Michaela A. Riddell

A random cluster survey and a convenience sample give comparable estimates of immunity to vaccine preventable diseases in children of school age in Victoria, Australia.

We compared estimates of the age-specific population immunity to measles, mumps, rubella, hepatitis B and varicella zoster viruses in Victorian school children obtained by a national sero-survey, using a convenience sample of residual sera from diagnostic laboratories throughout Australia, with those from a three-stage random cluster survey. When grouped according to school age (primary or secondary school) there was no significant difference in the estimates of immunity to measles, mumps, hepatitis B or varicella. Compared with the convenience sample, the random cluster survey estimated higher immunity to rubella in samples from both primary (98.7% versus 93.6%, P = 0.002) and secondary school students (98.4% versus 93.2%, P = 0.03). Despite some limitations, this study suggests that the collection of a convenience sample of sera from diagnostic laboratories is an appropriate sampling strategy to provide population immunity data that will inform Australias current and future immunisation policies.

Identification of Immunodominant and Conformational Epitopes in the Capsid Protein of Hepatitis E Virus by Using Monoclonal Antibodies

ABSTRACT Antibody to the capsid (PORF2) protein of hepatitis E virus (HEV) is sufficient to confer immunity, but knowledge of B-cell epitopes in the intact capsid is limited. A panel of murine monoclonal antibodies (MAbs) was generated following immunization with recombinant ORF2.1 protein, representing the C-terminal 267 amino acids (aa) of the 660-aa capsid protein. Two MAbs reacted exclusively with the conformational ORF2.1 epitope (F. Li, J. Torresi, S. A. Locarnini, H. Zhuang, W. Zhu, X. Guo, and D. A. Anderson, J. Med. Virol. 52:289–300, 1997), while the remaining five demonstrated reactivity with epitopes in the regions aa 394 to 414, 414 to 434, and 434 to 457. The antigenic structures of both the ORF2.1 protein expressed in Escherichia coli and the virus-like particles (VLPs) expressed using the baculovirus system were examined by competitive enzyme-linked immunosorbent assays (ELISAs) using five of these MAbs and HEV patient sera. Despite the wide separation of epitopes within the primary sequence, all the MAbs demonstrated some degree of cross-inhibition with each other in ORF2.1 and/or VLP ELISAs, suggesting a complex antigenic structure. MAbs specific for the conformational ORF2.1 epitope and a linear epitope within aa 434 to 457 blocked convalescent patient antibody reactivity against VLPs by approximately 60 and 35%, respectively, while MAbs against epitopes within aa 394 to 414 and 414 to 434 were unable to block patient serum reactivity. These results suggest that sequences spanning aa 394 to 457 of the capsid protein participate in the formation of strongly immunodominant epitopes on the surface of HEV particles which may be important in immunity to HEV infection.

Review of the temporal and geographical distribution of measles virus genotypes in the prevaccine and postvaccine eras

Molecular epidemiological investigation of measles outbreaks can document the interruption of endemic measles transmission and is useful for establishing and clarifying epidemiological links between cases in geographically distinct clusters. To determine the distribution of measles virus genotypes in the prevaccine and postvaccine eras, a literature search of biomedical databases, measles surveillance websites and other electronic sources was conducted for English language reports of measles outbreaks or genetic characterization of measles virus isolates. Genotype assignments based on classification systems other than the currently accepted WHO nomenclature were reassigned using the current criteria. This review gives a comprehensive overview of the distribution of MV genotypes in the prevaccine and postvaccine eras and describes the geographically diverse distribution of some measles virus genotypes and the localized distributions of other genotypes.

ELISA for IgG-class antibody to hepatitis E virus based on a highly conserved, conformational epitope expressed in Eschericia coli

In assays based on most recombinant hepatitis E virus (HEV) antigens, the IgG antibody responses to HEV are observed commonly to wane or disappear after the acute phase of infection. Such IgG assays have therefore been used for the diagnosis of acute HEV infection, but they have limited usefulness in seroepidemiological studies. Using western immunoblotting, it was shown previously that the open reading frame (ORF) 2.1 antigen, representing the carboxy-terminal 267 amino acids (aa) of the capsid protein, exposes a conformational epitope which allows optimal detection of convalescent antibody compared to other proteins expressed in Escherichia coli. This conformational epitope is shown to be highly conserved between divergent human HEV isolates, and the development of a sensitive and highly specific enzyme immunoassay (ELISA) based on this recombinant antigen is described. The ORF2.1 ELISA allows the detection and quantitation of both acute- and convalescent phase HEV-specific IgG, and will help to define better the antibody responses to the virus and the prevalence of HEV infection worldwide.

A decline in varicella but an uncertain impact on zoster following varicella vaccination in Victoria, Australia.

