INTRODUCTION TO POX VIRUSES
Pox viruses are the largest and the most complex of all viruses, belongs to the family poxviridae and causes a number of diseases, are large enough to be seen under the light microscope.
MORPHOLOGY OF POX VIRUSES
⇒ Poxviruses are brick-shaped.
⇒ Genetic Material – dsDNA
⇒ Poxviruses have complex symmetry.
⇒ Largest animal viruses of size – 300*200*100 nm.
⇒ Enveloped viruses.
⇒ Poxviridae consists of 3 genera as –
- Orthopoxvirus –
- Variola & Vaccinia ( in human)
- Cowpox (in cows)
- Monkeypox (in monkey)
- Parapoxvirus – milker’s node & orf (in cow & Sheep)
- Yatapoxvirus – Tanapox & Yabapox (in monkeys)
CULTIVATION OF POX VIRUSES
⇒ Poxviruses grow in Chorioallantoic membrane (CAM) of chick embryo and in tissue culture; Variola & Vaccinia produce pocks on the CAM in 48-72 hours.
⇒ Tissue cultures of monkey kidney, HeLa & chick embryo cell can be used to grow these viruses.
VARIOLA & VACCINIA VIRUS
⇒ Variola virus causes smallpox
- Has narrow host range i.e. humans & monkeys only.
- The virus causing classical smallpox was called Variola major that causing alastrim called Variola minor, are antigenically identical but differs in certain biological characteristics.
- Smallpox has been eradicated and routine vaccination is now stopped.
- On May 8, 1980, WHO announced the global eradication of smallpox.
⇒ Origin of Vaccinia virus is unknown.
- In past, was used for smallpox vaccination.
- ‘Artificial virus’ that doesn’t occur in nature and may have evolved from smallpox or cowpox virus.
- Causes localized skin infection.
- Employed as a vector for the development of recombinant vaccines.
- Vaccinia & Variola viruses are similar in their properties.