Concomitant ectopic Enterobius vermicularis infection in uterine cervical cancer.

BACKGROUND: Enterobius vermicularis (E. vermicularis), also referred to as pinworm, is a widespread human intestinal parasite which predominantly occurs in young children, making their caretakers a population at risk for the transmission of this helminth. It can occasionally affect extraintestinal organs and tissues, including the female genital tract. Infestation can be asymptomatic or manifest as different kinds of gynaecological disorders, such as pelvic inflammation mimicking tumours, abnormal uterine bleeding, or vaginitis. Diagnosis is made by identifying ova in the sample collected from the perineal skin using a transparent adhesive tape or microscopic examination of resected tissue. Mebendazole is the first-line medication and should also be administered to all household members. CASE PRESENTATION: We present a case of a patient who had undergone surgery for invasive cervical cancer with an accidental finding of E. vermicularis eggs in the cervix. CONCLUSIONS: Although not very common, infestation with E. vermicularis should be considered in differential diagnoses of various gynaecological disorders accompanied by histological findings of granulomatous inflammation.

Cockroaches as carriers of human medically important parasites.

Cockroaches have been identified as mechanical carriers of pathogens capable of infesting humans. The primary objective of this research was to detect and separate medically significant parasites found within the collected cockroaches. A total of 185 cockroaches were captured. In the laboratory, cockroaches underwent a series of steps. Initially, they were washed in a saturated salt solution and rinsed with 70% alcohol, dried, and subsequently dissected to examine endoparasites. In this study, a transport rate of 29.729% was documented, and four types of helminths were identified, which included Ascaris lumbricoides (47.27%), Enterobius vermicularis (30.91%), Trichuris spp. (7.27%), and Hymenolepis nana (14.55%). The parasites were more frequently found on the external surface of cockroaches (38/69.09%), compared to the internal surface (17/30.91%). Cockroaches captured in toilets were found to carry a higher percentage of parasites (31/16.75%) compared to those from kitchens (11/5.94%) and houses (13/7.02%). These findings suggest that cockroaches can serve as carriers for intestinal parasites and potentially act as mechanical agents in the dissemination of these parasites.

Pinworm Blatticola blattae infection and survival of starving German cockroach Blattella germanica.

The German cockroach Blattella germanica is commonly infected with the pinworm Blatticola blattae. To determine the effect of pinworm infection on cockroach survival, we artificially altered the pinworm infection status of cockroaches and determined the number of survival days under no-feeding conditions, with and without opportunities for fecal feeding. Four lines of the German cockroach (Wn, Wp, Nn, and Np groups) were used in the experiment. Wp and Np were pinworm-infected lines. Wn and Nn were pinworm-free lines. The 50% survival days of cockroaches in the absence of opportunities for fecal feeding were not significantly different in Wp (3.45 days) vs Wn (3.27), and in Np (4.60) vs Nn (4.48). In contrast, in the presence of fecal feeding, the 50% survival times for the pinworm-infected Wp (4.04) and Np (6.65) were significantly longer than those for the pinworm-free Wn (2.77) and Nn (5.46). The number of survival days without feeding was significantly higher in the pinworm-infected group given the opportunity to eat feces than in the non-infected group. These results suggest that pinworm infection of cockroaches during starvation, in association with fecal feeding, may be associated with longer survival.

Redescription of three pinworms of the genus Cephalobellus Cobb, 1920 (Nematoda: Oxyuridomorpha: Thelastomatidae) from scarab beetle grubs from Hungary.

Larvae of European rose chafer Cetonia aurata (Linnaeus, 1758) and cockchafer Melolontha sp. beetles were collected in Hungary for parasitological study. Intestinal examination revealed the presence of three well-known thelastomatid nematodes belonging to the genus Cephalobellus Cobb, 1920. We report for the first-time Cephalobellus cuspidatum (Rudolphi, 1814) Leibersperger, 1960, C. osmodermae Leibersperger, 1960, and C. potosiae Leibersperger, 1960 in Hungary, all found in scarab beetle larvae. Due to incomplete original descriptions, a comprehensive redescription with detailed morphological data is presented. Additionally, an identification key for closely related Cephalobellus, Thelastoma and Severianoia species infesting scarab beetles worldwide is provided. Newly generated 18S and 28S rDNA gene sequences of C. osmodermae place it as one of the early branches within Thelastomatidae.

