Low-intensity Infections Research Articles

The mucosal response of hamsters exposed to weekly repeated infections with the hookwormAncylostoma ceylanicum

An experiment was carried out to assess mucosal changes in hamsters exposed to weekly repeated low-intensity infections with the hookworm Ancylostoma ceylanicum. The experiment included control groups of naïve, uninfected hamsters and groups that received a single-pulse primary infection. Changes in the intestinal architecture and in the density of inflammatory cells in the mucosa, including mast cells, goblet cells, Paneth cells and eosinophils were examined in relation to changes in hookworm burdens. As in the single-pulse primary infection, hamsters exposed to repeated infections responded with marked changes in the intestinal architecture and in mucosal populations of inflammatory cells. However, there were distinct differences in the kinetics of the responses to these two types of infection (primary single-pulse and repeated). The reduction in villous height and the increase in crypt depth in animals exposed to repeated infections were both initially slower but eventually equalled and exceeded the responses in hamsters given a chronic primary infection, despite the presence of fewer adult worms in the former. Similarly, changes in the mitotic figures of epithelial cells in the mucosa and the mast cell response were both initially slower and less intense in repeatedly infected hamsters, but eventually exceeded the response to primary infection. Furthermore, the eosinophil response was found to be initially greater in repeated infections and overall more persistent. In contrast, both goblet and Paneth cell responses were less marked in repeatedly infected animals compared to those carrying a primary infection. These results are discussed in the context of host protective resistance to infection with A. ceylanicum.

Magnetic Affinity Enzyme-Linked Immunoassay for Diagnosis of Schistosomiasis Japonicum in Persons with Low-Intensity Infection

Most schistosome-endemic areas in China are characterized by low-intensity infections that are independent of prevalence. To establish an effective diagnostic method, we developed a magnetic affinity enzyme-linked immunoassay based on soluble egg antigens (SEA-MEIA) for diagnosing schistosomiasis in persons with low-intensity infection with Schistosoma japonicum by comparing it with a conventional enzyme-linked immunosorbent assay (ELISA). Our results showed that the SEA-MEIA had a higher sensitivity and greater precision in the diagnosis of low-intensity S. japonicum infections than the ELISA. In addition, when we used Pearson's correlation in associating SEA-MEIA with ELISA, a significant correlation existed between the two assays (r = 0.845, P < 0.001). Our data indicated that SEA-MEIA, with a higher sensitivity and greater ease of performance, would be valuable for diagnosis of schistosomiasis japonicum in persons with low-intensity infections.

Does avian malaria reduce fledging success: an experimental test of the selection hypothesis

Like many parasites, avian haematozoa are often found at lower infection intensities in older birds than young birds. One explanation, known as the “selection” hypothesis, is that infected young birds die before reaching adulthood, thus removing the highest infection intensities from the host population. We tested this hypothesis in the field by experimentally infecting nestling rock pigeons (Columba livia) with the malaria parasite Haemoproteus columbae. We compared the condition and fledging success of infected nestlings to that of uninfected controls. There was no significant difference in the body mass, fledging success, age at fledging, or post-fledging survival of experimental versus control birds. These results were unexpected, given that long-term studies of older pigeons have demonstrated chronic effects of H. columbae. We conclude that H. columbae has little impact on nestling pigeons, even when they are directly infected with the parasite. Our study provides no support for the selection hypothesis that older birds have lower parasite loads because parasites are removed from the population by infected nestlings dying. To our knowledge, this is the first study to test the impact of avian malaria using experimental inoculations under natural conditions.

