Maturation of rubella IgG avidity over time after acute rubella infection

Difficulty in Serologic Screening for Subclinical Rubella during Pregnancy

In Japan, rubella antibodies are tested in all pregnant women to detect subclinical infections. This study aimed to assess the validity of measuring rubella antibodies for detecting subclinical rubella among pregnant women in Japan. This single-center retrospective study measured rubella hemagglutination inhibition (HI) titers and rubella-specific IgM antibody index (IgM) values. IgM values were measured by conducting enzyme immunoassay, and IgM-values >1.2 were considered positive. Of 14,965 included pregnant women, 186 (1.2%) were IgM-positive. Only one patient was clinically diagnosed with rubella (HI titer, 1:2,048; IgM value, 10) and developed fever and skin rash. She decided to terminate her pregnancy without undergoing repeated blood tests. Of the IgM-positive patients, 136 (73.1%) had rubella HI titers of < 1:256. The correlation coefficient between rubella HI and IgM titers was weakly positive (0.2527; P < 0.0001). This study showed that a single combination of rubella HI and rubella-specific IgM measurements alone could not detect subclinical rubella. Creating awareness among pregnant women by informing them that almost all rubella-specific IgM-positive individuals without symptoms are not acutely infected could decrease their anxiety and prevent unnecessary pregnancy termination.

Rubella virus IgM and IgG antibodies with avidity in pregnant women and outcomes at a tertiary facility in Ghana

BACKGROUND

Congenital rubella syndrome (CRS) is a recognised cause of childhood deafness and blindness caused by the transplacental transmission of rubella virus during pregnancy. Women in the reproductive age group, and by extension their unborn babies may therefore be at increased risk. The prevalence of Rubella virus specific IgM and IgG antibodies, including IgG avidity, was determined in pregnant women attending the antenatal clinic at a Teaching Hospital in Ghana.

METHODS

One hundred and forty-five women in their second and third trimesters of pregnancy from the outpatient clinic were recruited over a period of 2 months after written informed consent was obtained. Study participants completed a questionnaire and venous blood drawn for IgM, IgG, and avidity testing using SERION ELISA (SERION® Immunologics, Würzburg, Germany). Babies of mothers with positive or indeterminate IgM and low avidity IgG antibodies were offered specialist cardiological, ophthalmological or hearing assessment during follow up.

RESULTS

One hundred and twenty-eight (88.3%) had only IgG antibodies, 5 (3.4%) had IgM and IgG antibodies, while 12 (8.3%) had no antibodies. No patient had IgM antibodies alone. Ten women (6.9%) had indeterminate levels of IgM antibodies. Majority of the women had high avidity IgG antibodies, while 5 (3.4%) had low avidity antibodies. No patient had IgM with low avidity antibodies. There was no statistical association between socio-demographic factors and the presence of IgM, IgG (low or high avidity) antibodies. Of all the children followed, none had the clinical definition of CRS.

CONCLUSIONS

Consistent with the World Health Organization elimination strategy for measles and rubella viruses, non-immune women in the reproductive age group should be vaccinated. The immunization programme should be expanded to include teenagers and adults. Though Congenital Rubella Syndrome was not detected, the risk still remains.

Positive predictive value of seroconversion or positive rubella IgM in diagnosis of maternal rubella infection: Seven-years review of French National Reference Laboratory for Rubella

BACKGROUND

In France, as in most developed countries, childbearing age women are routinely screened for rubella antibodies to identify and vaccinate susceptible women. Immunity to rubella is usually determined by measuring the rubella virus-specific immunoglobulin G (RV-IgG). In case of seroconversion for RV-IgG and/or positive RVIgM during pregnancy, laboratories usually send serum samples to the French National Reference Laboratory (FNRL) for Rubella in order to perform complementary investigations and confirm or exclude rubella infection during pregnancy.

OBJECTIVE

Our aim is to report results of these investigations during a seven-year period (2013-2019) and evaluate the positive predictive value (PPV) of RV-IgG seroconversion or positive RV-IgM to diagnose maternal rubella infection in France.

STUDY DESIGN

Between 2013 and 2019, 5398 serum samples collected from 4104 pregnant women, were addressed to FNRL because of RV-IgG seroconversion (N=899) or positive RV-IgM (N=3205). Additional serological tests were performed, mainly immunoblot (to look for the presence of anti-E1 protective antibody) and RV-IgG avidity (to exclude or confirm primary infection).

