**5. Transmission of COVID-19**

It is universally acknowledged that people-to-people transmission of SARS-CoV-2 occurs in the community, family settings, and health care. Substantial dissemination methods involve droplets from the respiratory duct and indirectly through fomites and aerosols. Some circumstantial evidence shows that PCR and culture are two important laboratory tests used to separate the virus from saliva and identify its feces [30–33]. It has also been observed that the virus appears differently in both blood and urine [34, 35]. If the COVID-19 is mild, the virus shedding in respiratory samples remains for a long period in the case of children; the virus having RNA is obtained in higher magnitude (83.3%) in feces with lasting shedding for a fortnight, whereas it lasts for more than one month in children [27]. Diverse research suggests that the spread of the virus can be seen during incubation on the day or the day before the signs are set forth and spread from very mild asymptomatic infections [36–40]. From the day of his admission, positive samples were collected from the nasopharynx of a half-year-old baby with a high viral load;

#### *Origin and Impact of COVID-19 on Socioeconomic Status DOI: http://dx.doi.org/10.5772/intechopen.98893*

these specimens were positive for several days [41]. Therefore, multiple instances may remain undetected and pose a sustainable challenge for virus transmission [42]. The replication number (Ro) is usually considered to be in the range of 2.0 and 2.8 [37–40]; in case higher multiplication numbers are recommended, the serial interlude remains within a span of 5 to 7 days [43–45]. The mean incubation period is between 4.75 and 7 days [46, 47], ranging from 3 to 14 days. Information about the virus load is increasing simultaneously with an increase in our understanding of the virus. In another instance, patients with higher viral loads were identified; the viral droplets in the nose were higher than those in the throat. The intensity of viral droplets was alike in the case of a single symptomatic patient and an asymptomatic patient [32]. On another occasion, for a comprehensive study, the assessment of the virus load was conducted in a pair of patients with a series of samples collected from swabs, throat, urine, stool, and sputum over consecutive days from admission to hospitalization. The viral loads peaked with 104 to107 copies/mL at approximately 5 to 6 days after the onset of symptoms. Similar samples of viral droplets from other patients were examined by the writers, who found the viral loads to be nearly 1011 copies/mL in the throat sample, but the sputum samples had a median of 7.99 × 194, 7.52 ×105. Additionally, the virus was examined using RT-PCR in feces from 9 out of 17 established studies [24]. An examination of nine pregnant women infected with the virus did not provide substantial proof of ureteral transmission to the fetus [48].

As a positive-stranded RNA virus, SARS-CoV-2 was discovered, which is said to belong to the genus beta coronavirus, having a crown-like spike composed of glycoproteins enveloping the surface (**Figure 2**) [18]. There are six categories of coronaviruses found in human beings along with SARS-CoV-2; they are MERS-CoV, HCoV-HKU1, HCoV-OC43, HCoV-229E, SARS-CoV, and HCoV-NL63 [22]. Evaluation of phylogenetics demonstrated that ARS-CoV-2 was nearly related to SARS, with 88–89% similarity; it is also deemed to be derived from bat-SL-CoVZXC21 (unique identifier: MG772934.1) and bat-SL-CoVZC45 (unique identifier: MG772933.1); however, it has a comparatively distant relationship with SARS-CoV and MERS-CoV being 79% and 50% similar, respectively [23–25]. SARS-CoV-2 is covered with a wrapper; it is circular, elliptic, and often

#### **Figure 2.**

*The main stockpile and medium of transmission of coronaviruses (presumed stocks of SARS-CoV-2 are circled red); the alpha and beta members of coronaviruses have the potential to afflict human beings; the devouring of animals, infected with the virus as an origin of food, is the prime reason of virus spreading from beasts to human beings. Owing to being in contact with a virus-infected person, finally, the virus spread to sound individuals. Arrow with dotted black lines demonstrates the likelihood of virus spread from the bat, whereas the arrow with solid black lines represents the accurate transferal. Reference: [49]. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).*

