NAME: Varicella-zoster virus
SYNONYM OR CROSS REFERENCE: VZV , chickenpox , shingles , Human herpesvirus 3 , Herpes Zoster.
CHARACTERISTICS: Varicella-Zoster virus belongs to the subfamily alphaherpesviridae in the Herpesviridae family, genus Varicellovirus. The Varicella-Zoster virus has a diameter of 150-200 nm and contains a linear, double stranded DNA (125 kbp) genome, enclosed within an icosahedral capsid, surrounded by a phospholipid envelope. VZV grows slowly in human diploid fibroblasts cells, and will remain attached to the host cell, resulting in less circulating viral particles.
PATHOGENICITY/TOXICITY: Varicella (Chickenpox) and Zoster (shingles) are the two different manifestations of the Varicella-Zoster virus.
Chickenpox: Varicella/chickenpox is a primary infection with VZV. It occurs mainly in children and is characterized by generalized itchy, vesicular eruptions/rash and fever. The lesions usually first appear on the back of the head and ears, and then spread to the face, neck, trunk and proximal extremities. The number of lesions may vary from 10 to several hundred. Progressive, generalized varicella, associated with viremia, visceral dissemination of the virus, pneumonia, hepatitis, and CNS complications such as encephalitis, transient ataxia, aseptic meningitis, and transverse myelitis may occur, particularly in immunocompromised children and adults. Thirty percent of children with leukemia develop disseminated varicella, and the accompanying mortality rate is 7%. Arthritis, glomerulonephritis, myocarditis, and purpura fulminans are other less common complications associated with varicella. Following acute infection, the virus becomes latent in sensory ganglia neurons and may persist indefinitely.
Shingles: Shingles/Zoster is due to reactivation of latent VZV. The risk of acquiring zoster infection increases with age, especially after 50 years of age. It is characterized by a painful eruption of vesicular lesions along with inflammation in the skin area supplied by the associated dorsal root or cranial nerve sensory ganglia. Postherpetic neuralgia, characterized by persistent pain in the dermatome for many months or years after the resolution of the infection, may occur. Disseminated infection involving visceral organs may occur in immunosuppressed patients.
EPIDEMIOLOGY: Varicella-zoster infections occur worldwide. Varicella/chickenpox is more common in temperate climates than in tropical countries. Before the introduction of VZV vaccine in 1995, an estimated 4 million cases of varicella and 1 million cases of zoster occurred annually in the United States. Most of the varicella cases occurred in children <15 years of age. The disease, however, is more severe in the low percentage of adults who became affected. The incidence of varicella in the United States has declined substantially (overall decrease of 90% between 1995 and 2005, with a 74% decrease among adults), since the introduction of the varicella vaccination program. Varicella-related morbidity and mortality have also declined since the introduction of the vaccine. Herpes zoster is caused by reactivation of the latent virus, and affects mainly adults. Risk factors for zoster infection include age >50 years, spinal trauma, irradiation, HIV infection, corticosteroid therapy and cancer. The incidence of herpes zoster declined by 55% among varicella vaccinated children < than 10 years of age, between the years 2001-2006, in the United States. The incidence of herpes zoster among adolescents and adults has remained stable or increased since 1995.
HOST RANGE:Humans are the only natural host.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: The main route of transmission is through aerosols carrying cell-free enveloped VZV particles. Transmission occurs from the skin vesicles of infected persons to the respiratory tract of susceptible person. Transmission can also occur through direct contact with infectious vesicular fluid from an infected person. In utero infection can also occur as a result of transplacental passage of virus during maternal varicella infection.
INCUBATION PERIOD: 10-21 days, with an average of 14 days.
COMMUNICABILITY: VZV is highly contagious. Highly infectious cell-free VZV, produced in the skin vesicles of patients, are responsible for high degree of contagiousness of this virus. Chickenpox is communicable 1-2 days before onset of rash and approximately 3-4 days after the appearance of rash, until all the vesicles are crusted over. Zoster is less communicable than varicella, but patients with zoster can transmit the virus to susceptible persons.
RESERVOIR: Humans are the only natural host.
DRUG SUSCEPTIBILITY: Acyclovir has been shown to inhibit viral replication. Some strains resistant to acyclovir have been reported, mainly in HIV infected patients.
SUSCEPTIBILITY TO DISINFECTANTS: Varicella-Zoster virus is easily inactivated by lipid solvents, detergents, and proteases. Although not much information is available on disinfectants specific for VZV, most herpes viruses are susceptible to 30% ethanol, 20% propanol, 200 ppm sodium hypochlorite, 0.12 % orthophenyl phenol, and 0.04% glutaraldehyde.
PHYSICAL INACTIVATION: It is a very fragile virus and can be easily inactivated by heating at 60oC, prolonged storage at a temperature of -70oC and above, extremes of pH (< 6.2 or >7.2), and ultrasonic disruption.
SURVIVAL OUTSIDE HOST: Labile outside host cell. It survives in the external environment for a few hours and occasionally for a day or two.
SURVEILLANCE: Monitor for symptoms. Varicella presents with a vesicular rash. Zoster presents with distinct unilateral vesicular rash with dermatomal distribution. Direct examination by EM of skin lesions for virus is the most rapid and sensitive method of identification. Direct examination may be performed using direct fluorescent antibody (DFA) test, PCR of viral DNA. Viral culture is also used from isolated of skin lesions and human diploid fibroblasts cells. Other methods employ serological test such as enzyme-linked immunosorbent assay.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Varicella is a mild and self-limited illness in healthy children; treatment with antiviral agents is not recommended. Non-specific methods such as frequent bathing, calamine lotion, and oatmeal bath can be used for symptomatic relief. Acetaminophen may be given to control fever. Acyclovir (ACV) has been recommended for treatment in healthy patients 12 years or older. Intravenous ACV is used for children, and adults with severe VZV infection or at a risk of developing serious infection such as immunocompromised patients. ACV is also used for treating herpes zoster in healthy patients, but is not very effective in immunocompromised patients. Oral famciclovir is more effective for treating zoster infection in adults, but is not approved for children or treatment of varicella. Infections resistant to ACV are treated with intravenous foscarnet.
IMMUNIZATION: A live attenuated vaccine, developed from the Japanese Oka strain, is recommended for use in healthy children after 12 months of age. The vaccine can also be used for immunocompetent adults, especially those at occupational risk of acquiring the disease. In Canada, herpes zoster vaccine, has also been recommended for immunization of immunocompetent adults >60 years of age.
PROPHYLAXIS: Passive immunization with intravenous immune globulin, varicella-zoster immune globulin (VZIG) or VariZIG™ (similar to VZIG, and produced in Canada), if given within 96 hours of exposure, is effective in preventing infection or reducing the severity of disease in susceptible individuals.
LABORATORY-ACQUIRED INFECTIONS: No infections reported.
SOURCE/SPECIMENS: Vesicular fluids, vesicular lesions, respiratory secretions.
PRIMARY HAZARDS: Direct contact with clinical material or viral isolates, inhalation of concentrated aerosolized materials, droplet exposure of mucous membranes of the eyes, nose, or mouth, ingestion, accidental parenteral inoculation are the primary hazards associated with herpes viruses.
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities. Women who are or may become pregnant, if seronegative, should consider being vaccinated and restricted from working with this agent.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism by autoclave, chemical disinfection, gamma irradiation, or incineration before disposing.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011