Viruses are tiny, infectious parasites that, unlike bacteria, fungi and protozoa, require a host to replicate. Viruses are typically sensitive to environmental conditions and cannot survive for long on surfaces. However, viruses can be highly infectious, easily transmitted and, being the smallest of the pathogens species, very difficult to eliminate with filtration.
A bacteriophage is a species of virus that invades bacteria and reproduces inside. Sometimes called phages, these viruses can be responsible for making bacteria pathogenic as well as a vehicle to combat superbugs. The most widely recognized examples of phage-encoded virulence factors are exotoxins, which is the major factor of several bacterial pathogens, including cholera, diphtheria and botulism.
Viruses can quickly spread through contaminated water and airborne droplets. Each year millions of school aged children are afflicted with Influenza (the “flu”), Rhinovirus (a cold), streptococcal pharyngitis (strep throat) and respiratory syncytial virus (RSV), with airborne transmission being a primary vector. During the 2016–2017 flu season, influenza infections resulted in an estimated 30.9 million people getting sick, 14.5 million going to a health care provider, and an estimated 600,000 people being hospitalized.
Coronaviruses, named for the crown-like projections on their surfaces, are a type of virus which usually cause mild to moderate upper-respiratory tract illnesses, and is typically associated with the common cold. Most people get infected with one or more of these viruses at some point in their lives and amongst humans coronaviruses are most common in the winter months and early spring.
Coronaviruses are zoonotic, meaning they are transmitted between animals and people. Investigations revealed that SARS-CoV was transmitted from civet cats to humans and MERS-CoV which surfaced in Saudi Arabia spread from dromedary camels to humans. Human to human transmission is typically through aerosolized droplets when an infected person coughs or sneezes without covering their mouth, or when someone touches a person or surface that has the virus.
However some coronaviruses can be responsible for more severe illnesses like bronchitis, pneumonia, severe-acute-respiratory syndrome (SARS) and coronavirus disease 2019. .