Coronavirus is a genus of animal
virus belonging to the family Coronaviridae. Coronaviruses are enveloped viruses
with a positive-sense single-stranded RNA genome and a helical symmetry. The
genomic size of coronaviruses ranges from approximately 16 to 30 kb. The name "coronavirus"
draws reference to the "corona" -- the "ring-like radiating structure" formed by
the outermost part of the atmosphere of the sun. When observed under electron
microscopy (E.M.), coronavirus particles exhibit a characteristic corona-like
morphology. The corona-like structures are actually formed by the viral spike
(S) peplomers, which are proteins that populate the surface of the virus and
determine host tropism.
Proteins that contribute to the overall structure of all coronaviruses are
the spike (S), envelope (E), membrane (M) and
nucleocapsid (N). In the specific case of SARS (see
below), a defined receptor-binding domain on S mediates the attachment of
the virus to its cellular receptor,
angiotensin-converting enzyme 2 (ACE2).
E.M. of SARS-CoV Particles
Diseases of coronavirus
Coronaviruses primarily infect the upper respiratory and gastrointestinal
tract. Four to five of total isolated strains of coronaviruses infect humans.
The most publized human coronavirus, SARS-CoV, has a unique pathogenesis because
it causes both upper and lower respiratory tract infections and can also cause
gastroenteritis. Coronaviruses are believed to cause a significant percentage of
all common colds in human adults. Coronaviruses cause colds in humans primarily
in the winter and early spring seasons. The significance of coronaviruses as
causative agents is hard to assess because, unlike rhinoviruses (another common cold virus), coronaviruses are difficult to
grow in the laboratory.
Coronaviruses also cause a range of diseases in farm animals and domesticated
pets, some of which can be serious and are a threat to the farming industry.
Economically significant coronaviruses of farm animals include porcine
coronavirus (transmissible gastroenteritis, TGE) and bovine coronavirus, which
both result in diarrhea in young animals. Feline enteric coronavirus is a
pathogen of minor clinical significance, but spontaneous mutation of this virus
can result in feline infectious peritonitis (FIP), a disease associated with
high mortality. Hence significant research efforts have been focused on
elucidating the viral pathogenesis of these animal coronaviruses, especially by
virologists interested in veterinary and zoonotic
In 2003, following the outbreak of Severe Acute Respiratory Syndrome which
had begun the prior year (SARS) in Asia, and secondary cases elsewhere in the
world, the World Health Organization issued a press release stating that a novel
coronavirus identified by a number of laboratories was the causative agent for
SARS. The virus was officially named the SARS coronavirus (SARS-CoV).
The SARS epidemic resulted in over 8000 infections, about 10% of which
resulted in death.
X-ray crystallography studies performed at the Advanced Light Source of Lawrence
Berkeley National Laboratory have begun to give hope of a vaccine
against the disease "since [the spike protein] appears to be recognized by the
immune system of the host."
Recent discoveries of novel human coronaviruses
Following the high-profile publicity of SARS outbreaks, there has been a
renewed interest in coronaviruses in the field of virology.
For many years, scientists know only about the existence of two human
coronaviruses (HCoV-229E and HCoV-OC43). The discovery of SARS-CoV added another
human coronavirus to the list. By the end of 2004, three independent research
labs reported the discovery of a fourth human coronavirus. It has been named
NL63, NL or the New Haven coronavirus by the different research groups. The
naming of this fourth coronavirus is still a controversial issue, because the
three labs are still battling over who actually discovered the virus first and
hence earns the right to name the virus. Early in 2005, a research team at the
University of Hong Kong reported finding a fifth human coronavirus in two
pneumonia patients, and subsequently named it HKU1.