RESULTS

Overall, for 3724/4104 (90.8 %) women, rubella primary-infection during pregnancy was formally excluded and maternal rubella primary-infection was only confirmed in 46/4104 (1.1 %) cases.

CONCLUSION

Clinicians and biologists should be particularly aware that RV-IgG seroconversion or positive RV-IgM, in the current context of low RV circulation in France are most often not rubella primary infections. PPV of seroconversion to assess maternal rubella primary infection is as low as 0.2 % (95 % CI: 0 %; 0.5 %) and PPV of positive RV-IgM is only of 1.4 % (95 % CI: 0.99 %; 1.81 %).

Sequential immunizations with a panel of HIV-1 Env virus-like particles coach immune system to make broadly neutralizing antibodies

Broadly neutralizing antibodies (bnAbs) are correlated with passive HIV/SHIV protection and are desirable components of a HIV protective immunity. In the current study, we have designed a sequential-immunization strategy with a panel of envelope glycoprotein (Env)-enriched virus-like particles (VLPs) from various HIV-1 clades (A-E) to elicit bnAbs with high breadth and potency of neutralization in rabbits. We have compared this regimen with repetitive immunizations of individual Env (subtype B) VLPs or a mixture of various Env VLPs. Our results demonstrate that the sequential immunization group of animals induced significantly higher IgG endpoint titers against respective HIV Env (autologous) antigen than other control groups. Animals vaccinated sequentially showed an increase in the antibody endpoint titers and IgG antibody secreting cells (ASCs) against Con-S Env protein. Sequential immunizations with various Env VLPs promoted antibody avidity indices and enhanced bnAb responses against a panel of HIV pseudotyped virions including some of the tier 3 pseudostrains. Sequential immunizations with various VLPs displaying "native-like" HIV-1 Envs elicited bnAb responses with increased breadth and potency of neutralization.

Two Imported Cases of Congenital Rubella Syndrome and Infection-Control Challenges in New York State, 2013-2015

Rubella was declared eliminated in the United States in 2004. During 2013-2015, 2 infants with congenital rubella syndrome (CRS) were born in New York State. Both mothers were foreign born and traveled to Yemen during their pregnancy. Delayed consideration of CRS led to preventable exposures and a substantial public health response.

Rubella Surveillance and Diagnostic Testing among a Low-Prevalence Population, New York City, 2012-2013

The New York City Department of Health and Mental Hygiene (DOHMH) receives clinical and laboratory reports for rubella. Because rubella immunoglobulin M (IgM) assays may produce false-positive results and rubella infections may be asymptomatic, interpretation of positive IgM results can be challenging. Rubella reports received by DOHMH in 2012 to 2013 were reviewed. The rubella IgM testing purpose was determined through case investigation. Results of IgM testing by indirect enzyme-linked immunosorbent assay (ELISA) and capture enzyme immunoassay (EIA) were compared to determine positive predictive value (PPV) and specificity. DOHMH received 199 rubella reports; 2 were true cases. Of all reports, 77.9% were tested for rubella IgM erroneously, 19.6% were tested for diagnostic purposes, 2.0% had unknown test purpose, and 0.5% were not tested. PPV of indirect ELISA was 6% overall, 14% for diagnostic tests, and 0% for tests ordered erroneously. PPV of capture EIA was 29% overall, 50% for diagnostic tests, and 0% for tests ordered erroneously. Overall, specificity was 52% for indirect ELISA and 85% for capture EIA. Limiting rubella IgM testing to patients for whom rubella diagnosis is suspected and using a more specific IgM assay have the potential to reduce false-positive rubella IgM results.

Standardization of Assays That Detect Anti-Rubella Virus IgG Antibodies

Rubella virus usually causes a mild infection in humans but can cause congenital rubella syndrome (CRS). Vaccination programs have significantly decreased primary rubella virus infection and CRS; however, vaccinated individuals usually have lower levels of rubella virus IgG than those with natural infections. Rubella virus IgG is quantified with enzyme immunoassays that have been calibrated against the World Health Organization (WHO) international standard and report results in international units per milliliter. It is recognized that the results reported by these assays are not standardized. This investigation into the reasons for the lack of standardization found that the current WHO international standard (RUB-1-94) fails by three key metrological principles. The standard is not a pure analyte but is composed of pooled human immunoglobulin. It was not calibrated by certified reference methods; rather, superseded tests were used. Finally, no measurement uncertainty estimations have been provided. There is an analytical and clinical consequence to the lack of standardization of rubella virus IgG assays, which leads to misinterpretation of results. The current approach to standardization of rubella virus IgG assays has not achieved the desired results. A new approach is required.

