[The benefit from mumps virus IgG antibody avidity testing in the population with high vaccine coverage in the context of other serological methods for laboratory diagnosis of mumps and the current epidemiological]

Abstract

Aim: Regular vaccination against mumps resulted in a significant reduction in epidemic mumps in the Czech Republic. However, mumps cases have recently shown an upward trend, even in the vaccinated population where a considerable proportion of cases have occurred. The aim of this study was to find out, by mumps virus IgG antibody avidity testing, whether the high incidence of mumps in the vaccinated population is a result of primary or secondary vaccine failure and whether the vaccinated differ from the naturally immunised in anamnestic antibody avidity. Given the problematic laboratory diagnosis of mumps in the population with high vaccination coverage, the informative value of the detected IgM, IgA, and IgG antibodies was also considered as well as the potential of antibody avidity testing for improving laboratory diagnosis from a single sample of blood, the most commonly analysed clinical material, in patients with suspected mumps.

Material and methods: Sixty-four patients laboratory confirmed with mumps, whose vaccination status was known, were included in the study (groups 1 and 2). Other study groups were 30 healthy naturally immunised subjects (group 3) and 22 vaccinated children 2-4-years of age with no etiological link to the mumps virus (group 4). The avidity index (AI) was determined using the Siemens Enzygnost Anti-Mumps/IgG kit and 6M urea, able to induce the dissociation of antigen-antibody bonds proportionally to the antibody avidity. IgM, IgG, and IgA antibodies were tested using the Siemens Enzygnost Anti-Mumps/IgM and /IgG, and Mast Diagnostica Mastazyme Mumps IgA kits. The EPIDAT system served as the data source.

Results: The results showed that the mumps virus induces antibodies with a low AI after both vaccination, even recent, and natural immunisation. Antibodies with a high AI were only detected in convalescent sera of the vaccinated patients or in re-infected, naturally immunised persons, as a result of recent contact with the mumps virus. The comparison of the results of acute sera testing revealed that in the vaccinated patients, 56% of cases were laboratory confirmed based on IgA positivity, i.e. 20% more cases in comparison with routine detection of IgM antibodies, while of unvaccinated cases, 87% were IgA positive and 74% IgM positive.

Conclusion: The results of mumps virus IgG antibody avidity testing suggest that the high proportion of cases in the vaccinated patients result from secondary vaccine failure, also known as waning immunity. Diagnostic benefit from antibody avidity testing has been observed in convalescent sera and/or acute sera from both vaccinated and naturally immunised patients collected from day 6 after the onset of the disease when significant increase in AI occurs.The comparison of the serological methods for the detection of IgM, IgG, and IgA antibodies in acute sera revealed that the highest percentage of mumps infection was detected by IgA antibody testing. The addition of this serological method to mumps laboratory diagnosis made the latter considerably more effective, particularly in the vaccinated patients.

Keywords: mumps virus - IgG antibody avidity - primary and secondary vaccine failure - serological diagnosis..