An informal proposal has been made to group together a number of recently recognized
viruses under the head of coronaviruses . They affect a variety of hosts causing
a diversity of diseases, but they are grouped together mainly because they have similar
electron microscopic appearances, are ether-labile, and probably contain RNA. However,
remembering that influenza and parainfluenza viruses were once thought to be quite
closely related on similar grounds, much of the grouping should be regarded as tentative.
Nevertheless, murine strains (MHV) are antigenically related to some human strains
and, morphologically, human, avian, and murine viruses replicate in a similar way;
it is therefore likely that at least some of the groupings will be confirmed by further
investigation. There is now some more detailed information on the structure of the
prototype virus IBV (avian infectious bronchitis virus), the striking features being
the large number of peptides and the large single RNA strand. Some strains possess
hemagglutinin and there seems to be a hemagglutinin receptor-destroying enzyme which
is not a neuraminidase; also there is evidence of a viral RNA polymerase. These features
confirm that IBV is quite distinct from other viruses. We still have no detailed information
about the biochemical characteristics of its nucleic acid, the process of replication
or the lipid composition of the envelope. All in all, the time is now ripe for completing
these basic studies of IBV and checking whether the same characteristics are found
in the other viruses at present included in the group. It may take years to reach
certainty on these points, but we believe this early attempt at taxonomy can be valuable
in indicating which facts should be sought first, in order to clarify as soon as possible
our understanding of this interesting and superficially diverse group.
The Study Group believes that the coronaviruses are sufficiently distinct from other
viruses to constitute a family, Coronaviridae; at present, it will have to be considered
a monogeneric family.
To save space, references included in the review by McIntosh  will not be repeated.
1 Taxonomy 
1.3 Family with only one genus, Coronavirus
2 The virion
2.1 Chemical composition
2.1.1 Nucleic acid
184.108.40.206 IBV2: single-stranded [5, 6]. HCV: single-stranded 
220.127.116.11 Number of pieces: IBV, one 
18.104.22.168 Sedimentation coefficients: IBV, 50S 
22.214.171.124 Molecular weight: IBV, 9 × 10G 
126.96.36.199 Infectivity: Not demonstrated for any member.
188.8.131.52 Number of polypeptides: HCV: 6-8 polypeptides : IBV: 16 polypeptides 
184.108.40.206 Molecular weight of polypeptides: HCV, 13,000-210,000 . IBV, 14,000-180,000
220.127.116.11 Enzymes: IBV: possible receptor-destroying enzyme activity , possible
RNA polymerase [10, 11]. HCV: RNA-dependent RNA polymerase .
18.104.22.168 Other functional proteins: hemagglutinin (HCV: some strains; HEV; IBV: some
2.1.3 Lipids: Present
2.1.4 Carbohydrates: IBV. HCV, TGEV: glycopeptides present.
2.2 Physicochemical properties
2.2.1 Density: 1.16-1.23 g/cm3 in sucrose: 1.23-1.24 g/cm3 in CsCl.
2.2.2 Sedimentation coefficient: HCV: 374-416S, strain OC43: 378-400S, strain 229E
. IBV: 330S.
2.2.4 Stability of infectivity
22.214.171.124 pH: TGEV: optimum stability at pH 6.5 . IBV: optimum stability between
pH 6.0 and 6.5 . Conflicting or no evidence for other viruses.
126.96.36.199 Heat: Rapidly inactivated at 56°; slow inactivation at 37°; moderately stable
at 4°, assuming optimal suspending medium.
188.8.131.52 Other agents: Unstable with common disinfectants and detergents.
2.3.1 Nucleocapsid: See 2.3.3.
2 See 10.3 for abbreviations of species.
2.3.2 Envelope: Lipid envelope present, containing peptides and glycopeptides.
2.3.3 Cores: Electron-dense inner shell visible in thin section. HCV: ribonucleoprotein
(RNP) core, density 1.31 g/cm3 (CsCl), sedimentation 180S ; linear appearance
by negative staining .
184.108.40.206 Dimensions: 55-nm diameter in thin section.
2.4.1 Overall shape: Round, non-rigid, some elongated forms.
2.4.2 Dimensions: 60-220 nm
2.4.3 Surface projections: Characteristic bulbous projections, 12-24 nm long, widely
2.4.4 Special features in thin sections: Inner and outer shells, sometimes separated
by electron-lucent space. Some reports of internal threadlike structure.
2.4.5 Other features: Fragile attachment of projections to surface of virion. Inner
tongue-shaped membrane sometimes visible by negative staining.
