNA (+ssRNA) virus, belonging to order Nidovirales, family Coronaviridae, and subfamily Orthocoronavirinae [13]. According to the characteristics of serotype and genome, the coronavirus subfamily is divided into four genera: α, β, γ, and δ [14]. There are six kinds of coronaviruses known to infect humans, including 229E and NL63 of α genus [15,16], OC43, HKU1, Middle East respiratory syndrome-associated coronavirus (MERSr-CoV), and severe acute respiratory syndrome-associated coronavirus (SARSr-CoV) of β genus [16,17]. The coronavirus isolated from the lower respiratory tract of patients with unidentified pneumonia in Wuhan is a new type of coronavirus (SARS-CoV-2) belonging to genus β, and subgenus sarbe [5]. SARS-CoV-2 is different from the zoonotic MERSr-CoV and SARSr-CoV and becomes the seventh coronavirus to infect humans [5]. The phylogenetic analysis of the coronaviruses based on full-length genome sequences shows that SARS-CoV-2 has the smallest genetic distance from bat coronavirus, but only about 45%–90% similarity with SARSr-CoV, and a lower similarity of 20%–60% with MERSr-CoV [18]. Therefore, a bat is probably the original host of SARS-CoV-2, although the intermediate host may still exist in the process of transmission from bats to human beings.
Coronavirus has an envelope, the particles are round or oval, often pleomorphic, with a diameter of 50–200 nm [18]. S protein is located on the surface of the virus and forms a rod-shaped structure. As one of the main antigenic proteins of the virus, the S protein gene is the main target used for typing [19]. Xu et al. also reported that SARS-CoV-2 S-protein supports a strong interaction with human angiotensin-converting enzyme 2 (ACE2) molecules, which means that the virus poses a significant public health risk for human transmission by the S-protein–ACE2 binding pathway [18].
The knowledge of the physical and chemical characteristics of coronaviruses mostly comes from the study of SARS-CoV and MERS-CoV. The coronaviruses are sensitive to heat and can be killed at 56 °C for 30 min. In addition, ether, 75% ethanol, chlorine disinfectant, peracetic acid, and chloroform can effectively inactivate the virus, but not chlorhexidine [20].