Identification of Serologic Markers for School-Aged Children With Congenital Rubella Syndrome

BACKGROUND

Congenital rubella syndrome (CRS) case identification is challenging in older children since laboratory markers of congenital rubella virus (RUBV) infection do not persist beyond age 12 months.

METHODS

We enrolled children with CRS born between 1998 and 2003 and compared their immune responses to RUBV with those of their mothers and a group of similarly aged children without CRS. Demographic data and sera were collected. Sera were tested for anti-RUBV immunoglobulin G (IgG), IgG avidity, and IgG response to the 3 viral structural proteins (E1, E2, and C), reflected by immunoblot fluorescent signals.

RESULTS

We enrolled 32 children with CRS, 31 mothers, and 62 children without CRS. The immunoblot signal strength to C and the ratio of the C signal to the RUBV-specific IgG concentration were higher (P < .029 for both) and the ratio of the E1 signal to the RUBV-specific IgG concentration lower (P = .001) in children with CRS, compared with their mothers. Compared with children without CRS, children with CRS had more RUBV-specific IgG (P < .001), a stronger C signal (P < .001), and a stronger E2 signal (P ≤ .001). Two classification rules for children with versus children without CRS gave 100% specificity with >65% sensitivity.

CONCLUSIONS

This study was the first to establish classification rules for identifying CRS in school-aged children, using laboratory biomarkers. These biomarkers should allow improved burden of disease estimates and monitoring of CRS control programs.

Screening cytomegalovirus, rubella and toxoplasma infections in pregnant women with unknown pre-pregnancy serological status

PURPOSE

To determine the prevalence of acute cytomegalovirus (CMV), rubella and T. gondii infections among pregnant women who had no serological status tested for these microorganisms prior to pregnancy in a metropolitan area.

METHODS

A cross-sectional study was undertaken between January 2009 and January 2013 in 1,258 women presenting for their first antenatal visit (between 6 and 11 weeks of gestation). All women were tested for IgG and IgM antibodies. Subsequently, avidity test was utilized for inconclusive results. They were followed until delivery and all newborns were examined by a pediatrician.

RESULTS

Presence of IgM antibody positivity alone was not detected in any women. Avidity test excluded primary infection in 15 out of 16 (93.7 %) women who were positive for both IgG and IgM antibodies. Amniocentesis was performed in one case with borderline IgG avidity for T. gondii. No primary infections were detected in any newborn for the infections screened. The prevalences of IgG antibodies were 95 % for rubella, 84.1 % for CMV and 23.1 % for T. gondii.

CONCLUSIONS

Assessment of IgG and IgM antibodies followed by IgG avidity testing for inconclusive results may be an acceptable approach in pregnant women with unknown serological status prior to pregnancy. Utilization of IgG avidity as a supplemental test prevented unnecessary intervention in IgG and IgM antibodies positive patients. No primary infection was detected for CMV, rubella and T. gondii infections in the urban population screened.

Clinicolaboratory study of mother-to-neonate transmission of hepatitis E virus in Egypt

OBJECTIVES

To study the presence of hepatitis E viremia in neonates with congenital infections.

METHODS

We included 29 neonates with clinical signs and symptoms suggesting congenital infections, along with their mothers. The control group comprised 29 healthy neonates and their mothers. Laboratory evaluations were performed for each sample for liver function profiles and virological studies for hepatitis viruses B, C, and E.

RESULTS

The most common viral markers in mothers were for hepatitis C immunoglobulin G (IgG) (41%), followed by hepatitis B surface antigen (34%) and hepatitis E virus (HEV) IgG (31%). The most common presentations in neonates were respiratory distress syndrome, followed by preterm birth and signs of sepsis (both 41%) and hepatosplenomegaly (13%).

CONCLUSIONS

This study highlights the occurrence of HEV infection among other etiological conditions causing congenital infections. Vertical transmission from mothers was common in our patients. Although HEV ran a milder course, more studies are needed.

