The occurrence of neutralizing and complement fixing antibodies in rubella

A novel cell-based high throughput assay to determine neutralizing antibody titers against circulating strains of rubella virus

A large rubella outbreak occurred in Japan 2013, and 14,344 rubella and 45 congenital rubella syndrome (CRS) cases were reported. At that time, the populational immunity was above the protective threshold assessed by hemmaglutination inhibition (HI) titer. The genotype 2B rubella virus (RV) strains were responsible for the outbreak, which are non-indigenous in Japan. In this work, a cell-based high throughput assay was established to measure the neutralizing antibody (NA) titer against circulating RV isolates. RV infection poorly induces cytopathic effects in tissue culture, preventing the casual measurement of NA titer. Our assay system has overcome this hurdle. Using this assay, we re-evaluated the antibody prevalence rate against circulating viral isolates using human sera collected before the outbreak. Individuals with protective IgG titer (≥10 IU/ml) represented 88.1% of the population. Consistently, 85.2% of the population had protective neutralizing antibody titers (≥1:8) against the vaccine strain. In contrast, 50.5% of the population had protective neutralizing antibody titers against circulating genotype 2B RV strains. These data suggest that the herd immunity assessed by HI titer should have been appreciated deliberately.

Retrospective investigation of an influenza A/H1N1pdm outbreak in an Italian military ship cruising in the Mediterranean Sea, May-September 2009

Background

Clinical surveillance may have underestimated the real extent of the spread of the new strain of influenza A/H1N1, which surfaced in April 2009 originating the first influenza pandemic of the 21^st century. Here we report a serological investigation on an influenza A/H1N1pdm outbreak in an Italian military ship while cruising in the Mediterranean Sea (May 24-September 6, 2009).

Methods

The contemporary presence of HAI and CF antibodies was used to retrospectively estimate the extent of influenza A/H1N1pdm spread across the crew members (median age: 29 years).

Findings

During the cruise, 2 crew members fulfilled the surveillance case definition for influenza, but only one was laboratory confirmed by influenza A/H1N1pdm-specific RT-PCR; 52 reported acute respiratory illness (ARI) episodes, and 183 reported no ARI episodes. Overall, among the 211 crew member for whom a valid serological result was available, 39.3% tested seropositive for influenza A/H1N1pdm. The proportion of seropositives was significantly associated with more crowded living quarters and tended to be higher in those aged <40 and in those reporting ARI or suspected/confirmed influenza A/H1N1pdm compared to the asymptomatic individuals. No association was found with previous seasonal influenza vaccination.

Conclusions

These findings underline the risk for rapid spread of novel strains of influenza A in confined environment, such as military ships, where crowding, rigorous working environment, physiologic stress occur. The high proportion of asymptomatic infections in this ship-borne outbreak supports the concept that serological surveillance in such semi-closed communities is essential to appreciate the real extent of influenza A/H1N1pdm spread and can constitute, since the early stage of a pandemic, an useful model to predict the public health impact of pandemic influenza and to establish proportionate and effective countermeasures.

Rubella epidemiology in South East England

Analyses of data collected in a large survey (sample size greater than 3000) of rubella antibody in South East England, finely stratified according to age, reveal age-dependent changes in the pattern of virus transmission. The rate or force of infection changes from low in the young children to high in the 5- to 15-year-olds and back to low again in the adult age classes (there is a 50% reduction between the 5- to 15-year-olds and the 20+-year-olds). Raised levels of immunity are recorded in the teenage and young adult female segments of the population as a consequence of the UK rubella immunization programme. Mean antibody concentrations show a decline with age and are, on average, lower in vaccinated females when compared with unvaccinated males of the same age. The interpretation of horizontal cross-sectional serological data and future research needs are discussed.

Quantitative investigations of different vaccination policies for the control of congenital rubella syndrome (CRS) in the United Kingdom

The paper examines predictions of the impact of various one-, two- and three-stage vaccination policies on the incidence of congenital rubella syndrome (CRS) in the United Kingdom with the aid of a mathematical model of the transmission dynamics of rubella virus. Parameter estimates for the model are derived from either serological data or case notifications, and special attention is given to the significance of age-related changes in the rate of exposure to rubella infection and heterogeneous mixing between age groups. Where possible, model predictions are compared with observed epidemiological trends. The principal conclusion of the analyses is that benefit is to be gained in the UK, both in the short and long term, by the introduction of a multiple-stage vaccination policy involving high levels of vaccination coverage of young male and female children (at around two years of age) and teenage girls (between the ages of 10-15 years), plus continued surveillance and vaccination of adult women in the child-bearing age classes. Model predictions suggest that to reduce the incidence of CRS in future years, below the level generated by a continuation of the current UK policy (the vaccination of teenage girls), would require high rates of vaccination (greater than 60%) of both boys and girls at around two years of age. Numerical studies also suggest that uniform vaccination coverage levels of greater than 80-85% of young male and female children could, in the long term (40 years or more), eradicate rubella virus from the population. The robustness of these conclusions with respect to the accuracy of parameter estimates and various assumptions concerning the pattern of age-related change in exposure to infections and 'who acquires infection from whom' is discussed.

