PubMed Health⌕ Search

Biomedical subjects

A M van Loon

Publications and source records attributed to A M van Loon.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1994

A poliovirus type-specific IgM antibody-capture enzyme-linked immunosorbent assay for the rapid diagnosis of poliomyelitis.

OBJECTIVES: To develop and evaluate an IgM antibody-capture ELISA for the rapid detection of poliovirus type-specific IgM antibodies in serum and CSF of patients suspected of poliomyelitis. STUDY DESIGN: The assay uses monoclonal antibody to human IgM as catching antibody, monovalent IPV as antigen and type-specific monoclonal antibodies labeled with horseradish peroxidase as detecting antibody. RESULTS: Sera from 21 of 24 patients, contacts of these patients or recently vaccinated children were positive in the IgM assay. Sera from 100 healthy individuals were negative in all three poliovirus type-specific ELISAs. Sera from 5 of 81 patients with non-polio viral infections showed (weak) reactivity in one or more of the IgM assays. In a prospective study, sera and/or CSFs from 72 patients with a recent clinical diagnosis of poliomyelitis were tested. A homotypic IgM antibody response was found in 51 of the 55 patients which shedded wild poliovirus in stool or throat. Poliovirus type-specific IgM antibodies were also detected in serum from 13 of the 17 patients, from whom no poliovirus was isolated. Poliovirus type-specific IgM-antibodies could be detected from the second day up till at least 28 days after onset of paralysis. BACKGROUND: Poliovirus infections still create measurable morbidity and mortality in the world. Rapid diagnosis methods are needed to detect infection. CONCLUSION: The use of the poliovirus type-specific IgM antibody-capture ELISA allows rapid diagnosis of poliomyelitis within 24 h after obtaining serum or a CSF specimen.

Journal Article↗
PubMed1994

Variable outcome of a congenital cytomegalovirus infection in a quadruplet after primary infection of the mother during pregnancy.

A congenital cytomegalovirus (CMV) infection in a quadruplet has not been reported previously in the literature. We describe a congenital CMV infection in a quadruplet after primary CMV infection of the mother during pregnancy. One infant died antenatally, while another had cholestatic jaundice at birth and died of liver failure at three months of age. Of the two surviving infants, one showed no signs or symptoms of congenital CMV infection at 18 months of age, whereas the other had hearing loss and delayed development. CMV cultures of urine were positive at six weeks of age in all three infants born alive. The diagnosis of congenital CMV infection after primary CMV infection of the mother during pregnancy was made retrospectively by detection of CMV-immediate early antigen in three placentas as well as by examination of serum obtained from the mother during pregnancy.

Adult↗
PubMed1994

Comparison of two panels of monoclonal antibodies for determination of Chlamydia trachomatis serovars.

A panel of monoclonal antibodies was developed for serovar typing of clinical isolates of Chlamydia trachomatis. The panel could distinguish all 15 established serovars from one another, although the hybridomas of the panel were developed by fusions of myeloma cells and spleen cells from mice immunized with antigen derived from the urogenital serovars D to L3. The typing assay was based on a dot enzyme immunoassay, and the monoclonal antibodies that were included in the panel reacted strongly in this assay. A collection of 289 clinical isolates from The Netherlands was typed. The observed serovar frequency distribution was 51 isolates of serovar D (17.6%), 103 isolates of serovar E (35.6%), 62 isolates of serovar F (21.5%), 28 isolates of serovar G (9.9%), 14 isolates of serovar H (4.8%), 2 isolates of serovar I' (0.7%), 20 isolates of serovar J (6.9%), and 9 isolates of serovar K (3.1%). These results were confirmed by typing these isolates with a panel of monoclonal antibodies purchased from the Washington Research Foundation, Seattle. No strain variation was observed within serovar D with both panels. However, restriction fragment length polymorphism analysis of the gene encoding the major outer membrane protein showed that 32 isolates were similar to the prototype D and 17 were similar to the variant D-. The two others showed a new restriction pattern. Our panel of monoclonal antibodies contained one monoclonal antibody that divided the serovar G isolates into two groups. This differentiation was confirmed by restriction fragment length polymorphism analysis, confining this difference to a known sequence variation in variable domain IV. These data support the subdivision of serovar G into serovars G (prototype strain UW-57) and Ga (prototype strain IOL-238).

