IgG Avidity Index Research Articles

A technique for dating toxoplasmosis in pregnancy and comparison with the Vidas anti-toxoplasma IgG avidity test

A comparative evaluation of 384 selected sera was performed using the Beckman Coulter Access and Abbott Axsym Toxo-IgG assays. The Axsym assay yields positive early results following infection, while the Access assay gives higher titres during chronic infection. The ratio between the two complementary tests, Axsym Toxo-IgG/Access Toxo-IgG (Ax/Ac), was compared with the Vidas anti-Toxoplasma IgG avidity index (AI). The Ax/Ac ratio decreased progressively as the time between infection and sampling increased. The mean Ax/Ac values (±SE) were 2.50 (±0.26), 2.14 (±0.13), 2.33 (±0.22), 1.34 (±0.09), 1.32 (±0.10), 0.92 (±0.08) and 0.74 (±0.07) for groups of sera sampled at 1, 2, 3, 4–5, 6–8, 9–12 and 13–24 months, respectively, after infection in pregnant women. These values were much smaller for cases with chronic infection (>24 months), i.e., 0.56 (±0.03), 0.44 (±0.04) and 0.53 (±0.04), respectively, for pregnant women and immunodepressed patients with and without reactivation. Taking a ratio of 1 as a threshold for recent infection, the patients in the groups sampled at 1, 2 and 3 months had Ax/Ac ratios >1 in 49/50 (98%), 53/55 (96.4%) and 36/36 (100%) cases, respectively. Thus, an Ax/Ac ratio of <1 in serum from a pregnant woman allows a recent infection (<3 months) to be excluded. This technique has the advantage of yielding positive results that develop much more rapidly than the AI, thereby helping to reassure large numbers of pregnant women and avoiding costly and unnecessary prophylactic treatment and follow-up.

New advances in the diagnosis of congenital cytomegalovirus infection

Although the diagnosis of congenital CMV infection is still complex, important goals have been achieved in recent years, among which are: the availability of more reliable IgM tests for screening pregnant women whose pre-pregnancy serological status for CMV is unknown, tests to determine the avidity index of anti-CMV IgG, allowing the diagnosis of a primary CMV infection and innovative and traditional virological tests to detect the virus in amniotic fluid. When a woman is found to be IgM-positive, further diagnostic evaluation focused on determining whether this is due to a primary infection should be carried out. Maternal primary infections that were difficult to determine until a few years ago unless documented by seroconversions can now be readily diagnosed from the presence of low/moderate avidity anti-CMV antibody which persists for approximately 18–20 weeks after primary infection. In mothers at risk of transmitting the virus prenatal diagnosis can be performed between 21 and 22 weeks of gestation, and the amniotic fluid represents the pathological material of choice to determine intrauterine virus transmission. At birth or in the first 2/3 weeks of life, it is essential to use appropriate tests for diagnosis of CMV congenital infection.

Relationship of IgG avidity index and IgM levels for the differential diagnosis of primary from recurrent cytomegalovirus infections.

Since the incidence of symptomatic congenital cytomegalovirus infection is low (~0.05%) and risk factors are not well defined, it is difficult to develop strategies for prevention. The aim of this study was to recognise the utility of specific Immunoglobulin G avidity analysis for distinguishing primary infection from past/recurrent infection. Sera from 50 women with cytomegalovirus specific Immunoglobulin M antibodies without proven seroconversion and infants born to these women were tested for presence of Immunoglobulin M antibodies by commercial enzyme immunoassay. For cytomegalovirus specific immunoglobulin G avidity, sera were measured by commercial kit according to manufacturer's recommendations. Among 50 sera form mothers, 26 showed the presence of Immunoglobulin M antibodies out of which 15 had low avidity antibodies. Out of 50 sera from children, 18 showed the presence of Immunoglobulin M antibodies. Out of these 18 sera from children, 12 were symptomatic, which all showed the presence of low avidity antibodies. The results showed that an avidity index <40% and presence of Immunoglobulin M antibodies is highly suggestive of a recent primary infection.