Antibody responses in patients with rubella infection determined by passive hemagglutination, hemagglutination inhibition, complement fixation, and solid-phase radioimmunoassay tests

Antibody responses in serial serum specimens collected from 31 patients with an acute rubella infection were determined by passive hemagglutination (PHA), hemagglutination inhibition (HI), complement fixation (CF), radioimmunoassay (RIA) immunoglobulin G (IgG), and RIA immunoglobulin M (IgM) tests to evaluate the effectiveness of these tests in diagnosing a recent infection. The HI, RIA IgG, and RIA IgM antibodies appeared almost simultaneously and reached the maximum level about 1 week after the onset of rash. Compared to these, the CF antibodies developed only slightly later, whereas the development of the PHA antibodies was much more delayed. The RIA IgM response was shown to be transient, lasting approximately 1.5 to 2.5 months postinfection. The results of this study indicate that demonstration of specific IgM antibodies is the best method for diagnosing a recent infection, one within 2 months after the onset of the illness. If an IgM test is not available, a combination of the HI and PHA tests is recommended.

Epidemiological studies on rubella

Serological surveys of rubella antibody were carried out using the hemagglutination-inhibition test, with a view to studying the distribution of seroimmune individuals according to age and intermingling with other populations. Specimens were collected from different age groups including infants, children and adults, among the inhabitants of Montreal from 1963 to 1968. From the results obtained it was possible to establish the pattern of rubella antibody development in this urban community. Surveys were also conducted among the inhabitants of Les Iles de la Madeleine, a Canadian island in the Gulf of St. Lawrence, and among the population of Easter Island, an isolated island in the South Pacific remote from any large land mass.It was seen that, among the inhabitants of Montreal, presumably maternally acquired rubella antibody was present in 95% or more of the infants, the same percentage of seroimmune individuals as was found among the adult women 25 to 30 years of age. Passively acquired rubella antibodies decreased rapidly, attaining their lowest levels among children 1 to 2 years old. Rubella infection occurred in young children and its incidence rose steeply from school age to adolescence, leaving 7 to 9% of the adults without antibody. The highest geometric mean antibody titres were found among children 4 to 10 years of age.The same pattern of rubella antibody development was found among the population of Les Iles de la Madeleine, except that in adults the percentages of seropositives reached practically 100%. Antibody titres decreased with advancing age and became lower than those found among children.Detection of rubella antibody in serum samples derived from the inhabitants of Easter Island indicated that this population had experienced rubella infection not long before the Canadian Medical Expedition of 1964-1965. This status is determined from the high proportion of seroimmune individuals in each age group and the uniformly high antibody titre.Island populations appear to represent the ideal subjects for estimating the duration of the immunity conferred by any attenuated rubella vaccine that will eventually be licensed.

Frequency of rubella antibodies among adult population in Greece

No significant sex difference in the incidence of immunity to rubella at the ages of 20–25 was found in a comparative study of young adults from the Greater Athens area as well as from the rural department of Corinthia. The immunity to rubella of Greek adults on a national scale was then studied in a respresentative sample of 1200 males 20–25 years old. In 83·2% of them neutralizing antibodies to rubella were detected. A statistically higher proportion of immunes was found among those from urban areas. The factors responsible for the relative prevalence of immunity to rubella in various population groups are discussed.

Studies on rubella in pregnancy. Report of the Public Health Laboratory Service Working Party on Rubella

In a further survey of women of child-bearing age neutralizing antibody to rubella virus was found in 80 to 96% of those sampled from different parts of the country.When assessment was restricted to susceptible pregnant contacts and rubella in the index case was confirmed by virus isolation immunoglobulin in the dosage used did not appear to give any appreciable protection.One instance of a confirmed second attack after known exposure to rubella among more than 100 immune contacts is recorded.The implications of all these findings are discussed.

Measurement of rubella antibody in immunoglobulin: its disappearance from the blood after injection. Report of the Public Health Laboratory Service Working Party on Rubella

Rubella antibody titrations were done on samples of human immunoglobulin by neutralization and haemagglutination-inhibition methods. No significant variation was found in the antibody content of different batches. The specificity of the methods was confirmed by tests on a batch of human globulin specially prepared from plasma samples lacking rubella antibody.Divided doses of immunoglobulin were given to volunteers who had no rubella antibody. Low titres were then detected in the blood for a limited period and the disappearance of this antibody was followed.