SARS-CoV-2 origin, classification and transmission: a mini-review ABSTRACT SARS-CoV-2 is the seventh zoonotic pathogenic novel member of the human coronaviruses and the third coronavirus to cause a large-scale epidemic in the twenty-first century, highly contagious, spreading quickly around the world and affecting all individuals, especially the elderly, those with diverse genetic and immunological backgrounds, also those with multiple underlying disorders and varied demographics like sex and environmental conditions. This work introduces the virology of the novel virus, reveals its possible origin and describes how it spreads via the diverse routes of infection, showing the biological characteristics related to its risk of causing a pandemic, and the kind of diagnostic tools used to identify it. The virus pandemic rapidly progressed worldwide and is still ongoing; the numbers of affected and those deceased are increasing, with devastating societal, economic and political impacts. KEYWORDS: SARS-CoV-2, COVID-19, virus, pandemic, pneumonia. 1. Introduction Coronaviruses have caused two large-scale epidemics in the past [1], and gained much attention as the causative agents for the outbreaks of human respiratory syndromes such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) which arose from zoonotic transfer from animals to humans [2]. Severe Acute Respiratory Syndrome (SARS- CoV) outbreak occurred in between November 2002 and July 2003 and had a 9.6% fatality rate, leading to 8098 infections and 774 deaths with the majority of cases in mainland China and Hong Kong; it transmitted from animals in open- air markets [3]. Middle East Respiratory Syndrome Coronavirus (MERS-CoV) which was first detected in Saudi Arabia in 2012, nine years later after SARS outbreak. It spread to the Middle East with a 35% fatality rate of cases [4]; it caused 2465 confirmed cases worldwide, 896 fatalities and is still circulating with lower severity [3]. Both SARS-CoV and MERS-CoV are zoonotic viruses, and bat/civet and dromedary camels are their hosts, respectively [5]. Nevertheless, it is likely that SARS-CoV-2 may also have had an intermediate animal host before it was transmitted to humans similarly to SARS and MERS [6]. The end of 2019 was marked by the emergence of a novel coronavirus, severe acute respiratory syndrome coronavirus 2, which caused an outbreak of viral pneumonia, firstly documented in Wuhan, China that started from a local seafood market in Huanan, where a probable zoonotic source has been speculated to originate [7]. The outbreak caused by COVID-19 virus was identified in Wuhan City, in the Hubei province of Laboratory of Microbiology Applied to the Food Industry, Biomedical and the Environment, Faculty of Nature and Life Sciences, Earth and Universe Sciences, University of Tlemcen, Algeria. Ilyes Zatla * , Lamia Boublenza and Hafida Hassaine *Corresponding author: ilyes.zatla@aol.com Current Topics in Virology Vol. 18, 2021