Antibody avidity in humoral immune responses in Bangladeshi children and adults following administration of an oral killed cholera vaccine

Antibody avidity for antigens following disease or vaccination increases with affinity maturation and somatic hypermutation. In this study, we followed children and adults in Bangladesh for 1 year following oral cholera vaccination and measured the avidity of antibodies to the T cell-dependent antigen cholera toxin B subunit (CTB) and the T cell-independent antigen lipopolysaccharide (LPS) in comparison with responses in other immunological measurements. Children produced CTB-specific IgG and IgA antibodies of high avidity following vaccination, which persisted for several months; the magnitudes of responses were comparable to those seen in adult vaccinees. The avidity of LPS-specific IgG and IgA antibodies in vaccinees increased significantly shortly after the second dose of vaccine but waned rapidly to baseline levels thereafter. CTB-specific memory B cells were present for only a short time following vaccination, and we did not find significant memory B cell responses to LPS in any age group. For older children, there was a significant correlation between CTB-specific memory T cell responses after the second dose of vaccine and CTB-specific IgG antibody avidity indices over the subsequent year. These findings suggest that vaccination induces a longer-lasting increase in the avidity of antibodies to a T cell-dependent antigen than is measured by a memory B cell response to that antigen and that early memory T cell responses correlate well with the subsequent development of higher-avidity antibodies.

Protective role of humoral immune responses during an outbreak of hepatitis E in Egypt

Although the seroprevalence of hepatitis E virus (HEV) is approximately 80% in adult Egyptians living in rural areas, symptomatic HEV-caused acute viral hepatitis (AVH) is sporadic and relatively uncommon. To investigate the dichotomy between HEV infection and clinical AVH, HEV-specific immune responses in patients with symptomatic and asymptomatic HEV infection during a waterborne outbreak in Egypt were examined. Of 235 acute hepatitis patients in Assiut hospitals screened for HEV infection, 42 (17.9%) were acute hepatitis patients confirmed as HEV-caused AVH; 37 (88%) of the 42 patients were residents of rural areas, and 14 (33%) were from one village (Kom El-Mansoura). Another 200 contacts of AVH cases in this village were screened for HEV and 14 (7.0%), all of whom were family members of AVH cases, were asymptomatic HEV IgM-positive. HEV infections in this village peaked during the summer. Asymptomatic HEV seroconverters had significantly higher levels of epitope-specific neutralising (p=0.006) and high avidity (p=0.04) anti-HEV antibodies than the corresponding AVH cases. In conclusion, naturally acquired humoral immune responses appear to protect HEV-exposed subjects from AVH during an HEV outbreak in Egypt.

Measles virus IgG avidity assay for use in classification of measles vaccine failure in measles elimination settings

In regions where endemic measles virus has been eliminated, diagnostic assays are needed to assist in correctly classifying measles cases irrespective of vaccination status. A measles IgG avidity assay was configured using a commercially available measles-specific IgG enzyme immunoassay by modifying the protocol to include three 5-min washes with diethylamine (60 mM; pH 10.25) following serum incubation; serum was serially diluted, and the results were expressed as the end titer avidity index. Receiver operating characteristic analysis was used for evaluation and validation and to establish low (≤30%) and high (≥70%) end titer avidity thresholds. Analysis of 319 serum specimens expected to contain either high- or low-avidity antibodies according to clinical and epidemiological data indicated that the assay is highly accurate, with an area under the curve of 0.998 (95% confidence interval [CI], 0.978 to 1.000), sensitivity of 91.9% (95% CI, 83.2% to 97.0%), and specificity of 98.4% (95% CI, 91.6% to 100%). The assay is rapid (<2 h) and precise (standard deviation [SD], 4% to 7%). In 18 samples from an elimination setting outbreak, the assay identified 2 acute measles cases with low-avidity results; both were IgM-positive samples. Additionally, 11 patients (15 samples) with modified measles who were found to have high-avidity IgG results were classified as secondary vaccine failures; one sample with an intermediate-avidity result was not interpretable. In elimination settings, measles IgG avidity assays can complement existing diagnostic tools in confirming unvaccinated acute cases and, in conjunction with adequate clinical and epidemiologic investigation, aid in the classification of vaccine failure cases.

