Causative Agent
Varicella-Zoster Virus (VZV)
Incubation Period
10 - 21 days
Infectious Period
Infectious 1 - 2 days before the onset of rash and 5 - 7 days after the appearance of vesicles until scabbing.
Transmission
Highly contagious (secondary household attack rate of susceptible individuals of >90%). Transmission is mainly by airborne route (respiratory secretions) and less often by direct contact with vesicular fluid of lesions.
Epidemiology
A total of 23,476 cases were reported in 2007 (overall incidence of 511.6/100,000 population). The age-specific incidence rate for 2007 was highest in the 5-9 year age group, which was 5 times that of the overall rate. The male to female ratio was1.4:1. Malays had the highest incidence rate among the three major ethnic groups of resident population. Cases occurred throughout the year. Outbreaks in institutional and child-care settings are common.
The age-specific immunity is lowest in those less than 6 years of age (34.5%) and increases steadily with age; 60.5% of those aged 7-12 years, 71% aged 13-17 years and 87.9% aged 18 years and above have VZV antibodies.
- Clinical diagnosis is usually adequate for uncomplicated varicella or zoster syndromes.
- For more timely confirmation of diagnosis or in atypical cases, viral antigen detection by immunofluorescence (IF) or PCR can be done from vesicular fluid/cell smears.
- Serological assays for detection of VZV-IgG and -IgM antibodies are of limited value in diagnosis due to the need for paired sera, long turnaround time and false positives for IgM antibodies.
- Usually symptomatic treatment including anti-histamines and anti-pyretics for uncomplicated disease.
- Acyclovir, famciclovir and valcyclovir can be used for the early treatment of chickenpox (start within 24 - 48 hours of rash).
- Antivirals are also efficacious for the early treatment of complicated disease like pneumonitis and encephalitis.
- Immunosuppressed children should be treated with intravenous acyclovir, even if more than 24 hours have passed since the onset of symptoms (mortality rate of 7-14 %).
