(+)sense RNA (plus-sense RNA):

A virus with a single-stranded RNA genome of the same polarity ('sense') as mRNA.

(-)sense RNA (minus-sense RNA):

A virus with a single-stranded RNA genome of the opposite polarity ('sense') as mRNA.

Abortive Infection:

When a virus infects a cell (or host), but cannot complete the full replication cycle, i.e. a non-productive infection.

Acute Infection:

Relatively brief infections, i.e. a few days to a few weeks, following which the virus is usually eliminated completely from the body by the immune system.

'Arboviruses':

A large a diverse group of viruses, taxonomically unrelated which are classically transmitted by arthropod vectors, e.g. mosquitoes, ticks, etc.

Assembly:

The stage of replication during which all the structural components come together at one site in the cell and the basic structure of the virus particle is formed.

Attachment:

The binding of a virus particle to a specific receptor on the surface of a host cell.

Capsid:

A protein shell comprising the main structural unit of a virus particle.

Chronic Infection:

The converse of acute infections, i.e. prolonged and stubborn. Caused by viruses which are able to persist in the body.

Complement fixation (CF):

An assay for detecting the presence of antibodies reactive against a particular antigen, e.g. a virus.

Envelope:

A lipid membrane enveloping a virus particle.

Fusion Protein:

The protein(s) on the surface of a virus particle responsible for fusion of the virus envelope with cellular membranes.

Gene expression:

An important stage of viral replication at which virus genetic information is expressed: one of the major control points in replication.

Genome replication:

The stage of viral replication at which the virus genome is copied to form new progeny genomes.

Haemagglutination-inhibition:

An assay used for certain types of viruses which are able to agglutinate red blood cells. Haemagglutination-inhibition records blocking of this process by antibodies, and thus, the presence of antibodies against the virus.

Latent Infection:

Viruses which are able to down-regulate their gene expression can establish a truly latent state, i.e. with strictly limited gene expression and without ongoing virus replication. Latent virus infections typically persist for the entire life of the host.

Matrix Protein:

A structural protein of a virus particle which underlies the envelope and links it to the core.

Maturation:

The stage of viral replication at which a virus particle becomes infectious.

Molecular epidemiology:

The use of nucleotide sequence information to study the diversity and distribution of virus populations.

mRNA:

Messenger RNA, translated on ribosomes to produce proteins.

Neutralization:

Blocking of virus infection by antibodies; also, an assay which measures this.

Nucleocapsid:

The core of a virus particle consisting of the genome plus a complex of proteins.

Penetration:

The stage of viral replication at which the virus genome enters the cell.

Persistent Infection:

Infections in which ongoing virus replication occurs, but the virus adjusts its replication and pathogenicity so as to avoid killing host. They differ from chronic infections in that whereas in chronic infections, the virus is usually eventually cleared by the host (unless the infection proves fatal), in persistent infections, the virus may continue to be present and to replicate in the host for its entire lifetime.

Polyprotein:

A long polypeptide encoding several mature proteins which are subsequently released by protease cleavage.

Receptor:

A specific molecule on the surface of a cell which is used by a virus for attachment.

Release:

The stage of viral replication at which virus particles escape the infected cell.

Tropism:

The ability of a virus to infect specific cell or tissue types.

Uncoating:

The stage of viral replication at which structural proteins are lost and the virus genome is exposed to the replication machinery.

Vector:

An organism responsible for transmitting a pathogen from one host to another, e.g. a mosquito. (In molecular biology, a molecule used to clone nucleic acid sequences).

Virions:

Structurally mature, extracellular virus particles.

Virus attachment protein:

The protein on the surface of a virus particle responsible for binding the receptor.

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