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Virus / Herpesviridae / Type:

Alpha Herpesviridae: Varicella-Zoster Virus

INDEX - INFORMATION AVAILABLE

GENERAL & REFERENCES

• Virus Summary
• Alternative Names and Taxonomy
• Associated Diseases
• TAXA Group (for collective information)
• All References

VIRUS STRUCTURE & IDENTIFICATION

• Virus Morphology
• Virus Genome
• Viral Type Diversity (Sub-type/Subspecies)
• Virus Detection and Identification

ASSOCIATED HOST SPECIES OF VIRUS AND HAZARD / RISK

• Definitive Host Species (Agent undergoes final stage of replication for transmission)
• Intermediate Hosts and Vector Species (Agent uses intermediate species to develop and/or specific indirect transmission)
• Paratenic Species (Agent survives on/in the species, without replication or further development)
• Degree of Hazard (Risk to Humans / other Species)

VIRUS LIFE CYCLE, TRANSMISSION, PHYSICAL/CHEMICAL FACTORS & BIOGEOGRAPHICAL - CLIMATIC RANGE

• Virus Life Cycle and Transmission (General cycle of replication and mechanisms of movement between hosts and habitats)
• Chemical Toxicities / Disinfectants
• Physical Susceptibility (Inactivation)
• Environments - External Habitat (Biogeographical / Climate Type)
• Distribution and Geographical Occurrence

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THE FOLLOWING INFORMATION IS HELD ON THE DISEASE INFORMATION PAGE
Chicken Pox:

• Epidemiology, Disease Characteristics & Diagnosis
• Treatment & Control

CLICK THIS LINK FOR Chicken Pox

Virus Summary

Alternative Names (Synonyms)

(Classification of virus types is an evolving discipline. The information in Wildpro has been carefully referenced to the source material, as far as possible. Readers requiring further clarification should consult the source materials and more recent publications. Classification information in Wildpro will be altered when clear and scientifically endorsed new information regarding taxonomic divisions becomes available to us.)

• VZV
• Human herpesvirus 3 (HHV-3)

Associated Diseases

TAXA Group (where information has been collated for an entire group on a modular basis)

Parent Group

References

Species Author

Referee

References

Virus Morphology

• Herpesviridae (Virus Family): Icosahedral capsid with 162 capsomeres. (B81, B560.66.w66)
• Varicella-Zoster Virus
  • The capsid is an icosahedron with 162 capsomere proteins and a 5:3:2 axial symmetry "pentameric proteins form the vertices of an 80-nm to 120-nm icosahedron and hexameric elements comprise its facets." (B560.70.w70)
  • Mature virions are pleomorphic to spherical. (B560.70.w70)

• Herpesviridae (Virus Family)
  • 120-150 nm diameter. (B81)
  • 120 - 260 nm or larger in diameter, partly because the thickness of the tegument is variable; the state of the envelope also varies. (B560.66.w66)
• Varicella-Zoster Virus: Mature virions are 180 - 220 nm diameter. (B560.70.w70)

• Herpesviridae (Virus Family): 
  • Enveloped (B81, B560.66.w66)
• Varicella-Zoster Virus: Enveloped. Consists of a core, nucleocapsid, tegument and envelope, as other herpesviruses. (B560.70.w70)

• Herpesviridae (Virus Family)
  • >20 (B81)
  • There may be about 35 - 45 major polypeptides and a total of between 24 and 71 virally encoded proteins. (B560.66.w66)
• Varicella-Zoster Virus: 

Virus Genome

• Herpesviridae (Virus Family): Double-stranded DNA (B81, B560.66.w66)
• Varicella-Zoster Virus: DNA, linear. (B560.70.w70)
  • Rarely, a circular, supercoiled form. (B560.70.w70)

• Herpesviridae (Virus Family): 
  • One molecule, linear (B81)
  • Linear; 120 - 250 kb long (approximately). (B560.66.w66)
• Varicella-Zoster Virus:
  • Double-stranded. (B560.70.w70)
  • Single copy of DNA per virion. (B560.70.w70)
  • Linear, double-stranded. (J128.9.w3)

