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Biomedical subjects

A M Polderman

Publications and source records attributed to A M Polderman.

At least 55 records · Page 3Linked to original sources
PubMed1999

Geographic distribution and epidemiology of Oesophagostomum bifurcum and hookworm infections in humans in Togo.

In contrast to the rest of the world, infections with Oesophagostomum bifurcum are commonly found in humans in northern Togo and Ghana. In addition, infections with hookworm are endemic in this region. In the present study, a detailed map of the geographic distribution of O. bifurcum and hookworm infections in northern Togo was made. There were a number of foci with high prevalence of infection with O. bifurcum. All the villages examined were infected with hookworm, and the distribution was quite patchy. Women were infected with O. bifurcum more often than men, while infections with hookworm were more prevalent in men than in women. The prevalence and intensity of infection with both parasites were clearly age-dependent. We estimate that more than a 100,000 people in Togo are infected with O. bifurcum and more than 230,000 are infected with hookworm.

Adolescent↗
PubMed1998

A mutation scanning approach for the identification of hookworm species and analysis of population variation.

To overcome limitations in the morphological identification of different developmental stages of hookworms to species, we have established a polymerase chain reaction-linked single strand conformation polymorphism technique (PCR-SSCP) utilizing the internal transcribed spacers (ITS) of ribosomal (r)DNA. These spacers were specifically chosen because they provide reliable species markers for strongylid nematodes. ITS spacers were amplified by PCR from DNA derived from individual parasites of seven species of hookworm, then denatured and subjected to electrophoresis in a mutation detection enhancement (MDE) (non-denaturing) gel matrix. PCR SSCP analysis showed that the single-strand ITS patterns produced allowed the unequivocal identification of all species. The method also allowed the direct display of sequence variation within some species where multiple individual worms were examined. These findings demonstrate the usefulness of the SSCP approach for hookworm identification, the detection of population variation and the direct display of sequence variation in rDNA.

Ancylostomatoidea↗
PubMed1998

Necator americanus (Nematoda: Ancylostomatidae) from Africa and Malaysia have different ITS-2 rDNA sequences.

The nucleotide sequences of the second internal transcribed spacer of rDNA were determined for adult worms of Necator americanus originating from Togo (Africa) and Sarawak (Malaysia). The length of the sequences of specimens from Togo (325 bp) were shorter than those from Sarawak (327 bp). There were six fixed genetic differences in the aligned sequences of N. americanus from Sarawak and Togo, excluding one or two polymorphic sites within the sequence of N. americanus from each geographical region. These findings suggest that there is either population variation in the sequence of N. americanus, or that N. americanus from the two countries may represent genetically distinct but morphologically similar (i.e. cryptic) species, however, comparison of the sequence differences among other hookworm species supports the latter conclusion.

Africa↗
PubMed1997

Differentiation of Oesophagostomum bifurcum from Necator americanus by PCR using genetic markers in spacer ribosomal DNA.

Oesophagostomiasis in humans due to infection with Oesophagostomum bifurcum (nodular worm) is of major human health significance in northern Togo and Ghana where Necator americanus (human hookworm) also exists at high prevalence. However, very little is known about the transmission patterns of O. bifurcum, partly due to the difficulty in differentiating O. bifurcum from N. americanus at some life-cycle stages using morphological features. To overcome this limitation, a molecular approach utilizing genetic markers in the second internal transcribed spacer (ITS-2) of ribosomal (r) DNA was developed. The ITS-2 sequence of each species was determined, and specific oligonucleotide primers were designed to the regions of greatest sequence difference between the species. Utilizing these primers, rapid PCR assays were developed for the specific amplification of DNA of O. bifurcum or N. americanus, which have the potential to confirm the identity of eggs from faeces and larvae from the intestine or environment. The application of species-specific PCR has important implications for studying the epidemiology and population biology of O. bifurcum.

Animals↗
PubMed1997

Sensitivity of microscopy versus enzyme immunoassay in the laboratory diagnosis of giardiasis.

The substitution of enzyme immunoassay (EIA) techniques for microscopy as a screening tool for Giardia lamblia infection was assessed. Paired stool samples obtained within a ten-day period from 366 patients with persistent diarrhea were examined by microscopy. In addition, two commercially available Giardia lamblia-specific EIAs were performed. Compared with microscopy, EIA for copro-antigen detection was more sensitive, based on examination of either one or two stool samples. Repeated examinations increased the number of cases detected, more so for microscopy than EIA. The negative predictive values of the two EIAs performed on the first stool sample were 98.7% and 97.8%. The results show that EIA for detection of copro-antigens in a single stool sample may be almost as sensitive for identifying Giardia infection as repeated microscopy on two sequential stool samples.

