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Ambisense Virus

A virus whose genome contains both positive-sense and negative-sense sequences.

Antibody

An immunoglobulin protein, produced by B cells, that can bind to a specific part of an antigen, tagging it for attack by the immune system. All antibody molecules have a similar Y-shaped structure and, in their monomer form, consist of two identical light chains and two identical heavy chains.

Antiviral

Any drug or other agent that can kill or inhibit the transmission or replication of viruses.

Bacteriophage

Any virus that infects bacteria.

capsid

A shell of protein enclosing the genome of a virus particle.

CD4

A membrane protein on the surface of some T cells in humans. CD4+ T cells can give rise to helper T cells.

cDNA

DNA produced in the laboratory using an RNA transcript as a template and reverse transcriptase; corresponds to a gene but lacks introns. Also produced naturally by retroviruses.

co-receptor

Any membrane protein that acts with some other membrane protein in a cell interaction or cell response.

emerging virus/disease

Any infectious disease, often a viral disease, which suddenly afflicts significant numbers of humans for the first time; often due to changes in the host species for a pathogen or host population movements.

envelope, viral

A membrane-like covering that encloses some viruses and their capsid coats, shielding them from attack by the host's immune system.

epidemic

The spread of an infectious disease throughout a population in a short time period.

helper T cell

An effector T cell that secretes cytokines and in other ways promotes the activation of other lymphocytes. Is descended from an activated CD4+ T cell that has interacted with antigen presented by dendritic cells, macrophages, or B cells.

immune system

In vertebrates, the system whose primary function is to defend the body against pathogens. Includes several types of cells (e.g., lymphocytes and macrophages) and several organs where they develop or reside (e.g., lymph nodes and thymus).

latency

In viruses that infect animals, the ability to exist in a quiescence state without producing new virions.

lysogenic cycle

A type of viral replication in which a viral genome enters a host cell, is inserted into the host's chromosome, and is replicated whenever the host cell divides. When activated, the viral DNA enters the lytic cycle, leading to production of new virus particles.

lytic cycle

A type of viral replication in which a viral genome enters a host cell, new virus particles (virions) are made using host enzymes and eventually burst out of the cell, killing it. Also called replicative growth

mammary glands

Specialized exocrine glands that produce and secrete milk for nursing offspring. A diagnostic feature of mammals.

negative-sense virus

A virus whose genome contains sequences complementary to those in the mRNA required to produce viral proteins.

pandemic

The spread of an infectious disease in a short time period over a wide geographic area and affecting a very high proportion of the population.

positive-sense virus

A virus whose genome contains the same sequences as the mRNA required to produce viral proteins.

protease

An enzyme that can degrade proteins by cleaving the peptide bonds between amino acid residues.

retrovirus

A virus with an RNA genome that reproduces by transcribing its RNA into a DNA sequence and then inserting that DNA into the host's genome for replication.

reverse transcriptase

An enzyme of retroviruses (RNA viruses) that can synthesize double-stranded DNA from a single-stranded RNA template.

RNA replicase

A viral enzyme that can synthesize RNA from an RNA template.

strain

A population of genetically similar or identical individuals.

vaccine

A preparation designed to stimulate an immune response against a particular pathogen without causing illness. Vaccines consist of inactivated (killed) pathogens, live but weakened (attenuated) pathogens, or portions of a viral capsid (subunit vaccine).

virion

A single mature virus particle.

virulent

Referring to pathogens that can cause severe disease in susceptible hosts.

virus

A tiny intracellular parasite, consisting of a DNA or RNA genome enclosed within a protein shell (capsid), that uses host cell enzymes to replicate. In enveloped viruses, the capsid is surrounded by a phospholipid bilayer derived from the host cell plasma membrane, whereas nonenveloped viruses lack this protective covering.

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