3.1 Site of accumulation of viral proteins: Cytoplasm.
3.2 Nonstructural proteins: Probably present.
3.3 Mode of nucleic acid replication
3.3.2 Effect of inhibitors: Sensitive to 6-azauracil, virazole . Insensitive to
5′-iododeoxyuridine, 5′-bromodeoxyuridine, 5′-fluorodeoxyuridine, cytosine arabinoside,
aminopterin and actinomycin D.
3.4 Site and mechanism of maturation: Matures in cytoplasm by budding through endoplasmic
3.5 Other features: No budding at plasma membrane.
4 Cooperative interactions: No information available.
5 Host range
5.1 Natural: Generally restricted to normal host species.
5.2.1 In vivo: Generally specific for species of origin: chicken embryos (IBV), suckling
mice (MHV, some strains of IBV3 and HCV), newborn rabbits (IBV3). suckling white rats
(IBV3), suckling hamsters (HCV), hamsters (MHV).
5.2.2 In vitro: HCV: 1°4 and 2° human embryonic cells, 1° monkey kidney cells, human
embryonic tracheal organ cultures. IBV3: 1°
3 Isolation in chicken embryos is essential before adaptation to hosts or cells indicated.
4 1° = First passage.
chicken and chicken embryonic cells, 1° monkey kidney, chicken tracheal organ cultures,
VERO cells. MHV: L cells, WI-38 cells, 1° mouse and mouse embryonic cells, mouse macrophages,
NCTC-1469 cells. TGEV and HEV: 1° porcine cells. TGEV: 1° canine kidney cells. RCV
and SDAV: 1° rat kidney cells.
6.1 Association with diseases: IBV: acute respiratory disease and nephritis in chickens.
HCV: common colds in humans. MHV: hepatitis and encephalitis in mice (most strains
cause primarily one or the other). TGEV: gastroenteritis in pigs. HEV: encephalitis
in pigs. RCV: pulmonary infections of rats. SDAV: sialodacryoadenitis in rats.
6.2 Tissue tropisms: IBV: respiratory and reproductive tract. HCV: upper respiratory
tract. TGEV: small intestine, lung. HEV: intestine, brain. MHV: brain, liver, spleen.
RCV: lung. SDV: salivary gland.
6.3 Cytopathology: Cellular vacuolation and syncytium formation.
7 Geographic distribution: Probably worldwide.
8.1 Vertical: HCV: no. IBV: yes. No data available for other strains.
8.2 Horizontal: Yes.
8.3.1 Biological: Not known.
8.3.2 Mechanical: IBV: contaminated equipment, personnel, etc. TGEV: fecal-oral route.
HCV: presumed airborne. No data for other strains.
9 Antigenic properties
9.1 Number of distinct antigenic molecules in virion: IBV: up to 3. HCV: 3, possibly
4. MHV: 2.
9.2 Antigens involved in virus neutralization: No adequate information.
9.3 Number of distinct nonstructural antigens: No adequate information.
9.4 Specificity of different antigens: No information.
10.1 Definition of family Coronaviridae: Pleomorphic enveloped particles, averaging
100 nm diameter, containing RNA and essential lipid. Bear unique definitive projections.
Multiply in cytoplasm, mature by budding through endoplasmic reticulum. No defined
subgroups, but a tentative grouping may be made on basis of serology. IBV, many recognized
serotypes, however, all seem to be interrelated, possibly by a common antigen. No
interrelationship demonstrated with any of the other coronaviruses. HCV, several serotypes,
two main groups-those isolated in tissue culture and those isolated in organ culture.
Serologically related to MHV. The three rodent coronaviruses, MHV, RCV and SDAV, are
interrelated serologically, and also related to HCV. No adequate information on relationship
or diversity between individual strains of MHV. TGEV, no antigenic diversity between
strains, possible relationship to HEV. HEV, no antigenic diversity between strains,
possible relationship to TGEV. TBDV, only one report available, no relationship shown
to other coronaviruses.
10.2 Only one Genus, Coronavirus. Type species: IBV.
10.3 Species: Avian infectious bronchitis virus (IBV)
Human Coronavirus (HCV)
Murine hepatitis virus (MHV)
Porcine transmissible gastroenteritis virus (TGEV)
Porcine hemagglutinating encephalitis virus (HEV)
Rat Coronavirus (RCV)
Sialodacryoadenitis virus of rats (SDAV)
Turkey bluecomb disease virus (TBDV) 
Neonatal calf diarrhea Coronavirus (NCDCV)