Animals↗
PubMed1994

Enzyme immunoassay with enhanced specificity for detection of antibodies to Chlamydia trachomatis.

Two different methods for preventing the binding of cross-reacting antibodies to the genus-reactive chlamydial lipopolysaccharide (LPS) were used to improve the specificity of an enzyme immunoassay for the determination of antibodies to Chlamydia trachomatis. Coated elementary bodies were treated with either sodium periodate, to oxidize the antigenic sites of the LPS, or Triton X-100, to extract the LPS. By using these new enzyme immunoassays, the standard enzyme immunoassay, and the whole inclusion fluorescence (WIF) assay, antibodies to C. trachomatis were determined in sera from different groups of patients and controls. Paired serum samples from patients with culture-proven urogenital C. trachomatis infections showed similar responses in all three assays. Paired serum samples from patients with Chlamydia psittaci infections showed similar responses in the WIF assay and the standard enzyme immunoassay, whereas significantly reduced titers were obtained in the enzyme immunoassays with treated antigen, especially in the convalescent-phase serum samples. Serum samples from patients with symptoms suggestive of infection with C. trachomatis, pregnant women, and blood donors were evaluated by all three types of assays. Eighty percent of the significant reductions in immunoglobulin G (IgG), IgA, and IgM titers were observed in sera with WIF assay titers in the lower classes (IgG, 1: < or = 256; IgA, 1: < or = 32; IgM, 1: < or = 16). From these results we conclude that oxidation of the antigen by sodium periodate is a simple and effective method of producing an enzyme immunoassay with enhanced specificity that could be useful for diagnostic purposes and seroepidemiological studies.

Acute Disease↗
PubMed1993

[Poliomyelitis in The Netherlands, 1979-1991: immunity and exposure].

An overview is presented of serological and virological studies on poliovirus immunization and circulation in the Netherlands, performed between 1979 and 1991. In this period, only three patients with poliomyelitis were notified. All had acquired the infection abroad. The vaccinations in the national immunization programme, using inactivated poliovirus vaccine, build a strong immunity. This can also be seen in age-stratified serological profiles of the Dutch population. In these surveys, persons from the time at which vaccination was offered have neutralizing antibodies. Older persons, especially those born between 1930 and 1945, sometimes lack antibodies. However, 85-90% of them show a rapid booster response upon vaccination, demonstrating immunological memory. Hence, they will be protected against poliomyelitis upon contact with wild poliovirus. Virological data show a regular import of poliovirus, especially in adoptive children tested on entry into the Netherlands, coming from developing countries. Nearly all other virus isolates in Dutchmen were related to import from such countries. None of the imported patients or other persons in whom poliovirus was detected spread the virus over the country. It demonstrates that as a rule the herd immunity of the well-vaccinated Dutch population is good. Exceptions occur, however, as demonstrated by the epidemics in 1978 and 1992. Large socio-geographic clusters of susceptible people who refuse vaccinations are not sufficiently protected.

Antibodies, Viral↗
PubMed1993

[Virological and serological aspects of the Dutch polio epidemic in 1992].

During the 1992 poliovirus type 3 outbreak in the Netherlands virological and serological investigations were conducted. No molecular epidemiological link was traced between poliovirus type 3 that caused the outbreak of poliomyelitis in the Netherlands and isolates from previous epidemics investigated. Serological neutralization assessments indicate that the inactivated poliomyelitis vaccine used in the Dutch national immunization schedule induces immunity to the causative agent.

Antibodies, Viral↗
PubMed1992

Chlamydia keratoconjunctivitis determination of Chlamydia trachomatis specific secretory immunoglobulin A in tears by enzyme immunoassay.

Determination of Chlamydia trachomatis specific antibodies in serum and tears, isolation of C. trachomatis in cell culture and C. trachomatis antigen detection by direct immunofluorescence test were evaluated for the laboratory diagnosis of Chlamydia trachomatis infection in 30 patients with chronic conjunctivitis. C. trachomatis specific secretory immunoglobulin A (s-IgA) was detected in the tears of all 8 patients with a positive result in culture and the direct immunofluorescence test. In 4 additional patients, the s-IgA assay of tears was also positive. A presumptive clinical diagnosis of Chlamydia conjunctivitis was correlated with the presence of s-IgA in tears. S-IgA was not detected in the serum of any of the patients, indicating that s-IgA is locally produced and not transudated from the serum. For the diagnosis of chronic Chlamydia conjunctivitis, we recommend the determination of s-IgA in tears in addition to a test for Chlamydia detection.

