Cockatoo enterolike virus CELV An

unassigned virus in the family Picornaviridae.

cockle agent A virus resembling a par-vovirus found in many outbreaks of gastroenteritis involving ingestion of shellfish or cold foods. See cockle virus.

cockle virus A probable species in the genus Erythrovirus. A virus associated with gastroenteritis following ingestion of cockles. Particles 25-26nm, distinct from Norwalk virus, later found to have a single-stranded DNA genome with sequence homology to B19 virus.

Appleton H and Pereira MS (1977) Lancet ii, 780

Turton J et al (1990) Epidemiol Infect 105, 197

co-cultivation A mixed culture of two or more different types of cell. If one of them is permissive for the replication of a latent virus present in the other cell line, this virus may replicate and become detectable, i.e. be 'rescued'. The cells in which replication takes place are known as 'indicator cells'. The frequency of virus rescue during co-cultivation can often be increased by artificially fusing the cells, with resulting heterokaryon formation. An example of rescue is the recovery of measles virus from the brain tissue of patients with subacute sclerosing panen-cephalitis by co-cultivation with Vero cells.

Codajas virus An unclassified arbovirus isolated from Culicine mosquitoes in the Amazon region of Brazil. Not associated with disease in humans.

Code of Safety Practices The appropriate practices for handling viruses in the laboratory are described in detail in the US Government HHS publication number (CDC) 93-8395 entitled 'Biosafety in Microbiological and Biomedical Laboratories', Fourth edition, edited by JY Richmond and RW McKinney (1999).

coding sequence The portion of a gene that directly specifies the amino acid sequence of its protein product. Non-coding sequences include control regions such as promoters, and polyadenylation signals and the intron sequences of unknown function found in certain eukaryotic genes.

codon A group of three consecutive bases in a nucleic acid molecule which together specify a particular amino acid during translation from mRNA. Since there are four bases, there are 64 possible codons, but as only 21 amino acids need to be specified most are coded for by several alternative codons (degeneracy of the code). However, no codon specifies more than one amino acid. The sequence of bases which make up a gene is translated as a series of codons, beginning with an initiation codon AUG. This establishes the reading frame within the gene. In some virus nucleic acids there is more than one reading frame, so that up to three different proteins may be specified by a single sequence of bases. Termination of translation is specified by a terminator codon UAG, UAA or UGA except in mitochondria where UGA appears to code for tryptophan. There is also evidence that UGA may code for selenocysteine in certain contexts in eukaryotic cells (Taylor, 1994).

Barrell BG et al (1979) Nature 282, 189

Crick FHC (1963) Prog Nucl Acid Res Mol Biol 1,

Taylor EW et al (1994) J Med Chem 37, 2637

codon bias The non-uniform distribution of codon usages which results in preferred codons being used by viruses or organisms to specify a particular amino acid.

cod ulcus virus A virus found in association with ulcus syndrome of cod, Gadus morhua. A tentative member of the family Iridoviridae.

Jensen NJ et al (1979) Norg Vet Med 31, 436

Coe virus An old name for coxsackie virus A2l, which can cause a 'common cold'-like disease.

cofactor Additional (non-protein) component required by an enzyme for its action.

COFAL test A complement /ixation test for the common group-specific (gs) antigen present in all avian leukosis viruses. See Avian leukosis virus.

cohort study A type of prospective epi-demiological study of a group of people which aims to gather new data and identify cause-effect relationships. When successful, can provide incontrovertible proof of a cause-effect relationship.

cohesive ends The projecting 5' single-stranded ends occurring on certain double-stranded nucleic acid molecules which, through sequence complementarity, can base-pair and thus form a circular molecule. Such structures occur in the genome DNA of temperate bacterio-phages and facilitate integration into host DNA.

Cohn fractionation technique A method for fractionation of proteins from plasma by precipitation with cold ethanol. It yields three fractions, enriched in cryo-precipitates, globulins and albumin, respectively. A modification of the original technique is used to prepare human immunoglobulins for viral immunopro-phylaxis or treatment.

Cunningham-Rundles C (1992) In Encyclopedia of Immunology, edited by IM Roitt and PJ Delves. London: Academic Press, p. 598

Coho salmon reovirus CSR (CSRV) A strain of Aquareovirus B in the genus Aquareovirus.

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