Rubella antibody screening during pregnancy in an urban area of Northern Italy

Various countries have implemented anti-rubella vaccination campaigns with the main aim of preventing congenital infection. In 2003, Italy joined the European WHO programme for the elimination of congenital rubella and issued a special healthcare plan, one of the objectives of which was to reduce the proportion of rubella-susceptible pregnant women to less than 5% by 2005. The aim of this study was to determine the percentage of seronegative pregnant women after the implementation of this plan. Anti-rubella IgG and IgM antibodies were sought in 2385 pregnant women who attended our hospital for serological screening between 1 July 2008 and 30 June 2010. They included 750 women of foreign origin (31.4%). Eight percent of the women were anti-rubella seronegative: 6.2% of the Italians and 11.7% of the non-Italians. Among the women of foreign origin, the percentage of seronegativity ranged from 5.6% of those coming from Eastern Europe to 17.7% of those coming from Latin America. The level of seropositivity among women of Italian origin is high, although the objective of ensuring less than 5% of susceptible pregnant women has not yet been quite reached in our area. However, particular attention needs to be given to women coming from geographical areas characterised by different epidemiologies and vaccination strategies because the percentage of seronegativity is in some cases double that of Italian women.

Primary and probable secondary dengue virus (DV) infection rates in relation to age among DV IgM-positive patients residing in the United States mainland versus the Caribbean islands

Dengue virus (DV) primary infection and probable secondary infection rates in relation to patient age (years) were determined for DV IgM-positive U.S. mainland residents (presumed travelers to areas of DV endemicity) and Caribbean island (area of DV endemicity) residents by evaluating IgG status and IgG avidity. Regardless of place of residence, most patients ≤20 years old exhibited primary infection and most patients >60 years old exhibited probable secondary infection. Among patients 21 to 60 years old, the primary infection rate was markedly higher in U.S. residents.

Comparison of methods to detect recent HIV type 1 infection in cross-sectionally collected specimens from a cohort of female sex workers in the Dominican Republic

Interest in estimating HIV-1 incidence using specimens obtained as part of cross-sectional surveys has led to the development of new methods to detect recent HIV-1 infection through the testing of a single anti-HIV-positive specimen. These assays are based on quantitative and qualitative differences in anti-HIV-1 antibodies between recent and long-standing infections. An ongoing vaccine preparedness study enrolled female sex workers in the Dominican Republic. Specimens from women found to be HIV positive at baseline were tested for recent HIV-1 infection using the detuned assay, avidity index, and BED-CEIA assay. An unweighted kappa statistic in pairwise comparisons was used to estimate the correlation of recent HIV-1 infection detection by the three methods. Nineteen (3.9%) of 482 women were positive for HIV-1 infection. The incidence of HIV infection was 1.4% [95% confidence interval (CI): 0.2, 5.3], 0.9%(95% CI: 0.1, 4.4), and 1.0%(95% CI: 0.1, 4.4) using detuned assay, avidity index, and BED-CEIA techniques, respectively. The overall agreement between both detuned assay and avidity index and detuned assay and BED-CEIA was 94%(kappa = 0.8, 95% CI; 0.3, 1.0). The correlation was highest between BED-CEIA and avidity index methods (100%; kappa = 1.0). All three methods performed similarly in detecting recent HIV-1 infection in this region dominated by clade B HIV-1 infection. Although incidence estimates were slightly higher using the detuned assay method, they were not significantly different. These assays may be of value in both clinical research and practice. The utility of individual assays for recent infection detection will depend upon operating characteristics, HIV-1 subtype limitations, and selection of appropriate assay cutoff values.

Malaria-specific antibody responses and parasite persistence after infection of mice with Plasmodium chabaudi chabaudi

While it is known that antibodies are critical for clearance of malaria infections, it is not clear whether adequate antibody responses are maintained and what effect chronic infection has on this response. Here we show that mice with low-grade chronic primary infections of Plasmodium chabaudi or infections very recently eliminated have reduced second infections when compared with the second infection of parasite-free mice. We also show that parasite-specific antibody responses induced by infection of mice with Plasmodium chabaudi contain both short- and long-lived components as well as memory B cells responsible for a faster antibody response during re-infection. Furthermore, parasite-specific antibodies to the C-terminal fragment of merozoite surface protein-1 (MSP-1) undergo avidity maturation. However, antibodies with both low and high avidity persist throughout infection and after re-infection, suggesting repeated rounds of activation and maturation of memory B cells. Neither the avidity profile of the antibody response, nor its maintenance is affected by persisting live parasites. Therefore, differences in parasitemia in re-infection cannot be explained solely by higher levels of antibody or greater affinity maturation of malaria-specific antibodies. These data suggest that there may be an antibody-independent component to the early control of secondary infections in mice that are chronically infected.