Adolescent↗
PubMed1997

Validation of a chart to estimate true Schistosoma mansoni prevalences from simple egg counts.

Schistosoma mansoni egg counts by faecal examination vary considerably and are not very sensitive, so prevalences are underestimated. The distribution of egg counts can adequately be described by a stochastic model which distinguishes variation in counts between persons and variation in repeated counts within a person. Based on this model a pocket chart has been developed which predicts the proportion of individuals harbouring at least 1 S. mansoni worm pair-the 'true prevalence'-from a simple single survey prevalence and geometric mean egg count (using common duplicate 25 mg Kato-Katz smears). The current paper describes the validation of this chart by comparing predicted true prevalences with prevalences observed after 5-7 repeated Kato-Katz faecal examinations (Burundi), by examination of a large quantity of stool using the Visser filter (Brazil) or a selective sedimentation-filtration method (Surinam). Because 5-7 repeated examinations do not suffice to measure all infections, predictions have been made of the cumulative proportion positives over 5-7 surveys-the 'approximate true prevalence'-as well. After dividing the data into age groups, 12 different subsets were considered for validation. In all 12 cases, predicted true prevalences (or approximate true prevalences for the Burundi data) agree well with those observed. The overall agreement depends only slightly on the assumed relationship between worm numbers and mean egg counts, with a good fit for a productivity between 0.8 and 4.4 eggs per gramme faeces (EPG) per worm pair (WP). This interval includes the most plausible value from the literature, i.e. 1.0 EPG/WP, which has been applied in the initial pocket chart. These findings support the validity of the chart to predict true prevalences for a wide range of productivity assumptions, and reinforces the applicability of its underlying stochastic model to describe egg count variation. However, as predictions appear to vary importantly when using only part of the data, it is also concluded that the pocket chart never compensates for limited validity of initial single survey prevalences and geometric means in consequence of small sample sizes.

Adolescent↗
PubMed1997

Detection of the circulating antigens CAA and CCA in a group of Dutch travellers with acute schistosomiasis.

Detection of circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) in serum and urine is a highly specific and sensitive alternative for the diagnosis of schistosome infections in endemic areas. However, it is not known how soon after the onset of infection these antigens can be detected in humans. Neither has there been much research on the detection of these antigens in individuals normally living in non-endemic areas. We studied the kinetics of CAA and CCA in serum and urine of a group of 28 Dutch tourists, shortly after accidental exposure to a Schistosoma infection during a visit to Mali. Twenty-seven were found to be positive for Schistosoma eggs and/or specific antibodies. From each individual, 1-4 serum samples were tested for circulating antigen level, 4-15 weeks after exposure, and urine samples were also tested from 22 subjects. CAA and CCA levels were quantified by monoclonal antibody-based ELISAs and TRIFMAs. In serum, 23 individuals (85%) were positive at least once for one or both antigens, but titres were generally very low. CAA and CCA could be detected 5 and 6 weeks after exposure, respectively. Urines were all found to be negative. Almost all cases were negative at 7 months' follow-up.

Adult↗
PubMed1997

Characterization of Oesophagostomum bifurcum and Necator americanus by PCR-RFLP of rDNA.

Esophagostomiasis in humans due to infection with Oesophagostomum bifurcum (nodular worm) is of major human health significance in northern Togo and Ghana, where Necator americanus (human hookworm) also exists at high prevalence. Yet, very little is known about the transmission patterns of O. bifurcum, which is in part due to the difficulties in diagnosis and in differentiating some life-cycle stages of O. bifurcum from N. americanus using morphological features. As a first step toward developing a molecular-diagnostic assay, it was evaluated whether ribosomal (r)DNA could provide genetic markers for the identification of O. bifurcum and N. americanus to species. Internal transcribed spacer rDNA (plus flanking and intervening sequences) was analyzed by polymerase chain reaction-linked restriction fragment length polymorphism (PCR-RFLP) using several restriction endonucleases. The analysis showed that there was no detectable intraspecific difference in the size of the PCR products among multiple samples, that there was a consistent size difference in the products (of 110 bp or 350 bp, depending on region amplified) between the species, and that there was no significant variation in restriction patterns within each species. These results indicate that the rDNA spanning the internal transcribed spacers provides useful genetic markers for the identification of O. bifurcum and N. americanus to species, which has important implications for developing PCR-based tools to study the epidemiology and population biology of O. bifurcum.