• Herpesviridae (Virus Family): 80-150 x 10⁶ (B81)
• Varicella-Zoster Virus: About 125,000 bp long. (B560.70.w70)

• Herpesviridae (Virus Family): No virion transcriptase (B81)
• Varicella-Zoster Virus: 
  • At least 69 open reading frames. (J128.9.w3)
  • The genome encodes at least 70 unique genes. (B560.70.w70)
  • Viral enzymes include a thymidine kinase, ribonucleotide reductase, protein kinases, a deoxyuridine 5'-triphosphate nucleotidehydrolase (dUTPase), viral thymidylate synthetase, VZV uracil DNA glycolase, a DNase and a serine protease. (B560.70.w70)

Viral Type Diversity (Sub-type/Subspecies)

There are no recognised distinct subtypes of VZV and there is very little antigenic variation between epidemiologically distinct VZV strains. While it has been suggested that some cases of apparent chickenpox in chimpanzees may be caused by a closely-related alpha herpes virus, chimpanzee herpesvirus (CZHV), this has not been recognised by the International Committee on the Taxonomy of Viruses.

• There are no recognised distinct subtypes of VZV; there is very little antigenic variation between epidemiologically distinct VZV strains. (J128.9.w3)
• Variants have been recovered from infected individuals, for example strains negative for thimidine kinase or gC protein. (J128.9.w3)
• It has been suggested that some cases of apparent chickenpox in chimpanzees may be caused by a closely-related alpha herpes virus, chimpanzee herpesvirus (CZHV). (B209.7.w7a, J117.50.w1)
  • Limited testing using guinea pig antiserum to a VZV-like virus isolated from a chimpanzee showed that the virus shared at least one antigen with VZV which was not shared with other primate varicella-type viruses. (J223.45.w1)
  • The Seventh Report of the International Committee on Taxonomy of Viruses (2000) does not list any distinct chimpanzee varicella virus. It lists only one non-human primate Varicellovirus: Cercopithecine herpesvirus 9 (CeHV-9) (including the previously separately named Simian varicella virus, Liverpool vervet herpesvirus, Patas monkey herpesvirus deltaherpesvirus and Medical lake macaque herpesvirus. (W752.w2)
  • There is no listing of this putative virus in the most current [October 2009] listing of viruses by the International Committee on the Taxonomy of Viruses. (W753.Oct09.w1)

Virus Detection and Identification

SAMPLE COLLECTION & SHIPPING:

For virus isolation, vesicular fluid plus cells swabbed from the base of a lesion is the preferred sample. Vesicles in which the fluid is still clear are recommended. Virus may be isolated from lesions for only 2 - 3 days. The sample should be frozen down to -70 C or below as it may be inactivated after as little as 24 hours at -20 °C; samples can be shipped on dry ice. Samples with lower initial titres show faster decrease in titre. Swabs should be removed once they have been agitated in virus transport medium to reduce virus loss. For direct detection using immunofluorescence or immunoperoxidase assays, the base of a fresh lesion is scraped with a scalpel blade or vigorously rubbed with a Dacron or rayon swab, then the recovered material is transferred to a microscope slide. 