Nutritional risk factors for hookworm infection among school age children in the Kintampo North Municipality, Ghana

Hookworm is highly prevalent in the Kintampo North Municipality of Ghana, and a previous study identified a significant relationship between BMI and infection status in adults.ObjectivesTo investigate the role of nutritional status and dietary risk factors on hookworm infection and response to deworming treatment in school‐age children.MethodsChildren (n=812) ages 6 to 11 years attending 16 schools were screened for participation on the basis of HAZ scores (low and high). Household level food security and socioeconomic variables, child‐level dietary diversity, hookworm and malaria infection status and response to albendazole were measured in a cross sectional sample (n=286).ResultsPrevalence of hookworm was 39%, and anemia was 62%. Significant risk factors for hookworm infection included lower consumption of protein‐rich food groups (p&lt;0.05), malaria co‐infection (p&lt;0.05), access to health care (p&lt;0.01), and household geographic location (p&lt;0.05) after controlling for age, gender, household wealth, and recent deworming. The degree of stunting and anemia did not correlate with hookworm infection status.ConclusionsDietary diversity may influence the risk of hookworm infection in Ghana. In areas of high prevalence but low intensity infection, hookworm may not cause traditionally recognized clinical sequelae such as anemia and stunting.

Equine cestodosis: a sero-epidemiological study of Anoplocephala perfoliata infection in Ethiopia

A 12/13 kDa antigen, tapeworm ELISA test, developed for use in horses, was used to detect parasite-specific serum antibody, IgG(T), in the serum of donkeys. In a pilot study the 12/13 kDa antigen was tested and proved to detect the antibody, IgG(T), in donkey sera. Blood samples from 797 donkeys, naturally exposed to cestode infection, from four geographical localities were collected and sera were prepared and analysed. There was substantial serological evidence that donkeys were potentially infected with A. perfoliata. A range of ELISA OD values were obtained from the serological assay. Over 26% and 7.5% of the donkeys were moderately and highly infected, respectively, showing at least a 34% sero-prevalence. The rest, 66.1%, were either with low infection intensity or negative for A. perfoliata infection. The risk of infections, both in sero-prevalence and intensity, as determined by ELISA optical density (OD), were highest in the highland areas of Ethiopia where pastures are low-lying and wet, and permanent pasture management is regularly practised. Sex, age and body condition of the donkeys had no significant effect either on prevalence of the infection or on the serum antibody level. These results indicate a risk of intestinal disorders, particularly, colic, associated with A. perfoliata infection in donkeys.

Coinfection with Malaria, Hookworm and Schistosomiasis among School Children in Zambezi: A School-based Rapid Survey

Introduction: A school based rapid survey was conducted th th from the 17 to the 19 of May 2011in Zambezi District of Zambia to determine the prevalence and coinfection rate of malaria, hookworm and schistosomiasis in schoolchildren in other to inform decision maker. Methodology: The study design, sampling methods, sample collection and processing used have been described in WHO's guidelines for the evaluation of soiltransmitted helminthiasis and schistosomiasis at community level. Additionally height, weight and haemoglobin were measured and malaria screened. Results: We report high prevalence of parasitic infections in schoolchildren in Zambezi district with 79.4% (n = 253; 95% CI: 74.1% - 84.1%) of the children tested positive at least to one parasitic infection. Estimated prevalence of malaria, hookworm, haematuria, S. haematobium, S. mansoni, and E. vermicularis were 50.6% (95% CI: 44.5-56.6%), 42.4% (95% CI: 36.448.5%), 37.9% (95% CI: 32.2-43.9%), 29.5% (95% CI: 24.2-35.2%), 14.5% (95% CI: 10.6-19.2%), and 1.2% (95% CI: 0.3-3.2%) respectively. Generally these were low intensity infections with the exception of S. haematobium. High prevalence of anaemia (46%; 95%CI: 40-52.1) and nutritional deficiency (79.1%; 73.983.7) were also detected. The prevalence of multiparasitism was 44.3% (95%CI: 38.2-50.4%) representing 55.7% of all parasitic infections.

Correlation between infection intensity, serum immunoglobulin profile, cellular immunity and the efficacy of treatment with praziquantel in murine schistosomiasis mansoni.