Designation of an In-House ELISA for Detection of VZV IgG and Determination of Antibody Avidity by Use of Diethylamine

Herpesviruses are ubiquitous in nature and both humans and animals harbour different species of this diverse family. However, only 8 species have been so far recovered from human beings. Different techniques (molecular and non-molecular) have been employed for rapid and efficient diagnosis of herpesviruses especially in case ofimmunocompromised hosts who are considered as high risk individuals. An indirect in-house ELISA was standardized to measure IgG antibody against Varicella-Zoster Virus (VZV) in sera from different groups of individuals. In the process of optimization of in-house ELISA, optimal dilutions of antigen, serum, conjugate and monoclonal IgG antibody along with selection of efficient blocking buffer and washing steps of microtitre plates were studied by the help of checkerboarding. The results were calculated according to Specific Binding Ratio (SBR) and cut-off procedures. The efficiency of newly developed indirect in-house ELISA was attempted and results were compared with data previously obtained by the agency of commercial kits or other serological techniques. The latter helped to investigate different technical aspects of in-house ELISA. When accuracy of ELISA was confirmed the protocol was applied in screening of the sera from immunocompetent and immunocompromised hosts that facilitated examination of the clinical aspects of the hosts. Diethylamine (DEA) in 20, 35 and 70 mM concentrations were used in order to assay IgG antibody avidity. The IgG avidity index was calculated by dividing OD of each sera obtained with denaturant to OD of the same specimen without application of denaturants. Avidity indices proved to be an important tool to differentiate between primary and recurrent infections and between seropositivity and seronegativity.

Immunoglobulin G Avidity in Differentiation between Early and Late Antibody Responses to West Nile Virus

In 1999 West Nile virus (WNV) surfaced in the United States in the city of New York and spread over successive summers to most of the continental United States, Canada, and Mexico. Because WNV immunoglobulin M (IgM) antibodies have been shown to persist for up to 1 year, residents in areas of endemicity can have persistent WNV IgM antibodies that are unrelated to a current illness with which they present. We present data on the use of IgG avidity testing for the resolution of conflicting data arising from the testing of serum or plasma for antibodies to WNV. Thirteen seroconversion panels, each consisting of a minimum of four samples, were used. All samples were tested for the presence of WNV IgM and IgG antibodies, and the avidity index for the WNV IgG-positive samples was calculated. Panels that exhibited a rise in the WNV IgM level followed by a sequential rise in the WNV IgG level were designated "primary." Panels that exhibited a marked rise in the WNV IgG level followed by a sequential weak WNV IgM response and that had serological evidence of a prior flavivirus infection were designated "secondary." All samples from the "primary" panels exhibited low avidity indices (less than 40%) for the first 20 to 30 days after the recovery of the index sample (the sample found to be virus positive). All of the "secondary" samples had elevated WNV IgG levels with avidity indices of > or =55%, regardless of the number of days since the recovery of the index sample. These data demonstrate that it is possible to differentiate between recent and past exposure to WNV or another flavivirus through the measurement of WNV IgG avidity indices.

Valutazione pilota di un sistema automatico per lo screening anticorpale della toxoplasmosi

The aim of this study was the comparison of a fully automated random access system IMMULITE 2000 (DPC) with a semiautomated system VIDAS (bioMérieux) for the first level detection of Toxoplasma-specific IgG and IgM antibodies. In total, 295 samples were examined for Toxoplasma- specific IgG.The comparison between the VIDAS IgG assay and IMMULITE IgG assay showed the same result for 290 samples (98.3%). Particularly, 220 samples were negative, 70 positive and 4 samples were positive with IMMULITE and equivocal with VIDAS. Only one sample showed a discrepant result: positive with IMMULITE and negative with VIDAS. A total of 124 samples were tested for Toxoplasma-specific IgM and 33 were positive or equivocal with VIDAS IgM assay and 30 of these were also tested for Toxoplasma-specific IgG avidity. The comparison between the VIDAS IgM assay and IMMULITE IgM assay showed the following results: 23 samples were positive in the two systems, 4 samples were equivocal with the VIDAS IgM assay but positive in IMMULITE IgM assay, 6 samples were positive or equivocal in the VIDAS IgM assay but negative in IMMULITE IgM assay.The study of the 6 discrepant samples showed: 2 samples with the presence of natural IgM, 3 samples with a high IgG avidity index and 1 with an intermediate IgG avidity index. IgM was not detected with both assays in any of the other samples.The IMMULITE system seems to be a valuable system for the first level diagnosis of Toxoplasma infection.

