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Biomedical subjects

A M van Loon

Publications and source records attributed to A M van Loon.

At least 19 recordsLinked to original sources
PubMed1997

Immunogenicity of two versus three injections of inactivated hepatitis A vaccine in adults.

AIM: To investigate the immunogenicity of two versus three injections of inactivated strain CR326F-derived hepatitis A vaccine in healthy adults. METHODS: Healthy adult volunteers (n = 105) at Utrecht University Hospital, The Netherlands, were randomly assigned to receive intramuscular injections (deltoid muscle) of 25 Units (U) at 0 and 6 months (group A, n = 53), or at 0, 2 and 6 months (group B, n = 52). Blood was drawn before and at various time points after vaccination for determination of serum antibody to hepatitis A (anti-HAV). RESULTS: One month after the first injection, the seroconversion rates (> or = 10 mIU/ml, international units) were 88% for group A and 90% for group B. Only 2/ 103 (one in each group) showed IgM anti-HAV. One month after the second injection, seroconversion rates were 100% in both groups. At months 3, 6 and 7, anti-HAV geometric mean titers were significantly different because of the different vaccination schedules, but they were similar at months 1, 2 and 12. The anti-HAV geometric mean titer increase after the second injection was higher when the interval between the two doses was of longer duration. Anti-HAV titers of females were significantly higher than those of males and vaccinees < or = 30 years had higher titers than those > 30 years. CONCLUSIONS: Two 25 U doses of the vaccine investigated given at 0 and 6 months, induce adequate anti-HAV titers in all adult healthy vaccinees and are as immunogenic as three doses given at 0, 2 and 6 months.

Adolescent↗
PubMed1997

Human immunodeficiency virus (HIV) antibodies detected by new assays that are enhanced for HIV-1 subtype O.

BACKGROUND: Human immunodeficiency virus type 1 (HIV-1) subtype O infections are not reliably detected by commonly used anti-HIV-1/2 screening assays. Therefore, anti-HIV-1/2 assays have been modified to increase their sensitivity in detecting antibodies to HIV-1 subtype O. STUDY DESIGN AND METHODS: Two new anti-HIV-1/2 enzyme-linked immunosorbent assays (ELISAs) (Abbott Plus and Ortho Enhanced) were compared with a currently used anti-HIV-1/2 ELISA (Abbott Recombinant) in various serum panels: 91 Western blot-confirmed anti-HIV-1-positive samples, 20 samples from Western blot-confirmed HIV-1-infected patients in log3 serial dilutions, and 1463 samples from consecutive, volunteer, nonremunerated blood donors. RESULTS: Among 91 anti-HIV-1 Western blot-positive samples, 2 (2.2%) were missed by the Abbott Recombinant ELISA, but all 91 were detected by the Abbott Plus and Ortho Enhanced ELISAs. In contrast, two discrepant samples were found to react in viral lysate-based assays. In serial dilutions, Ortho Enhanced ELISA was significantly less sensitive than the Abbott Recombinant and Abbott Plus ELISAs, with the latter two being of comparable sensitivity. The specificities of Abbott Recombinant, Abbott Plus, and Ortho Enhanced ELISAs in 1463 blood donors were 100, 99.93, and 99.86 percent, respectively. Routine testing of 29,102 donations with the enhanced Abbott Plus ELISA revealed a specificity of 99.93 percent. CONCLUSION: Two Western blot-confirmed anti-HIV-1-positive samples were missed by the Abbott Recombinant ELISA but detected by the Abbott Plus and Ortho Enhanced ELISAs. The analytic sensitivity of the Ortho Enhanced ELISA was inferior to that of both Abbott ELISAs. The specificities of the Abbott Recombinant, Abbott Plus, and Ortho Enhanced ELISAs were comparable.

Blood Donors↗
PubMed1997

Genetic analysis of wild-type poliovirus importation into The Netherlands (1979-1995).

