Smallest RNA Viruses

Orthomyxoviridae and Picornaviridae

Picornaviridae is the largest virus family (over 230 serotypes)
One linear (+) RNA
5 genera :

• Aphtovirus
  
• Cardiovirus


• Enterovirus


• heptovirus


• Rhinovirus
  

Picornaviridae -Rhinovirus

• upper Respiratory tract infection


• serum IgG persists for years


• over 100 rhinoviruses

Symptoms :

Cold

• watery nasal discharge
  
• congestion
  
• sneezing


• no fever
  

Orthomyxoviridae- Influenza Virus

• Enveloped
• Pleomorphic
• Spikes on envelope
• Groups of HA or NA
• Ratio of HA to NA is 5:1

There are three types of influenza virus, A, B and C. A and B types are known to cause flu like symptoms in humans. Type C is rare in humans and only causes mild symptoms.

Genome of Influenza A & B

• ss (-) RNA in 8 segments
• 3 ploymerase polypeptides with each segment
• 5' and 3' end at all segments highly conserved

The Virus strains are characterised by the nature of the two proteins found on there surface, namely Neuraminidase and Hemagglutinin. Approximately 80 percent of the spikes are hemagglutinin, a trimeric protein that functions in the attachment of the virus to a host cell. The remaining 20 percent or so of the glycoprotein spikes consist of neuraminidase, which is thought to be predominantly involved in facilitating the release of newly produced virus particles from the host cell. The inner of the cell contains the RNA nucleotides which are the genetic code for the virus replication.

• 14 subtypes of HA


• 9 subtypes of NA


• HA 1,2,3 and NA 1 and 2 are found in human.
  

Antigenic Drift and Shift

• Antigenic drift is a mutation in the genetic code of surface antigens (HA/NA) (type A and B)


• Antigenic shift occurs when genes re-assort from different subtypes (only for type A)

Symptoms :

Flu

• fever


• headache


• aches and pains


• fatigue


• exhaustion


• cough