polymorphic elements have a radius ranging between 30 nm and 70 nm [26]. The phylogenetic reports and additional research on entire genome sequencing have shown that COVID-19 is inconsistent with SARS-CoV. It can thus be considered the latest beta-coronavirus damaging human organs [27]. The genesis of the 2019-nCoV has been mysterious ever since, but the rising surge is deemed to be connected to the Seafood Market of Huanan in South China [28]. Researchers have been striving to discover the sources in animals to do away with the spread of this novel coronavirus, but none are certain until now. The maximum number of hosts is consistent with the prospective sources of the 2019-nCoV that it belongs to seafood, pangolins, or even bats [3, 4, 26]. The immediate work is to track down the transitory source instrumental in transmitting the coronavirus to human beings. Therefore, determining the source of the virus must bear the potential to help discover the zoonotic transmission method [26]. SARS-CoV-2 demonstrates the risk of high pathogenicity and communicability [29]. It is likely to be transferred from one person to another by the viral loads of infected persons who are directly in contact with the surfaces already contaminated by the respiratory droplets through sneezing, coughing, and physical contact with infected patients [29]. According to several reports, symptomatic individuals are the most recurring sources of COVID-19 escalation [27]. Furthermore, there are opinions that asymptomatic individuals can also transmit the virus as intensely as symptomatic individuals. Besides, more studies are required to understand and explain the durability of infectiveness, the procedures of transmission, and the incubation period of the virus. As HCoV-19 is the latest phenomenon among human beings, much effort is needed to be acquainted with the sources of this virus. Based on a twisted explanation or inappropriate delineation of the early released and restricted amount of data on the HCoV-19 genome, different suppositions or hypotheses are prevalent in that HCoV-19 was artificially produced in mysterious circumstances [50, 51] Specifically, the installation of a polybasic (furin) at the cleavage site of the spike protein was discovered in betacoronaviruses for the first time (48). Based on the comprehension and information collected from the MERS-CoV and SARS-CoV outbreaks, SARS (Bat-CoVRaTG13) in *Rhinolophus* affinis was successfully detected and separated; it was 95% similar to HCoV-19. It could be propounded that the COVID-19 virus possibly belongs to bats with a higher degree of conviction [52]. Additionally, phenylacetic acid amide on the cleavage region of S1 and S2 has recently been observed in the coronavirus genetic arrangement detected in a different *Rhinolophus malayanus* [52]. These outcomes imply that there are nearly two bat types: *Rhinolophus malayanus* and *Rhinolophus* affinis. They are presumed to be the native sources of HCoV-19. Bats are believed to be a possible animal pool for HCoV-19- and SARS-like [53] coronaviruses. Presently, non-comprehensive evidence is found to show the bats responsible for directly spreading HCoV-19-like coronaviruses to human beings. Recent research shows that the Malayan pangolin (Manisjavanica) has been considered a potential natural storehouse or transitional source of HCoV-19 [54–56]. In another study, community genomic sequencing of blood, intestine, and lung samples from Malayan pangolins was examined by Lam et al. [54, 57]. They detected virus sequences with a connection with a pair of subcategories of HCoV-19 like coronaviruses. Specifically, five analytical remnants of the pangolin virus, which play a significant role in human receptor binding, are similar in every detail to HCoV-19 [57]. Based on a re-evaluation conducted on a formerly announced virus metagenomics dataset of Malayan pangolins [58], it is recommended that there is a prospective pangolin origin of HCoV-19 [59]. The all-inclusive feature of HCoV-19 concerning Pangolin-CoV in pangolins has repeatedly suggested that Malayan pangolin could be a prospective transitional source for HCoV-19 [55]. It is believed that HCoV-19 could spring from a probable intermingling of the aforementioned

*Origin and Impact of COVID-19 on Socioeconomic Status DOI: http://dx.doi.org/10.5772/intechopen.98893*

Bat-CoV-RaTG13-like virus [52] and Pangolin-CoV-like virus [55]. Malayan pangolins are reported to have been spotted in the natural habitat across Southeast Asia. However, it has never been considered to belong to China, where HCoV-19 was confirmed for the first time [3, 27, 45, 52] because it was significant as an origin of food and herbal treatment.

Irrespective of its whereabouts still not being identified, multiple cases of COVID-19 have been referred to those who have visited the Seafood Wholesale Market of Huanan, situated in the city of Wuhan, China. On February 11, 2020, the WHO came up with COVID-19, a shortened form for COVID 2019. The virus responsible for this flare-up is recognized as SARS-CoV-2; recently, it has been unearthed and is closely related to bat coronaviruses, SARS-Cov, and pangolin coronaviruses.