Animals↗
PubMed1996

SCHISTOSIM: a microsimulation model for the epidemiology and control of schistosomiasis.

A computer simulation model, SCHISTOSIM, has been developed for the epidemiology and control of schistosomiasis, based on the stochastic microsimulation technique. The eventual aim is to evaluate and predict the effects of different control strategies. In the current state of the model, human-, worm-, and infection-related aspects have been included. However, many others, including most transmission and transmission-related mechanisms, have yet to be modeled. By simulating a series of surveys and treatments in Burundi, short-term effects of this program were satisfactorily explained by the model. However, long-term predictions did not match the observed data. Possible extensions of the model to properly describe these effects are identified. The potential of SCHISTOSIM as a tool for the prediction of outcomes of alternative control strategies is illustrated and discussed.

Animals↗
PubMed1995

[Underestimation of intestinal protozoa as a cause of diarrhea in family practice].

OBJECTIVE: To assess the frequency of intestinal protozoa in stool samples of patients with diarrhoea in general practice. SETTING: General practitioners' laboratory in Haarlem, Netherlands. DESIGN: Descriptive study. METHOD: During one year (1 February 1992 to 31 January 1993) all stool samples from patients with diarrhoea visiting a general practitioner were examined according to a standard protocol consisting of bacterial and protozoal examination. RESULTS: Among 1703 stool examinations requested by general practitioners and performed according to the protocol, pathogenic protozoa were found in 10.8% and pathogenic bacteria in 8.6%. Of the 184 patients who tested positive for pathogenic protozoa 156 harboured Giardia lamblia, 22 Entamoeba histolytica and 6 Cryptosporidium spp. Pathogenic protozoa were predominantly found in patients with diarrhoea persisting for longer than 1 week and in cases with intermittent diarrhoea. In patients with acute diarrhoea (duration < 1 week) we predominantly found pathogenic bacteria (Campylobacyter jejuni). If the search for protozoa in the stool samples would not have been performed routinely, 34% of the pathogenic protozoa (Giardia lamblia) would not have been found. CONCLUSION: Intestinal infections with protozoa are not rare in general practice. It seems worthwhile to perform protozoal examination of the stool samples in case of persistent diarrhoea.

Adolescent↗
PubMed1995

Comparison of fresh versus sodium acetate acetic acid formalin preserved stool specimens for diagnosis of intestinal protozoal infections.

The use of sodium acetate acetic acid formalin (SAF)-preserved stool specimens was compared with that of nonpreserved specimens for the recovery of intestinal protozoa. A total of 247 patients, 170 with diarrhea of more than one week's duration and 77 refugees, were asked to collect a stool specimen. Each specimen was placed into two vials, one empty, the other containing SAF fixative. Laboratory investigations included microscopic examination of the concentrated sediment and direct wet smears from both types of stool specimens and the microscopic examination of a permanent stained smear from the unsedimented, SAF-preserved stool specimens. Examination of SAF-preserved stool specimens revealed intestinal protozoa in 149 of the 247 patients. With the conventional procedure using unpreserved stool specimens, intestinal protozoa were found in 89 of the 247 patients. The results show that the examination of SAF-preserved stool specimens, consisting of the microscopic examination of both the concentrated sediment and the permanent stained smear from the unsedimented material, increases the chance of recovering intestinal protozoa as compared to the conventional procedure.

Acetates↗
PubMed1995

Immunodiagnosis of schistosomiasis mansoni in a low endemic area in Surinam by determination of the circulating antigens CAA and CCA.

We evaluated the applicability of circulating antigen detection in serum and urine for the diagnosis of Schistosoma infections in a low endemic area. In total 389 individuals from Saramacca (Surinam) participated in the survey. Stool samples were examined using the Kato method, while circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were determined by highly specific monoclonal antibody-based ELISA's. Also schistosome specific IgM antibodies were measured by the indirect immunofluorescence assay, but the diagnostic performance of this test was found to be poor in this population. S. mansoni eggs were found in 29% of the examined cases, while CAA and CCA could be demonstrated in 23% and 17% of the serum samples and in 3% and 28% of the urine samples, respectively. Forty three percent of the study population was positive in at least one of these diagnostic assays, indicating that each individual test misses a substantial part of the subjects with an active infection. In most positive cases, intensities of infection were very low. As 204 individuals participated in all screening assays, diagnostic performance of each test was evaluated in this sub-population. The highest sensitivities were achieved with the urine-CCA assay and the parasitological examination, detecting 59 and 58 out of the 107 cases with an active infection, respectively. The serum-CAA assay detected 47 positive cases. Our results demonstrate that determination of circulating antigens, especially CCA in urine and CAA in serum, provides information additional to the parasitological examination, for the assessment of prevalence and intensity of Schistosoma infection in low endemic areas.

