Chickenpox

Varicella(Chickenpox)

Disease

CHANANART YUAKYEN : ICN

Definition

• Varicella (Chicken pox) is a disease caused by the varicella zoster virus; it causes fever and an itchy rash

• Varicella-zoster virus (VZV) is a DNA virus of the herpes virus family.

•It causes two diseases: •varicella (chickenpox), the primary infection, •and herpes zoster (shingles), a secondary infection due to a reactivation of latent varicella infection in the dorsal root ganglia

Infectious agent

Signs and Symptoms

• Symptoms include a skin rash of blister-like lesions, covering the body but mostly concentrated in the face, scalp and trunk. Most infected individuals experience fever developing either just before or when the rash appears. If a vaccinated individual is exposed they may experience a milder illness with less severe rash and mild or no fever.

dewdrops on a rose petal

Occurrence

•Worldwide.• At lease 90% of the population has had chickenpox by

age 15

• At lease 95% by young adulthood

• In temperate zones, chickenpox occurs most frequently in winter and early spring.

• The epidemiology of varicella in tropical countries differs from temperate climates, with a higher proportion of cases occurring among adults.

• Herpes zoster occurrence has been described most commonly in developed countries where Zoster occurs more commonly in older people 50 years of age.

Occurrence

•Chickenpox typically infects children under the age of 10; 5-10 % of the population remains susceptible to the disease in adulthood.

• Lifetime risk of reactivation as zoster/shingles is about 15-20 % and can occur at any time, most often in the elderly population.

Reservoir

•Humans

Mode of transmission

•Person-to-person by direct contact,

•Droplet or airborne spread of vesicle fluid,

•Secretion of the respiratory tract of chickenpox cases

•Vesicle fluid of patients with herpes zoster

• Indirectly through articles freshly soiled by discharges from vesicle and mucous membranes of infected people

Mode of transmission (cont.)

•Varicella in unvaccinated persons is one of the most readily communicable of diseases, especially in the early stages of the eruption,

•Secondary attack rates in susceptible household contacts range from 61% to 100%

•Scabs from varicella lesion are not infective.

Mode of transmission (cont.)

•Herpes zoster has a lower rate of transmission:

•Data from a household study showed that 20% of those who are varicella seronegative develop varicella when they are in contact with persons who have herpes zoster

Incubation period

•10-21 days

•Commonly 14-16 days

•May be prolonged as long as 28 days after passive immunization against varicella

•And may be shortened in the immunodeficient. (8-21 days)

Period of communicability

•As long as 5 days,

•But usually 1-2 days before onset of rash,

•And continuing until all lesions are crusted (usually about 5 days).

Period of communicability (cont.)

•Contagiousness may be prolonged in patients with altered immunity.

•The secondary attack rate among susceptible siblings is 60-100%.

•Patients with herpes zoster may be infectious for a week after the appearance of vesiculopustula lesion.

•Susceptible individuals should be considered infectious for 10-21 days following exposure.

Contagiousness

1-2 days

all lesions

are crusted

5 days

Susceptibility

•Susceptibility to varicella is universal among those not previously infected or vaccinated;•Ordinarily a more severe disease of adults than of children.

• Infection usually confers long immunity;• Second attack are rate in immunocompetient persons but have been documented ;• Subclinical reinfection is common.

Susceptibility

•Viral infection remains latent;•Disease may recur years later as herpes zoster.

•Herpes zoster occurs in about 15% of older adults, and rearly in children.

Susceptibility

•Neanates whose mothers are not immune and patients with leukemia may suffer severe,• Prolonged or fetal chickenpox.

•Adults with cancer-especially of lymphoid tissue, with or without steroid therapy-immunodeficint patients and those on immunosuppressive therapy may have an increased frequency of severe herpes zoster, both localized and dissaminated.

Methods of control

•Preventive measures.

•Control of patient, contacts and the immediate environment.

•Epidemic measures.

Methods of control ; Preventive measures

•Protect high-risk individuals who cannot be immunized • e.g. non-immune neonates and the immunodeficient-from exposure, by immunizing household or other close contacts.

Methods of control ; Preventive measures

•A herpes zoster vaccine • for older adults has been approved and recommended for use in the USA for healthy persons aged 60 years or older.

•Varicella-zoster immune globulin (VZIG or VariZIG), • prepared from the plasma of noemal blood donors with high VZV antibody titer, • effectively modifies or prevents disease if given within 96 hours after exposure.

Methods of control ;Control of patient, contacts and the immediate environment.

• Isolation• Exclude children from school, medical offices, emergency rooms or public places until vesicles become dry and crusted, usually after 5 days in non-immunized children and 1-4 days with breakthrough varicella in immunized children; • Exclude infected adults from workplace and avoid contact with susceptibles.

• In hospital, observe strict isolation, because of the risk of varicella in susceptible immunocompromised patients.

Methods of control ;Control of patient, contacts and the immediate environment. (cont.)

•Quarantine.• in places where susceptible children with known recent exposure must remain for medicle reasons, the risk of spread to steroid-treated or immunodeficient patients may justify quarantine of known contacts for at lease 10-21 days after exposure (up to 28 days if VZIG was given).

•Protection of contacts:•Varicella vaccine is effective in preventing illness or modifying severity if used within 3 days, and possibly up to 5 days, of exposure; it is recommended for susceptible persons following exposure to varicella.

Methods of control ;Control of patient, contacts and the immediate environment. (cont.)

•Protection of contacts: (cont.)

•VZIG•Within 96 hours of exposure may prevent or modify disease in susceptible close contacts of cases.• It is available in several countries for high-risk persons exposed to chickenpox, and indicated for newborns of mothers who develop chickenpox within 5 days prior to or 2 days after delivery.• There is no assurance that administering VZIG to a pregnant woman will prevent congenital malformations in the fetus, but it may modifify varicella severity in the pregnant woman.

Methods of control ; Control of patient, contacts and the immediate environment. (cont.)

•Protection of contacts: (cont.)

•Antiviral drugs such as acyclovir• appear useful in preventing or modifying varicella in exposed in individuals if given within a week of exposure. Most studied have been carried out in immunocompromised children, with few data available for healthy children.•A dose of 8o mg/kg/day in 4 divided doses has been used,•But no regimen is as yet generally recommended for this purpose.

Methods of control ; Control of patient, contacts and the immediate environment. (cont.)

Methods of control ; Control of patient, contacts and the immediate environment. (cont.)

•Specific treatment:

•Antiviral therapy is moderately effective in treating varicella and herpes zoster infections: acyclovir, valacyclovir or famcyclovir are considered the agents of choice for treatment or varicella…