Wild polioviruses were isolated a number of times in The Netherlands outside the epidemic periods (1978 and 1992-1993) from patients infected abroad, from subclinically infected persons, and from river water. Sequence comparisons revealed discrete sources of importation: the Mediterranean, India, and Indonesia. The observed wide genetic variation is indicative of repeated importation and not of indigenous circulation. Isolates identical or closely related to the epidemic type 1 strain of 1978 were found in clinical and environmental specimens until 1983, probably due to repeated importation from Turkey. Viruses related to the 1992-1993 epidemic type 3 virus had already been isolated six times before the epidemic. Of particular importance are two documented isolations of prototype wild poliovirus indistinguishable from that used to produce the inactivated vaccine. These data underscore the continued risk to the unvaccinated religious population of exposure to wild poliovirus.

Adoption↗
PubMed1997

Poliovirus-specific immunoglobulin A in persons vaccinated with inactivated poliovirus vaccine in The Netherlands.

In The Netherlands the inactivated poliovirus vaccine (IPV) is used for protection against poliomyelitis. It is not clear if parenteral vaccination with IPV can lead to priming of the mucosal immune system. We developed and evaluated enzyme-linked immunosorbent assays for the detection of poliovirus serotype-specific immunoglobulin A (IgA) and secretory IgA antibodies. Using these assays we examined the kinetics of the IgA response in sequential serum samples from 15 poliomyelitis patients after natural infection with serotype 3 poliovirus. In 36% of the patients IgA remained present for up to 5 months postinfection. Furthermore, we examined, in an IPV-vaccinated population, the presence of IgA antibodies in sera from young children (4 to 12 years of age; n = 177), sera from older children (between 13 and 15 years of age; n = 123), sera from healthy blood donors (n = 66), and sera from naturally immune elderly persons (n = 54). The seroprevalence of IgA to all three serotypes was low in young vaccinated children (5 to 7%), and the seroprevalence of IgA types 2 and 3 was low in older vaccinated children (2 to 3%). The seroprevalence of antibodies to type 1 was significantly higher (18%) in older children than in younger children. This higher seroprevalence is most likely explained by the persistence of IgA following infection with the serotype 1 wild-type poliovirus strain during the 1978 epidemic. In healthy adults, the seroprevalence of type 1- and type 2-specific IgA was significantly higher than that in young children. These results suggest that at least part of the IgA found in the older population is induced by infections unrelated to the IPV vaccination schedule. Finally, we found that parenteral vaccination with IPV was able to boost secretory IgA responses in 74 to 87% of a naturally exposed elderly population (n = 54). While the presence of secretory IgA in IPV-vaccinated persons has been documented previously, our findings suggest that mucosal priming with live virus is necessary to obtain an IgA response after IPV booster vaccination.

Adolescent↗
PubMed1996

[Causative role of infections with viruses or atypical pathogens in acute exacerbations of chronic bronchitis less frequent than expected].

OBJECTIVE: To determine the prevalence of viruses and atypical pathogens as causes of acute severe exacerbations of chronic bronchitis. DESIGN: Retrospective. SETTING: University Hospital Utrecht, the Netherlands. METHODS: In 4 studies with 305 patients with severe type-1 exacerbations (increase of dyspnoea, of sputum volume and of sputum purulence) serological tests for viral and atypical pathogens were performed. RESULTS: Positive serology for viral infections was seen in 18 (5.9%) patients and for the atypical pathogens in 12 (3.9%) patients. CONCLUSIONS: Since viruses and atypical pathogens are the cause of the exacerbation in only few cases, clinical signs can be used in decision-making whether or not to prescribe antibiotics in acute exacerbations of chronic bronchitis.

Anti-Bacterial Agents↗
PubMed1996

Circulation of poliovirus during the poliomyelitis outbreak in The Netherlands in 1992-1993.

A population-based study on the circulation of epidemic poliovirus during 1992-1993 outbreak in the Netherlands was carried out in order to assess whether the virus circulated outside the group of people who reject vaccinations on religious grounds and outside the area where these groups form sociodemographically closely knit network. The prevalence of poliovirus excretion was estimated in a cross-sectional study with a random sample of 2,400 children aged 5-14 years and 3,000 adults age 40-64 years; the sample was drawn from the municipal population registers in four regions (three inside and one outside the risk area). Fecal samples of virus isolation and characterization were submitted by mail, and a questionnaire was completed with age, sex, type and level of education, vaccination history, and religious denomination. Both a completed questionnaire and a fecal sample were received from 3,182 persons (response, 58.9%). Wild poliovirus was isolated only from children within the risk group and in the area at risk. The crude excretion rate of the epidemic poliovirus type 3 per 1,000 persons was 2.5, but it amounted to 70.7 for those belonging to Orthodox Reformed churches. The prevalence of vaccine virus excretion per 1,000 persons was 10.2 for children and 5.2 for adults. It was concluded that, during the 1992-1993 outbreak, the risk of poliovirus was restricted to religious subpopulations rejecting vaccination. The lack of evidence of poliovirus circulation outside these groups at risk supports the hypothesis that herd immunity is sufficiently maintained in a population vaccinated with inactivated polio vaccine.

