A comparison of antibody capture radio- and enzyme immunoassays with immunofluorescence for detecting IgM antibody in infants with congenital rubella

Modeling the impact of rubella vaccination in Vietnam

Supported by GAVI Alliance, measles-rubella vaccination was introduced in Vietnam in 2014, involving a mass campaign among 1–14 year olds and routine immunization of children aged 9 months. We explore the impact on the incidence of Congenital Rubella Syndrome (CRS) during 2013–2050 of this strategy and variants involving women aged 15–35 years. We use an age and sex-structured dynamic transmission model, set up using recently-collected seroprevalence data from Central Vietnam, and also consider different levels of transmission and contact patterns. If the serological profile resembles that in Central Vietnam, the planned vaccination strategy could potentially prevent 125,000 CRS cases by 2050 in Vietnam, despite outbreaks predicted in the meantime. Targeting the initial campaign at 15–35 year old women with or without children aged 9 months–14 years led to sustained reductions in incidence, unless levels of ongoing transmission were medium-high before vaccination started. Assumptions about contact greatly influenced predictions if the initial campaign just targeted 15–35 year old women and/or levels of ongoing transmission were medium-high. Given increased interest in rubella vaccination, resulting from GAVI Alliance funding, the findings are relevant for many countries.

Laboratory diagnosis of intrauterine and perinatal virus infections

BACKGROUND

Intrauterine infection with rubella, cytomegalovirus (CMV), varicella zoster virus (VZV), parvovirus B19 and human immunodeficiency virus type 1 (HIV-1) may occur following maternal infection. Diagnosis of congenital infection in the neonate is dependent on the appropriate laboratory techniques being used. Prenatal diagnosis of intrauterine infection may also be indicated. Herpes simplex virus (HSV), HIV-1, VZV, enteroviruses, hepatitis B (HBV) and hepatitis C viruses (HCV), human T-cell lymphotropic viruses (HTLV-1 and 2) and genital papillomaviruses (PVs) may be acquired at delivery. Neonatal HSV, VZV and enterovirus infections may be severe or even fatal. Perinatally acquired HBV, HCV, HIV-1 and HTLVs are associated with persistent infection and chronic disease in later life. However, if the mother is identified as a carrier in the antenatal period, mother-infant transmission of HBV may be prevented by active/passive immunisation of the neonate, HIV-1 by caesarian section or antiviral therapy, and of HTLV-1 by avoiding breast feeding.

OBJECTIVES AND STUDY DESIGN

To review the techniques available for the diagnosis of intrauterine infections, neonatal infections with HSV, HIV-1, VZV and enteroviruses, maternal infection with HBV, HCV and HIV-1 and prenatal diagnosis of intrauterine rubella, CMV and B19.

RESULTS

Congenital rubella may be diagnosed by detection of specific IgM, but virus detection is the technique of choice for congenital cytomegalovirus. Congenital VZV may be diagnosed by serological techniques in up to 71% of cases. Detection of virus in vesicle scrapings or swabs from the oropharynx is the technique of choice for neonatal HSV, while enterovirus infections are best diagnosed by detection of viral RNA. A clinical diagnosis of congenital VZV is often possible. HIV-1 may be diagnosed within 3 months of birth by testing serial blood samples with a combination of techniques. Maternal infection with HBV, HCV, HIV and HTLV1/11 may be diagnosed by serological techniques and genital PVs by detection of viral DNA. Chorionic villus samples, amniotic fluid and fetal blood may be obtained for prenatal diagnosis of infection. Although detection of virus in amniotic fluid is the technique of choice for prenatal diagnosis of CMV, insufficient data is currently available to determine whether it may be used for intrauterine rubella. The most reliable technique for diagnosis of fetal B19 infection is detection of viral DNA in fetal blood.

CONCLUSIONS

Close liaison between clinicians and microbiologists/virologists is required in order that appropriate specimens are collected from infant and/or mother and appropriate tests conducted. The use of TORCH screening should be discouraged.

