I. Etiological Characteristics

The novel coronaviruses belong to the β genus. They have envelopes, and the particles are round or oval, often polymorphic, with diameter being 60 to 140 nm.

Their genetic characteristics are significantly different from SARS-CoV and MERS-CoV.

Current research shows that they share more than 85% homology with bat SARS-like coronaviruses (bat-SL-CoVZC45).

When isolated and cultured in vitro, the 2019-nCoV can be found in human respiratory epithelial cells in about 96 hours, however it takes about 6 days for the virus to be found if isolated and cultured in Vero E6 and Huh-7 cell lines.

Most of the know-how about the physical and chemical properties of coronavirus comes from the research on SARS-CoV and MERS-CoV.

The virus is sensitive to ultraviolet and heat. Exposure to 56°C for 30 minutes and lipid solvents such as ether, 75% ethanol,
chlorine-containing disinfectant, peracetic acid, and chloroform can effectively inactivate the virus. Chlorhexidine has not been effective in inactivating the virus.

II. Epidemiological Characteristics

1. Source of infection

Now, the patients infected by the novel coronavirus are the main source of infection; asymptomatic infected people can also be an infectious source.

2. Route of transmission

Transmission of the virus happens mainly through respiratory droplets and close contact. There is the possibility of aerosol transmission in a relatively closed environment for a long-time exposure to high concentrations of aerosol. As the novel coronavirus can be isolated in feces and urine, attention should be paid to feces or urine contaminated environmental that leads to aerosol or contact transmission.

3. Susceptible groups

People are generally susceptible.

III.Pathologial Changes

Pathological findings from limited autopsies and biopsy studies are summarized below:

1. Lungs

Solid changes of varying degrees are present in the lungs.

Alveolar damage involves fibromyxoid exudation and hyaline membrane formation. The exudates are composed of monocytes and macrophages, with plenty of multinucleated syncytial cells. Type II alveolar epithelial cells are markedly hyperplastic, some of which are desquamated. Viral inclusions are observed in type II alveolar epithelial cells and macrophages. Alveolar interstitium is marked with vascular congestion and edema, infiltration of monocytes and lymphocytes, and vascular hyaline thrombi. The lungs are laden with hemorrhagic and necrotic foci, along with evidence of hemorrhagic infarction. Organization of alveolar exudates and interstitial fibrosis are partly present.

The bronchi are filled with desquamated epithelial cells, mucus and mucus plugs. Hyperventilated alveoli, interrupted alveolar interstitium and cystic formation are occasionally seen.

On electron microscopy, cytoplasmic NCP virions are observed in the bronchial epithelium and type II alveolar epithelium. NCP virus antigen positivity in some alveolar epithelia and macrophages are revealed through immunohistochemistry staining, which are positive for NCP virus nucleic acid via RT-PCR.

2. Spleen, hilar lymph nodes and bone marrow

The spleen is evidently shrunk. Lymphocytopenia and focal hemorrhage and necrosis are present. Macrophagocyte proliferation and phagocytosis are noted in the spleen. Lymph nodes are found with sparse lymphocytes and occasional necrosis. CD4+ and CD8+ T cells are present in reduced quantity in the spleen and lymph nodes, revealed by immunohistochemistry staining. Pancytopenia is identified in bone marrow.

3. Heart and blood vessels

Degenerated or necrosed myocardial cells are present, along with mild infiltration of monocytes, lymphocytes and/or neutrophils in the cardiac interstitium. Endothelial desquamation, endovasculitis and thrombi are seen in some blood vessels.

4. Liver and gall bladder

Appearing enlarged and dark-red, the liver is found degenerated with focal necrosis infiltrated with neutrophils. The liver sinusoids are found hyperemic. The portal areas are infiltrated with lymphocytes and monocytes and dotted with microthrombi. The gall bladder is prominently filled.

5. Kidneys

The kidneys are noted with protein exudation in the Bowman’s capsule around glomeruli, degeneration and desquamation of the epithelial cells of renal tubules, and hyaline casts. Microthrombi and fibrotic foci are found in the kidney interstitium.

6. Other organs

Cerebral hyperemia and edema are present, with degeneration of some neurons. Necrosis foci are noted in the adrenal glands. Degeneration, necrosis and desquamation of epithelium mucosae at varying degrees are present in the esophageal, stomach and intestine.