3.5 Additional Reading:COVID-19
Description
COVID-19 is a contagious viral disease caused by severe acute respiratory syndrome coronavirus 2，or SARS-CoV-2，a coronavirus that is genetically related to SARS-CoV.Symptoms generally develop between 2 and 14 days after exposure，with many persons showing symptoms after incubation for 5 days.Although some infected individuals may experience no or very mild symptoms，patients typically present with fever，dry cough，upper airway congestion，sputum production，and shortness of breath，but rarely with headache，hemoptysis，and diarrhea.Loss of smell（anosmia）and loss of taste（ageusia）have also been reported.Some patients experience chills（in some cases with shaking），body aches，headache，fatigue，sore throat，nausea，vomiting，or diarrhea.More serious illness may progress to pneumonia，unusual blood thickening and clotting，heart failure and arrhythmia，and acute respiratory distress syndrome.
Virology and pathogenesis
Coronaviruses are enveloped single-stranded RNA viruses that are zoonotic in nature and cause symptoms ranging from those similar to the common cold to more severe respiratory，enteric，hepatic，and neurological symptoms.Other than SARSCoV-2，there are six known coronaviruses in humans：HCoV-229E，HCoV-OC43，SARS-CoV，HCoV-NL63，HCoV-HKU1，and MERS-CoV.Coronavirus has caused two large-scale pandemics in the last two decades：SARS and MERS.The virus-specific nucleic acid sequences in the SARS-CoV-2 sample are different from those of known human coronavirus species.Laboratory results also indicated that SARS-CoV-2 is similar to some of the beta（β）coronaviruses genera identified in bats，which is situated in a group of SARS/SARS-like CoV.
The next-generation sequencing from bronchoalveolar lavage fluid and cultured isolates showed that SARS-CoV-2 is more distant from SARS-CoV（with about 79%sequence identity）and MERS-CoV（with about 50%sequence identity）than from two bat-derived SARS-like coronaviruses—bat-SL-CoVZC45（with 87.9%sequence identity）and bat-SL-CoVZXC21（with 87.2%sequence identity）.Studies also reported that COVID-19 S-protein supported strong interaction with human ACE2 molecules despite the dissimilarity of its sequence with that of SARS-CoV.
Transmission patterns
Many domestic and wild animals，including camels，cattle，cats，and bats，may serve as hosts for coronaviruses.It is considered that，generally，animal coronaviruses do not spread among humans.However，there are exceptions，such as SARS and MERS，which are mainly spread through close contact with infected people via respiratory droplets from coughing or sneezing.With regard to COVID-19，early infection cases were due to animal-to-person transmission.However，later cases indicated human-to-human transmission.
The guidelines from Chinese health authorities describe that the main transmission routes for COVID-19 are droplets transmission，contact transmission，and aerosol transmission.Droplets transmission occurs when respiratory droplets（as produced when an infected person coughs or sneezes）are ingested or inhaled by individuals nearby；contact transmission may occur when a subject touches a surface or object contaminated with the virus and subsequently touches their mouth，nose，or eyes；and aerosol transmission may occur when respiratory droplets mix into the air，forming aerosols and may cause infection when high dose of aerosols are inhaled into the lungs in a relatively closed environment.In addition to these routes，the digestive system is also indicated as a potential transmission route for COVID-19 infection.Since patients have abdominal discomfort and diarrhea symptoms，the analysis on four datasets with single-cell transcriptomes of digestive systems indicates that ACE2 is highly expressed in absorptive enterocytes from the ileum and colon.
Diagnosis
Early diagnosis and isolation of suspected patients play a vital role in controlling the outbreak.The specificity and sensitivity of different diagnostic techniques differ among populations and the types of equipment employed.Several procedures have been recommended for the diagnosis of COVID-19.(https://www.daowen.com)
The findings of most blood tests are usually nonspecific but could help determine the causes of the disease.A complete blood count typically shows a normal or low count of white blood cells and lymphopenia.C-reactive protein（CRP）and erythrocyte sedimentation rate are generally increased，which would optimally be rechecked on days 3，5 and 7 after admission.Creatine kinase plus myoglobin，aspartate aminotransferase and alanine aminotransferase，lactate dehydrogenase，D-dimer，and creatine phosphokinase levels could be increased in severe forms of COVID-19 disease.
Chest X-ray examination may display diverse imaging characteristics or patterns in COVID-19 patients with different disease severity and durations.Imaging results differ based on patient’s age，disease stage during screening，immune competency and drug therapy protocols.On the other hand，computed tomography（CT）imaging is essential for monitoring disease progression and assessing therapeutic effectiveness.It can be reexamined 1 to 2 days after admission，based on the Diagnostic and Treatment Protocols Regulation（DTPR）.
The clinical diagnosis of COVID-19 is mainly confirmed by epidemiological data，clinical symptoms and some adjuvant technologies，such as nucleic acid detection and immunological assay.In addition，the isolation of SARS-CoV-2 requires high-throughput equipment（biosafety level-3）to ensure personnel safety.Moreover，serological tests have not yet been validated.In the field of molecular diagnosis，the main issues are decreasing the false negatives by detecting minimal amounts of viral RNA，avoiding the false positives through correct differentiation of positive signals between different pathogens，and increasing the capacity for fast and accurate testing of a large number of samples.
Treatment
Until now，no specific antiviral therapy has been available to treat COVID-19 respiratory damage.Nevertheless，efforts are ongoing to test several antiviral drugs both at the preclinical and clinical levels.Based on their modes of action，anti-COVID-19 therapies might either target an enzyme involved in viral replication，or interfere with the viral entry into the host cells.Others might target the host immune system to enhance host immunity，or inhibit the cytokine release storm（CRS）associated with the massive damage of lung tissues.
Based on previous therapeutic experience with SARS and MERS，available treatment consists of medication that can alleviate the symptoms and other supportive care.The antiviral remdesivir may shorten recovery time by several days，and some corticosteroids have been found to improve survival rates for severely ill patients.Monoclonal antibody treatments have been authorized on an emergency basis to treat mild to moderate cases，and blood plasma from recovered patients，which contains antibodies to the virus，has also been used on an emergency basis to treat the severely ill cases.Significant and rapid research into a potential cure or vaccine had led to the experimental or emergency use of several vaccines by late 2020.These include approaches using nucleic acid（DNA and RNA），virus-like particles，peptides，viral vector recombinant protein（replicating and non-replicating），as well as live-attenuated virus and inactivated virus.
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Task 9 Identify the word elements and define the meaning of each medical term.