Rubella

Maternal rubella is now rare in many developed countries that have rubella vaccination programmes. However, in many developing countries congenital rubella syndrome (CRS) remains a major cause of developmental anomalies, particularly blindness and deafness. WHO have provided recommendations for prevention of CRS, and, encouragingly, the number of countries introducing rubella vaccination programmes has risen. However, declining uptake rates due to concerns about the measles-mumps-rubella vaccine in the UK, and increasing numbers of cases in some European countries coupled with poor uptake rates might jeopardise this progress. Surveillance of postnatally and congenitally acquired infection is an essential component of CRS prevention since rubella is difficult to diagnose on clinical grounds alone. Laboratory differentiation of rubella from other rash-causing infections, such as measles, parvovirus B19, human herpesvirus 6, and enteroviruses in developed countries, and various endemic arboviruses is essential. Reverse transcriptase PCR and sequencing for diagnosis and molecular epidemiological investigation and detection of rubella-specific IgG and IgM salivary antibody responses in oral fluid are now available.

New horizons in the control of rubella and prevention of congenital rubella syndrome in the Americas

Data from the regional measles surveillance system have documented widespread rubella virus circulation in many different countries in the Americas. In response to the ongoing endemic incidence of the disease and the potential for a major rubella epidemics in the region, the Pan American Health Organization Technical Advisory Group on Vaccine Preventable Diseases recommended the implementation of a regional initiative to strengthen rubella and congenital rubella syndrome (CRS) preventive efforts in 1997. This article summarizes and highlights the progress toward accelerated rubella control and CRS prevention in the English-speaking Caribbean and in Chile, Costa Rica, and Brazil. Useful knowledge is being generated for the adaptation of similar rubella strategies elsewhere. The findings also document the feasibility of implementing the recommended strategies and their rapid impact on disease burden.

Comparison of four enzyme immunoassays for detection of immunoglobulin M antibodies against rubella virus

We evaluated four tests for the detection of rubella virus-specific immunoglobulin M antibodies. Primarily, consecutive serum samples were tested by two different assays. Selected panels of sera from patients with proven or likely recent rubella and false-positive and true-negative results in the two primary assays were further tested with two recently developed, fully automated techniques. The four tests were comparable in overall accuracy, but their dynamic ranges may differ considerably. Ways to optimize the predictive values are discussed. We conclude that automated assays may be used without causing significant changes in diagnostic accuracy or distortions in notifications of the incidence of rubella compared with the use of established tools.

Slow maturation of IgG1 avidity and persistence of specific IgM in congenital rubella: implications for diagnosis and immunopathology

Without appropriately timed specimens, serological confirmation of congenital rubella infection may be a problem. We have compared the persistence of specific IgM and low avidity specific IgG1 in 141 sera from 120 cases of serologically confirmed congenital rubella infection with the known time scales for postnatal primary rubella. The results demonstrate that the maturation of the immune response to the rubella virus is abnormally slow in congenital rubella cases both in terms of the isotype switch and especially the development of high avidity specific IgG1. Thus avidity studies may permit serological confirmation of congenital rubella for longer than is possible with tests currently in use. The pathological implications of prolonged low avidity antibody production are discussed.

A lymphocyte transformation assay for the diagnosis of congenital rubella

A rubella-specific lymphocyte transformation assay, using cryopreserved mononuclear cells, has been developed and used to evaluate specific responses among 21 children with congenitally acquired rubella (CAR), 25 healthy control children and 10 children with sensorineural deafness of unknown aetiology. Although all 21 children with CAR were seropositive, 12 (57.1%) failed to respond to rubella antigen in the transformation assay. Negative in vitro lymphocyte transformation responses were detected significantly more frequently among congenitally infected children below 3 years of age. Thirteen of the 25 (52%) control children were seropositive; only one of these seropositive children (7.6%) gave a negative transformation response. A negative rubella-specific lymphocyte transformation response in a seropositive child, particularly when aged 3 years or younger, is therefore suggestive of CAR. Four of the 10 children with deafness of unknown aetiology were rubella seropositive but gave negative responses in the transformation assay, suggesting that these children had CAR. Our assay may provide a very useful test for retrospective diagnosis of CAR, particularly in children under the age of 3.

