What causes an epidemic?

Introduction

 

Global health threats come in various flavors: vaccine-preventable diseases, antimicrobial resistance, noncommunicable diseases, air pollution and climate change, weak primary health care, lack of access to treatments, lack of access to sanitation and water, underinvestment in health workers, and lack of epidemic/pandemic preparedness. Focusing on the epidemic and pandemic crises, it all starts with a single virus, humble and seemingly minuscule, yet belonging to the most diverse body of all domains in the phylogenetic tree. A virus is a non-living entity composed of different types of nucleic acids (i.e. single-stranded DNA, single-stranded RNA, double-stranded DNA, etc.) that requires a vector in order for transmission to occur. A vector is a living or non-living agent that can spread viruses from one to another, serving as a means not only for virus distribution but also amplification for the infection. Transmission occurs when a primary host passes on the viral infection to a secondary host, which may include multiple host species [1].

 

An epidemic begins with a virus that becomes successful in spreading by infecting hosts in a localized context. Then as it infects more hosts, the virus gets disseminated through multiple disease reservoirs, such as inanimate (soil, water, door handles, chairs, paper) and animate (hands, pets, humans, microbes) objects. Once the virus has infected a specific area, it gets named as an epidemic. Understanding the biology aspect is crucial to halting or controlling an epidemic from spreading even further and reaching pandemic status, becoming a global health crisis. The basis of epidemiology knowledge for any particular virus and disease depends on the infection’s transmissibility, the scope of clinical severity and illness, and the number of infected people determine any epidemic’s impact [2]. Disease severity ranges in a spectrum: asymptomatic, asymptomatic-but-mild, to severe, to requiring hospitalization, to fatal. 

 

Epidemic → Pandemic

 

So how did a minuscule viral entity bring society to its metaphorical knees and become one of the most powerful forces shaping 2020? A simple epidemiological framework is exactly how one can trace the events of how the coronavirus disease-2019 (Covid-19) evolved into a pandemic. The novel coronavirus, severe acute respiratory virus-2 (SARS-CoV-2), spread within the Wuhan region first, then transcended beyond into neighboring countries. Once SARS-CoV-2 continued spreading within each of those countries, the problem became a global health threat, ultimately becoming a worldwide pandemic affecting nearly all human populations.

 

The document below will outline the basics of virology as it relates to Covid-19 as well as the transmission of the novel coronavirus. By understanding these mechanisms of replication and transmission, the necessary actions and precautions to prevent its spread will become clear.

 

REFERENCES:

[1] Cann, A. J. (2016). Principles of molecular virology. Amsterdam: Acad. Press.

[2] Lipsitch, M., Swerdlow, D. L., & Finelli, L. (2020). Defining the Epidemiology of Covid-19—Studies Needed. New England Journal of Medicine, 382(13), 1194–1196. https://doi.org/10.1056/NEJMp2002125

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