Systematic Veterinary Virology

MORPHOLOGY

• PPR virus is pleomorphic. It is single stranded, negative sense RNA viruses. They are enveloped viruses and are ether sensitive. They possess helical symmetry. 
• Virus measures approximately 150 nm in diameter. The envelopes are covered with minute projections, which are the surface glycoproteins (H and F proteins) responsible for cell attachment and fusion.
• The nucleocapsid is hollow, coiled, rod-shaped with herring-bone pattern of sub-units. PPR virus is differentiated from rinderpest virus (PPR is a very important infection resembling rinderpest in small ruminants) through nucleic acid probes for N gene. In total the virus has 6 six structural proteins:
  • Nucleocapsid protein - Np covers and protects the virion RNA.
  • Phosphoprotein P - polymerase-associated or phosphoprotein.
  • Large protein  - L - acts as a virus transcriptase and replicase in association with P protein.
  • Matrix protein – M – acts as a link between nucleocapsid and virus external glycoprotein H.
  • Fusion – F - enables virus and host cell membrane to fuse.
  • Haemagglutinin H - haemagglutinin or attachment protein, enables virus to attach to host cell membrane.
• C / V - two non-structural virus-encoded proteins produced in infected cells. They have function in virus reproduction.
• The matrix protein, intimately associated with the internal face of the viral envelope, makes a link between the nucleocapsid and the virus external glycoproteins H and F, which are responsible for the attachment and the penetration of the virus into the cell to be infected.