Eosinophilia and potential antibody cross-reactivity between parasites in a child with pinworm and immune dysregulation: a case report.

BACKGROUND: Intestinal parasitic infections are common in humans, especially among young children. These conditions are often asymptomatic and self-limiting, and diagnosis is mainly based on the search for ova and parasites in the stools since serology may be biased due to cross reactivity between parasites. Pinworm is common in children and is not usually associated with hypereosinophilia; adhesive-tape test is the gold standard testing for the microscopic detection of Enterobious vermicularis (Ev) eggs. CASE PRESENTATION: A 13-year-old boy was referred due to a self-resolving episode of vomiting and palpebral oedema after dinner, together with a history of chronic rhinitis, chronic cough, absolute IgA deficiency and Hashimoto's thyroiditis and hypereosinophilia (higher value = 3140/µl). On evaluation we detected only palpable thyroid and hypertrophic nasal turbinates. Food allergy was excluded, but skin prick tests showed sensitization to house dust mites and cat epithelium and spirometry showed a marked obstructive pattern with positive bronchodilation test prompting the diagnosis of asthma for which maintenance inhaled treatment was started. Chest x-ray and abdomen ultrasound were negative. Further blood testing showed positive IgG anti-Echinococcus spp. and Strongyloides stercoralis and positive IgE for Ascaris, while Ev were detected both by the adhesive tape test and stool examination, so that we made a final diagnosis of pinworm infection. Three months after adequate treatment with pyrantel pamoate the adhesive-tape test turned out negative and blood testing showed a normal eosinophil count. The child later developed also type 1 diabetes. CONCLUSIONS: We suggest the need to investigate for enterobiasis in children with hypereosinophilia and to consider autoimmunity as a potential confounding factor when interpreting serology for helminths.

Molecular data aids pinworm diagnosis in night monkeys (Aotus spp., Primates: Aotidae) with the resurrection of a Trypanoxyuris species (Nematoda: Oxyuridae).

Neotropical primates (Platyrrhines) are commonly parasitized by pinworm nematodes of the genus Trypanoxyuris Vevers, 1923. The taxonomic identity of Trypanoxyuris sampled in night monkeys (Aotus Iliger) has been rather controversial. Two species have been described, namely T. microon (Linstow, 1907) and T. interlabiata (Sandosham, 1950). The latter was synonymized with T. microon considering that the observed morphological differences corresponded to different developmental stages of the nematode rather than to differences between both species. Here, we used an integrative taxonomy approach, based on morphological and molecular data along with host identity, in order to assess the validity of both species. Our results evidenced that these different morphotypes correspond to different and reciprocally monophyletic groups; thus, we propose the resurrection of T. interlabiata. We redescribe both pinworm species using specimens sampled in Aotus monkeys from Colombia and discuss the advantages of combining molecular and morphological data to uncover pinworm diversity, and to understand the potential forces determining the diversification process in pinworms from platyrrhine primates.

Knowledge and Practice of Pinworm Infection in Preschool Children, Jiangsu Province, China, 2019-2020.

We conducted a two-year (2019-2020) longitudinal study in Jiangsu Province, China to analyze risk factors of pinworm infection and evaluate the effect of behavior change communication-based (BCC-based) interventions in preschool children. The positive rate of pinworm infection was higher in private preschool (2%) than in public preschool (0.24%). Poor sanitation behaviors were risk factors among private preschool children. BCC-based intervention could improve knowledge and practice and reduce pinworm infection. This study may help fill in gaps in pinworm control. (Am J Public Health. 2022;112(12):1716-1720. https://doi.org/10.2105/AJPH.2022.307067).

Enterobiasis and its risk factors in urban, rural and indigenous children of subtropical Argentina.

