Varicella zoster virus
Varicella is one of the typical viral rash illnesses of childhood .
The widespread vesicular rash is high recognizable and charcteristic of varicella .
Following primary infection , the virus remains latent and maybe reactivated in later life to cause zoster .
The recent approval of a vaccine in a number of countries has renewed interest in this virus.
A. properties
A member of the herpes virus family , belong to the alpha herpes virus subfamily with HSV-1 and HSV-2 ds DNA enveloped virus, genome size 125 kbp, long and short fragments with a total of 4 isometric forms .
like other herpes viruses , immediate early , early , and late protiens are synthesized .
One antigenic serotype only , although there is some cross reaction with HSV.
VZV cannot infect other animals except primates such as gorillas and chimpanzees.
It will grow readily in a range of human and simian cell culture , producing a characteristic CPE , which consists of typical ovoid focal pattern and appears 3 days to 2 weeks after inoculation.
C.Epidemiology
Primary varicella is an endemic disease. Cases of varicella are seen throughout the year but , like other viruses spread by the respiratory route eg.
Measles and rubella , they are seen more commonly in the winter and early spring.
This is unlike that for enteroviruses and lends some support to the view that varicella is spread mainly by the respiratory route. Herpes zoster , in contrast , occurs sporadically and evenly throughout the year.
Varicella is one of the classic diseases of childhood, with the highest prevalence occurring in the 4 – 10 years old age group.
Like rubella , infection is uncommon in preschool children.
Varicella is highly communicable , with an attack rate of 90 % in close contacts. Most people become infected before adulthood but 10 % of young adults remain susceptible.
However , this pattern of infection is not universal , eg. In rural India , varicella is predominantly a disease of adults , the mean age of infection being 23.4 years. It was suggested that this could be due to interference by other respiratory viruses that the children are exposed to at early age.