Development of a rapid and convenient method for determination of rubella virus-specific immunoglobulin G avidity

We describe here a rapid and semiautomated method for the determination of rubella virus immunoglobulin G (IgG) avidity with the VIDAS instrument. A total of 153 serum samples from persons with naturally acquired rubella virus infections (n = 98), from vaccinated persons (n = 44), and from patients with autoantibodies (n = 11) were included in this study. The rubella virus-specific IgG avidity assay we developed for the VIDAS instrument was evaluated by comparison with an in-house method. Results obtained with the VIDAS instrument allow considering this method valuable to help confirm or exclude acute primary infection or recent vaccination.

Humoral immune response after primary rubella virus infection and after vaccination

We measured rubella virus immunoglobulin G (IgG) and IgM levels, as well as IgG avidity indexes, in serum samples taken before or after 6 months either after infection or after vaccination. The results obtained indicate that humoral immune responses are different after primary infection and after vaccination. This may have important consequences on the serological diagnosis of rubella virus infection.

Evaluation of immunity against rubella in Iranian after mass campaign for measles-rubella vaccination on December 2003

BACKGROUND

Prevention of congenital rubella syndrome (CRS) is the main goal of rubella immunization. The World Health Organization (WHO) recommends that countries undertaking measles elimination should take the opportunity to eliminate rubella as well through use of measles-rubella (MR) or measles-mumps-rubella (MMR) vaccine in their childhood immunization programs and campaigns. On December 2003, during a mass campaign for measles-rubella vaccination in Iran, more than 33 million doses of vaccine were administered to 5- to 25-year-old males and females.

METHODS

In this study, immunoglobulin (Ig)G avidity assay was used to evaluate the rubella vaccine produced immunity among susceptible populations.

RESULTS

Findings indicated that 61.9% of vaccinees (1202 out of 1940) were immune against rubella before vaccination, and 38.1% (738 out of 1940) were susceptible to rubella before vaccination. Our results also showed that 98% of the susceptible group (723 out of 738) acquired immunity against rubella after vaccination, and 2% of them (15 out of 738) did not acquire vaccine-induced immunity to rubella.

CONCLUSION

Findings revealed that mass vaccination in December 2003 provided appropriate immune coverage among vaccinees. Also, rubella vaccine induced favorable immunity in a part of the childbearing age female (15-25 years) population, which could prevent congenital rubella syndrome among those females.

Assessment of IgM enzyme immunoassay and IgG avidity assay for distinguishing between primary and secondary immune response to rubella vaccine

The primary test for the laboratory confirmation of rubella is IgM serology. It is important to distinguish IgM reactivity caused by primary infection from that caused by reinfection or persistence, especially in pregnant women; as termination of pregnancy is considered when primary rubella is diagnosed during the first trimester. In this study, the performance of rubella IgM enzyme immunoassay (IgM-EIA) and rubella IgG avidity assay were compared using well-defined panels of sera from persons vaccinated against rubella and commercial rubella IgM and IgG enzyme immunoassay kits (Dade Behring, Marburg, Germany). The sensitivity and specificity of rubella IgM-EIA were found to be 77.4 and 97.9%, respectively, while the results for rubella IgG avidity assay were 100 and 100%. IgG avidity assay showed higher positive and negative predictive values than the IgM-EIA (100 and 100% compare to 96.9 and 82.9%). In conclusion, the rubella IgG avidity assay is more sensitive and specific than IgM-EIA for differential detection of primary rubella infection from rubella reinfection.

Utilization of follow-up specimens from viremic blood donors to assess the value of west nile virus immunoglobulin G avidity as an indicator of recent infection

The value of West Nile virus immunoglobulin G avidity for distinguishing recent from past infection was investigated using 348 follow-up specimens from 170 viremic blood donors. Low avidity accurately indicated infection within the previous 4 months. However, due to rapid avidity maturation in some individuals, high avidity did not accurately indicate past infection.

Laboratory investigations are indispensable to monitor the progress of measles elimination--results of the German Measles Sentinel 1999-2003

BACKGROUND

The elimination of measles is a goal set by the World Health Organisation to be reached by 2010 in the European region.