Significance of avidity and immunoblot analysis for rubella IgM-positive serum samples in pregnant women

A total of 512 IgM-positive serum samples from 449 pregnant women referred by microbiologists and medical laboratories for additional testing and final interpretation were collected over a 3-year period. Employment of an IgM capture enzyme immunoassay (EIA) confirmed only 31% of the initial EIA-IgM-positive samples. In order to discriminate acute rubella virus infections, which are associated with increased risk of fetal infection and embryopathy, from persistent or non-specific IgM, IgG avidity index and the presence of IgG with specificity to rubella virus E2 glycoprotein was determined by Western immunoblot. In only six patients (1.3%), a primary infection with rubella virus was diagnosed on the basis of IgM positivity, low avidity IgG, absence of E2-specific IgG in immunoblot concordant with clinical findings as well as consistent changes in follow-up samples. The serological results were not compatible with rubella re-infection. The infection status in 14 patients (3.1%) remained inconclusive even when both avidity assay and immunoblot were used, while restriction to either test did not allow a conclusive interpretation in 11.6% of patients. The use of both assays is clearly better, and therefore, recommended in IgM-positive samples.

Pre- and Periconceptional Primary Cytomegalovirus Infection: Risk of Vertical Transmission and Congenital Disease

In both the United States and West Europe, cytomegalovirus (CMV) infection is the most common viral form of congenital infection. Intrauterine transmission of CMV takes place in approximately 40% of infections, and approximately 10% of live-born infants have symptomatic disease at the time of birth and later. Late sequelae such as sensorineural hearing loss and neurodevelopmental disorders occur in 10% to 15% of infants lacking symptoms at birth. Recurrent maternal infection contributes substantially to the rate of congenital infection. This cohort study, covering the years 1990–2003, estimated the risk of congenital CMV infection and disease after primary maternal infection at approximately the time of conception and also in later stages of pregnancy. The study population included 166 pregnant women with serologically confirmed primary CMV infection. The timing of primary infection was studied by measuring CMV-specific immunoglobulin (Ig)M and IgG antibodies, the IgG avidity index, and titers of neutralizing antibodies. Prenatal diagnosis of CMV infection was attempted in 79 of the 166 pregnancies by analyzing amniotic fluid samples for viral DNA by the polymerase chain reaction technique and also for infectious virus. Women with symptomatic primary CMV infection and those with subclinical infection had similar transmission rates (41% and 37%, respectively). Fetal transmission of infection occurred in 45% of pregnancies with periconceptional infection, in 3 of 10 pregnancies before gestational week 6, and in none of 3 pregnancies with preconceptional infection. Eighty-nine women had primary CMV infection at gestational weeks 6–20 and 31 at weeks 20–38. The transmission rate was lowest (30%) when primary infection occurred in weeks 6–20. Rates were 39% for infection gestational at weeks 18–22 and 58% during weeks 20–38. Seven fetuses or newborn infants had congenital disease (defined as ultrasound abnormalities in cases of therapeutic abortion or the presence in newborn infants of neurologic or systemic manifestations of congenital CMV disease), all of them before gestational week 22. None of 18 infected live-born infants infected after 20 weeks gestation had congenital disease. Congenital disease was found in 4 of 25 pregnancies with vertical transmission after maternal infection in gestational weeks 6–20. Four pregnancies were ended at weeks 7–11 when primary infection was diagnosed, and there was 1 missed abortion. Only 1 of 5 live-born infants had mild symptoms at birth. Two of 3 subclinically infected newborn infants were healthy when followed up for 8 months or longer; 1 had late-onset hearing loss. The authors believe that women with periconceptional CMV infection should be managed like those having primary infection in the first 20 weeks of pregnancy. Prenatal diagnosis done at gestational weeks 21–23 can exclude fetal infection with a high degree of accuracy. Congenital infection should be sought in newborn infants of mothers having primary infection late in pregnancy or at approximately the time of conception.

