CORONA

Introduction

Do you like Corona? Then welcome to Aaron and Jenny's coronavirus web site. Coronavirus is a family of positive, RNA, helical, enveloped, viruses that infect mammals and birds. The word corona means "crown" because of the way the envelope proteins look under an electron microscope. The capped and poly-adenylated genome is the largest of the RNA viruses and has a unique method of replication. These viruses have the ability to genetically recombine with other members of the coronavirus family. Coronavirus is infamous for being a cause of the common cold. The family consists of two genera, coronavirus and torovirus, each of which contain viruses that infect humans. For more information, see web sites from previous years and the remainder of our webpage.

Human Torovirus

Relatively little is known about the human torovirus. Torovirus-like particles have been found in fecal matter of children with diarrhea since before 1994, however it has been dificult to determine the etiology of this illness. In a 1998 study of hospitalized children, torovirus was strongly associated with gastroenteritis; however, the virus tended to nosocomially infect children who were immunocompromised. Two side effects of infection included vomiting and diarrhea which is unusual for viral enteritis. Human torovirus is probably a significant cause of gastroenteritis in humans although it remains difficult to make a clear diagnosis and its epidemiology of non-hospitalized populations is not well known.

Structural Proteins

Depending on the coronavirus in question, the genome encodes 3 or 4 different structural proteins. Human Coronavirus-OC43 encodes for hemagglutinin-esterase (HE) whereas HCV-229E does not. This protein causes red blood cells to clump together, and can be used to determine how much virus is in a sample. HE can also initiate binding. As explained in an update below, Human Torovirus also encodes for HE. All coronaviruses encode for a nucleocapsid protein (N). This protein binds to RNA and forms a helical nucleocapsid. It may be involved in the regulation of RNA synthesis. The membrane glycoprotein (M) is involved with envelope formation. The spike protein (S) is also responsible for binding to cells. The corona cycle link to the left explains the involvement of these proteins in each step of the dynamic phase.

Recent Developments

Coronaviruses have been suspected as causal agents in multiple sclerosis. To test this possibility cerebrospinal fluid (CSF) from patients with acute monosymptomatic optic neuritis (AMON), a precursor to MS, was tested for human corona virus (HCV) using reverse transcriptase PCR. Two strands of HCV were tested, 229E and OC43. CSF from 4 patients (11%), and 1 control (7%) tested positive for the 229E strain while none tested positive for the OC43 strain. This is not a statistically significant difference and does not provide evidence for an assosiation of HCV and AMON.

Dessau, R. B., G. Lisby and J.L. Frederiksen. "Coronaviruses in spinal fluid of patients with acute monosymptomatic optic neuritis." Acta Neurol Scand. '99 Aug 100 (2) 88-91.

Sera collected from 2469 pigs in the Tohoku District of the Honshu Island of Japan were tested for various coronavirus strains (haemagglutinating encephalomyelitis virus- HEV67N strain, human coronavirus- HCV OC43 strain, and bovine coronavirus- BCV K strain). Serum of inoculated mice was used as a positive control. Of the swine tested, 82.1% of the sera were positive for HEV-67N, 91.4% were positive for HCV-OC43, and 44.2% tested positive for BCV-K. The percentage of infected swine varied significantly among farms. The swine had inapparent infections, none showing disease from the HEV-67N infection. Antibodies to the human strain, HCV-OC43, were more prevalent in swine than the other two strains, suggesting transmission from humans to swine and vice-versa.

Hirano, N., Y. Suzuki and S. Haga. "Pigs with highly prevalent antibodies to human coronavirus and swine haemagglutinating encephalomyelitis virus in the Tohoku district of Japan." Epidemiology of Infectious Diseases. '99 Jun;122(3):545-51.

This study attempts to determine if Human Coronavirus strains OC43 and 229E have an affinity for neural cells and can persist in them, possibly causing chronic disease. Evidence has pointed towards this conclusion. It has been shown that the CNS of mice can be infected by mouse hepatitis virus (MHV), causing meningitis and encephalitis. The CNS of non-human primates can also be infected by a coronavirus. Antibodies to HCV-OC43 have been detected in the CNS of multiple sclerosis and parkinson's disease patients. HCV-OC43 RNA has also been detected in human brains and has been shown to infect astrocytes and microglia in primary culture. Acute and chronic infection of HVC-OC43 was tested on neural cells (oligodendrocytes, astrocytes, microglia, and neurons) by measuring viral antigens, infectious viral particles, and viral RNA. Acute infection was maintained in all cell lines. Viral antibodies were detected and virions were being produced (although not as many as the control). Antibody staining showed that persistent infection was maintained in astrocytes, oligodendrocytes, and neurons. When the S1 gene fragment was sequenced (the S1 gene is highly variable and may determine neural virulence) point mutations were found in all viruses persistently infecting cells. The cell with the most cytopathic effects had the highest number of point mutations but there was no specific mutation that was common among persistently infecting viruses.

N. Arbour et al. "Acute persistent infection of human neural cell lines by human coronavirus OC43." Journal of Virology. '99 Apr; 73(4):3338-50.

