Thermodynamics of the adsorption of monoclonal antibodies in phenylboronate chromatography: Affinity versus multimodal interactions.

The aim of this work was to investigate the complex phenomena underlying the adsorption of an anti-human IL-8 (anti-IL8) monoclonal antibody (mAb) to m-aminophenylboronate (m-APBA) by Flow Microcalorimetry (FMC) and to understand the role of non-specific interactions in the adsorption process. FMC was exploited as a dynamic on-line method to measure instantaneous heat energy transfers in order to understand the surface phenomena underlying mAb's adsorption towards the synthetic ligand m-APBA under different pH (7.5, 8.5, 9.0, 9.5 and 10.0) and salt concentrations (0 and 150 mM NaCl). Results showed that the adsorption of anti-IL8 mAb to m-APBA is enthalpically driven (ΔHads<0), as expected for the predominant reversible esterification reaction between boronates and cis-diols-containing molecules. For all the pH conditions studied, thermograms presented a first exothermic peak, characteristic of the reversible esterification reaction between mAb (pI≥9.3) and m-APBA (pKa = 8.8), except at pH 9.0 in the presence of 150 mM NaCl, for which the thermogram presented a first endothermic peak. The heat of adsorption (ΔHads) obtained at conditions where cis-diol interactions were predominant was approximately -243 ± 38 kJ/mol against -82 ± 14 kJ/mol (p-value < 0.05) obtained at pH 9.0 with 150 mM NaCl. The observed shift in the thermogram profile at pH 9.0, 150 mM NaCl, and the consequent decrease of 60-70% in ΔHads were indicative of the promotion of electrostatic interactions between the protein and the ligand. Overall, and whereas the binding of the PBA ligand to mAb molecules has been described for decades as being affinity-based, our study demonstrates the multimodal behaviour of this interaction and contributes towards the understanding of the adsorption thermodynamics.

Value of the oxygen pulse curve for the diagnosis of coronary artery disease.

This study investigated the value of oxygen (O(2)) pulse curves obtained during cardiopulmonary exercise testing (CPET) for the diagnosis of coronary artery disease (CAD). Forty patients with known coronary anatomy (35.0 % normal, 27.0 % single-vessel and 38.0 % multivessel CAD) underwent CPET with radiotracer injection at peak exercise, followed by myocardial scintigraphy. O(2) pulse curves were classified as: A-normal, B-probably normal (normal slope with low peak value); C-probably abnormal (flat, with low peak value); or D-definitely abnormal (descending slope). Sensitivity, specificity, positive and negative predictive values of the O(2) pulse curve pattern (A or B vs. C or D) for the diagnosis of CAD were, respectively, 38.5 %, 81.3 %, 76.9 %, and 44.8 %. The concordance rate between the abnormal O(2) pulse curve pattern and ischemia in myocardial scintigraphy was 38.1 %. Age and the extent of scintigraphic perfusion defect, but not the abnormal O(2) pulse curve patterns (B or C or both combined) were independently associated with CAD. In conclusion, the O(2) pulse curve pattern has low diagnostic performance for the diagnosis of obstructive CAD, and the abnormal curve pattern was not associated with myocardial ischemia defined by scintigraphy.

Relationship between ovulation rate and embryonic characteristics in gilts at 35 d of pregnancy.

