Virion Health Dictionary

The term applied to a group of infective agents which are so small that they are able to pass through the pores of collodion ?lters. They are responsible for some of the most devastating diseases affecting humans: for example, INFLUENZA, POLIOMYELITIS, SMALLPOX and YELLOW FEVER. The virus of in?uenza measures 80 nanometres, whereas the STAPHYLOCOCCUS measures 1,000 nanometres (1 nanometre = one thousand-millionth of a metre).

A single virus particle, known as a virion, comprises an inner core of NUCLEIC ACID which is surrounded by one or two protective coverings (capsid) made of protein. Sometimes the capsid is enclosed by another layer called the viral envelope (also a protein structure). The envelope often disintegrates when the virus invades a cell. Viruses enter cells and then indulge in a complex and variable process of replication using some of the cells’ own structure. Viruses may stay in a host’s nucleus, being reactivated months or years later. There are more than a score of large families of viruses, from papoviruses, which cause WARTS, through HERPES viruses (cold sores, CHICKENPOX, SHINGLES) and orthomyxoviruses (in?uenza), to corona viruses (common cold) and retroviruses (AIDS/HIV). Viral diseases are more dif?cult to treat than those caused by bacteria: ANTIBIOTICS are ine?ective but INTERFERON, a group of natural substances, shows promise. IMMUNISATION is the most e?ective way of combating viral infections; smallpox, poliomyelitis, MUMPS, MEASLES and RUBELLA are examples of viral diseases which have been successfully combated. Research is progressing to ?nd a vaccine against HIV.... virus

The smallest known types of infectious agent. It is debatable whether viruses are truly living organisms or just collections of molecules capable of selfreplication under specific conditions. Their sole activity is to invade the cells of other organisms, which they then take over to make copies of themselves. Outside living cells, viruses are inert.

A single virus particle (virion) consists of an inner core of nucleic acid, which may be either DNA or RNA, surrounded

by 1 or 2 protective protein shells (capsids). Surrounding the outer capsid may be another layer, the viral envelope, which consists mainly of protein. The nucleic acid consists of a string of genes that contain coded instructions for making copies of the virus.

Common viral diseases include the common cold, influenza, and chickenpox (caused by the varicella–zoster virus). AIDS is caused by the human immunodeficiency virus (HIV).... viruses

(HA, H) a glycoprotein projecting from the surface layer of the lipid bilayer envelope of *influenza virions. This protein is involved in virus binding and may influence virulence. It is a key target for antibody attack and therefore is important in vaccination.... haemagglutinin

(NA, N) a glycoprotein projecting from the surface layer of the lipid bilayer envelope of *influenza virions. It attacks sialic acid residues on host cells and may be involved in virus release. It is a key target for antibody attack and therefore is important in vaccination.... neuraminidase