A cross-sectional survey to assess the prevalence of Enterobius vermicularis infection and its associated factors among the child population of infant, preschool and school age in the urban, rural and indigenous population of Iguazú city, in subtropical Argentina was presented. Additionally, the status of enterobiasis at country level was reviewed and analysed. Enterobius vermicularis presence was assessed employing an oviscopic serial sampling technique. Statistical analysis of socio-demographic determinants was performed by generalized linear mixed models at individual, household and community levels. Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines were used to gather national information about E. vermicularis prevalence spanning the decade 2010­2020. A total of 916 children from 470 families participated. Overall prevalence was 29.8%, with 25.3, 30.7 and 34.2% detected for children inhabiting urban, rural and indigenous villages, respectively. The multi-level analysis showed that the presence of E. vermicularis was mostly determined by individual (e.g. age, playing habits, previous pinworm infection) and household-level factors (e.g. family size, overcrowding conditions). Interestingly, WASH variables, such as waste disposal, analysed at community level were also important. Data were analysed to provide eco-epidemiological features of enterobiasis in a heterogeneous subtropical child population in the same territory but with different socio-sanitary realities. The importance of promoting multi-level actions against the determinants identified, to control this public health problem integratively was evidenced. The scoping review of national data updated the state of knowledge of this parasitosis, identifying risk determinants and gaps in knowledge at country level.

Is pinworm infection still a public health concern among children in resource-rich regions? Trends in pinworm infection prevalence and associated factors among children in Hualien County, Taiwan: a retrospective cross-sectional study.

BACKGROUND: Enterobius vermicularis (pinworm) is a common intestinal parasitic infection in children. A gradual decrease in the prevalence of pinworm infection has been noted in resource-rich settings, such as Taiwan. However, the influence of sociodemographic factors on the temporal trend in pinworm infection rates in children under the current pinworm infection prevention policy in Taiwan is not well characterized. This study aimed to evaluate the trend of pinworm infection prevalence and the associated factors among children in Hualien County, Taiwan. METHODOLOGY: In this retrospective cross-sectional study, we included a total of 56,197 students (aged 6-10 years) in grades 1 and 4 in Hualien in 2009-2018. Children were screened for pinworm infection using adhesive cellophane perianal swabs in the routine student health examination. Logistic regression was conducted to evaluate the factors associated with pinworm infection. Associations between dependent and independent variables were measured by odds ratios. The Cochran-Armitage test was used to assess whether there were significant trends in different stratifications. Variables with P-values < 0.05 were considered statistically significant. RESULTS: A total of 56,197 school-age children from grades 1 and 4 during 2009-2018 were included. Young age and male sex were risk factors for pinworm infection (P < 0.001). A negative correlation between body mass index and enterobiasis was observed, and decreased pinworm infection was noted during the study reference period. Children living in suburban and rural areas had higher odds of having a pinworm infection than those living in urban areas (P < 0.001). A significant decrease in the overall prevalence rate of pinworm infection was observed among children in 2009-2018 (P < 0.001). However, there was no obvious change in the pinworm infection rate in rural areas during this period (P = 0.953), and it was higher than that in urban and suburban areas. CONCLUSIONS: The overall prevalence of pinworm infection gradually decreased from 2009 to 2018 among school-age children in Hualien. However, there was no declining trend in pinworm infection in rural areas. Young age, male sex, and rural residence were significantly associated with pinworm infection. Pinworm infection remains a major public health concern among children in rural areas of Hualien.

Prevalence and genetic analysis of Enterobius vermicularis in schoolchildren in lower northern Thailand.

Enterobius vermicularis, a nematode parasite with a global distribution causes enterobiasis in schoolchildren and is considered a neglected parasite. An understanding of the prevalence and genetic diversity of enterobiasis is crucial for appropriate control measures. Therefore, the objectives of this research were to study the prevalence and genetic diversity of E. vermicularis in schoolchildren from lower northern Thailand, based on cytochrome c oxidase subunit I (COI) and internal transcribed spacer 2 (ITS2) sequences. Using the scotch tape technique, 7.4% (188/2544) of schoolchildren from 21 primary schools were found positive for E. vermicularis eggs, which is a relatively low infection rate. Phylogenetic trees of partial COI sequences (397 bp) revealed similar topologies using maximum likelihood (ML) and neighbor-joining (NJ) methods and identified E. vermicularis type A (105 sequences) and B (1 sequence). Haplotype network analysis of the COI sequences demonstrated a high haplotype diversity (Hd = 0.9028). In contrast, phylogenetic analysts of a 343 bp region of the ITS2 locus (52 sequences) revealed a monophyletic group. More sequence analyses of E. vermicularis from humans and other hosts in Thailand are necessary to better understand the genetic diversity of this parasite.

The relationship between pinworm (Trypanoxyuris) infection and gut bacteria in wild black howler monkeys (Alouatta pigra).