Adolescent↗
PubMed1996

Safety, tolerance, and efficacy of atevirdine in asymptomatic human immunodeficiency virus-infected individuals.

Atevirdine is a nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1 (HIV-1). In this study we investigated the effect of atevirdine in asymptomatic antiretroviral naive HIV-infected patients with CD4+ cell counts of between 200 and 750 cells per mm3. Patients were randomized to receive 600 mg of atevirdine (n = 15) or a placebo (n = 15) three times a day for 12 weeks. There was no statistically significant effect of atevirdine on viral loads (HIV p24 antigen and HIV-1 RNA levels by PCR) or CD4+ cell counts. The data do not support the use of atevirdine as a monotherapy in the treatment of HIV-infected patients.

Adult↗
PubMed1996

The role of laboratory investigation in the diagnosis and management of patients with suspected herpes simplex encephalitis: a consensus report. The EU Concerted Action on Virus Meningitis and Encephalitis.

As effective therapies for the treatment of herpes simplex encephalitis (HSE) have become available, the virology laboratory has acquired a role of primary importance in the early diagnosis and clinical management of this condition. Several studies have shown that the polymerase chain reaction (PCR) of CSF for the detection of herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) DNA provides a reliable method for determining an aetiological diagnosis of HSE. The use of PCR in combination with the detection of a specific intrathecal antibody response to HSV currently represents the most reliable strategy for the diagnosis and monitoring of the treatment of adult patients with HSE. The use of these techniques has also led to the identification of atypical presentations of HSV infections of the nervous system and permits the investigation of patients who develop a relapse of encephalitic illness after an initial episode of HSE. A strategy for the optimal use of the investigative laboratory in the diagnosis of HSE and subsequent management decisions is described.

Acyclovir↗
PubMed1995

Isolation of epidemic poliovirus from sewage during the 1992-3 type 3 outbreak in The Netherlands.

To examine the extent of wild poliovirus circulation during the 1992-3 epidemic in the Netherlands caused by poliovirus type 3, 269 samples from sewage pipelines at 120 locations were examined for the presence of poliovirus. The epidemic virus strain was found in 23 samples, all from locations inside the risk area which contained communities that refuse vaccination for religious reasons. By sewage investigation, the wildtype virus was shown to be present in the early phase of the epidemic at two locations, one week before patients were reported from that area. The wild type 3 poliovirus was also detected retrospectively in a river water sample collected for other reasons three weeks before notification of the first poliomyelitis case, at a site a few kilometres upstream the home village of this patient. Oral poliovirus vaccine (OPV) virus was found at 28 locations inside or at the border of the risk area. Trivalent OPV was offered to unvaccinated or incompletely-vaccinated persons living in this region as part of the measures to control the epidemic.

Adolescent↗
PubMed1995

Abortive and subclinical poliomyelitis in a family during the 1992 epidemic in The Netherlands.

We describe a case of abortive poliomyelitis due to poliovirus type 3 (PV3) in an unvaccinated woman and a subclinical poliovirus infection in her family during an epidemic in the Netherlands. The woman excreted the epidemic strain (PV3) for 7 weeks. Her two children received oral attenuated poliovirus vaccine and were subsequently found to excrete PV1 and PV2 vaccine strains in addition to the epidemic PV3 strain. Her husband, who had neutralizing antibodies to all three poliovirus types because of previous vaccination, initially excreted no virus; subsequently, however, the vaccine strain PV1 and the epidemic strain PV3 could be cultured from his feces. These observations demonstrate the ease with which poliovirus circulates among family members, including those with neutralizing antibodies.