This study investigated the relationship between ovulation rate (OR) and embryonic characteristics in gilts. Landrace ( = 86) and Yorkshire x Landrace ( = 212) gilts were inseminated with semen stored for 3 to 5 d (SS1, = 59), 6 to7 d (SS2, = 133), or 8 to 10 d (SS3, = 106), and slaughtered at 35 d of pregnancy. Ovulation rate was assessed by dissection of the corpora lutea on both ovaries. Embryos were classified as vital (VE) by visual appearance and individually weighed (VEg) and the SD of the weight calculated (SDVEg). Early embryonic mortality (EM) was estimated as the difference between OR and the number of vital plus nonvital embryos. Embryonic characteristics were analyzed with a model that included linear and quadratic terms of OR and fixed class effects of semen storage duration (SS) and genetic line (GL). Landrace gilts had a higher OR than Yorkshire x Landrace gilts (22.1 ± 0.4 vs. 20.3 ± 0.2, ≤ 0.05) and also a higher EM (6.1 ± 0.4 vs. 3.5 ± 0.3, ≤ 0.05). EM was also higher in gilts inseminated with semen stored for more than 8 d. Also, Yorkshire x Landrace gilts had a higher number of VE (16.9 ± 0.7) than the Landrace gilts (13.3 ± 0.8) when inseminations were done with semen stored for up to 5 d. Yorkshire x Landrace gilts had the highest VEg when inseminated with semen stored for 3 to 5 d (SS1: 4.9 ± 0.2 g, SS2: 4.1 ± 0.1 g, and SS3: 4.0 ± 0.2 g; ≤ 0.05). VE and VEg did not differ within Landrace gilts between different SS classes. A quadratic relationship of OR ( ≤ 0.05) was found with VE: a maximum of 16.8 VE was observed at 26 ovulations [(2.5 (± 0.6)*OR- 0.05 (± 0.01)*OR]. A quadratic relationship of OR ( ≤ 0.05) was also found for EM: a minimum of 3.33 EM was observed at 15 ovulations [(-1.1 (± 0.6)*OR -0.03 (± 0.01)*OR]. VEg was not related with OR, but SDVEg had a positive linear relationship with OR [0.01 (± 0.003)*OR, ≤ 0.05]. Results show that Yorkshire x Landrace gilts perform better than Landrace when inseminated with fresh semen, but not with semen stored for longer time. Also, the VE increases with an increase in OR up to 26, but at a lower level at higher OR, which is likely related with the increase in EM. The higher EM at higher OR might arise from a higher variation in follicular/oocyte quality leading to a higher variation in embryonic quality and development, increasing mortality before uterine implantation and the variation in embryonic weight already at 35 d of pregnancy.

Validation of transrectal ultrasonography for assessment of corpora lutea characteristics in pregnant sows and its relationship with litter characteristics at birth.

In experiment 1 we investigated the accuracy of transrectal ultrasonography (TUS) to assess the number (OR) and diameter of corpora lutea (CL) in 45 and 25 sows, respectively, at 23.4 ± 2.9 d of pregnancy. The diameter was calculated as the average diameter of 10 biggest CL. Sows were subsequently slaughtered and OR was assessed by dissection of CL from both ovaries (n = 45) and average diameter of the 10 biggest CL was also calculated after measurement of CL with the caliper rule (n = 25). There was a weak relationship between OR counted after dissection of the ovaries and OR counted with TUS (ß = 0.28 ± 0.01 CL/CL, P = 0.01), but there was a strong relationship between the average CL diameter measured with the caliper rule after dissection and the average CL diameter based on TUS (ß = 1.0 ± 0.1 mm/mm, P < 0.0001). This shows that TUS is not a valid method to assess OR in pregnant sows but it is a valid method to assess average CL diameter. In experiment 2, we investigated the relationship between the average CL diameter assessed by TUS (n = 100) at 23.8 ± 2.4 d of pregnancy and average piglet birth weight (BW) and observed an increase of 37.6 ± 17.8 g in piglet BW per mm increase in average CL diameter measured by TUS (P = 0.04). This relationship is probably because larger CL develop from bigger follicles at ovulation, which might have ovulated oocytes of higher quality that developed into embryos with higher growth potential and thus higher birth weight.

Extracellular matrix microarrays to study inductive signaling for endoderm specification.

During tissue development, stem and progenitor cells are faced with fate decisions coordinated by microenvironmental cues. Although insights have been gained from in vitro and in vivo studies, the role of the microenvironment remains poorly understood due to the inability to systematically explore combinations of stimuli at a large scale. To overcome such restrictions, we implemented an extracellular matrix (ECM) array platform that facilitates the study of 741 distinct combinations of 38 different ECM components in a systematic, unbiased and high-throughput manner. Using embryonic stem cells as a model system, we derived definitive endoderm progenitors and applied them to the array platform to study the influence of ECM, including the interactions of ECM with growth factor signaling, on the specification of definitive endoderm cells towards the liver and pancreas fates. We identified ECM combinations that influence endoderm fate decisions towards these lineages, and demonstrated the utility of this platform for studying ECM-mediated modifications to signal activation during liver specification. In particular, defined combinations of fibronectin and laminin isoforms, as well as combinations of distinct collagen subtypes, were shown to influence SMAD pathway activation and the degree of hepatic differentiation. Overall, our systematic high-throughput approach suggests that ECM components of the microenvironment have modulatory effects on endoderm differentiation, including effects on lineage fate choice and cell adhesion and survival during the differentiation process. This platform represents a robust tool for analyzing effects of ECM composition towards the continued improvement of stem cell differentiation protocols and further elucidation of tissue development processes. STATEMENT OF SIGNIFICANCE: Cellular microarrays can provide the capability to perform high-throughput investigations into the role of microenvironmental signals in a variety of cell functions. This study demonstrates the utility of a high-throughput cellular microarray approach for analyzing the effects of extracellular matrix (ECM) in liver and pancreas differentiation of endoderm progenitor cells. Despite an appreciation that ECM is likely involved in these processes, the influence of ECM, particularly combinations of matrix proteins, had not been systematically explored. In addition to the identification of relevant ECM compositions, this study illustrates the capability of the cellular microarray platform to be integrated with a diverse range of cell fate measurements, which could be broadly applied towards the investigation of cell fate regulation in other tissue development and disease contexts.