Gut bacteria may coexist with other groups of organisms, such as nematode parasites, that inhabit the gastrointestinal tract of primates; however, the possible effects of endoparasites on bacterial communities are frequently overlooked. Here we explored whether infection with Trypanoxyuris, an oxyurid gastrointestinal parasite, is associated with changes in the gut bacterial community of wild black howler monkeys (Alouatta pigra), by comparing gut bacterial communities of consistently infected individuals and individuals that never tested positive for Trypanoxyuris throughout different months across the year. We additionally controlled for other sources of variation reported to influence the primate microbiome including individual identity, social group, and seasonality. Trypanoxyuris infection was not related to differences in gut bacterial alpha diversity, but was weakly associated with differences in gut bacterial community structure. In contrast, among the covariates considered, both individual identity and social group were more strongly associated with variation in the howler gut bacterial community. Our results suggest that gastrointestinal parasites may be associated, to some extent, with shifts in the gut bacterial communities hosted by free-ranging primates, although a causal link still needs to be established. Further studies of wild primate hosts infected with parasite species with different pathogenicity are needed to better elucidate health-related consequences from the parasite-microbiome interplay.

Changes in Light Energy Utilization in Photosystem II and Reactive Oxygen Species Generation in Potato Leaves by the Pinworm Tuta absoluta.

We evaluated photosystem II (PSII) functionality in potato plants (Solanum tuberosum L.) before and after a 15 min feeding by the leaf miner Tuta absoluta using chlorophyll a fluorescence imaging analysis combined with reactive oxygen species (ROS) detection. Fifteen minutes after feeding, we observed at the feeding zone and at the whole leaf a decrease in the effective quantum yield of photosystem II (PSII) photochemistry (ΦPSII). While at the feeding zone the quantum yield of regulated non-photochemical energy loss in PSII (ΦNPQ) did not change, at the whole leaf level there was a significant increase. As a result, at the feeding zone a significant increase in the quantum yield of non-regulated energy loss in PSII (ΦNO) occurred, but there was no change at the whole leaf level compared to that before feeding, indicating no change in singlet oxygen (1O2) formation. The decreased ΦPSII after feeding was due to a decreased fraction of open reaction centers (qp), since the efficiency of open PSII reaction centers to utilize the light energy (Fv'/Fm') did not differ before and after feeding. The decreased fraction of open reaction centers resulted in increased excess excitation energy (EXC) at the feeding zone and at the whole leaf level, while hydrogen peroxide (H2O2) production was detected only at the feeding zone. Although the whole leaf PSII efficiency decreased compared to that before feeding, the maximum efficiency of PSII photochemistry (Fv/Fm), and the efficiency of the water-splitting complex on the donor side of PSII (Fv/Fo), did not differ to that before feeding, thus they cannot be considered as sensitive parameters to monitor biotic stress effects. Chlorophyll fluorescence imaging analysis proved to be a good indicator to monitor even short-term impacts of insect herbivory on photosynthetic function, and among the studied parameters, the reduction status of the plastoquinone pool (qp) was the most sensitive and suitable indicator to probe photosynthetic function under biotic stress.

Enterobius vermicularis Infection among Preschool Children: A 12-Year (2008-2019) Survey in Large Cities and Provinces of the Republic of Korea.

A 12-year nationwide survey (2008-2019) was performed to investigate the prevalence of Enterobius vermicularis infection among preschool children in Seoul, 4 large cites (Busan, Incheon, Daegu, and Ulsan), and 9 provinces (grouped into 5 localities) in the Republic of Korea (=Korea). The survey was carried out once a year by 16 regional offices of the Korea Association of Health Promotion. The cello-tape perianal swab method (1 smear per child) was applied to detect eggs of E. vermicularis and other helminths. According to the results, the egg positive rate of E. vermicularis infection in 2008-2009 was 1.8-2.0%, but it decreased gradually to 0.6% in 2019 (P<0.05). The prevalence was significantly higher in boys (0.7-5.0%, mean 1.8%) than in girls (0.5-2.8%, mean 1.3%) (P<0.05). The 2 most southern localities, Jejudo (Province) and Jeolla-do (inclusive of Jeollabuk-do and Jeollanam-do) and a mid-western province, Gyeonggi-do, revealed higher prevalences, whereas Seoul and Gangwon-do showed lower prevalences. The results indicate that a low-grade prevalence of E. vermicularis infection (less than 4%) has been maintained for the recent 12 years among preschool children in Korea. Continuous monitoring of enterobiasis in the child age group is necessary in Korea.