Pre‐ and periconceptional primary cytomegalovirus infection: risk of vertical transmission and congenital disease

To estimate the risk of congenital cytomegalovirus infection and disease following primary maternal infection around the time of conception compared with the risk during later stages of pregnancy. Cohort study between 1990 and 2003. Germany. One hundred and sixty-six pregnant women with serologically confirmed primary cytomegalovirus infection and known outcome. Timing of primary cytomegalovirus infection by analysing the kinetics of cytomegalovirus-specific IgG and IgM antibodies, the IgG avidity index and neutralising antibodies. Onset of maternal primary infection in relation to congenital infection and disease. Preconceptional (between eight and two weeks before onset of the last menstrual period) was determined in three women and did not lead to congenital infection. Periconceptional infection (between one week before and five weeks after last menstrual period) occurred in 20 women with congenital infection in nine cases (45%). Timing was less precise (between eight weeks before and five weeks after last menstrual period) in an additional 10 women, three cases of which resulted in congenital infection. Of the 12 pregnancies in which congenital infection occurred, seven were terminated, six before the 12th week of gestation (WG 12) and one at WG 19 due to fetal hyperechogenic bowel. One of the five infected live-born infants delivered to a mother with periconceptional infection showed dystrophy and mild microcephaly at birth, but had a rather normal development at two years of age. Primary infections occurring between WG 6-20 and WG 20-38 resulted in transmission rates of 30% (27/89) and 58% (18/31), respectively. Counselling of women with periconceptional primary cytomegalovirus infection should be adjusted to offer prenatal diagnosis and high-level ultrasound controls due to the considerable risk for fetal infection and uncertainty of clinical outcome and disease.

Effect of a booster dose of serogroup B meningococcal vaccine on antibody response to Neisseria meningitidis in mice vaccinated with different immunization schedules

The generation and maintenance of memory antibody response by different primary immunization schedules with the Cuban-produced outer membrane protein based vaccine was investigated in a murine model. We analyzed the duration of the antibody response (IgG-ELISA and bactericidal titer) and the effect of a booster dose on the antibody response. The IgG avidity index was determined in an attempt to find a marker for memory development. This study also included an analysis of IgG subclasses induced by primary and booster immunization. The specificity of bactericidal antibodies was investigated using local strains of the same serotype/serosubtype (4,7:P1.19,15) as the vaccine strain and mutant strains lacking major outer membrane proteins. A significant recall response was induced by a booster dose given 7 months after a primary series of 2, 3 or 4 doses of vaccine. The primary antibody response showed a positive dose-effect. In contrast, a negative dose-effect was found on the booster bactericidal antibody response. There was a significant increase in IgG1 levels after the fourth and booster doses. Three doses of vaccine were required to induce a significant increase in IgG avidity. Two injections of vaccine induced a significant antibody response to PorA protein, while 4 injections induced a larger range of specificities.

Algorithme diagnostique de la primo-infection à cytomégalovirus (CMV) chez la femme enceinte

Diagnosis of CMV primary infection is usually based on the detection of specific IgM antibody. However, as IgM antibody is not always correlated with primary infection, measurement of IgG avidity must be performed. The aim of our study was to evaluate the best procedure for diagnosis of CMV primary infection. In other words, is it better to first search for IgM antibody, and, if positive, then measure IgG avidity, or, first measure IgG avidity without detection of IgM antibody? CMV IgM detection and CMV IgG avidity measurement were performed on 310 IgG positive sera from pregnant women. CMV IgM antibody was detected positive for nine of 310 sera. Using CMV IgG Avidity Index (AI), dating of infection was difficult in 81/310 cases (26%), while it failed in only 3/310 cases using CMV IgM plus CMV IgG AI. The diagnosis of primary CMV infection could be based on the detection of CMV IgM antibody first and then on the measurement of CMV IgG avidity index.

