An Introduction to a real understanding of the coronavirus.

A few months ago I read this paper "Bat Coronaviruses in China Yi Fan, Kai Zhao, Zheng-Li Shi, and Peng Zhou." This paper was submitted to 29 January 2019; Accepted: 26 February 2019; Published: 2 March 2019. When a read the paper I thought it was very interesting but I do not pay attention so far. Inspired by this paper "Bat Coronaviruses in China Yi Fan, Kai Zhao, Zheng-Li Shi, and Peng Zhou" I want to give a scientific overview of Coronavirus.

Introduction

In past two decades, three coronaviruses have been identified as the cause of the large-scale disease: Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and Swine Acute Diarrhea Syndrome (SADS). SARS and MERS emerged in 2003 and 2012 and caused a worldwide pandemic that claimed thousands of human lives, while SADS struck the swine industry in 2017. Thus, it is highly likely that future SARS- or MERS-like coronavirus outbreaks will originate from bats, and there is an increased probability that this will occur in China. All the outbreaks began in China and were caused by coronaviruses of bat origin. 

Coronavirus Taxonomy

Coronaviruses (CoVs) belong to the subfamily Orthocoronavirinae in the family Coronaviridae and the order Nidovirales. CoVs have an enveloped, crown-like viral particle from which they were named after. Faced with other RNA viruses, the expanded genome size of CoVs is believed to be associated with increased replication fidelity. Genome expansion further facilitates the acquisition of genes encoding accessory proteins that are beneficial for CoVs to adapt to a specific host. The CoV subfamily is expanding rapidly, due to the application of next-generation sequencing which has increased the detection and identification of new CoV species. The CoV taxonomy is constantly changing. According to the latest International Committee of Taxonomy of Viruses (ICTV) classification, there are four genera (α-, β-, δ-, and γ-) consisting of thirty-eight unique species in the subfamily. The number of species will continue to increase, as there are still many unclassified CoVs.

Two highly pathogenic β-CoVs, SARS-CoV, and MERS-CoV have caused pandemics in humans since 2002. Originating in China and then spreading to other parts of the world, SARS-CoV infected around 8000 individuals with an overall mortality of 10% during the 2002–2003 pandemic. Since its emergence in 2012 in the Middle East, MERS-CoV spread to 27 countries, resulting in 2249 laboratory-confirmed cases of infection with an average mortality of 35.5% (until September 2018). 

Linking Bats to Coronaviruses

Bats are now recognized as important reservoir hosts of CoVs. They hypothesized that flight provided the selection pressure for coexistence with viruses, while the migratory ability of bats has particular relevance in the context of disease.

Long-term surveillance revealed an average 10% SARS-related CoV nucleotide positivity in bats. Similarly, bats have been proposed to harbour the progenitor viruses of MERS-CoV. In addition, bats also carry α-CoVs that are related to pathogenic human 229E- and NL63-CoVs, as well as pandemic swine coronavirus PEDV. 

Why China?

China is the third-largest territory and is also the most populous nation in the world. A vast homeland plus diverse climates bring about great biodiversity. Chinese food culture maintains that live slaughtered animals are more nutritious, and this belief may enhance viral transmission.

The majority of the CoVs can be found in China. Moreover, most of the bat hosts of these CoVs live near humans, potentially transmitting viruses to humans.

Geographical distribution of bat coronaviruses (CoVs) and their corresponding bat hosts in China. Each red box represents one CoV positive sample found in that particular bat species. Guangdong Province, where SARS and SADS began, is circled in red. Abbreviations of bat species and virus species are indicated.

SARS-Related Coronaviruses

In November 2012, the first case of SARS was recorded in Foshan city, Guangdong Province, China. In 2005, two independent Chinese groups reported the first bat SARS-related CoV (SARSr-CoV) that was closely related to human SARS-CoV, implying a bat origin of the latter. SARSr-CoVs are present in different bat species but all belong to the family of Rhinolophidae and Hipposideridae. The most variable regions among bat SARSr-CoVs are the S and ORF8 genes. The S protein in certain strains is capable of using human ACE2 as a receptor and thus poses a direct threat to humans. Another protein, ORF8, was suggested to be important for interspecies transmission. It was strongly suggested that SARS-CoV most likely originated from Yunnan Rhinolophus bats via recombination events among existing SARSr-CoVs.

COVID-19

At the moment, COVID-19, it's a global emergency. The COVID-19 has infected more than 110,000 people worldwide after human activity led to bats spreading the disease. There is global attention to take under control the spread of this disease. Different countries are asking the population to keep in home to control the spread disease.

Thank you for your attention,

Matteo Testi