• The preferred sample for virus isolation from cutaneous lesions is vesicular fluid together with cells swabbed from the base of the lesion. (J128.9.w3)
  • Early vesicles containing clear fluid are preferable for isolation of virus, rather than lesions which are cloudy or crusted. (J128.9.w3)
  • Usually, infectious virus may be recovered from lesions for only 2 - 3 days. (J128.9.w3)
  • The sample should be frozen at or below -70 °C or shipped on dry ice; virus in the sample may be inactivated after 24 hours at -20 °C. (J128.9.w3)
  • Factors influencing virus recovery include: (J93.19.w1)
    • Temperature: less than 1% recovery following freezing at -20 for 24 hours, versus >78% +/- 14% recovery following freezing at -70 for 24 hours. (J93.19.w1)
    • Initial titre: for initial high titre (2 x 10⁴ PFU/mL), only 25% titre decrease following holding at 4°C in transport medium for 24 hours, and 60% decrease at room temperature for 24 hours but at lower initial titre (< 2 x 10³ PFU/mL) recovery was much (5 - 10 fold) lower. (J93.19.w1)
    • Exposure to swab, and swab material: virus was lost on exposure to a swab; swabs should be removed as soon as possible following agitation in virus transport medium, and should be squeezed against the side of the tube. (J93.19.w1)
    • Use of a Swinex filtration system for sterilisation: this resulted in loss of > 99% of virus. (J93.19.w1)
    • Cell line used: e.g. human embryonic lung fibroblasts were eightfold more sensitive than human foreskin fibroblasts (line 350Q) which in turn were more sensitive than the foreskin fibroblast cell line FS-9. (J93.19.w1)
    • Timing of sample collection: in individuals with herpes zoster, VZV was isolated from 72% at the time of first sampling and from 60% 72 hours later. (J93.19.w1)
• In some clinical circumstances it may be possible to isolate VZV from PBMCs (peripheral blood mononuclear cells), CSF, joint fluid or bronchial washings. (J128.9.w3)
• In individuals with encephalitis, CSF may be taken for testing with PCR. (J128.17.w1)
• At necropsy it may be possible to isolate VZV from multiple tissues, particularly the lungs but also heart, liver, pancreas, gastro-intestinal tract, brain and eyes. (J128.9.w3)
• For direct detection of VZV antigens using immunofluorescence or immunoperoxidase assays, optimal sensitivity is obtained if cells are acquired from the base of the lesions after unroofing of a fresh vesicle or vesicles. (J128.9.w3)
  • A scalpel blade is used to scrape the base of a lesion, or a Dacron or rayon swab is used to vigorously rub the base of the lesion. Material obtained is then placed on one or more microscope slides. (B560.17.w17)
  • Note: poor quality clinical specimens with a low cell content are less likely to give positive results in direct detection techniques (indirect fluorescence assay (IFA) or direct fluorescence assay (DFA) with monoclonal antibodies). (J93.32.w2)
• CSF can be taken for testing for intrathecal antibodies. (J128.17.w1)
• For mucocutaneous infections, preferably unroof a vesicle and soak up the vesicular fluid with a swab, also using the swab to scrape the base of the lesion; this material can then be submitted for virus culture. (B560.17.w17)

  (B560.17.w17)

ANTIBODY DETECTION:

In humans, the fluorescent-antibody membrane assay (FAMA) which detects binding of antibodies in sera to membranes of unfixed VZV-infected cells is the reference test for IgG antibodies, but LAT, EIA and IFA are used more commonly; neutralisation and radioimuneassa are very sensitive tests while commercial ELISa are highly specific but less sensitive. Detection of seroconversion in paired serum samples provides strong evidence of infection. VZV IgM assays support the diagnosis of recent infection; they may be positive with primary infection and with reactivation of latent infection and do not distinguish between these; additionally, they lack both specificity and sensitivity.