Laboratory diagnosis of rubella: past, present and future

Fifty years ago in New South Wales the late Sir Norman Gregg [1] described congenital cataracts in 78 babies, 67 of whose mothers had had clinical rubella in early pregnancy; he concluded that the disease in the mother caused the abnormality in the baby. Gregg [1–3] and Swan [4, 5] and their colleagues reported that deafness, heart disease and microcephaly were also major components of the congenital rubella syndrome. The need to prevent this tragic outcome stimulated intensive work on laboratory diagnosis and vaccine development, leading to the isolation of rubella virus in 1962 and then to methods for antibody detection. These complementary advances established the two traditional pillars of virological diagnosis and opened the way to immunization, with the result that some countries are now on the verge of eliminating a disease which for over 100 years was regarded as no more than a mild and harmless exanthem of childhood.

Detection of early hemagglutination inhibitory antibodies to rubella virus by pretreatment of sera with streptococcal cells

A technique that is based on absorption of sera with streptococcal cells and hemagglutination inhibition (HI) was evaluated for its feasibility for serologic diagnosis of recent rubella. The mixture of AR1 and AW43 cells removes IgG and IgA from the kaolin-treated sera, leaving IgM and a trace of IgA, probably oligomeric IgA. Consequently, after the absorption with streptococci, the HI antibodies are detectable exclusively in the early sera of patients with rubella. The streptococci (AR1 and AW43) have several advantages as the absorbent over the staphylococcus (Cowan I) that has been used routinely.

Selection and performance of monoclonal and polyclonal antibodies in an IgM antibody capture enzyme immunoassay for rubella

Monoclonal anti-human IgM and anti-rubella antibodies were prepared and tested in an IgM capture enzyme immunoassay (MACEIA) for rubella-specific IgM and compared with polyclonal reagents. Assay sensitivity was increased with monoclonal antibodies resulting in the improved discrimination of adult sera with low levels of specific IgM. Despite high IgM binding, interference by IgM anti-Ig was not a major problem. The use of monoclonal antibodies allowed assay simplification by the simultaneous rather than sequential addition of antigen and conjugate. Although comparable results were obtained with 33 test samples in the sequential and simultaneous MACEIA, the specificity and sensitivity of this modification requires further evaluation.

Public Health Laboratory Service IgM antibody capture enzyme linked immunosorbent assay for detecting rubella specific IgM

A total of 468 sera were selected for the evaluation of the Public Health Laboratory Service's IgM antibody capture enzyme linked immunosorbent assay kit (MACELISA) for detecting rubella specific IgM. The results obtained were compared with those obtained by IgM antibody capture radioimmunoassay (MACRIA). Sera from patients with primary postnatal rubella, congenital rubella, remote rubella, infectious mononucleosis, and recent infection with other agents were included, in addition to sera taken after rubella immunisation and sera containing rheumatoid factor and rubella specific IgG antibody. The assay exhibited a similar ability and comparable specificity to MACRIA for detecting rubella specific IgM antibody. The Public Health Laboratory Service MACELISA can be recommended if, as for all assays that detect rubella specific IgM, all the available clinical and serological data are taken into account when the results are interpreted.

Comparison of various serological methods and diagnostic kits for the detection of acute, recent, and previous rubella infection, vaccination, and congenital infections

The antibody development after natural rubella infection and rubella vaccination has been followed in 802 sera from 493 patients and 71 sera from 22 vaccinees. Also examined were 67 sera from 28 infants with rubella embryopathy and sera from 50 children with presumed prenatal infection. In addition, 777 sera from 641 patients tested for routine rubella diagnosis were studied. Anamnestic information was available from all these patients. These sera were assayed for IgM antibody detection by sucrose density gradient (SDG), the commercial ELISAs (Enzygnost IgM and Rubazyme M), and the non-commercial anti-my-hemadsorption immunosorbent technique (HIT). For the determination of IgG antibodies the hemagglutination inhibition test (HAI), the commercial ELISAs (Enzygnost IgG, Rubazyme), and a single radial hemolysis test (SRH) were used. The SDG and HIT were less sensitive for IgM antibody detection than the two ELISAs, particularly when IgM concentrations were low. In total 26.5% of the IgM results with the newer tests were discordant with SDG, but only 0.5-1.3% of these results were not explicable when the clinical data was considered. Problems were encountered with all IgM assay systems used. For the detection of rubella antibodies after acute infection and vaccination the ELISA Enzygnost IgG was as sensitive as the HAI whereas the ELISA Rubazyme and SRH detected antibodies with some delay. Corresponding results with all tests were found more than 25 days after acute infection and more than 50 days after vaccination. All methods can be used for detection of antibodies in infants with rubella embryopathy. The results of this study suggest that certain combinations of tests can be used for the reliable detection of rubella infection.

