AVIAN FLU - THE IMMINENT PLAGUE: The Virus

The Virus

a) Properties

Influenza Virus
Genus	Orthomyxovirus
Family	Orthomyxoviridae
Diameter	80 - 120 nm
Core Diameter	9 nm
Shape	Rounded and can be long and filamentous
Replication Method	Nuclear
Genome	Segmented (-)sense RNA
RNA Structure	Helical
Properties	Labile, susceptible to heat, drying, detergents and solvents (due to the lipoprotein envelope)

b) Structure

In total, the influenza virus has 4 types of antigens. Haemagglutinin (HA) and neuraminidase (NA) are found in the outer surface of the particle and the matrix (M) and the nucleoprotein (NP) are found in the inner surface of the particle. It is the type of the nucleoprotein (NP) which determines the type of the virus. There are three forms of the nucleoprotein (NP) and hence there are three main types of the influenza virus.

Outer Surface

A lipid envelope forms the outer covering of the particle and two types of glycoprotein are projected from the envelope. They are haemagglutinin (HA) and neuraminidase (NA) which appear as rod-shaped projections of the particle. Haemagglutinin (HA) has two types of subunits, HA1 and HA2 respectively and they are responsible for the attachment of the virus to the receptor protein on the cell membrane. There are 13 major types of haemagglutinin (HA). On the other hand, neuraminidase (NA) is responsible for enzymic properties of the virus and there are 9 main types of neuraminidase (NA). It is also observed that there is a smaller quantity of neuraminidase (NA) surface proteins than haemagglutinin (HA) surface proteins.

Inner Surface

The matrix protein (M) is found. The RNA of the virus is related to the nucleoprotein (NP) closely and they form a helical structure. The genome of the virus is segmented and there are 7-8 RNA fragments of ribonucleoprotein (RNP), all of which are needed for replication. (7 RNA fragments for Type C Influenza Virus) Ribonucleoproteins (RNP) are chemically binded to the matrix (M). The matrix protein (M protein) surrounds the nucleocapsid and makes up 35-45% of the particle mass.

c) Classification

Influenza Viruses
Type	Type A	Type B	Type C
Classification Within Each Type (based on nucleocapsid and M protein antigens)	Classified by specific internal proteins	Classified by specific internal proteins	Classified by specific internal proteins
	Further classified by subtypes on the basis of the two main surface glycoproteins hemagglutinin (HA) and neuraminidase (NA)	Not further classified by subtypes	Not further classified by subtypes
Magnitude Of Illness	Can cause influenza epidemics and pandemics	Causes less severe clinical illness epidemics rather than pandemic outbreaks	Causes a very mild illness and does not cause significant clinical illness
Host Range	A wide variety of mammals, including man, horses, pigs, ferrets and birds	Mammals only	Mammals only

Tamiflu is a neuraminidase inhibitor that blocks viruses from breaking free from an infected cell after replication, thus limiting the spread of infection in the body.

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