OBJECTIVES

To enhance the measles surveillance in Germany, a country-wide laboratory supported a sentinel was established.

STUDY DESIGN

A network of >1200 representatively distributed practitioners reported detailed data on all clinically diagnosed cases and provided specimens for laboratory diagnosis.

RESULTS

A total of 3225 suspected cases were reported between October 1999 and December 2003. The incidence in Western Germany decreased from >15 cases per 100,000 population to one case in 2003, while in Eastern Germany <1 case per 100,000 population was observed during these years. Laboratory investigations were undertaken in 40% of cases in 2000/2001. This rate increased to 79% in 2003. Simultaneously, the rate of confirmed cases dropped from 60% in the former years to 23% in 2003. Measles virus (MV) detection by serology and by PCR revealed concordant results in 92%. Most suspected cases (85%) were unvaccinated with 66% being laboratory confirmed. Only 10% of suspected cases occurred in vaccinated individuals and very few (22%) could be confirmed. Analyses of confirmed measles in vaccinated patients (n = 49) revealed 24.5% primary vaccine failures, 24.5% reinfections after successful vaccination and 31% MV infection before or shortly after vaccination. The genetic characterisation of 389 MV isolates identified eight genotypes: B3, C2, D4, D5, D6, D7, G2 and H1. Only the C2, D6 and D7 MV genotypes circulated endemically in Western Germany. The newly emerged MV D7 almost completely replaced the pre-existing C2 and D6 MVs in 2001. The few measles cases detected in Eastern Germany were mostly caused by imported MVs.

CONCLUSION

The data demonstrate that laboratory investigations including molecular methods are an indispensable tool for surveillance in all countries advanced in measles elimination.

Measurement of EBV-IgG anti-VCA avidity aids the early and reliable diagnosis of primary EBV infection

Current serological methods for the diagnosis of Epstein-Barr virus (EBV) infection still differentiate poorly between primary infection and reactivation. This is particularly true when IgG and IgM antibodies are present simultaneously and only a single serum sample is provided for analysis. The demonstration of the IgG avidity state has the potential to distinguish recent from past or reactivated infection. An analysis of the kinetics of avidity maturation of anti-VCA antibodies in primary EBV infection was undertaken with longitudinally collected sets of sera from 28 well-characterised EBV cases and in sera from 35 cases with previous EBV infection and recent primary infection due to HIV, CMV, or hepatitis A. Antibodies directed against the viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA-1) were sought, using a commercial enzyme immunoassay (EIA). In parallel with standard IgG anti-VCA detection, serum was incubated with 8 M urea to disrupt low-avidity complexes to allow calculation of the percentage avidity. In cases with primary EBV infection, the mean avidity rose from 54% at 6 weeks to 82% by 28 weeks after the onset of symptoms, but remained lower than that of the control sera (96%). The addition of the avidity measurement improved the sensitivity of IgG and IgM anti-VCA testing in diagnosis of primary EBV infection from 93% to 100%. The specificity of IgM anti-VCA testing alone was poor, with 14 of 35 cases (49%) demonstrating false-positive results, but it improved to 97% by the demonstration of high-avidity IgG anti-VCA. The combination of negative IgG anti-EBNA and low-avidity IgG anti-VCA had a sensitivity and specificity of 100%. The routine addition of IgG anti-VCA avidity estimation to diagnostic EBV serology is recommended.

Prenatal diagnosis of congenital rubella infection in the second trimester of pregnancy

OBJECTIVES

This case report describes the clinical presentation, diagnosis and management of a case of acute rubella infection in the second trimester. The complex issues of prenatal diagnosis of a congenital rubella infection are discussed.

METHODS

A 30-year-old woman presented with a fine macular rash at 15 weeks' gestation. Laboratory testing included maternal rubella-specific IgG and IgM detection (booking blood and acute-phase sample) together with measurement of IgG avidity. Prenatal diagnosis at 19 weeks (amniocentesis) and 23 weeks (amniocentesis and fetal blood) was done using a reverse-transcriptase polymerase chain reaction to detect rubella-specific RNA. The fetal blood sample was also tested for rubella-specific IgM.