This study was conducted to evaluate the efficacy of praziquantel (CAS 55268-74-1, EMBAY 8440, Biltricide) in different grades of Schistosoma mansoni infection. Moreover, the relationship between the post treatment worm burden, hepatic granuloma volume, and serum immunoglobin profile was also investigated. Four groups of Swiss albino mice infected with Schistosoma mansoni cercariae were used: Highly infected untreated control mice (infected with 120 Schistosoma mansoni cercariae) and their corresponding praziquantel treated group. Lightly infected untreated control mice (infected with 60 Schistosoma mansoni cercariae) and their corresponding praziquantel treated group. Praziquantel was given seven weeks post infection in a dose of 500 mg/kg body weight for two consecutive days. Animals were sacrificed two weeks post treatment. Praziquantel achieved better cure rates in mice with heavy infection than in less intensely infected animals. The drug reduced the hepatic granuloma in animals with light intensity infection. This reduction was more accentuated in highly infected animals. The serum immunoglobulin profile (immunoglobulin G and immunoglobulin M) showed a higher level in highly infected treated mice (1.2 +/- 0.6 optical density unit and 1.1 +/- 0.5 optical density unit, respectively) and was reduced in animals with low intensity infection (1.18 +/- 0.6 optical density unit and 0.7 +/- 0.6 optical density unit, respectively). This study may be of value in tropical regions, where schistosomiasis with low worm burden is a common occurrence.

Tools to Support Policy Decisions Related to Treatment Strategies and Surveillance of Schistosomiasis Japonica towards Elimination

BackgroundAppropriate diagnostics to monitor disease trends and assess the effectiveness and impact of interventions are essential for guiding treatment strategies at different thresholds of schistosomiasis transmission and for certifying elimination. Field validation of these assays is urgently needed before they can be adopted to support policy decisions of the national programme for control and elimination of schistosomiasis in P.R. China. We compared the efficacy and utility of different immunoassays in guiding control strategies and monitoring the endemic status of S. japonicum infections towards elimination.Methodology/Principal FindingsA cross-sectional survey was conducted in seven villages with different transmission intensities settings to assess the performance and utility of three immunoassays, e.g., an indirect hemagglutination assay (IHA_JX), an enzyme linked immunosorbent assay (ELISA_SZ), and a dot immunogold filtration assay (DIGFA_SH). 6,248 individuals aged 6–65 years old who gave consent and supplied their stool and blood samples were included for data analysis. Results showed that ELISA_SZ performed significantly higher sensitivity (95.45%, 95%CI: 92.94–97.97%) than IHA_JX (87.59%, 95%CI: 83.51–91.49%) and DIGFA_SH (79.55%, 95%CI: 74.68–84.41%), especially in subgroups with very low infection intensity. The specificity of ELISA_SZ, IHA_JX, DIGFA_SH in 6–9 year olds with occasional exposure was nearly 90%. DIGFA_SH performed the highest screening efficacy for patients among three assays with overall positive predicative value of 13.07% (95%CI: 11.42–14.72%). We found a positive correlation of antibody positive rate of IHA_JX with results of stool examination in age strata (r = 0.70, P<0.001). Seropositivity of IHA_JX in children aged 6–9 years old showed an excellent correlation with prevalence of schistosome infection in the seven communities (r = 0.77, P<0.05).Conclusions/SignificanceStudies suggest that ELISA_SZ could be used to guide selective chemotherapy in moderate or low endemic regions. IHA_JX could be used to as a surveillance tool and for certifying elimination of schistosomiasis through monitoring children as a sentinel population.

