Influenza A virus

INTRODUCTION

Influenza virus family comprises of the three known types: Type A, B and C and it is called

Orthomyxoviridae. Only Type A is capable of infecting birds, but all three types are known

to infect humans. Influenza Type A also known as Avian flu comes in subtypes depending on

the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA) and it further divides

into the specific strains depending on the levels of pathogenicity and structural variation

Wild birds are natural hosts of the virus and as opposed to the domesticated kind (chicken)

do not become sick when infected. Type A is also categorized into groups of low and high

pathogenicity called LPAI and HPAI accordingly. Most avian flu viruses are considered to be

LPAI and associated with very mild cases of disease in birds, while HPAI types cause severe

symptoms and death in those animals. LPAI type is capable of evolving into HPAI type.

THere are cases of HPAI virus such as H5N1 infect humans with severe symptoms and cause no

illness among ducks (host).

Influenza A virus uses RNA in its propagation, which is enclosed in the capsid. Inside of

the capsid the so called internal protein is residing in the form of transcriptase complex

(PB1, PB2, PA, NP) that would under favorable conditions lead to a formation of polymerase

enzyme for virus particle assembly. Matrix protein surrounds the nucleocapsid and is

responsible for maintaing virus' integrity by communicating with the external lipid

envelope. The lipid coat has a very important role because it carries the glycoproteins NA

(neuraminidase) and HA (hemagglutinin) which are necessary tools virus uses to enter its

host.