Impact of Enterobius vermicularis infection on biochemical parameters in the blood of children in Erbil Province, Iraq.

BACKGROUND: Enterobius vermicularis is an intestinal helminthic parasite that causes a gastrointestinal infection called enterobiasis. Children are more susceptible to infection than adults. The current study aimed to explore the prevalence of E. vermicularis infection among children in Erbil City concerning demographic factors and certain blood parameters. METHODS: A cross-sectional and analytical study was conducted on 505 children (3-10 years). Cellophane tape samples and blood samples were taken from participants. The cellophane tape samples were examined microscopically, whereas blood samples were examined using the auto-analyzer and Cobas. RESULTS: The overall prevalence of E. vermicularis infection was 27.13%, and the infection rate was non-significantly (P = 0.371) higher in females (28.85%) than in males (25.31%). The incidence of enterobiasis was directly proportional to family size. This study demonstrated that the mean serum total protein and iron levels were significantly decreased in infected children, while other trace element levels were not significantly affected. CONCLUSIONS: The prevalence of E. vermicularis is relatively lower than that in previous studies. Serum total protein and iron levels significantly decreased in the enterobiasis-positive group.

Effects of anthelmintics on the pinworm Blatticola blattae in laboratory-reared German cockroaches Blattella germanica.

The efficacy of pyrantel pamoate, pyrvinium pamoate, ivermectin, and piperazine citrate against pinworm in cockroach was evaluated. Laboratory-reared German cockroaches naturally infected with Blatticola blattae were treated with the anthelmintics and necropsied at 3 to 35 days after treatment. Ivermectin at over 5 ppm and piperazine citrate at over 2000 ppm killed all the treated cockroaches. Pinworms were still detected in cockroaches given lower concentration of the aforementioned drugs. Administration of pyrantel pamoate (100-1000 ppm) and pyrvinium pamoate (2000 ppm) did not kill the cockroaches, and no pinworms were detected at 3 and 17 days after treatment. Thus, pyrantel pamoate and pyrvinium pamoate were found to be effective for deworming B. blattae in the German cockroaches, without causing mortality for the host. Our results showed that anthelmintics selection is essential for eradication of pinworms in cockroaches because of the toxicity for the host such as ivermectin or piperazine citrate. This is the first report of piperazine citrate toxicity in cockroaches.

Cluster of Parasite Infections by the Spatial Scan Analysis in Korea.

This study was performed to find out the clusters with high parasite infection risk to discuss the geographical pattern. Clusters were detected using SatScan software, which is a statistical spatial scan program using Kulldorff's scan statistic. Information on the parasitic infection cases in Korea 2011-2019 were collected from the Korea Centers for Disease Control and Prevention. Clusters of Ascaris lumbricoides infection were detected in Jeollabuk-do, and T. trichiura in Ulsan, Busan, and Gyeongsangnam-do. C. sinensis clusters were detected in Ulsan, Daegu, Busan, Gyeongsangnam-do, and Gyeongsangbuk-do. Clusters of intestinal trematodes were detected in Ulsan, Busan, and Gyeongsangnam-do. P. westermani cluster was found in Jeollabuk-do. E. vermicularis clusters were distributed in Gangwon-do, Jeju-do, Daegu, Daejeon, and Gwangju. This clustering information can be referred for surveillance and control on the parasitic infection outbreak in the infection-prone areas.

Detection of Enterobius vermicularis in greater Berlin, 2007-2017: seasonality and increased frequency of detection.

The pinworm (Enterobius vermicularis) causes mostly mild infections characterised by nocturnal anal pruritus, mainly in children. Still, the infection is stigmatising and sleep disturbances may lead to lack of concentration. For Germany, no epidemiological data are available. Laboratory data of all patients for whom detection of E. vermicularis by cellulose tape test had been requested between 2007 and November 2017 were analysed retrospectively. E. vermicularis was detected in 971/5578 (17.4%) samples collected from 3991 patients. The detection rate increased significantly within the period of investigation. It was higher in male than in female patients (20.0 vs. 15.4%). Children 4 to 10 years old and, if also examined, their relatives were most frequently affected. Control investigations at an interval of at least 1 month, which could indicate insufficient therapy or re-infection, were performed in 90/714 patients (12.6%). While parasite detection in children < 6 years was evenly distributed throughout the year, in older patients, it peaked between October and December. In conclusion, in the area of investigation, the frequency of E. vermicularis is higher in males than in females and is subject to a hitherto undescribed seasonality. The causes of the increased frequency of parasite detection warrant further investigations.