Immunodiagnostic efficacy of detection of Schistosoma japonicum human infections in China: a meta analysis

Objective To assess the diagnostic efficacy of the currently most widely used indirect hemagglutination assay (IHA) and enzyme-linked immunosorbent assay (ELISA) for detection of Schistosoma japonicum human infections. Methods A comprehensive search was undertaken from China National Knowledge Infrastructure, Wanfang Database, VIP Database, PubMed, Cochrane Library, Science Citation Index Expanded, Proquest, and the inclusion and exclusion criteria were strictly settled. The funnel plot was used to assess the publication bias, Cochran's Q test was employed to measure the homogeneity between studies, a summary receiver operating characteristic (SROC) curve was used to compare the diagnostic accuracy between the IHA and ELISA qualitatively by means of the Weighted Least Square method, the Ordinary Least Square method and the Robust regression method, and the diagnostic odds ratio (DOR) was drawn to compare the accuracy quantitatively. Results Out of 785 publications, 19 papers were eventually selected for analysis. Literature quality assessment indicated that minor publication bias existed in studies pertaining IHA test, but no bias was found in literatures regarding ELISA test. The heterogeneity test showed a heterogeneity between studies was present (χ 2=466.07 and 34.67, both P values<0.0001). The areas under the SROC curves of IHA were all higher than that of ELISA test using the three methods (Weighted Least Square method: 0.766 vs. 0.695, Ordinary Least Square method: 0.826 vs. 0.741, Robust regression: 0.815 vs. 0.715). The TPR* values for IHA and ELISA were 0.710, 0.759, 0.749, and 0.650, 0.686 and 0.666, respectively, and OR values were 5.997, 9.937, 8.893, and 3.432, 4.784 and 3.959, respectively. The DOR of IHA was 9.41 (95% CI: 4.88-18.18), and 4.78 (95% CI: 3.21-7.13) for ELISA. Conclusions All above results revealed that the diagnostic performance of IHA is better than that of ELISA. However, taking into account their unsatisfactory diagnostic value in areas with low infection intensity, a search for a better diagnostic test that can be applied in field situations in China should be given high priority.

The challenge of effective surveillance in moving from low transmission to elimination of schistosomiasis in China

Until recently, intensified efforts in China to suppress the transmission of Schistosoma japonicum relied principally on routine praziquantel treatment, extensive use of molluscicides and health education programs. These efforts, now supplemented by a broader range of control measures, have been quite successful in reducing the prevalence and intensity of human infection to very low levels. However, re-emergent transmission has occurred in formerly endemic areas of several provinces, signalling the need for more locally effective, integrated control strategies. We argue that these low but persistent levels of transmission also require important changes in both the tactics and strategy of disease surveillance to move forward towards elimination. Here we present recent data exemplifying the low transmission environment which suggests that we are reaching limits of detection of current diagnostic techniques used for human infection surveillance in these communities. However, both epidemiological data and theoretical results indicate that (i) transmission in the human population can persist at very low infection intensities even in the presence of routine control activities; (ii) the parasite can be reintroduced into parasite-free environments by very modest external inputs; and (iii) transmission at these low infection intensities exhibits very slow inter-year dynamics. These observations motivate the need for new, sensitive tools to identify low-level infections in mammalian or snail hosts, or the presence of S. japonicum in environmental media. Environmental monitoring offers an alternative, and perhaps more efficient, approach to large-scale surveillance of human infections in low transmission regions.

Nearshore ecosystem predictors of a bacterial infection in juvenile Chinook salmon

Disease epidemiology requires information about ecological and environmental condi- tions to identify factors that can influence disease progression. Bacterial kidney disease (BKD) is an endemic disease among Pacific Northwest salmonids that causes significant morbidity and mortality in artificially propagated stocks, but risk factors for infection among free-living salmon are unknown. We evaluated infection by the causative agent of BKD, Renibacterium salmoninarum, in 1752 fish across 52 sampling sites monthly from May to November 2003 as a component of a broader study of neritic habitat use in Puget Sound by juvenile Chinook salmon Oncorhynchus tshawytscha. Infection intensity was ≤10 cells per slide for 77% of the fish. Correlations between the density of Chinook salmon with infection prevalence and with infection intensity were observed across multiple spatial scales. Capture location was a stronger predictor of infection than fish origin (based on coded wire tags) or genetic stock. Influential risk factors by logistic regression were temperature, densities of marked and unmarked Chinook salmon, and density of river lamprey Lampetra ayresis. Renibac- terium salmoninarum were found in gut contents and kidney of river lamprey, suggesting this species may be a transmission vector. The low infection intensity, lack of an effect of fish origin, effect of capture bay, and strong associations with Chinook salmon density are consistent with horizontal transmission of R. salmoninarum during the juvenile neritic phase, posing a potential for infectious interaction between sympatric hatchery and wild fish.