Adult↗
PubMed1995

Antibody response to diphtheria, tetanus, and poliomyelitis vaccines in relation to the number of CD4+ T lymphocytes in adults infected with human immunodeficiency virus.

A prospective study of antibody production by adults infected with human immunodeficiency virus (HIV) after vaccination with T lymphocyte-dependent diphtheria toxoid, tetanus toxoid, and inactivated trivalent poliovirus vaccine was conducted. Individuals were divided into three groups according to CD4+ T-lymphocyte count: group 1 had a count of < or = 100-300 x 10(6)/L; and group 3, > 300 x 10(6)/L. After vaccination, 61%, 70%, and 73% of the individuals in groups 1, 2, and 3, respectively, developed protective titers of antibody to diphtheria toxin; the mean postvaccination antibody titer of HIV-infected individuals was significantly lower than that of healthy controls not infected with HIV. Furthermore, the mean titers of antibodies to tetanus toxin and poliovirus were significantly lower in HIV-infected individuals with CD4+ lymphocyte counts of < 300 x 10(6)/L than in controls. Of the HIV-infected vaccinees, 83%-100% were protected against tetanus and 78%-100% against polio. We conclude that HIV-infected individuals with CD4+ lymphocyte counts of < 300 x 10(6)/L have an impaired (secondary) antibody response after receipt of T lymphocyte-dependent vaccines.

Adult↗
PubMed1995

Molecular epidemiology of wild poliovirus type 1 in Europe, the Middle East, and the Indian subcontinent.

The genomic relationships of wild poliovirus type 1 strains recently isolated in Europe, the Middle East, and the Indian subcontinent was analyzed by automated amplicon sequencing of the VP1/2A junction region of the genome. Four major genotypes of poliovirus type 1 were found to circulate. Two genotypes were found predominantly in Eastern Europe, one of these in the Caucasian Region and the other in countries bordering the Black Sea. A third genotype circulated mainly in Egypt. The fourth and largest genotype circulated in the largest geographic area. Strains belonging to this genotype could be found in countries as far apart as Malaysia and Ukraine. Considerable genetic variation was observed among strains isolated in Egypt, Pakistan, and India, where poliovirus is endemic. Strains belonging to all four genotypes circulated in Pakistan. Data confirm the extent of poliovirus circulation in certain regions, stressing the need for intensification of vaccination in these regions.

Base Sequence↗
PubMed1995

Comparative study of five methods for intratypic differentiation of polioviruses.

A coded panel of 90 poliovirus isolates, 30 of each of the three known serotypes, was used to evaluate five methods for the intratypic differentiation of polioviruses: (i) an enzyme-linked immunosorbent assay with polyclonal cross-absorbed antisera (PAb-E), (ii) a neutralization assay with type-specific monoclonal antibodies (MAb-N), (iii) a restriction fragment length polymorphism (RFLP) assay, (iv) a Sabin vaccine strain-specific PCR assay, and (v) a Sabin vaccine strain-specific cRNA probe hybridization (ProHyb) assay. Sequence analysis was used for the definitive characterization of the strains. The panel was distributed to five laboratories; each laboratory analyzed the strains by at least two methods. Each method was used by three or four laboratories. The total performance scores (percentage correct results per number of tests) of the five methods were 96.7% for PAb-E, 93.9% for MAb-N, 91.9% for RFLP assay, 93.3% for Sabin vaccine strain-specific PCR, and 97.4% for Sabin vaccine strain-specific ProHyb. Consistent results were obtained by each laboratory for 88 of 90 isolates (97.8%) examined by PAb-E, 81 of 90 isolates (90.0%) examined by MAb-N, 78 of 90 isolates (86.7%) examined by RFLP assay, 81 of 90 isolates (90.0%) examined by PCR, and 89 of 90 isolates (98.9%) examined by ProHyb assay. Six strains were classified differently by different methods. It is recommended that at least two methods be used for the intratypic differentiation of poliovirus isolates, and each method should be based on a different principle (i.e., antigenic properties and nucleotide sequence composition). If two assays yield discrepant results, further characterization, preferably by partial sequence determination, will be required for correct identification.