Relationships between ovulation rate and embryonic and placental characteristics in multiparous sows at 35 days of pregnancy.

The objective of this study was to investigate relationships between ovulation rate (OR) and embryonic and placental development in sows. Topigs Norsvin® sows (n=91, parity 2 to 17) from three different genetic backgrounds were slaughtered at 35 days of pregnancy and the reproductive tract was collected. The corpora lutea (CL) were counted and the number of vital and non-vital embryos, embryonic spacing (distance between two embryos), implantation length, placental length, placental weight and embryonic weight were assessed. The difference between number of CL and total number of embryos was considered as early embryonic mortality. The number of non-vital embryos was considered as late mortality. Relationships between OR and all other variables were investigated using two models: the first considered parity as class effect (n=91) and the second used a subset of sows with parities 4 to 10 (n=47) to analyse the genetic background as class effect. OR was significantly affected by parity (P<0.0001), but was not affected by the genetic background of the sows. Parity and genetic background did not affect embryonic and placental characteristics at 35 days of pregnancy. OR (varying from 17 to 38 CL) was positively related with early embryonic mortality (ß=0.49±0.1 n/ovulations, P<0.0001), with late embryonic mortality or number of non-vital embryos (ß=0.24±0.1 n/ovulations, P=0.001) and with the number of vital embryos (ß=0.26±0.1 n/ovulations, P=0.01). However, dividing OR in four classes, showed that the number of vital embryos was lowest in OR class 1 (17 to 21 CL), but not different for the other OR classes, suggesting a plateau for number of vital embryos for OR above 22. There was a negative linear relationship between OR and vital embryonic spacing (ß=-0.45±0.1 cm/ovulation, P=0.001), implantation length (ß=-0.35±0.1 cm/ovulation, P=0.003), placental length (ß=-0.38±0.2 cm/ovulation, P=0.05) and empty space around embryonic-placental unit (ß=-0.4±0.2 cm/ovulation, P=0.02), indicating uterine crowding. Further analyses showed that effects of OR on embryonic and uterine parameters were related with the increase in late mortality and not early embryonic mortality. Therefore, we conclude that a high OR results in an moderate increase in the number of vital embryos at day 35 of pregnancy, but compromises development in the surviving embryonic/placental units, suggesting that the future growth and survival of the embryos might be further compromised.

A Dual Role for P2X7 Receptor during Porphyromonas gingivalis Infection.

Emerging evidence suggests a role for purinergic signaling in the activation of multiprotein intracellular complexes called inflammasomes, which control the release of potent inflammatory cytokines, such as interleukin (IL) -1ß and -18. Porphyromonas gingivalis is intimately associated with periodontitis and is currently considered one of the pathogens that can subvert the immune system by limiting the activation of the NLRP3 inflammasome. We recently showed that P. gingivalis can dampen eATP-induced IL-1ß secretion by means of its fimbriae in a purinergic P2X7 receptor-dependent manner. Here, we further explore the role of this purinergic receptor during eATP-induced IL-1ß processing and secretion by P. gingivalis-infected macrophages. We found that NLRP3 was necessary for eATP-induced IL-1ß secretion as well as for caspase 1 activation irrespective of P. gingivalis fimbriae. Additionally, although the secretion of IL-1ß from P. gingivalis-infected macrophages was dependent on NLRP3, its adaptor protein ASC, or caspase 1, the cleavage of intracellular pro-IL-1ß to the mature form was found to occur independently of NLRP3, its adaptor protein ASC, or caspase 1. Our in vitro findings revealed that P2X7 receptor has a dual role, being critical not only for eATP-induced IL-1ß secretion but also for intracellular pro-IL-1ß processing. These results were relevant in vivo since P2X7 receptor expression was upregulated in a P. gingivalis oral infection model, and reduced IFN-γ and IL-17 were detected in draining lymph node cells from P2rx7(-/-) mice. Furthermore, we demonstrated that P2X7 receptor and NLRP3 transcription were modulated in human chronic periodontitis. Overall, we conclude that the P2X7 receptor has a role in periodontal immunopathogenesis and suggest that targeting of the P2X7/NLRP3 pathway should be considered in future therapeutic interventions in periodontitis.