Adolescent↗
PubMed1992

Efficacy of single-dose azithromycin versus doxycycline in the treatment of cervical infections caused by Chlamydia trachomatis.

The efficacy of single-dose azithromycin therapy in the treatment of cervical Chlamydia trachomatis infections was compared to that of a standard seven-day course of treatment with doxycycline. Cervical samples from 60 patients reacted positively in an enzyme immunoassay for detection of Chlamydia trachomatis. In 31 patients Chlamydia trachomatis was isolated from the sample taken before treatment. Fourteen of the 31 patients were treated with doxycycline and 17 with azithromycin. All cultures of samples taken one and four weeks after the start of therapy were negative. All 31 isolates showed a similar pattern of MICs for the seven antibiotics tested, including azithromycin and doxycycline. No differences were observed between isolates of different serovars. In samples from four patients chlamydial DNA could be detected by PCR one week after the start of the therapy and in two patients also after four weeks. No difference in microbiological parameters could be observed between the two treatment groups. It is concluded that single-dose azithromycin is as effective as a seven-day course of doxycycline in the therapy of cervical Chlamydia trachomatis infections.

Azithromycin↗
PubMed1992

Antibody-capture enzyme-linked immunosorbent assays that use enzyme-labelled antigen for detection of virus-specific immunoglobulin M, A and G in patients with varicella or herpes zoster.

Antibody-capture enzyme-linked immunosorbent assays (AC-ELISA) which use enzyme-labelled antigen were developed for detection of varicella-zoster virus-(VZV) specific IgM, IgA and IgG antibody in patients with varicella or herpes zoster and in sera from healthy individuals. All 18 patients with varicella developed a VZV-IgM and a VZV-IgG response, 17 also a VZV-IgA response. In contrast, all 19 patients with herpes zoster were shown to be positive for VZV-IgA whereas only 13 of these reacted positively for VZV-IgM. A VZV-IgM response was detected in only two sera from 100 healthy individuals and an IgA response in only one. The presence of virus-specific IgA and IgG in the cerebrospinal fluid as determined by AC-ELISA was a useful indicator of VZV infection of the central nervous system. By AC-ELISA, VZV-IgG was detected predominantly in sera from patients with acute or recent VZV infection. Only 14 sera from 100 healthy individuals were positive for VZV-IgG by AC-ELISA, whereas all were positive by an indirect ELISA. These results indicate that AC-ELISA's may be useful assays for determination for acute or recurrent VZV infection, but are not suitable for determination of past infection with this virus.

Acute Disease↗
PubMed1992

Detection of HIV antibodies in saliva as a tool for epidemiological studies.

OBJECTIVE: To evaluate the use of saliva specimens for the detection of HIV antibodies among high-risk groups in epidemiological studies. DESIGN: Testing of saliva specimens collected by different methods from individuals with known HIV status. The most reliable method was examined for its usefulness in a field study among a high-risk group. METHODS: Saliva samples were obtained either by using a cotton-wool roll ('Salivette') or as 'whole saliva'. HIV antibodies were determined using commercial enzyme-linked immunosorbent assays (ELISA). Confirmation was performed using a line immunoassay or an immunoblot assay. RESULTS: In 'Salivette' samples, HIV antibodies were detected by ELISA in seven out of 22 seropositive individuals. In contrast, testing of 'whole saliva' samples from 79 HIV-seropositive and 115 HIV-seronegative individuals resulted in a 100% correlation with HIV serum status. The positive reaction of 20 'whole saliva' specimens was confirmed in a line immunoassay, whereas in an immunoblot assay only seven specimens were positive, one negative, and 12 indeterminate. In an HIV prevalence study among drug users, 395 'whole saliva' samples were tested in two different ELISA. Both assays showed complete agreement in detecting 58 positive and 337 negative samples. All positive samples were confirmed by the line immunoassay. CONCLUSION: Our study demonstrates that 'whole saliva' specimens are a good alternative to blood samples in epidemiological studies of HIV prevalence in high-risk groups.

Adult↗
PubMed1992

Development and clinical evaluation of a polymerase chain reaction test for detection of Chlamydia trachomatis.