In humans

• Assay for VZV IgG. (B560.70.w70)
  • IgG tests are useful in determining whether an individual is susceptible to VZV and whether an immunocompromised individual is at risk of VZV reactivation. (J128.9.w3)
  • Fluorescent-antibody membrane antigen assay (FAMA) is the reference test. LAT, EIA and IFA are used more commonly. (B560.17.w17)
  • Fluorescent-antibody membrane antigen assay (FAMA), neutralisation and radioimmuneassay are the most sensitive. (B560.70.w70)
    • FAMA detects binding of antibodies in sera to membranes of unfixed VZV-infected cells and is highly sensitive and specific. (J128.9.w3)
    • Virus neutralization is sensitive and specific but not practical for use in clinical diagnostic laboratories. (J128.9.w3)
    • Radioimmunoassay is sensitive and specific but not practical for use in clinical diagnostic laboratories. (J128.9.w3)
  • Latex agglutination methods can be used and are sensitive. (B560.70.w70) and specific. (J128.9.w3)
    • In a study, a latex agglutination test (LAT) was found to be nearly as sensitive as the standard fluorescent antibody to membrane antigen test and more sensitive than an ELISA. The LAT was noted to be rapid and simple to perform. (J93.29.w2)
  • An EIA using VZV infected cells grown in situ on microscope slides and fixed with 0.5% glutaraldehyde was found to give results correlating well with FAMA. The format ensured that the only virus antigens available were VZV-specific antigens expressed at the cell membrane; this prevented cross-reactions with other herpes virus antibodies (particularly herpes simples virus). (J217.8.w)
  • Commercial ELISAs tend to have high specificity but lower sensitivity; they may falsely identify as high as 10 - 15% of immune individuals as susceptible. (B560.70.w70)
  • Commercial ELISAs are highly specific but less sensitive than FAMA. (J128.9.w3)
  • Complement fixation does not consistently detect VZV IgG antibodies, particularly several years after primary infection. (J128.9.w3)
  • Detection of seroconversion in paired serum samples provides strong evidence of infection. (B560.17.w17)
    • Serological testing is useful when appropriate samples for culture or antigen detection are not available, or if antigen tests/culture results were negative but clinically varicella was considered the correct diagnosis. (B560.17.w17)
• VZV IgM assays support the diagnosis of recent infection; they may be positive with primary infection and with reactivation of latent infection. (B560.17.w17) 
  • VZV IgM assays lack specificity. (B560.70.w70)
  • VZV IgM assays lack both specificity and sensitivity. IgM is often induced in reactivation of infection, therefore tests for IgM do not differentiate primary from recurrent infection. High IgG titres (often present in individuals with acute infection) also lead to false-positive IgM results. (J128.9.w3)

ANTIGEN DETECTION:

• VZV can be detected in appropiate cell cultures. However, the range of cell types in which it will grow is limited (human fibroblast cells, monkey kidney cells) and typically 4 - 8 days are required for CPE to become visible; confirmation of the identity of the virus as VZV requires staining with virus-specific antisera. Shell vial culture techniques increase sensitivity and in combination with centrifugation and staining with fluorescein-conjugated monoclonal antibodies may allow positive results in 1- 3 days of inoculation. 
• VZV antigen can be detected directly from appropriate material (scrapings from fresh vesicles) placed on a microscope slide detected using immunohistochemical staining. Alternatively, enzyme immunoassay can be used to detect VZV proteins in swab specimens from cutaneous lesions.
• VZV nucleic acids can be detected by PCR. Development of real-time PCR and multiplex PCR assays has increases sensitivity of virus detection and allows rapid diagnosis. Great care is required to avoid cross-contamination leading to false positives. Internal controls are required to avoid false negatives which may occur due to the presence in clinical samples of inhibitors preventing PCR.

Cell culture

• VZV grows in primary human cells including human embryo lung fibroblasts. Nonhuman cells which can be used include Vero cells, primary monkey kidney cells, rabbit kidney calls and guinea pig embryo fibroblasts. (J128.9.w3)
• VZV can be grown in cell culture. However, the range of cell types in which it will grow is limited (human fibroblast cells, monkey kidney cells) and typically 4 - 8 days are required for CPE to become visible. (B560.17.w17)
  • Culture sensitivity is relatively low. (B560.17.w17)
  • Shell vial culture techniques can be used and increases culture sensitivity. (B560.17.w17)
  • A mixed cell culture (CV-1 plus MRC-5 cells) can be used to allow simultaneous detection of either HSV or VZV. (B560.17.w17)
• CPE may be visible in cell culture within 2 - 7 days, using phase contrast microscopy; as long as 14 days may be required if the sample contained only a low titre of virus. (J128.9.w3)
  • If no CPE is visible by seven days, trypsinisation of the monolayer and passage to fresh cell cultures may be used to amplify the virus. (J128.9.w3)
  • Confirmation of the identity of the virus as VZV requires staining with virus-specific antisera. (J128.9.w3)
  • Use of shell vial cultures, combining centrifugation and staining with fluorescein-conjugated monoclonal antibodies may allow positive results in 1- 3 days after inoculation, without waiting for CPE, and may improve detection sensitivity. (J128.9.w3)
  • In a trial involving culture of clinical specimens, while 35% of cultures were positive by five days, 40% did not become positive until more than 10 dpi (CPE was detectable in 9% of cultures by three days, in 35% by 3 - 5 days, in 60% by 6 - 10 days and in all positive cultures by 11 - 15 days - cumulative totals). (J93.19.w1)
• Diagnosis can be made by virus isolation followed by antigen detection using immunofluorescence, employing monoclonal antibodies. (J549.29.w1)
  • Fresh specimens containing viable virus are required. (J549.29.w1)
  • Special facilities are required. (J549.29.w1)
• VZV will grow in certain cell lines such as melanoma cells. CPE develops by about 24 hours in these cells, with syncytia developing to involve about 75% of cells by 48 hours; after about 60 hours the fused cells detach from the surface.
  • Immunohistochemical staining allows detection of VZV-infected cells by about 4 - 10 hours post inoculation. (B560.70.w70)