Varicella vaccine was licensed in Australia in 1999 and publicly funded in 2005. We examined trends in varicella and zoster hospitalisations and community consultations in Victoria during periods of no vaccine, private availability of vaccine and funded vaccination. Varicella hospitalisation rates declined 7% per year (95% CI 5-9%) from 2000 to 2007, predominately in children under five (12% per year, 95% CI 9-16%). A similar decline was seen in community data. The zoster hospitalisation rate increased from 1998 to 2007 (5% per year, 95% CI 3-6%), before introduction of varicella vaccine. Among those aged 80 and over the hospitalisation rate increased 5% per year (95% CI 3-7%) from 1998 to 2007. Zoster increased in community data from 2001.

Elimination of endemic measles transmission in Australia

Elimination of endemic measles transmission is the culmination of a range of control measures at a national level. Current documentation of elimination proposed by WHOs regional offices requires achieving specific targets for surveillance process indicators. We demonstrate how Australia, although not meeting these specific targets, has satisfied multiple criteria that justify the formal declaration of measles elimination. Our review shows that few countries previously declaring measles elimination have satisfied the current WHO surveillance targets. We argue that the requirements for recognition of measles elimination should not restrict countries to a particular type of surveillance system or surveillance criteria.

Studies of measles viruses circulating in Australia between 1999 and 2001 reveals a new genotype

Nineteen distinct measles virus (MV) strains associated with nine different genotypes were identified in five Australian states (Victoria, New South Wales, Queensland, Northern Territory and Western Australia) between 1999 and 2001. One of the strains identified is likely to represent a new genotype within the clade D viruses (proposed to be d9). No evidence for an indigenous MV strain was found. When epidemiologic information associated with the index case was available for the outbreaks, it usually supported introduction of the virus from overseas, with the main source being South East Asia. Changes in the circulation of MV in Australia since the early 1970s were also observed. Prior to the introduction of measles vaccine, the majority of the population acquired immunity through infection with wild-type virus in early childhood. Nowadays in Australia, young adults are at most risk of infection. The age range of cases in the study period was from 1 month to 48 years, with the majority (59%) of cases from individuals aged 18-30 years.

Detection of Measles Virus-Specific Immunoglobulin M in Dried Venous Blood Samples by Using a Commercial Enzyme Immunoassay

ABSTRACT The optical densities (ODs) of 216 dried venous blood (DVB) samples submitted to the Victorian Infectious Diseases Reference Laboratory as part of enhanced measles surveillance were compared to the ODs of the corresponding serum samples collected at the same time. DVB samples, stored for up to 24 months at 4°C, were tested by the Dade Behring Enzygnost Anti-Measles-Virus/IgM immunoassay. Elution and testing conditions were optimized with the use of spiked DVB samples. The assay showed an overall sensitivity of 90.2% and a specificity of 98.8% for DVB samples compared to the results for serum. When the results were analyzed according to the length of time that the DVB sample had been stored, the assay was 100% sensitive and 97% specific according to the ODs for those samples stored for less than 6 months compared to the results for the corresponding serum samples, with 97.7% agreement between the results for the two sample types. These results demonstrate the potential for the use of DVB samples for the diagnosis of measles in routine diagnostic laboratories.

Dried venous blood samples for the detection and quantification of measles IgG using a commercial enzyme immunoassay

OBJECTIVES To determine whether samples of dried venous blood (DVB) were an acceptable alternative to serum for detecting measles-specific IgG in a commercial enzyme immunoassay. METHODS Paired samples of serum and DVB were collected from 98 suspected cases of measles and 1153 schoolchildren in Victoria, Australia. All samples were tested using the Dade Behring Enzygnost Anti-Measles-Virus/IgG immunoassay. DVB samples were eluted using either the sample buffer provided with the kit or 5% dry milk powder in phosphate-buffered saline-Tween 20. FINDINGS DVB samples eluted by sample buffer showed significantly better linear correlation to the serum samples than did DVB samples eluted in 5% dry milk in phosphate-buffered saline-Tween 20. To improve the comparability of serum and DVB samples an adjustment factor of 1.28 was applied to the optical density (OD) values of DVB. This adjustment also enabled quantification of the titre of measles IgG in mIU/ml directly from the OD value using the alpha calculation as specified by the kit protocol. For DVB samples stored for less than six months at 4 degrees C, the assay showed an overall sensitivity of 98.4% and a specificity of 97.2% compared with the results of serum testing. CONCLUSION These results illustrate the potential for DVB samples to be widely used with the Dade Behring enzyme immunoassay system for determining the immunity of the individual and the population to the measles virus.

Investigation of Optimal Specimen Type and Sampling Time for Detection of Measles Virus RNA during a Measles Epidemic

ABSTRACT At various times postonset of rash, 74 patients positive for measles virus-specific immunoglobulin M provided samples for detection of measles virus RNA by a reverse transcriptase PCR. Of lymphocytes, urine, throat swab, and serum specimens, throat swab specimens were optimal for detection of measles virus RNA during the first 2 weeks after the rash.