MicrobiologyBytes: Virology: Caliciviruses Updated: September 11, 2007 Search

Caliciviruses

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The human pathogens in this group have been poorly studied since for the most part, they do not grow in culture. Only recently has molecular information on the nature of their genomes become available. The taxonomy of these viruses is still somewhat confused and they have previously been grouped on the basis of their appearance in the EM (unreliable).

Genome structures

The taxonomy of these viruses is still evolving rapidly, but is currently something like:

Group IV: (+)sense RNA Viruses

Family

Genus

Type Species

Hosts

Caliciviridae Lagovirus Rabbit haemorrhagic disease virus Vertebrates
Norovirus Norwalk virus Vertebrates
Sapovirus Sapporo virus Vertebrates
Vesivirus Swine vesicular exanthema virus Vertebrates

Calicivirus sequence database

Human caliciviruses (HCV) are still commonly identified by electron microscopy in faecal specimens from patients with diarrhoea, although serological assays are now becoming available (cannot be diagnosed on clinical grounds. These viruses cannot be cultured in vitro & there are no animal models available other than experimental transmission to human volunteers. These viruses are very widely distributed worldwide & infection is very common, especially in children - most adults appear to have been infected & may or may not be immune to reinfection. Calicivirus infection is associated with diarrhoea or vomiting lasting 1-4 days (incubation period 1-2 days). The most frequent source of infection appears to be contaminated food/beverages - may cause up to 90% of food-related gastroenteritis outbreaks. Treatment: supportive only (rehydration). To view an electron micrograph of calicivirus particles, click here. The cup-like depressions which give this family of viruses their name are just visible if you observe the perimeter of these negatively stained particles.

Norovirus structure

Studies have shown that Noroviruses (NV) are the most commonly identified cause of infectious intestinal diseases in Western Europe. These viruses account for an estimated 6% and 11% of all infectious intestinal diseases in England and the Netherlands, respectively, and for an estimated 23 million cases of NV in the United States each year (Lopman et al. Two Epidemiologic Patterns of Norovirus Outbreaks: Surveillance in England and Wales, 1992–2000. Emerging Infectious Diseases, Vol. 9, No. 1, January 2003). Noroviruses are responsible for >85% of all nonbacterial outbreaks of gastroenteritis. Three thousand and twenty-nine laboratory confirmed reports of NV infection were reported to the PHLS Communicable Disease Surveillance Centre (CDSC) in the first ten months of 2002. This represents a substantial increase from preceding years. The bulk of the recent increase was in the elderly. Sixty-eight per cent of all cases reported were aged 65 years or above. The rise in reports does not necessarily mean that the incidence has increased. Factors potentially influencing the number of reports include increased ascertainment due to awareness and improvements in diagnostic capability. The impact of noroviruses on healthcare facilities is increasingly recognized both in the medical and popular press. Since 1992, over three-quarters of norovirus outbreaks reported to the PHLS CDSC occurred in either hospitals or residential homes.

Hutson AM, et al. Norovirus disease: changing epidemiology and host susceptibility factors. Trends in Microbiol. 2004 12: 279-287.

Some people are resistant to norovirus virus infection; however, the factor(s) responsible for resistance or susceptibility to NV infection has not been identified. Hutson AM, Atmar RL, Graham DY, Estes MK. Norwalk virus infection and disease is associated with ABO histo-blood group type. J Infect Dis 2002 185: 1335-1337. This study investigated the relationship between a person's ABO histo-blood group type and the risk of NV infection and symptomatic disease after clinical challenge. Individuals with an O phenotype were more likely to be infected with NV, whereas people with blood group B antigen had decreased risk of infection and symptomatic disease. This is the first report demonstrating an association between a genetic factor and the risk of NV infection and symptomatic disease.

 


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