Direct rapid diagnosis

• Material from lesions is placed on microscope slides, air died, fixed with acetone then stained with monoclonal antibodies against VZV and HSV, labelled with fluorescence. (B560.17.w17)
• Immunohistochemical staining can be carried out on cells from cutaneous lesions for rapid diagnosis. (B560.70.w70)
• Direct detection of VZV antigen using monoclonal antibodies in direct or indirect fluorescent antibody assays. (J93.32.w2)
  • These methods are specific (100% specific in this study) and are more sensitive than viral culture: 73.6 - 86.0% in this study, compared with 56.0% for two cell culture techniques together. (J93.32.w2)
  • Two methods using IFA, with two different MAbs were more sensitive than a direct fluorescent antibody test using the same MAb as one of the IFAs. (J93.32.w2)
  • None of the tests using MAbs gave false-positive results with HSV lesions. (J93.32.w2)
  • The direct diagnostic tests were positive with nearly all specimens obtained in the first five days of disease, and the IFAs were able to confirm infection in specimens taken within 1 - 3 days of the onset of antiviral treatment - significantly higher detection than was possible using culture methods. (J93.32.w2)
  • These tests are rapid (1 - 2 hours laboratory turnaround time) and simple to perform. (J93.32.w2)
  • Use of MAbs directed against membrane antigens may be preferred to those detected against nuclear antigens due to easier recognition of positive fluorescent cells. (J93.32.w2)
  • Poor quality clinical specimens with a low cell content are less likely to give positive results. (J93.32.w2)
• In a study in HIV-infected individuals, antigen detection using a direct immunofluorescence assay with a fluorescein-labelled monoclonal antibody was found to be more sensitive than virus isolation or serological detection of IgG or IgM antibodies. (J93.35.w3)
• Enzyme immunoassay can be used to detect VZV proteins in swab specimens from cutaneous lesions. (J128.9.w3)

Nucleic acid detection

• VZV nucleic acids can be detected by PCR. (B560.70.w70)
• PCR can be used in the detection of VZV from clinical specimens. (B560.70.w70)
  • Development of real-time PCR and multiplex PCR assays has increases sensitivity of virus detection and allows rapid diagnosis. (J93.41.w7, J549.29.w2, J549.30.w2, J549.42.w1)
  • Internal controls are required to avoid false negatives, since clinical specimens may contain inhibitors preventing PCR. (J549.29.w2)
  • Closed systems such as RT-PCR not requiring post-amplification of samples are preferred to reduce the risk of carry-over contamination and to improve speed of the assay. (J549.30.w2)
  • Multiplex and parallel assays are now available allowing detection (and distinction) of several viruses at one time (e.g. HSV-1, HSV-2, Varicella-Zoster Virus (VZV), Epstein-Barr virus and cytomegalovirus). (J549.29.w2, J549.42.w1)
• Real-time PCR is rapid and highly sensitive. (B560.17.w17)
  • Meticulous care is required to avoid cross-contamination of samples. (B560.17.w17)

Definitive Host Species (Agent undergoes final stage of replication for transmission)

The primary definitive host is Homo sapiens - Human. Quite high percentages of captive great apes (Pan troglodytes - Chimpanzee, Pan paniscus - Pygmy chimpanzee, Pongo pygmaeus - Orang-utan, and Gorilla gorilla - Gorilla) have been found seropositive for this virus and natural infection has been described in Pan troglodytes - Chimpanzee, Pongo pygmaeus - Orang-utan, and Gorilla gorilla - Gorilla.