Responses to a fourth dose of Haemophilus influenzae type B conjugate vaccine in early life

Objective: To describe the immune response of preterm infants, with a reduced response to primary Haemophilus influenzae type B (Hib) immunisation, to a fourth dose of Hib conjugate vaccine given...

Adjuvant can improve protection induced by OMV vaccine against Neisseria meningitidis serogroups B/C in neonatal mice

Meningococcal outer membrane vesicle (OMV) vaccines are weak antigens in infants. This study aimed at investigating alternative adjuvants for induction of functional antibodies in newborn mice. Serogroup B/C anti-meningococcal vaccines, consisting of capsular polysaccharide from serogroup C (PSC) conjugated to OMV from one serogroup B serosubtype prevalent in Brazil, combined with OMV from another prevalent serosubtype, were tested in newborn and adult mice with the following adjuvants: aluminum hydroxide, MPL (monophosphoryl lipid A), Titermax and MF59. Total IgG, IgG avidity index determination and bactericidal assay were performed with sera from immunized mice. Antibodies induced against PSC in newborn mice showed avidity and bactericidal titers, similar to those obtained in adult mice, independently of the adjuvant. Evidence is presented that the inclusion of MF59 enhanced the immune response against OMV in newborn mice.

Identification of primary and secondary measles vaccine failures by measurement of immunoglobulin G avidity in measles cases during the 1997 São Paulo epidemic.

Despite almost universal use of measles vaccines in recent decades, epidemics of the disease continue to occur. Understanding the role of primary vaccine failure (failure to seroconvert after vaccination) and secondary vaccine failures (waning immunity after seroconversion) in measles epidemics is important for the evaluation of measles control programs in developing countries. After a measles epidemic in São Paulo, Brazil, 159 cases previously confirmed by detection of specific immunoglobulin M (IgM) antibodies were tested for IgG avidity, and a secondary immune response, defined by an IgG avidity index of at least 30%, was established in 30 of 159 (18.9%) patients. Among the 159 patients, 107 (67.3%) had not been vaccinated and 52 (32.7%) had received one or more doses of measles vaccine. Of the 107 unvaccinated patients, 104 (97.2%) showed a primary immune response, defined as an IgG avidity index of less than 30%. Among the 52 patients with documented vaccination, 25 (48.1%) showed a primary immune response and 27 (51.9%) showed a secondary immune response, thereby constituting a secondary vaccine failure. Primary vaccine failure was observed in 13 of 13 patients vaccinated prior to 1 year of age and in 43.5 and 12.5%, respectively, of patients receiving one or two doses after their first birthdays. These results provide evidence that measurement of IgG avidity can be used to distinguish between primary and secondary vaccine failures in vaccinated patients with measles; the method can also be a useful tool for the evaluation of measles control programs.

Experimental Corynebacterium pseudotuberculosis primary infection in goats: kinetics of IgG and interferon-γ production, IgG avidity and antigen recognition by Western blotting

Corynebacterium pseudotuberculosis is the cause of caseous lymphadenitis (CLA) in small ruminants, a chronic granulomatous disease that provokes significant zootechnics losses to ovine and goat breeders in northern Brazil. The present work was conducted to analyse aspects of humoral and cellular immune responses after experimental infection. Eight goats were infected intradermally with a single dose of virulent C. pseudotuberculosis strain and specific IgG, interferon-γ (IFN-γ) production as well as IgG avidity and antigens pattern recognition dynamics against an excreted–secreted antigen were recorded during 20 weeks. At the end of the follow-up, animals were slaughtered and necropsied. Although no animals showed apparent clinical signs of infection at the end of the trial, IFN-γ response, even more so than the humoral response, differentiated animals into two groups of high or medium/low response. The time-course of IFN-γ production presented a short-lived primary response on day 5 after infection of animals of both groups, and a strong and long lasting secondary response starting on day 16 after infection in the high response group. The indirect ELISA used was able to detect a positive antibody titre between 6 and 11 days after infection in the two groups. IgG avidity index oscillated initially between 15 and 45%, and showed approximately 5% units increment during the 20 follow-up weeks. With only one individual exception, the qualitative antigens pattern recognition showed on day 11 after infection remained constant through the experiment. IgG avidity is highly correlated with IgG production, but could not be related with specific immunodominant bands. Both humoral and cellular responses kinetics presented a similar pattern of activation/deactivation but necropsy results suggested that the IFN-γ test would be a very specific marker of CLA status.