Environmental Microbiology↗
PubMed1995

Molecular characterization of a wild poliovirus type 3 epidemic in The Netherlands (1992 and 1993).

An outbreak of poliomyelitis due to wild poliovirus type 3 (PV3) occurred in an unvaccinated community in The Netherlands between September 1992 and February 1993. The outbreak involved 71 patients. The aim of this study was to characterize the virus at the molecular level and to analyze the molecular evolution of the epidemic virus. Molecular analysis was carried out by sequencing the VP1/2A junction region (150 nucleotides) of 50 PV3 strains isolated in association with this outbreak and the entire VP1 gene of 14 strains. In addition, the sequence of the VP1/2A junction region of strains from geographical regions endemic for PV3 (Egypt, India, and Central Asia) was analyzed and compared with the nucleotide sequence of the epidemic strain from The Netherlands. The earliest isolate was obtained from river water sampled 3 weeks before diagnosis of the first poliomyelitis patient and was found by VP1/2A sequence analysis to be genetically identical to the strain isolated from the first patient. Sequence divergence among the strains from the epidemic in The Netherlands was less than 2%. The closest genetic similarity (97.3%) was found with an Indian isolate (New Delhi, December 1991), indicating the likely source of the virus. A more than 99% sequence similarity was found in the VP1/2A region. Finally, the sequence information was used to design primers for the specific and highly sensitive molecular detection of PV3 strains during the epidemic.

Base Sequence↗
PubMed1994

Poliomyelitis outbreak in an unvaccinated community in The Netherlands, 1992-93.

An outbreak of poliomyelitis occurred in the Netherlands between September, 1992, and February, 1993, after 14 years without endemic cases. The outbreak was due to poliovirus type 3 and involved 71 patients, of whom 2 died and 59 had paralysis. The patients were aged between 10 days and 61 years (median 18 years). None of the patients had been vaccinated, and all but 1 belonged to a socially and geographically clustered group of people who refuse vaccination for religious reasons. Control measures were taken within 5 days of notification of the first patient and included a wide offer of vaccination with the trivalent oral poliovirus vaccine to the population at risk. Sequence analysis of the viral genome showed closest similarity (96.7%) with a strain isolated in India in 1992, indicating that the virus probably originates from the Indian subcontinent. The difference, however, is still too large to assume direct import. Extensive outbreak investigation at schools, in the environment, at virus diagnostic laboratories, and in the general population showed no evidence of widespread circulation of the epidemic virus outside the groups at risk and area where these groups live. As in the previous outbreak in 1978, the general population, including the majority of unvaccinated people who live dispersed in the population, seemed to be well-protected against poliomyelitis.

Adolescent↗
PubMed1994

Detection of amplified Chlamydia trachomatis DNA using a microtiter plate-based enzyme immunoassay.

A microtiter plate-based method to detect amplified DNA was developed. The method uses on biotin-labeled primer in the polymerase chain reaction (PCR) mixture. The labeled amplicon is bound to streptavidin-coated microtiter plates, denatured and hybridized to a digoxigenin-labeled probe. The specificity of the hybridization reaction was optimized by varying the temperature of the subsequent washing step and adding urea to the washing buffer. The digoxigenin label was detected using an enzyme immunoassay (EIA). This PCR-EIA was compared with a standard PCR assay that uses gel electrophoresis, blotting and hybridization to detect the amplicon, with isolation in cell culture, and with an antigen detection EIA (Chlamydiazyme) in the diagnosis of Chlamydia trachomatis infection in 309 female patients attending a sexually transmitted diseases outpatient clinic. The prevalence of Chlamydia trachomatis infection as determined by isolation in cell culture, EIA, PCR-EIA and standard PCR assay was 9.1%, 8.7%, 12.3%, and 12.9%, respectively. Compared with results of a reference set of confirmed-positive cases (defined by a positive result in two or more independent assay after analysis of discrepancies), the sensitivity and specificity was 71.1% and 99.6% for cell culture, 65.8% and 99.3% for the EIA, 92.1% and 98.9% for the PCR-EIA, and 97.4% and 98.9% for the standard PCR assay. It is concluded that the PCR-EIA described is a fast, sensitive and specific method for detecting Chlamydia trachomatis in clinical specimens.

Amino Acid Sequence↗