HELMINTOFAUNA DE DOS LAGARTOS GECONÍDEOS, HEMIDACTYLUS AGRIUS Y LYGODACTYLUS KLUGEI (GEKKONIDADE), EN EL BIOMA CAATINGA, NORESTE DEL BRASIL

Este estudio presenta datos sobre la fauna de helmintos de dos lagartos geconídeos, Hemidactylus agrius y Lygodactylus klugei, en el bioma caatinga en el noreste del Brasil. Hay cuatro especies de helmintos parásitos de H. agrius, cistacanto de Centrorhynchidae (Acanthocephala) y nematodos Physalopteridae (estadios larvarios), Parapharyngodon alvarengai (Pharyngodonidae) y Skrjabinelazia sp. (Seuratidade). El hospedador Lygodactylus klugei presentó dos especies de helmintos, un individuo de Mesocoelium monas (Trematoda: Mesocoeliidae) en el intestino delgado y una larva enquistada de Physalopteridae (Nematoda: Physalopteridae) adjunta a la pared del estómago. Las especies de lagarto mostraron una baja prevalencia y baja riqueza de helmintos. Además, H. agrius mostró una baja intensidad de infección. El modo de búsqueda de alimento, el hábito arbóreo y la composición de una dieta restringida pudieran haber favorecido la baja prevalencia, las bajas tasas de infección y riqueza baja de helmintos que se encontraron en las especies hospedadoras.

Epidemiology of Hookworm Infection in Kintampo North Municipality, Ghana: Patterns of Malaria Coinfection, Anemia, and Albendazole Treatment Failure

A cross-sectional pilot study of hookworm infection was carried out among 292 subjects from 62 households in Kintampo North, Ghana. The overall prevalence of hookworm infection was 45%, peaking in those 11-20 years old (58.5%). In children, risk factors for hookworm infection included coinfection with malaria and increased serum immunoglobulin G reactivity to hookworm secretory antigens. Risk factors for infection in adults included poor nutritional status, not using a latrine, not wearing shoes, and occupation (farming). Although albendazole therapy was associated with an overall egg reduction rate of 82%, 37 subjects (39%) remained infected. Among those who failed therapy, treatment was not associated with a significant reduction in egg excretion, and nearly one-third had higher counts on repeat examination. These data confirm a high prevalence of low-intensity hookworm infection in central Ghana and its association with poor nutritional status. The high rate of albendazole failure raises concern about emerging resistance.

Evaluation of two doses of triclabendazole in treatment of patients with combined schistosomiasis and fascioliasis

To determine the safety and efficacy of 2 consecutive doses of triclabendazole (TCBZ) in the treatment of Schistosoma mansoni infection in human cases infected with both S. mansoni and Fasciola sp., we conducted a field survey involving 6314 individuals from 15 villages. The overall prevalence of schistosomiasis alone was 15.8%, of fascioliasis alone 2.2%, and of combined infection 0.7%. Treatment with 2 doses of TCBZ was given to the 49 cases with combined infection. Eight weeks after treatment, the cure rate was 96% for fascioliasis and was 32.7% for schistosomiasis. All schistosomiasis cases cured had a low intensity infection. Liver function tests done before treatment and 8 weeks after substantiate the safety of 2 doses of TCBZ given to those with combined infection. Administration of TCBZ should precede praziquantel in treatment of combined infection, however TCBZ cannot be recommended for infection with S. mansoni alone.