Techniques biologiques du diagnotic anténatal des infections virales et de la toxoplasmose

The main infections prenatally detected in fetuses are : cytomegalovirus parvovirus B19, rubella virus, and varicella-zoster infections. Today, prenatal diagnosis is currently performed after detection of maternal primary infection or because of abnormal ultrasound findings. Diagnosis of maternal primary infection is essentially based on the detection of specific IgM antibodies, but it was greatly improved by the use of complementary tests such as the measurement of the IgG avidity index. Prenatal diagnosis is based on the direct detection of the microorganism (CMV, toxoplasma), of its antigens (CMV) or of its genome. This direct detection can be done either on fetal blood or on amniotic fluid. Prenatal diagnosis can also be performed by detection of specific IgM in fetal blood (rubella). Non specific markers of fetal infection can also help in diagnosis. At the present time, prenatal diagnosis is essentially based on the detection of the genome in amniotic fluid.

A light in the darkness: Predicting outcomes for congenital cytomegalovirus infections

A light in the darkness: Predicting outcomes for congenital cytomegalovirus infections

Differentiation between early and late complicated Lyme borreliosis by specific IgG avidity

Patients with early complicated forms of Lyme borreliosis had a low specific IgG avidity index and patients with late forms had a high avidity index. Naturally exposed individuals had intermediate values.

Predictive value of maternal-IgG avidity for congenital human cytomegalovirus infection.

Human cytomegalovirus (HCMV) is now the most common cause of viral intrauterine infection. Fetal damage is mostly linked to maternal primary infection. It is therefore important to differentiate primary from recurrent or persistent HCMV infection in pregnant females. For this purpose, IgM tests are not reliable enough and the measurement of the IgG avidity appears to be presently the best method. To evaluate the performance of the measurement of HCMV-IgG avidity by a 8 M urea denaturation assay in predicting congenital infection in the offspring. Seventy-eight women were included in this study on the basis of a HCMV IgM positive or equivocal result on a first serum during pregnancy, but without a documented seroconversion history. The IgG avidity was measured and correlated with the outcome of the pregnancy. In eight cases of HCMV in utero infection the maternal HCMV-IgG avidity index was below 50%. One case of HCMV in utero infection was observed despite a high avidity index during the second trimester of the pregnancy. High or intermediate HCMV-IgG avidity indexes during the first trimester of pregnancy were not associated with a congenital infection. Even in the presence of an IgM positive result, an HCMV IgG avidity index above 65% on a serum obtained during the first trimester of pregnancy could reasonably be considered as a good indicator of past HCMV infection. In these conditions invasive prenatal diagnosis is not necessary.

Value of cytomegalovirus (CMV) IgG avidity index for the diagnosis of primary CMV infection in pregnant women.

This study assessed the diagnostic value of the cytomegalovirus (CMV)-specific IgG avidity index (AI) for pregnant women without a history of CMV seroconversion. Sera were studied from 40 women with CMV seroconversion (group I), 70 with past CMV infection (group II), 10 (20 sera) with serologic reactivation (group III), and 41 with CMV-specific IgM without proven seroconversion (group IV). Sera from women in group I collected <14 weeks after seroconversion had a low AI (mean, 30% +/- 12%), whereas all sera from women in group II had an AI >60% (mean, 88% +/- 9%). Among the 41 babies born to group IV women, only 4 were infected with CMV (all born to mothers with a low [<30%] AI early in pregnancy). These results suggest that AI determination may help to date a primary CMV infection in pregnant women who lack seroconversion history.