Basic Microbiology of Coronavirus

984 views | Charles Adisa MD. | March 16, 2020

Taxonomic structure of the family

Family: Coronaviridae

Subfamily: Coronavirinae and Torovirinae

Corovirinae Genuses :
Alpha coronavirus,
Beta coronavirus,

Torovirinae Genuses:
Torovirus and Bafinivirus


Virus species
Alphacoronavirus 1
Canine coronavirus type I Dog
Canine coronavirus type II Dog
Feline coronavirus type I Cat
Feline coronavirus type II Cat
Transmissible gastroenteritis virus Pig
Human coronavirus 229E
Human coronavirus NL63

Betacoronavirus 1
Bovine coronavirus Cow
Equine coronavirus Horse
Human coronavirus OC43
Porcine hemagglutinating encephalomyelitis virus Pig
Murine coronavirus Mouse
and now with the new COVID 19 disease (named SARS-CoV-2.

SARS-CoV-2 is the cause of COVID 19

The SARS-CoV-2 virus is a betacoronavirus, like MERS-CoV and SARS-CoV.  All three of these viruses have their origins in BATS.

This is the first pandemic known to be caused by the emergence of a new coronavirus. In the past century, there have been four pandemics caused by the emergence of novel influenza viruses.

Risk of Severe Illness:

Early information out of China, where COVID-19 first started, shows that some people are at higher risk of getting very sick from this illness. This includes:

Older adults, with risk increasing by age.
People who have serious chronic medical conditions like:
Heart disease
Lung disease


The members of the family Coronaviridae are enveloped and positive-stranded RNA viruses. They could be spherical as in (Coronavirinae), bacilliform, as in (Bafinivirus) or found as a mixture of both, with bacilliform particles characteristically bent into crescents (Torovirus)

Origin of the word Corona

The virions are typically decorated with a large, club- or petal-shaped surface projections (the “peplomers” or “spikes”), which in electron micrographs of spherical particles create an image reminiscent of the solar corona.

Size of Coronaviridae

In terms of genome size and genetic complexity, the Coronaviridae is the largest RNA viruses identified so far, rivaled only by the okaviruses, large nidoviruses of invertebrates assigned to the family Roniviridae.

Distribution among Animals

The Coronaviruses are found in three classes of vertebrates, which include

A. Corona- and toroviruses for mammals,
B. Coronaviruses for birds, and
C. Bafiniviruses for fishes.

The incubation period of COVID 19

The maximum incubation period is assumed to be up to 14 days,
whereas the median time from onset of symptoms to the intensive care unit (ICU) admission is around 10 days.
Recently, WHO reported that the time between symptom onset and death ranged from about 2 weeks to 8 weeks

Biological properties

Coronaviruses infect birds and mammals and include several pathogens of clinical, veterinary and economic interest.

Transmission is not by biological vectors, but – depending on the virus species – via fomites or via aerogenic and/or fecal-oral routes.
As CoVs primarily target epithelial cells, they are generally associated with gastrointestinal and respiratory infections that may be acute or become chronic with prolonged shedding of the virus.

In general, these infections are mild and often asymptomatic. Some coronaviruses, however, cause severe, even lethal disease.

Murine coronavirus  (genus Betacoronavirus) may cause hepatitis and severe neurologic infection, resulting in paralysis and demyelination, providing a rodent model for the study of the neuropathogenesis of human multiple sclerosis.

Some members of the species Alphacoronavirus 1 (feline, canine and ferret coron­avirus) cause fatal immune-mediated systemic infections in their respective hosts, presumably through the infection of cells of the macrophage/monocyte lineage, with widespread inflammatory lesions in multiple organs.

The human coronaviruses that were identified early on (Betacoronavirus-1 subspecies HCoV-OC43 and Alphacoronavirus HCoV-229E) mostly cause common colds and have long been considered of modest clinical importance.
It is now recognized that these viruses may also cause severe lower respiratory tract infections (LRTI) in infants and elderly, and apparently are responsible for about 5% of infant hospitalizations from LRTI, globally.

In 2002–2003, a previously unknown coronavirus, SARS-CoV, caused an epidemic in human populations of severe pulmonary disease with a mortality rate of 10% that rapidly spread to four continents, infecting 8,096 individuals and claiming 774 victims before it was contained.

COVID 19 which is now a pandemic has spared no continent apart from Oceania with over 160,994 people infected and mortality numbers of 5973 as of today.

The coronavirus COVID-19 is affecting 155 countries and territories around the world and 1 international conveyance (the Diamond Princess cruise ship harbored in Yokohama, Japan).
Epidemiological evidence indicates that this novel human virus originated in bats, spread to Himalayan palm civets, Chinese ferret badgers and raccoon dogs at the wet markets of Guangdong, China, to enter the human population through handling or consumption of these exotic species. Although SARS has since vanished, the episode does underline the pathogenic potential of coronaviruses and the possibility of novel emerging coronavirus infections arising from cross-species transmissions. Similar incidents, though with a less dramatic outcome, seem to have given rise to human coronavirus OC43 (a single cross-species transmission of bovine coronavirus from cattle to humans), to human coronavirus 229E (transmitted from bats?) and, more recently, to canine respiratory coronavirus (transmission of bovine coronavirus to dogs). In the wake of the SARS epidemic, molecular surveillance and virus discovery studies have yielded evidence for at least 60 novel coronaviruses among which are two new human respiratory coronaviruses, HCoV-HKU1, and HCoV-NL63. The latter is considered an important cause of (pseudo)croup and bronchiolitis in children. These studies also revealed a new lineage of predominantly avian viruses (Thrush, Bulbul and Munia coronavirus), with possible relatives in mammals (Asian leopard cat, Chinese ferret badger), that on the basis of rooted phylogeny appears to belong to a new genus (Figure 2).

Bats harbor an exceptionally wide diversity of coronaviruses and have been proposed to play a vital role in coronavirus ecology and evolution, maybe even as the original hosts from which many if not all alpha- and betacoronavirus lineages were derived. Bat population densities and their roosting and migration habits would all favor such a role. Although this hypothesis has its merits and the recent virus discovery studies that prompted this view have been of truly Herculean proportions, it is of note that the actual coronavirus sampling size remains, in fact, limited and as efforts so far focused mainly on bats, our present perceptions may be biased. Further surveillance studies of a similar extent must be performed in other host species (rodents, birds) before final conclusions can be drawn.




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