Magnetoresistive chip cytometer.

Although conventional state-of-the-art flow cytometry systems provide rapid and reliable analytical capacities, they are bulky, expensive and complex. To overcome these drawbacks modern flow cytometers have been developed with enhanced portability for on-site measurements. Unlike external fluorescent/optical detectors, magnetoresistive sensors are micro-fabricated, can be integrated within microfluidic channels, and can detect magnetically labelled cells. This work describes the real-time detection of single magnetically labelled cells with a magnetoresistive based cell cytometer. For Kg1-a cells magnetically labelled with 50 nm CD34 microbeads (Milteny) flowing through a 150 µm wide, 14 µm high microchannel, with speeds around 1 cm s(-1), bipolar signals with an average amplitude of 10-20 µV were observed corresponding to cell events. The number of cells counted by the spin valve cytometer has been compared with that obtained with a hemocytometer. Both methods agree within the respective error bars.

Nonviral gene delivery to mesenchymal stem cells using cationic liposomes for gene and cell therapy.

Mesenchymal stem cells (MSCs) hold a great promise for application in several therapies due to their unique biological characteristics. In order to harness their full potential in cell-or gene-based therapies it might be advantageous to enhance some of their features through gene delivery strategies. Accordingly, we are interested in developing an efficient and safe methodology to genetically engineer human bone marrow MSC (BM MSC), enhancing their therapeutic efficacy in Regenerative Medicine. The plasmid DNA delivery was optimized using a cationic liposome-based reagent. Transfection efficiencies ranged from approximately 2% to approximately 35%, resulting from using a Lipid/DNA ratio of 1.25 with a transgene expression of 7 days. Importantly, the number of plasmid copies in different cell passages was quantified for the first time and approximately 20,000 plasmid copies/cell were obtained independently of cell passage. As transfected MSC have shown high viabilities (>90%) and recoveries (>52%) while maintaining their multipotency, this might be an advantageous transfection strategy when the goal is to express a therapeutic gene in a safe and transient way.

A quantitative method to evaluate mesenchymal stem cell lipofection using real-time PCR.

Genetic modification of human mesenchymal stem cells (MSC) is a powerful tool to improve the therapeutic utility of these cells and to increase the knowledge on their regulation mechanisms. In this context, strong efforts have been made recently to develop efficient nonviral gene delivery systems. Although several studies addressed this question most of them use the end product of a reporter gene instead of the DNA uptake quantification to test the transfection efficiency. In this study, we established a method based on quantitative real-time PCR (RT-PCR) to determine the intracellular plasmid DNA copy number in human MSC after lipofection. The procedure requires neither specific cell lysis nor DNA purification. The influence of cell number on the RT-PCR sensitivity was evaluated. The method showed good reproducibility, high sensitivity, and a wide linear range of 75-2.5 x 106 plasmid DNA copies per cell. RT-PCR results were then compared with the percentage of transfected cells assessed by flow cytometry analysis, which showed that flow cytometry-based results are not always proportional to plasmid cellular uptake determined by RT-PCR. This work contributed for the establishment of a rapid quantitative assay to determine intracellular plasmid DNA in stem cells, which will be extremely beneficial for the optimization of gene delivery strategies.

Birth weight variation according to maternal characteristics and gestational weight gain in Brazilian women.