Segmental Sedimentation and Counting Technique (SSCT): An adaptable method for qualitative diagnosis of Echinococcus multilocularis in fox intestines

A modified Segmental Sedimentation and Counting Technique (SSCT) to examine the presence of Echinococcus multilocularis helminths in segments of fox (Vulpes vulpes) intestine is described and compared to the “gold standard”, SCT. Out of the 358 intestines collected, 117 were E. multilocularis positive. Using SSCT methods we compare the sensitivity of individual or pairs of segments to establish a tradeoff between saving time and the reliability of the diagnosis, especially in areas with low infection intensities. The results show that the analysis of segment S4 associated with segment S1 or S2 give 98.3% sensitivity, with specificity close to 100%. Based on our results and the time saved, we recommend using SSCT for routine examination of fox intestines for large epidemiological studies, particularly where the endemic prevalence of E. multilocularis is low or unknown.

Poly-helminth infection in east guatemalan school children

Background:Soil transmitted helminths (STH) remain a global public health concern in spite of occasional dosing campaigns.Aims:To determine baseline prevalence and intensity of STH infection in east Guatemalan school children, and describe the associated epidemiology of anemia, stunting, and wasting in this population. Setting and design: Ten schools in Izabal province (eastern Guatemala) were identified, and 1,001 school children were selected for this study. Half of the schools were used as clinical testing sites (blood and stool).Materials and Methods:Anthropometric measures were collected from all children. Over 300 children were tested for anemia and 229 for helminth infection. Ova and parasite specimens were examined via Direct, Kato Katz, and McMaster techniques. Hemoglobin was measured from venipuncture following the hemacue system. Statistical analysis: Correlation between infection intensities and growth indicators were examined. Chi Square or t tests were used for bivariate analysis. Multiple logistic regression was performed on significant variables from bivariate techniques.Results:Over two-thirds of school children were positive for infection by any STH. Prevalence of Hookworm was 30%; Ascaris, 52%; and Trichuris, 39%, most as low-intensity infection. Over half of the children were co-infected. In bivariate analysis, anemia was significantly associated with polyparasitism.Conclusions:For a Guatemalan child who experiences a unit decrease in hemoglobin, one expects to see a 24% increase in the odds of being infected with STH, controlling for age, sex, lake proximity, and growth characteristics. Infection with more than one STH, despite low intensity, led to a significant decrease in hemoglobin.

Interactions of environmental stressors impact survival and development of parasitized larval amphibians

Infected hosts are exposed to many environmental stressors that must be taken into account in order to determine the importance of disease, as various combinations can interact in unpredictable ways. Here, northern leopard frog (Rana pipiens) tadpoles, a species in decline, were exposed to stressors singly or in combination. Stressors included infection by Echinostoma trivolvis (a trematode parasite), exposure to predator chemical cues (larval dragonflies), and exposure to varying concentrations of the herbicide atrazine. Parasitism decreased survival only in combination with exposure to 3 microg/L atrazine, with a negative interaction observed for mass as well. Similarly, a negative interaction of parasitism and predation on survival occurred. However, atrazine exposure alone negatively affected the survival, mass, and developmental stage of tadpoles. These results indicate that certain stressor combinations are particularly deleterious for young parasitized tadpoles. Notably, very common low-intensity parasite infection can be particularly harmful in certain situations. Such negative impacts on larval amphibians in certain scenarios may contribute to ongoing amphibian population declines, emphasizing that the combination of environmental stressors must be considered when evaluating the general role of disease in species extinctions.

Observed Reductions in Schistosoma mansoni Transmission from Large-Scale Administration of Praziquantel in Uganda: A Mathematical Modelling Study