RESULTS

Maternal serological results confirmed an acute rubella infection at 15 weeks' gestation. Rubella-specific RNA and IgM were detected in the fetal blood taken at 23 weeks' gestation. However, no rubella RNA was detected in either of the amniotic fluid samples collected at 19 and 23 weeks.

CONCLUSION

In second-trimester rubella where risk of fetal damage is low, prenatal diagnosis can identify the rubella-infected fetus, allowing the parents to make a more informed decision about their options. The optimal sample for prenatal diagnosis is fetal blood as no rubella-specific RNA was detected in the amniotic fluid.

Avidity of islet cell autoantibodies in non-diabetic children and children with insulin-dependent diabetes

Low-avidity immunoglobulin G antibodies, which commonly occur after microbial infections and form unstable complexes with the antigen, are within weeks replaced by high-avidity antibodies, which bind the antigen tightly and characterise mature immune response. We hypothesised that avidity of islet cell autoantibodies (ICA), found in the sera of patients with insulin-dependent diabetes mellitus (IDDM) usually months or years before disease onset, might reflect the stage of progression towards overt IDDM. ICA were quantitated before and after treatment of antigen-antibody complexes with 5 M urea in a new assay, in which the fluorescence intensity of europium chelate-labelled detecting antibody is measured from a digital time-resolved fluorescence image. The proportion of urea-resistant ICA of all ICA was defined as the avidity index. The median avidity indices (range) of 119 children with recent-onset IDDM and 64 non-diabetic ICA-positive children were 74% (23-100%) and 11% (0-100%), respectively (p = 0.0001). The avidity indices of only 3 children with IDDM (2.5%), but of 55 non-diabetic ICA-positive children (86%) were < 40%. In conclusion, our data show that ICA avidity indices of ICA-positive non-diabetic children and children with IDDM differ, suggesting that measurement of ICA avidity may improve prediction of the time of onset of clinical IDDM.

Do escape mutants explain rapid increases in dengue case-fatality rates within epidemics?

During the Cuban dengue epidemics of 1981 and 1997, significant monthly increases were observed in the proportion of total cases that presented as dengue haemorrhagic fever or dengue shock syndrome (DHF/DSS), and in case-fatality rates for both dengue fever and DHF/DSS. We believe that theses increases can be explained by the hypothesis that some of the population of antibodies against dengue 1 virus raised after natural primary infections react with "neutralisation" determinants found on dengue 2 viruses. These heterotypic antibodies do not prevent secondary dengue 2 infections, but serve to down-regulate the disease to mild illness or symptomless infections. A population of dengue 2 viruses that replicates in dengue-1-immune hosts escape heterotypic neutralisation. When inoculated into a new dengue-1-immune host, these viruses are free to interact with the more abundant infection-enhancing antibodies to produce severe disease.

Comparison of Humoral Immune Responses Elicited by DNA and Protein Vaccines Based on Merozoite Surface Protein-1 from Plasmodium yoelii, a Rodent Malaria Parasite

Immunization with DNA vaccines encoding relevant Ags can induce not only cell-mediated immune response but also humoral immune responses against pathogenic microorganisms in several animal models. Our previous results demonstrated that, when the C terminus (PyC2) of Plasmodium yoelii merozoite surface protein-1 (MSP-1), a leading vaccine candidate against erythrocytic stages of malaria, was expressed as a fusion protein (GST-PyC2) with glutathione S-transferase (GST), it elicited Ab-mediated protective immune responses in BALB/c mice. In our present study, we wished to examine the humoral responses to a DNA vaccine (V3) encoding GST-PyC2. The GST-PyC2 expressed in V3-transfected Cos 7 cells was recognized by a protective monoclonal Ab to PyC2 (mAb302), although the secreted product had undergone N-linked glycosylation. When BALB/c mice were immunized with V3 plasmid, anti-PyC2 Abs were successfully induced. These Abs immunoprecipitated native PyMSP-1 protein and competed with mAb302 for binding to its epitope at a level similar to those elicited by GST-PyC2 protein immunization. However, these Abs had significantly lower titers and avidities, and different isotype profiles and protective capacities against a lethal erythrocytic stage challenge, than those resulting from immunization with GST-PyC2 protein. Most surprising was the finding that, in contrast to protein immunization, there was no significant increase in the avidity of either GST-specific or PyC2-specific IgG Abs during the course of DNA immunization. This suggests that there may be little or no affinity maturation of specific Abs during DNA immunization in this system.