The Mouse Hepatitis Virus (MHV) JHM strain can only bind to its receptor, mouse biliary glycoprotein (mBGP), expressed in the liver and the intestine of mice. In mice JHM causes a multiple sclerosis-like syndrome. To date, no wild-type MHV strain has been found to infect human cells. The experimenters infected the human hepatocellular carcinoma cell line HuH-7 with two strains of this virus: JHM-DL and JHM-DS. The infected cells showed cytopathic effect and viral replication. It was determined that the S protein is involved in binding with the receptor and infection by using a neutralizing antibody specific for the JHM S protein. Induction of fusion of the cells appeared to be by a different route in the HuH-7 cells. Recombinant infections suggested that there are more than one genes involved in tropism. Addition of MHV receptor mBGP to various strains of MHV in human cells increased infectivity, suggesting that there is insufficient endogenous receptor in the cells. In discussion, it should be noted that a coronavirus strain which most closely resembles MHV has been isolated from the brain of a multiple sclerosis patient. In primate brains, the JHM strain replicates and causes demyelination and encephalitis. There is evidence implying MHV-like coronavirus strains in humans. But the receptor for the JHM strain on HuH-7 is not known. The HE protein is a candidate for involvement in syncytia or viral infection in these cells. This study raises the question of an assosiation of MHV and hepatitis.

Koetters, Peter J, et al. "Mouse Hepatitis Virus Strain JHM Infects a Human Hepatocellular Carcinoma Cell Line." Virology. 1999 Nov 25; 264(2):398-409.

This study extends the known function of the coronavirus E protein. It is demonstrated that the E protein can induce apoptosis in mouse DBT cells, but the S, M, N, or hemagglutinin-esterase proteins cannot induce apoptosis. The Bcl-2 oncogene did not prevent apoptosis in this experiment.

Chen, An S. et al. "Induction of apoptosis in murine coronavirus-infected cultured cells and demonstration of E protein as an apoptosis inducer." Journal of Virology. Sep '99; 73(9):7853-9.

This study demonstrates by using mutational analysis that a 54-nucleotide hairpin-type pseudoknot on the 3' end of the coronavirus genome is required for the replication of a defective interfering genome. It possibly has two conformational states and it might function as a regulatory control element in normal viral RNA replication.

Williams, GD, et al. "A phylogenetically conserved hairpin-type 3' untranslated region pseudoknot functions in coronavirus RNA replication." Journal of Virology. Oct '99; 73(10): 9349-55.

Two toroviruses, human torovirus (HTV), and Breda virus (BRV) express the hemagglutinin-esterase (HE) gene. The HE protein may help the virus bind and enter the mucus layer of the intestine. By using RT-PCR to sequence the BRV-1 and HTV HE gene, this group found that they have 85% sequence identity to each other. They are both related to the HE gene of BRV-2 and the torovirus prototype BEV. The HE protein from HTV and BRV were expressed, and using hyperimmune sera it was determined that there was substantial cross-immunoreactivity among species.

Duckmanton, Lynn, et al. "The novel hemagglutinin-esterase genes of human torovirus and Breda virus." Virus Research. Jun '99;64:137-49.

The narrow host range of coronaviruses appears to be regulated by interactions of the S protein and the virus receptor. A chimeric mouse hepatitis virus (MHV) was created with the ectodomain of the spike glycoprotein (S) replaced with the ectodomain of the S protein of feline infectious peritonitis virus. The chimeric virus could infect feline cells but not murine cells in culture.

Kuo, L, et al. "Retargeting of coronavirus by substitution of the spike glycoprotein ectodomain: crossing the host cell species barrier." Journal of Virology. Feb '00;74(3):1393-406.

Only the E and M protein are necessary for formation of the coronavirus envelope. This study characterizes the MHV-A59 E protein. The protein is stable during infection and becomes integrated into the membrane without a cleaved signal peptide. Electron microscope pictures show that expression of E protein in cells produces similar tubular, convoluted membranes as cells infected with MHV-A59. By co-labeling with antibodies to E and to the ER, it was shown that the E protein accumulates in and induces curvature of the pre-Golgi membranes where the virus assembles.

Raamsman, MJ, et al. "Characterization of the coronavirus mouse hepatitis virus strain A59 small membrane protein E." Journal of Virology. May 2000;74(5):2333-42.

Corona versus Rhino

Both coronaviruses and rhinoviruses can cause colds; however, these viruses differ in structure and symptoms. Below is a table which compares the two.

	Coronavirus	Rhinovirus
Nature of pathology	Epithelium of upper respiratory tract poor immune response-no cross immunity importance of IgA is unknown	upper respiratory tract inflammation, edema, copious exudation immunity (IgA) declines w/in a month
Viral family characteristics	Enveloped, helical, + ss RNA, 30kb, capped, poly A tail, infectious, replicates in cytoplasm	Non-enveloped, icosahedral, + ss RNA, 7-8 kb, poly A tail, infectious, similar translational properties
Route of transmission	Same as rhinovirus	Sneeze- aerosal, hands, fomites
Incubation period	2-5 days	1-3 days
Duration of disease	Virus shed for about 1 week	3 days to 2 weeks, virus shed nasally for 2-3 days
Severity of disease	Nasal discharge, malaise, cough, sore throat not as prominent as in rhinovirus, little or no fever, lower respiratory tract not involved	Nasal discharge, congestion, sneezing, headache, mildly sore throat and/or cough, little or no fever
At-risk group for infection	Asthmatic children and adults with chronic bronchitis	Asthmatic children, adults with chronic bronchitis and smokers, preschool children susceptible
Seasonality	More common in winter	Common in autumn and spring

Cool links:
A replication puzzle
Basic corona virus info
Coronaviridae info
More corona virus stuff
Common cold info
Pictures
Search Pubmed for updates
All the virology on the Web

Coronaviridae References

Fields Virology 1996 Chapters 34 and 35

Torovirus references
Jamieson, Frances B. "Human Torovirus: A New Nosocomial Gastrointestinal Pathogen." Journal of Infectious Diseases. Jun 1998;178:1263-9.

Koopmans, Marion, et al. "Enzyme-linked immunosorbent assay reactivity of torovirus-like particles in fecal specimens from humans with diarrhea." Journal of Clinical Microbiology. Oct 1993, p. 2738-44.

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