OBJECTIVES: This study aims to identify birth weight variation according to maternal characteristics and gestational weight gain. METHODS: It is a cross-sectional descriptive study with 433 puerperal women (> or = 20 years old) who attended a public maternity hospital in Rio de Janeiro. The data were collected through interviews with the women and access to their medical records. Several models were tested using linear regression, using the stepwise method to identify the predictive variables of birth weight. RESULTS: The mean maternal age and gestational age at the end of pregnancy were 27 years old (+/- 5.09 years) and 39 weeks (+ 1.68 weeks), respectively. The data shows that the mean number of prenatal and nutritional prenatal care appointments were 8.24 (+/- 2.98) and 2.26 (+/- 2.33), respectively. Among the predictor variables of birth weight, total gestational weight gain (beta = 25.29; p = 0.000), pre-gestational BMI (beta =13.02; p = 0.037), and the number of pre-natal care appointments (beta = 28.21; p = 0.007) were highlighted. The association of weight gain in the three trimesters was also verified. CONCLUSIONS: This study confirms the interface between adequacy of the pre-gestational and gestational nutritional status and some maternal characteristics with birth weight. Nutritional care should be recognised as part of the actions during pre-natal assistance.

The molluscicidal activity of the latex of Euphorbia splendens var. hislopii on Melanoides tuberculata (Thiaridae), a snail associated with habitats of Biomphalaria glabrata (Planorbidae).

The use of the latex of Euphorbia splendens var. hislopii was considered as an effective control method for Biomphalaria glabrata in Sumidouro, Rio de Janeiro. However, the appearance and expansion of the snail Melanoides tuberculata since August 1997, with the concomitant reduction of the population of B. glabrata suggest that competitive exclusion might be taking place. Depending on the susceptibility of the thiarid to the E. splendens toxin, the natural control that is occurring could be interrupted by the employment of the latex if the planorbid were less susceptible to the toxin. The aim of this study is to investigate the molluscicidal activity of the latex on M. tuberculata. We used 420 M. tuberculata, from Sumidouro. Fourteen different latex concentrations were tested using World Health Organization general methodology. Probit analysis was used for LD90 and LD50 determination. The LD50 was 3.57 mg/l and LD90 was 6.22 mg/l. At the highest concentration (10 mg/l) there was no survival. No significant differences among replicas (chi2 = 8.31; gl = 13; p > 0.05) were found. The LD90 dose for M. tuberculata was 13.8 times greater than that for B. glabrata, so that the molluscicide in the presence of the thiarid may have a synergic effect on reduction of Biomphalaria populations.

Cluster of Candida parapsilosis primary bloodstream infection in a neonatal intensive care unit.

Candida parapsilosis is an increasingly important bloodstream pathogen in neonatal intensive care units (NICU). We investigated a cluster of bloodstream infections in a NICU to determine whether nosocomial transmission occurred. During a 3-day period, 3 premature infants hospitalized in the same unit presented with sepsis caused by C. parapsilosis. Electrophoretic karyotype of the organisms was performed by using pulsed field gel electrophoresis in a countour-clamped homogeneous electric field system. The isolate from 1 newborn could not be typed, and the isolates from the remaining 2 infants had identical patterns. All 3 cases are described. We conclude that nosocomial transmission of C. parapsilosis occurred and that neonates under intensive care may represent a risk group for this pathogen.

Determination of Cu, Pb, Cd, and Zn in river sediment extracts by sequential injection anodic stripping voltammetry with thin mercury film electrode.

Determination of Cu, Pb, Cd and Zn was performed in sediment extracts obtained according to the three steps sequential extraction procedure proposed by the European Community Standards, Measurements and Testing Program. The metal content was determined by anodic stripping voltammetry with a thin mercury film electrode controlled by a sequential injection (SIA) system. The proposed method improved the reproducibility of conventional anodic stripping voltammetry, as well as the sample throughput, allowing analysis of 30 to 45 samples per hour. The influence of flow rate and sample volume was studied to achieve an adequate sensitivity for the leachate studied. No interferences due to adsorption of organic matter, colloids, or complexes with slow rate of dissociation were observed. The intermetallic formation of Cu-Zn was avoided by forming the mercury film in presence of Ga(III) ions in the SIA system, resulting in low consumption of reagent in comparison to flow injection or continuous flow systems. Results were in good agreement with those obtained by Induced Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES).

[Nongovernmental organizations and AIDS, social intervention, and new ties in social solidarity]. / ONGs/Aids, intervenções sociais e novos laços de solidariedade social.

