**4. Clinical symptoms**

SARS-CoV-2 attacks the lower airway as the primary target of infection, causing a respiratory and systemic illness that subsequently progresses to a severe form of pneumonia in 10–15% of patients [26, 27]. Clinical symptoms of COVID-19 vary from asymptomatic state to critical illness, with acute respiratory distress (ARDS), acute cardiac injury, multi-organ failure (MOF) and at the end, development of small blood clots throughout the bloodstream (intravascular coagulopathy) [17, 28]. The symptoms of COVID-19 illness are cough, fever, fatigue, headache, muscle pain (myalgia),

difficulty in breathing (dyspnoea), decreased lymphocytes in blood (lymphocytopenia), lower platelet count (thrombocytopenia), etc., which are indifferent from other respiratory infections [29]. However, the unique clinical symptoms of COVID-19 are runny nose (rhinorrhea), sneezing, sore throat, presence of infiltrate in the upper lobe of the lung that causes shortness of breath and subsequent decreased level of oxygen in the blood (hypoxemia), detection of viral RNA in samples of plasma, serum, whole blood, etc., (RNAemia) and sometimes gastrointestinal symptoms like diarrhea [29]. The incubation period of the virus is usually between 3 to 7 days on average, however with 1 day as the shortest and 14 days longest is observed in some circumstances. The symptoms of infection appear after the average incubation period of 5 days approximately however, the average time from onset of symptom to dyspnoea is five days, ARDS is eight days, and death is 6 to 41 days with a median of 14 days [18, 29, 30]. These periods are variable and dependent on several parameters like age and immunity of the patient, typically shorter periods are observed for patients above 70 years old [30].

## **5. Diagnosis and treatment**

As discussed in the previous section, based on the preliminary clinical features such as fever, sore throat, and dry cough of a suspected COVID-19 infectee can be investigated to confirm the exposure history of the person. In some of the cases, this may be asymptotic, i.e., showing none of the above mentioned clinical symptoms, hence, in those cases, the detection of viral genomic material is considered as the only reliable source of COVID-19 diagnosis. The method includes taking the samples from the (suspected) infectee in the form of nasopharyngeal swab, sputum, bronchoalveolar washing, endotracheal aspirates, followed by RNA extraction and subsequent analysis by reverse transcription polymerase chain reaction (RT-PCR) for synthesis, amplification, and identification of viral nucleic acid [18, 25]. Since RT-PCR based techniques take a relatively longer time, therefore, the development of rapid diagnosis kits is on works. Clustered regularly interspaced short palindromic repeats (CRISPR) based diagnostics are such techniques believed in delivering the results within an hour without the need for sophisticated laboratory equipment. Based on this technology, SHERLOCK and DETECTR are two test methods developed by Sherlock Biosciences, and Mammoth Biosciences, respectively and waiting for clinical verifications and approvals [31]. Another sophisticated approach would be a serological assay in which the antibodies from the blood sample of the patients are analyzed to detect viral infections. Computed tomography (CT) imaging is also a highly specific and sensitive method and a chest CT scan of the patients generally shows ground-glass opacities and infiltrates [17, 18].

As of the time, there are no specific, effective and proven antiviral drugs (and/ or) vaccines for the treatment of COVID-19 infection, so treatments are limited to support and palliative care only. The first-line treatment emphasizes maintaining hydration and controlling fever and cough through routine dosages of antipyretics and expectorants [32]. Patients with severe respiratory distress should be administered with supplemental oxygen. The alternative treatment is based on the use of broad-spectrum antiviral drugs like neurominidase inhibitor (oseltamivir), nucleotide analogues (remdesivir), nucleoside analogues (ganciclovir), HIV-protease inhibitors (lopinavir, ritonavir) that can reduce the virus infection [33, 34]. As per a recent report by Chen et al. (2020), the effective dosage for the treatment of COVID-19 patients includes oral administration of 75 mg oseltamivir, 500 mg lopinavir, 500 mg ritonavir twice a day and the intravenous administration of 0·25 g ganciclovir for 3–14 days [35]. Also, it is reported by many researchers that

#### *COVID-19: An Updated Insight of the Pandemic DOI: http://dx.doi.org/10.5772/intechopen.99097*

the antimalarial-drug chloroquine could effectively inhibit the virus by virtue of its immune-modulating activity [36, 37]. Deng et al. (2020) confirmed the antiviral activity of Arbidol (small indole derivative molecule) on COVID-19 patients and the antiviral activity against SARS-CoV and also it blocks the viral fusion against the influenza A and B viruses and hepatitis C viruses [10, 38]. A clinical candidate, EIDD-2801, with high therapeutic potential against the influenza virus, is in development, which can be a promising drug to be considered for the COVID-19 [39].

In addition to this, the synthetic recombinant interferons could be used for the treatment of COVID-19 based on their effectiveness against SARS-CoVs and MERS-CoVs [10]. It is also discussed that a small recommended amount of vitamin C supplementation could effectively prevent COVID-19. Convalescent plasma therapy in which plasma of patients recovered from COVID-19 enriched with virus neutralizing antibodies is administered in a prophylactic manner to prevent infection in high-risk cases could also be an effective approach to alleviate COVID-19 infection. On 31st March 2020, the first US patient received convalescent plasma therapy for the COVID-19 treatment [40]. In the latest development, Caly et al. (2020) reported that Ivermectin existing anti-parasite inhibited SARS-CoV-2 and a single treatment, reduced approximately 5000 fold viral RNA in 48 h in in-vitro [41]. However, the anti-parasitic drug is not approved by U.S Food and Drug Administration (FDA) due to lack of well-designed clinical trials. It is also recommended that the existing related vaccines for RNA virus including encephalitis B and influenza, etc., could be explored as possible alternatives until the development of an effective COVID-19 vaccine. There is an urgent need to establish a nonhuman animal model for a better understanding of the virus-host interactions and subsequent testing of potential drug/vaccines for COVID-19 infections [17].