Clinical validation of an antibody-capture anti-rubella IgM-ELISA

An antibody-capture IgM-ELISA using monoclonal antibodies for conjugate was subjected to clinical validation with respect to sensitivity and specificity. In 103 serum specimens, known to contain anti-rubella IgM by a sucrose density gradient method, IgM was found by the ELISA in 99 sera. In a second study, 16 out of 17 acute rubella infections were detected by the IgM-ELISA. In 17 out of 17 vaccinees, a specific IgM response could be demonstrated. Specificity of the antibody-capture ELISA was found to be high; no interference was seen in 60 rheumatoid-factor positive sera, in 100 highly positive IgG sera or 10 sera with anti-CMV IgM. Only one out of 100 sera with heterophile antibodies showed a positive response. In acute rubella infections, IgM was shown to be detectable from 1 to 4 days after onset of illness up to about 12 wk, with peak values at about 1 wk after onset.

Prenatal detection of rubella-specific IgM in fetal sera

Serum specimens were obtained by fetoscopy at 19-25 weeks' gestation from four fetuses whose mothers had had confirmed rubella earlier in pregnancy. They were tested for rubella-specific IgM by antibody capture radioimmunoassay. No specific IgM was detected in one fetus and a healthy infant was delivered at term. Specific IgM was detected in the other three fetuses. In one case the level was low (1 unit) and this pregnancy went to term resulting in a neonate with clinical and laboratory evidence of congenital rubella infection. The remaining two fetuses had 2.8 and 2.4 units of specific IgM and the pregnancies were terminated. Blood obtained from these two fetuses after abortion showed levels of 5.4 and 2.9 units respectively. No specific IgM was detected in sera from eleven other fetuses aborted because of maternal rubella but five of these cases were terminated before 19 weeks and in five the interval between rash and abortion was three weeks or less. The results show that the human fetus can produce detectable specific IgM antibody by 19-20 weeks' gestation after exposure to rubella several weeks earlier. However, a larger study is required to define the reliability of fetoscopic blood sampling for the diagnosis of intrauterine infection.

Evaluation of a commercial antibody capture enzyme immunoassay for the detection of rubella specific IgM

A commercial M antibody capture ELISA kit ( Rubenz M) for the detection of rubella specific IgM was evaluated in comparison with M antibody capture radioimmunoassay. A total of 248 sera were evaluated, including sera from cases of primary postnatal rubella, congenital rubella, infectious mononucleosis, and sera which contained rheumatoid factor. No false positive results were obtained but two high positive sera gave Rubenz M values which were below the value recommended as indicative of a positive result. We therefore propose changes in the criteria used for assessing the significance of the results obtained. These changes improve the accuracy of the assay without loss of specificity.

Use of monoclonal antibodies to human immunoglobulin M in "capture" assays for measles and rubella immunoglobulin M

Monoclonal antibodies to human immunoglobulin M (IgM) were used in a four-phase enzyme immunofluorescence "capture" assay for determination of IgM antibodies to measles and rubella viruses. Little or no background reactivity was seen in the test system, and interfering effects of rheumatoid factor were avoided by preabsorption of test sera with aggregated human IgG. Virus-specific IgM antibody was demonstrable in 23 of 24 patients with serological evidence of measles virus infections and in 36 of 36 patients with serological evidence of postnatal rubella infection. A few of the rubella patients did not show IgM antibody until 5 days after onset of illness. The enzyme immunofluorescence assay was able to demonstrate rubella IgM antibody in congenitally infected newborns, whereas indirect immunofluorescence results for virus-specific IgM were negative. Viral IgM antibody was not detected in persons with past infections with the test viruses, in young children without evidence of past infection, or in patients infected with heterotypic viruses, rickettsiae, chlamydiae, or mycoplasmas.

Screening for anti-rubella IgM ad libitum

There are few applications of virology to clinical medicine that have received more attention than the laboratory diagnosis of rubella. Many laboratories attempt it and most readers of this journal will be familiar with the techniques that have been used. It would therefore be superfluous to review the ‘state of the artm’ had there not recently been an innovation that is likely to alter laboratory practice in this field.