• Homo sapiens - Human. (B560.70.w70, J128.9.w3)

Natural infection in nonhuman primates

• In a survey of samples submitted to a virus reference laboratory in San Antonio, Texas, 21/50 (42%) of chimpanzees (Pan troglodytes - Chimpanzee and Pan paniscus - Pygmy chimpanzee); 32/63 (51%) Gorilla gorilla - Gorilla, and 4/32 (13%) of Pongo pygmaeus - Orang-utan were positive for Varicella-Zoster Virus. [1997](J495.47.w6)
• Signs typical of, and diagnosed as, chicken pox, were seen in a 3.5-year-old Pan troglodytes - Chimpanzee, a 2.5-year-old Pongo pygmaeus - Orang-utan and a 20-month-old Gorilla gorilla - Gorilla at San Diego Zoological Gardens (published 1960). These young apes were in close contact with the public, including participating in children's parties held in the Children's Zoo. The signs occurred during a period when there was a high incidence of chicken pox in children in San Diego County. Diagnosis was made on clinical grounds and no virus isolation nor serological procedures were carried out to confirm the identity of the infection. (J4.136.w1)
• Signs typical of, and diagnosed as, chicken pox were seen in an eight-month-old female Gorilla gorilla - Gorilla, starting 15 days after development of chicken pox in a human in the household in which the gorilla was being raised. Serological testing five weeks later showed both the gorilla and a Pongo pygmaeus - Orang-utan in the same household, which had not developed clinical signs, to be seropositive for Varicella-Zoster virus. (J4.161.w2)
• Mild illness associated with "generalized vesicular eruptions similar to that seen in chicken pox of man" was noted in three laboratory-born, nursery-reared Pan troglodytes - Chimpanzees. There was no known contact with humans with chicken pox. Virus isolation was attempted from vesicular fluid of skin lesions of two of the chimpanzees, and herpes-type virus particles were found by electron microscopy of infected tissue culture cells. (J495.21.w3).
• Generalised rash (vesicles and pustules) with conjunctivitis, fever, lethargy and anorexia developed in a 2.5-year-old male Gorilla gorilla - Gorilla recently arrived at Moscow Zoo. The disease was considered to resemble smallpox. Typical herpesvirus particles were found on electron microscopic examination of vesicular fluid. Testing with herpes zoster sera gave "practically identical" results with the virus from the gorilla and with VZV. There was no known contact with any person with chicken pox or shingles (zoster). (J266.2.w1)
• Signs "clinically indistinguishable from varicella in the normal child" developed in a six-month-old Gorilla gorilla - Gorilla being hand-reared at Cincinnati Zoo, "during a period of community varicella activity". Electron microscopy of vesicular fluid revealed typical herpesvirus particles, seroconversion to VZV was demonstrated from paired (acute and convalescent) serum samples from the gorilla, and the virus was confirmed as VZV by Hind III and EcoR1 restriction analyses. (J117.23.w1)
• Varicella-Zoster virus was detected in a wild-born 34-year-old female Western lowland gorilla (Gorilla gorilla gorilla - Gorilla gorilla - Gorilla) at a UK zoo associated with severe axillary and thoracic cutaneous ulceration (T2/3 dermatome distribution). The gorilla was also infected with STLV; the cutaneous lesions were thought to be due to recrudescence of infection [shingles]. (P3.2008a.w2)

Experimental infection in great apes

• Experimental subcutaneous and intratracheal inoculation of an 8 - 9-year-old Pan troglodytes - Chimpanzee with SPu strain VZV resulted in no clinical signs and development of only low level antibodies to VZV. (J223.42.w1)
• Experimental subcutaneous inoculation of two Pan troglodytes - Chimpanzees [age not stated] with wild-type Oka strain VZV (passaged in tissue culture) resulted in fever, leukocytosis and development of a mild, transient (24 - 48 hour) localised, erythematous, papular rash. (J117.50.w1)

Intermediate Host and Vector Species (Agent uses an intermediate species for development and/or specific indirect transmission)

• Not applicable.