Let
us now take a look at Picornaviridae.It is known to be the largest virus family and it belongs to the Rhinovirus. It’s virions are naked and it’s nucleocapsid is isometric. It is an RNA virus which means its genome is infectious. It is made up of a single poly protein of 2100-2400 amino acids. Let me now explain how the virus infection takes place. The upper respiratory tract gets infected and the virus would be incubated for 2-3 days. IgA is locally synthesized but the titre declines with time but the IgG serum persists for years. There are over 100 rhinoviruses.
Symptoms of Picornaviridae are watery nasal discharge, congestion, sneezing and little or no fever. There are a few methods used in the lab to discover if the virus is present. The methods are virus culture, nasal washings
,EIA
or PCR. There are alot of virus present in the nasal discharge.
The common cold is Picornaviridae.
The virus would be easy to control of we follow these steps. We should always wash our hands, try as much as possible not to touch our eyes or nose, always sneeze into a tissue and throw it away rather than sneezing in the air and letting the germs to circulate in the air. Try to avoid if possible people who have a cold or if you are the one having it, stay home.
Now let me tell what I know about Orthomyxoviridae.
Influenza virus A and B comes from this group. The first report of influenza epidermic was from the Athens. In 1918 there was a flu epidermic which led to about 25 – 40 million deaths. In 1970 there was 11 epidermics. This was how serious the virus was.The virus was typically spherical (100nm diameter).
It is enveloped and pleomorphic which means it has many forms. It has spikes on envelope and has groups of HA (hemagglutinin) or NA (neuraminidase ) in the ratio of HA to NA 5:1.
The Genome of Influenza A and B is a single stranded negative RNA in 8 segments and 3 polymerase peptides with each segment.
The infection takes place in the respiratory tract of humans and there is an affinity of the HA for receptors in the epithelium of the tract. There would be an innate resistance and a mucus blanket. It is more easier for the elderly to get it. The existing antibodies are anti-HA AB, IgA and IgG.
To find out if the virus is present, a throat wash/ gargle/ nasal wash would be done. Virus culture ( cell line or chick embryo), Direct EIA or PCR
would also be done. Alot of virus is present in the nasal discharge.
Antigenic drift is a mutation in the genetic code of surface antigens (HA/NA) type A and B, results in new strain and happens all the time. Antigenic shift occurs when genes re-assort from different subtypes ( only for type A ), results in a new subtype and happens occasionally. The methods of control for influenza is a vaccine and antiviral drugs.