Adolescent↗
PubMed1995

The contribution of existing health facilities to the control of urinary schistosomiasis in northern Cameroon.

This paper attempts to analyse the impact of the regular functioning of existing health services on the control of urinary schistosomiasis in two villages in northern Cameroon. The health centres' diagnostic systems selectively recognise heavy infections. The efficacy of reaching and subsequently treating heavily infected subjects, however, is low. No more than around 5% of the heavily infected subjects in the health centres' catchments areas is reached on an annual basis. Further analysis shows that the percentage of infected and heavily infected subjects is not higher among the visitors of the health centre than in the inhabitants of the villages involved. Heavy infection is not a reason to visit the health centre, in these villages. To increase the role of the existing health structure in coping with Schistosoma haematobium infections, the diagnostic system, used in the health centres, could be improved by a standardized inclusion of laboratory examination of clinically suspected individuals. Simultaneously, the awareness of the infected population to respond to infection by visiting the health centre needs further development.

Adolescent↗
PubMed1995

Oesophagostomum infections in humans.

Oesophagostomum spp are normally found as nematode parasites of ruminants, pig and monkeys. Occasionally humans are involved. In the past decade it became clear that, in some parts of Africa, humans are adequate final hosts. In those areas, prevalences of infection are high and morbidity is significant. The presence of lumen-dwelling adult worms, which do not seem to cause a great deal of pathology, can be demonstrated through coproculture. The presence of immature worms, encapsulated in nodules and responsible for pathology, on the other hand, is more difficult to confirm. It is not known what factors limit the distribution of endemic human oesophagostomiasis to a small focus in West Africa. The relationship between the 'helminthomas' described a long time ago in Uganda and the human Oesophagostomum infections in West Africa is unclear and it remains a mystery how humans get infected so effectively by ingesting L3 larvae. In this overview, Ton Polderman and Coby Blotkamp give an account of what is known and what is still to be elucidated in human Oesophagostomum infections.

Journal Article↗
PubMed1995

Outbreak of schistosomiasis among travelers returning from Mali, West Africa.

Schistosomiasis in travelers often remains unrecognized because doctors are unfamiliar with the clinical presentation and diagnosis of this imported disease. We describe the epidemiological, clinical, and laboratory characteristics associated with an outbreak of schistosomiasis among nonimmune travelers. Of 30 travelers in two consecutive groups, 29 who had swum in freshwater pools in the Dogon area of Mali, West Africa, were followed for 12 months. Twenty-eight (97%) of those 29 became infected; 10 (36%) of the 28 had cercarial dermatitis, and in 15 (54%), Katayama fever developed. Eggs were found in 22 (79%) of the infected travelers: eggs of Schistosoma mansoni or terminally spined eggs (probably of Schistosoma intercalatum) were in the stools of 19 and 10 patients, respectively, and eggs of Schistosoma haematobium were in the urine of 7 patients. The eggs of 2 of these Schistosoma species were present in 6 cases, and in 4 cases eggs of all 3 species were found. The limited exposure of this group of travelers resulted in a high rate of infection with all three of the Schistosoma species that are prevalent in Africa. A diagnosis of schistosomiasis should be considered for any traveler with a history of exposure to fresh water in an area of endemicity. The only effective method of prevention is avoiding all contact with fresh water in these areas.

Adult↗
PubMed1995

Analysis of worm burden variation in human Schistosoma mansoni infections by determination of serum levels of circulating anodic antigen and circulating cathodic antigen.

Serum circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) concentrations, as a possible direct measure of worm burden, were compared with fecal egg counts in a heavily Schistosoma mansoni-infected population from Zaire to allow differentiation between worm loads and worm fecundity in relation to age and intensity of infection. Of the 517 subjects, 95% excreted eggs and 97% demonstrated circulating antigens. Fecal egg counts showed an age-related pattern characteristic for an area in which schistosomiasis is endemic with intense transmission levels. Regression analysis showed that antigen concentrations were strongly associated with egg counts. For CAA, but not for CCA, this relation was found to be nonlinear, which would be consistent with density-dependent fecundity or crowding. The trend was uniform for all age groups, which for this particular population indicated a genuine reduction of worm loads rather than reduced worm fecundity with age of the host.

Adolescent↗