BackgroundTo date schistosomiasis control programmes based on chemotherapy have largely aimed at controlling morbidity in treated individuals rather than at suppressing transmission. In this study, a mathematical modelling approach was used to estimate reductions in the rate of Schistosoma mansoni reinfection following annual mass drug administration (MDA) with praziquantel in Uganda over four years (2003–2006). In doing this we aim to elucidate the benefits of MDA in reducing community transmission.MethodsAge-structured models were fitted to a longitudinal cohort followed up across successive rounds of annual treatment for four years (Baseline: 2003, Treatment: 2004–2006; n = 1,764). Instead of modelling contamination, infection and immunity processes separately, these functions were combined in order to estimate a composite force of infection (FOI), i.e., the rate of parasite acquisition by hosts.ResultsMDA achieved substantial and statistically significant reductions in the FOI following one round of treatment in areas of low baseline infection intensity, and following two rounds in areas with high and medium intensities. In all areas, the FOI remained suppressed following a third round of treatment.Conclusions/SignificanceThis study represents one of the first attempts to monitor reductions in the FOI within a large-scale MDA schistosomiasis morbidity control programme in sub-Saharan Africa. The results indicate that the Schistosomiasis Control Initiative, as a model for other MDA programmes, is likely exerting a significant ancillary impact on reducing transmission within the community, and may provide health benefits to those who do not receive treatment. The results obtained will have implications for evaluating the cost-effectiveness of schistosomiasis control programmes and the design of monitoring and evaluation approaches in general.

Diagnostic Methodology is Critical for Accurately Determining the Prevalence of Ichthyophonus Infections in Wild Fish Populations

Several different techniques have been employed to detect and identify Ichthyophonus spp. in infected fish hosts; these include macroscopic observation, microscopic examination of tissue squashes, histological evaluation, in vitro culture, and molecular techniques. Examination of the peer-reviewed literature revealed that when more than 1 diagnostic method is used, they often result in significantly different results; for example, when in vitro culture was used to identify infected trout in an experimentally exposed population, 98.7% of infected trout were detected, but when standard histology was used to confirm known infected tissues from wild salmon, it detected ~50% of low-intensity infections and ~85% of high-intensity infections. Other studies on different species reported similar differences. When we examined a possible mechanism to explain the disparity between different diagnostic techniques, we observed non-random distribution of the parasite in 3-dimensionally visualized tissue sections from infected hosts, thus providing a possible explanation for the different sensitivities of commonly used diagnostic techniques. Based on experimental evidence and a review of the peer-reviewed literature, we have concluded that in vitro culture is currently the most accurate diagnostic technique for determining infection prevalence of Ichthyophonus , particularly when the exposure history of the population is not known.

Evaluation of polymerase chain reaction as an additional tool for the diagnosis of low-intensity Schistosoma mansoni infection

The aim of the present study was to evaluate polymerase chain reaction (PCR) as an alternative tool for diagnosing schistosomiasis in individuals with low-level parasite burden from areas of low endemicity or under occasional risk of infection by Schistosoma mansoni. A total of 102 samples were tested in this study using 2 PCR assays utilizing distinct primer pairs. One of the primer pairs was targeted to a highly repeated 121-base pair sequence of S. mansoni, and the other was targeted to Schistosoma 28S rDNA. The samples were divided into 4 groups according to parasite burden of the individual as follows: 16 individuals with schistosomiasis excreting less than 10 eggs per gram of feces (EPG), 18 individuals excreting higher than 10 EPG, 22 individuals with reactive IgG-ELISA against S. mansoni soluble membrane antigen and negative coproscopy, and 46 controls samples including 25 individuals with other intestinal parasites and 21 individuals with negative parasitologic examination. The results obtained with stool samples from individuals with schistosomiasis showed a high sensitivity for PCR as S. mansoni DNA was detected in 91% (31/34) of the samples analyzed. No amplification was observed in 3 stool samples from individuals excreting below 10 EPG. The specificity of the test for both pairs of primers was 100%. In the group of seropositive individuals, S. mansoni DNA was detected in 59% (13/22) of fecal samples, corroborating the serologic results. Overall, PCR can be an important tool for detecting S. mansoni infection in individuals excreting few eggs in feces. Moreover, the determination of the infection through the detection of S. mansoni DNA in stool samples from seropositive individuals represents a new means of confirming the results of IgG-ELISA for schistosomiasis. Therefore, studies in this direction should be encouraged and extended.