Unusual Etiology for Transaminitis.

An infection with Enterobius vermicularis (pinworm) commonly affects the gastrointestinal (GI) tract. The ectopic localization of an enterobius infectious is rare, especially in the liver. We report the case of a 37-year-old man who presented to the gastroenterology clinic with abdominal pain and was found to have elevated transaminases. Workup for acute/chronic liver disease was unrevealing. He underwent endoscopic evaluation showing a live pinworm in the colon. He was treated with albendazole with improvement in GI symptoms and resolution of his transaminitis. There are scarce reports in the literature describing pathognomonic, clinical, imaging, and laboratory findings for pinworm infection. Here, we attempt to review the literature for hepatic involvement with an enterobius infection and discuss the findings via this case.

Enterobius vermicularis infection: prevalence and risk factors among preschool children in kindergarten in the capital area, Republic of the Marshall Islands.

BACKGROUND: Enterobius vermicularis (pinworm) is one of the most common human parasitic helminths, and children are the most susceptible group. Some behavioral and environmental factors may facilitate pinworm infection. In the Republic of the Marshall Islands (RMI), the status of pinworm infections among children remains unknown. METHODS: In Majuro City, there are 14 kindergartens with a total of 635 preschool children (PSC) whose age range of 5~6 years. The present investigation attempted to determine the pinworm prevalence and associated risk factors as well as investigate whether eggs contaminated the clothes of PSC or the ground and tables in classrooms of 14 kindergartens. Informed consent form and a self-administered questionnaire were given to parents prior to pinworm screening. Perianal specimens were collected by an adhesive scotch tape method, and clothing of belly and hip sites and the ground and tables of the classrooms were inspected using a cellophane tape method to detect any eggs contamination. RESULTS: In total, 392 PSC (5.28 ± 0.56 yrs. old) participated in this project. The overall prevalence of pinworm infection was 22.4% (88/392). Boys (24.5%) had higher prevalence than girls (20.31%) (p = 0.32). PSC aged > 5 years (32.77%) showed a significantly higher prevalence than those aged ≤5 years (17.95%) (p = 0.01). A univariate analysis indicated that PSC who lived in urban areas (22.95%) had a higher prevalence than those who lived in rural areas (20.69%) (p = 0.69). The employment status of the parents showed no association with the pinworm infection rate (p > 0.05). A logistic regression analysis indicated that "having an older sister" produced a higher risk of acquiring pinworm infection for PSC compared to those who did not have an older sister (OR = 2.02; 95%CI = 1.05~3.88; p = 0.04). No significant association between various other risk factors and pinworm infection was found (p > 0.05). Also, no eggs contamination was found on the clothes of the belly and hip sites or on the ground and tables in the 14 kindergartens. CONCLUSIONS: Mass screening and treatment of infected PSC are important measures in pinworm control in the RMI.

Pinworm Infection at Salmon Ruins and Aztec Ruins: Relation to Pueblo III Regional Violence.

The study of coprolites has been a theme of archaeology in the American Southwest. A feature of archaeoparasitology on the Colorado Plateau is the ubiquity of pinworm infection. As a crowd parasite, this ubiquity signals varying concentrations of populations. Our recent analysis of coprolite deposits from 2 sites revealed the highest prevalence of infection ever recorded for the region. For Salmon Ruins, the deposits date from AD 1140 to 1280. For Aztec Ruins, the samples can be dated by artifact association between AD 1182-1253. Both sites can be placed in the Ancestral Pueblo III occupation (AD 1100-1300), which included a period of cultural stress associated with warfare. Although neither of these sites show evidence of warfare, they are typical of large, defensible towns that survived this time of threat by virtue of large populations in stonewalled villages with easily accessible water. We hypothesize that the concentration of large numbers of people promoted pinworm infection and, therefore, explains the phenomenal levels of infection at these sites.