Clinical manifestations & Pathological features
Based on the current epidemiological investigation fever, dry cough and fatigue are the main manifestations. A few patients have symptoms such as nasal congestion, runny nose, sore throat, myalgia and diarrhoea.(N. H. Commission, 2020) Severe patients usually have dyspnea and/or hypoxemia one week after the onset of symptoms, and severe patients can quickly progress to acute respiratory distress syndrome, septic shock, difficult to correct metabolic acidosis, and coagulation dysfunction and functional failure of multiple organs.(N. H. Commission, 2020) It is worth noting that the course of severe and critically ill patients can display a moderate or low fever, and even no obvious fever. Mild patients show only low fever and mild fatigue with no pneumonia manifestations. From the current cases, most patients have a good prognosis with only a few patients have a critical condition. The prognosis for the elderly and those with chronic underlying disease is poor. Symptoms in children are relatively mild.(N. H. Commission, 2020)
The pathological features of COVID-19 are very similar to those in SARS and MERS coronavirus infections.(Z. Xu et al.) Besides, liver biopsy specimens from patients with COVID-19 showed moderate microvascular steatoplasty and mild active inflammation of the hepatic lobular manifold area, suggesting that the injury may be due to SARS-CoV-2 infection or drug-induced liver injury. There was a small amount of inflammatory infiltration of mononuclear cells in the myocardial interstitium, but no other myocardial parenchymal damage was found.(Z. Xu et al.) The number of CD4+ and CD8+ cells in peripheral blood was greatly reduced, but their states were over-activated. In addition, CCR4 + CCR6 + Th17 cells with a high pro-inflammatory effect were increased. CD8+ T cells were found to have high concentrations of cytotoxic granules.(Z. Xu et al.)
To be short, in a study by Xu et al.(Z. Xu et al.), the chest radiograph showed a rapid progression of pneumonia with slight differences between the two lungs. Also, liver tissue exhibits moderate microvascular steatoplasty and mild lobular active inflammation, but there is no firm evidence to support SARS-CoV-2 virus infection or drug-induced liver damage. There were no obvious histological changes in the heart tissue, suggesting that SARS-CoV-2 infection may not directly damage the heart. Lymphopenia is a common feature in patients with COVID-19.
Moreover, another study had also provided some insight of the pathological findings of the SARS-CoV-2. A study by Mao et al.(Mao et al., 2020) found that severe patients often have neurological symptoms, compared with non-severe COVID-19 patients, with acute cerebrovascular disease, disturbance of consciousness, and skeletal muscle symptoms. After analysing 522 samples from the SARS-CoV-2 patients, Diao et al.(Diao et al., 2020) discovered that SARS-CoV-2 patients, especially elderly patients (over 60 years of age) and patients in need of intensive care unit (ICU) care, had a significant reduction in the total number of T cells, CD4+, and CD8+ T cells. The number of T cells was negatively correlated with serum IL-6, IL-10 and TNF-α concentrations. The levels of IL-6, IL-10 and TNF-α in patients with the disease declined with the count of T cell recovered. It is worth mentioning that patients with SARS-CoV-2 had significantly higher levels of PD-1, a marker of T cell depletion. In addition, the expression of PD-1 and Tim-3 from T-cells increased during the shift from the precursor stage to the apparent symptomatic stage, further implied a decrease in T-cells and functional depletion in SARS-CoV-2 patients. Finally, a study by Cheng et al.(Cheng et al., 2020) had discovered patients with kidney injury have a higher risk of in-hospital death after analysing 710 cases of SARS-CoV-2 patients.