Taxonomy
These single-stranded, positive sense RNA viruses belong to the order Nidovirales, along with the family Arteriviridae, a family of animal viruses that infect horses, donkeys, mice, pigs, and monkeys. There are two genera in the Coronaviridae family: Coronavirus and Torovirus, which differ on the basis of genome length, morphology, and nucleotide sequence.
* Note, only human viruses are listed below
Order: Nidovirales
Family: Coronaviridae
Genus: Coronaviruses
Species: Human Coronavirus (CoV)
Strain: 229E
Strain: OC43
Strain: NL63
Strain: HKU1
Strain: SARS-CoV
Genus: Toroviruses
Species: Human toroviruses
Genus coronavirus
SARS: By far, the best known member of the Coronaviridae family is SARS-CoV (Severe Acute Respiratory Syndrome), which recently caused an epidemic of lethal pneumonia in South East Asia - killing over 300 Taiwan, China, the Philippines, Singapore, Vietnam, and spreading to Canada. It causes the most severe disease of any human coronavirus, infecting the upper airway and alveolar epithelial cells. The case fatality rate in the 2002-2003 epidemic was 10%, but reached up to 50% in elderly patients and those with other underlying illnesses. In total, 8098 probable cases were confirmed by the WHO, with 372 mortalities. The horseshoe bat is the the only animal to have a tested pattern of infectivity consistent with being a natural reservoir for SARS. While animals are believed to be the original source (30-85% of horseshoe bats tested had SARS-CoV antibodies), the global spread of the virus occurred by human-to-human transmission through close contact.
However, this genus also contains other viruses, which are associated with respiratory and enteric disease:
- HCoV 229E
- HCoV OC43
- HCoV NL63
- HCoV HKU1
The common cold: Coronaviruses are second only to rhinoviruses as the cause of the common cold. HCoV 229E and HCoV OC43 are responsible for causing 30% of common colds and are transmitted through the respiratory route. The common cold is a collection of signs and symptoms (known as a syndrome) that has an incubation period of 2-3 days. Recovery is usually seen in about a week. HCoV229E and HCoV OC43 have been studied most intensely and have been shown to cause symptoms including fever, headache, malaise, chills, rhinorrhea, sore throat, and couch for about 3 days. Studies have shown that reinfection is common, suggesting that infection does not produce high levels of protective immunity.
Genus torovirus
Human toroviruses look distinctly different from their fellow coronaviruses. Torovirises are toroid in shape (bagel-looking: biconcave disk, rod, or kidney shaped) and are believed to be associated with human gastroenteritis and diarrhea. These viruses also have club-like projections, and are associated with enteric disease. Torovirus infection has been detected in various animals - horses, cattle, pigs, cats, goats, and humans - but it is not a particularly threatening pathogen to any.