A polymerase chain reaction (PCR) for the detection of Chlamydia trachomatis was developed and evaluated. Two primer-probe sets were designed; one detected a specific sequence of the plasmid, and the other detected the gene encoding the major outer membrane protein. Both sets reacted species specifically and amplified sequences from all human serovars. A simple protocol was used for sample pretreatment. The PCR was optimized by addition of tetramethylammonium chloride and bovine serum albumin. The results of the PCR with the plasmid primer-probe set were compared with those of culture and the Chlamydiazyme and Gen-Probe PACE 2 tests for urogenital specimens from 220 patients. The rates of prevalence of infection with C. trachomatis were 22.7, 16.4, 15.0, and 14.5%, respectively. The sensitivities of the Chlamydiazyme and Gen-Probe PACE 2 assays compared with culture were 66.7 and 61.1%, respectively, and their sensitivities compared with PCR were 60.0 and 60.0%, respectively. The sensitivity of culture compared with PCR was 70.0%. Forty-eight of the 50 specimens positive by PCR with the plasmid primer-probe set could be confirmed by PCR with the major outer membrane protein primer-probe set or culture. It is concluded that the PCR is the most sensitive technique for laboratory detection of C. trachomatis.

Bacteriological Techniques↗
PubMed1990

Hepatitis B pre-S1 and pre-S2 proteins: clinical significance and relation to hepatitis B virus DNA.

Pre-S proteins may have an important role in virus assembly and virus entry into the host cell. The presence of pre-S proteins in serum has also been thought to correlate with active viral replication. To investigate whether pre-S proteins in serum might have additional diagnostic and/or predictive value for liver sequelae in HBV infection, sera from six different serological groups of patients with HBV markers (total number 363) and different manifestations of liver histology were examined for the presence of pre-S1 and pre-S2 proteins using micro-ELISAs. Pre-S1 and pre-S2 proteins were detected significantly more often in HBV-DNA-positive than in HBV-DNA-negative sera from HBsAg carriers. However, pre-S1 and pre-S2 proteins were also found in HBV-DNA-negative HBsAg carriers irrespective of serum HBeAg/anti-HBe or liver histologic findings. These results suggest that the presence of the pre-S1 and or pre-S2 proteins in serum either does not seem to reflect the presence of active viral replication and active liver disease or pre-S proteins are more readily detectable than HBeAg and HB-DNA as measured by a dot-blot technique. Furthermore, the presence of pre-S proteins in serum is strongly correlated with that of HBsAg.

Chronic Disease↗
PubMed1989

Laboratory diagnosis of toxoplasmosis.

Acute infection with Toxoplasma gondii is diagnosed by (i) detection of the parasite directly in patients' specimens using histological or immunological methods, (ii) isolation of T. gondii from blood, body fluids or tissue by inoculation in laboratory mice or on tissue culture cells, or (iii) serological methods for determination of a significant, T. gondii-specific, antibody titre rise or of T. gondii specific IgM (or IgA) antibody. Because of their high sensitivity, specificity and relative ease of performance, serological methods are preferentially used for diagnosis of T. gondii infection. The diagnosis of acute, postnatally-acquired, primary toxoplasmosis is usually established by serological methods and will in general present few problems. However, diagnosis of congenital infections and their late sequelae or of reactivation of a latent infection in immunocompromised patients is often more troublesome because of the absence of a significant antibody titre rise or the lack of specific IgM antibody. In these cases a combination of various methods may be required for definitive diagnosis of T. gondii infection.

Animals↗
PubMed1989

Cytomegalovirus infection and disease in renal transplant patients treated with cyclosporin. A prospective study.

In this prospective study, the incidence of cytomegalovirus (CMV) infection and CMV disease was determined in 175 renal transplant recipients on cyclosporin and low-dose prednisone. CMV infection occurred in 51.4% of the patients, CMV disease in 13.7%. The major manifestations of CMV disease were fever of unknown origin and leukopenia. In the group with CMV infection, there was an increased occurrence of rejection (60% in infected vs 27% in noninfected patients). In most patients (41/54), the rejection preceded the CMV infection. CMV infection did not lead to a decreased graft survival. There was no close time relationship between the onset of clinical symptoms of CMV disease and the laboratory confirmation of CMV infection. A subgroup of patients at risk for the development of severe CMV disease could not be identified.

Cyclosporins↗