Starting with a brief contextual analysis of the social scenario in which the AIDS epidemic is occurring in Brazil, the article focuses on the formation of the country's first nongovernmental organizations in the struggle against AIDS. There are peculiarities to AIDS NGOs to the extent that they display an ambivalence between the characteristics of a professional institution and a lobbying group, apart from the fact that dealing with sexuality and death breaks down the line between the public and the private spheres. The case in point is the Grupo Pela Vidda (For Life Group) in Rio de Janeiro, which seeks to represent the enhancement of a group of individuals and the principle of universality. The study supports the hypothesis that AIDS NGOs renew ties of social solidarity through the relationships established between various researchers involved in this sector and other NGOs with governmental spheres.

[Neuro-AIDS]. / Neurosida.

The human immunodeficiency virus (HIV) type 1 is the retrovirus which is responsible for the human immunodeficiency syndrome (AIDS) described in infancy in 1983. It is the most serious disorder caused by HIV, by a neurotropic virus, and is particularly severe in infancy. In children infected by vertical transmission of HIV, there is a shorter clinical latent period than in adults, and more viraemia than in children over the age of three months infected by blood transfusion. The neurological disorder caused by HIV is a complex clinical syndrome in which there may be varying degrees of retardation of cognition, movement or behaviour. A growing number of HIV+ children are being followed-up in the Hospital de Clinicas de Porto Alegre (HCPA) to treat the neuropsychomotor development and the presence of neurological behaviour in these children. The neurological, analytical (laboratory), electro-encephalographic and tomographic changes seen in a sample of 344 HIV+ children were studied. Analysis of these results showed a significant difference between affected and non-affected children. Encephalopathy occurred in 36% of the cases, being progressive in 29% and static in 17%. There was a relationship between neurological involvement at the first consultation and progress to encephalopathy. The RDNPM showed a tendency towards encephalopathy, usually between 1 and 5 years of age, which might also be the first sign of the disease. We found a significant relationship between being infected and having alterations not seen in cerebrospinal fluid, EEG, TCC and neurological progress.

The use of glucan as immunostimulant in the treatment of paracoccidioidomycosis.

A group of 10 patients, nine of them seriously infected with Paracoccidioides brasiliensis (G1), received glucan (beta-1,3 polyglucose) as an immunostimulant intravenously once a week for one month, followed by monthly doses (10 mg) over an 11-month period, together with a specific anti-fungal agent as an immunostimulant. A second group of eight moderately infected patients (G2) was treated with only the anti-fungal agent. Among the patients in G1, there was only one case of relapse compared with five in G2. Values for the erythrocyte sedimentation rate (ESR) showed a significant difference (P < 0.001) post-treatment in G1 patients, when compared with the pretreatment levels. There was also a significant reduction (P < 0.001) in the level of serum antibodies to P. brasiliensis in the G1 patients in post-treatment examinations. The phytohemagglutinin (PHA) skin test showed a positive reaction among the patients in G1 (P < 0.01) post-treatment and there was a tendency towards an increase in the number of CD4+ T lymphocytes in both groups after treatment. The serum level of tumor necrosis factor (TNF) proved to be significantly higher (P < 0.02) in the G1 patients during treatment. In the G1 patients, the correlation between ESR and TNF tended to be negative whereas that between ESR and serum antibodies was positive. The present results indicate that the patients who received glucan, in spite of being more seriously ill, had a stronger and more favorable response to therapy.

Schistosomiasis in a low prevalence area: incomplete urbanization increasing risk of infection in Paracambi, RJ, Brazil.

The risk of schistosomiasis infection and heavy infection in the locality of Sabugo was evaluated in relation to housing in areas with different urbanization development and to residential supply with snail-infested water. Critical sanitary conditions were found in areas of incomplete urbanization, where healthy water supply sources were scarce, and draining of sewage, without previous treatment, was made directly to the water-bodies used for domestic and leisure activities, despite being Biomphalaria tenagophila snail breeding-places. Stool examinations (Kato-Katz and Lutz methods) showed prevalence of 2.9% mean intensity of 79 eggs per gram of stool and 47% of positive cases presenting intense infection. The use of snail-contaminated water for domestic purposes was considered a risk factor for infection. It is concluded that incomplete urbanization would facilitate transmission, probably enhancing the intensity of infection and that a low prevalence could hide a highly focal transmission. The relevance of these facts upon the efficiency of epidemiologic study methods and disease control planning are then discussed.