Old friends and friendly fire: Pregnancy, hookworm infection, and anemia among tropical horticulturalists.

OBJECTIVES: Despite public health concerns about hookworm infection in pregnancy, little is known about immune profiles associated with hookworm (Necator americanus and Ancylostoma duodenale) infection during pregnancy. Fetal tolerance requirements may constrain maternal immune response to hookworm, thereby increasing susceptibility to new infections or increasing hemoglobin loss. To explore this possibility, we study systemic immune response and hemoglobin levels in a natural fertility population with endemic helminthic infection. METHODS: We used Bayesian multilevel models to analyze mixed longitudinal data on hemoglobin, hookworm infection, reproductive state, eosinophils, and erythrocyte sedimentation rate (ESR) to examine the effects of pregnancy and hookworm infection on nonspecific inflammation, cellular parasite response, and hemoglobin among 612 Tsimane women aged 15-45 (1016 observations). RESULTS: Pregnancy is associated with lower eosinophil counts and lower eosinophil response to hookworm, particularly during the second and third trimesters. Both hookworm and pregnancy are associated with higher ESR, with evidence for an interaction between the two causing further increases in the first trimester. Pregnancy is moderately associated with higher odds of hookworm infection (OR: 1.23, 95% CI: 0.83 to 1.83). Pregnancy and hookworm both decrease hemoglobin and may interact to accentuate this effect in the first-trimester of pregnancy (Interaction: ß: -0.30 g/dL; CI: -0.870 to 0.24). CONCLUSIONS: Our findings are consistent with a possible trade-off between hookworm immunity and successful pregnancy, and with the suggestion that hookworm and pregnancy may have synergistic effects, particularly in the first trimester.

Restoration of hookworm egg development after prolonged storage in stool suspension.

Hookworm infection is still prevalent in southern Thailand despite control measures. Hookworm eggs submerged for an extended period under water from rainfall or in latrines may not survive, but they may recover their ability to develop into infective larvae when exposed to atmospheric air. This study examined the survival of the hookworm eggs in stool suspension and the restoration of development capability after prolonged storage. In stool mass, eggs developed normally and yielded infective filariform larvae (FL) in 7 days. On the contrary, in 1:10 stool suspension, hookworm eggs were found to remain at the 4-8 cell stage; degenerated eggs were observed after 15 days of storage, and the number of degenerated eggs reached 80 % on day 30. Aeration of the suspension, or transferring to a Petri dish or agar plate, restored the capacity of eggs stored for up to 15 days to develop into FL; thereafter, the capacity declined sharply. Retardation of egg development under water or in stool suspension may be due to a lack of atmospheric air. Use of "night soil" from latrines as fertilizer may be one factor in maintaining hookworm transmission, as worm eggs can undergo normal development upon exposure to atmospheric air.

Generalized urticaria induced by the Na-ASP-2 hookworm vaccine: implications for the development of vaccines against helminths.

BACKGROUND: Necator americanus Ancylostoma-secreted protein 2 (Na-ASP-2) is secreted by infective hookworm larvae on entry into human hosts. Vaccination of laboratory animals with recombinant Na-ASP-2 provides significant protection against challenge infections. In endemic areas antibodies to Na-ASP-2 are associated with reduced risk of heavy N americanus infections. OBJECTIVE: To assess the safety and immunogenicity of recombinant Na-ASP-2 adjuvanted with Alhydrogel in healthy Brazilian adults previously infected with N americanus. METHODS: Participants were randomized to receive Na-ASP-2 or hepatitis B vaccine. Major IgG and IgE epitopes of the Na-ASP-2 molecule were mapped by using sera from these same subjects. Seroepidemiologic studies in adults and children residing in hookworm-endemic areas were conducted to assess the prevalence of IgE responses to Na-ASP-2. RESULTS: Vaccination with a single dose of Na-ASP-2 resulted in generalized urticarial reactions in several volunteers. These reactions were associated with pre-existing Na-ASP-2-specific IgE likely induced by previous hookworm infection. Surveys revealed that a significant proportion of the population in hookworm-endemic areas had increased levels of IgE to Na-ASP-2. Epitope mapping demonstrated sites on the Na-ASP-2 molecule that are uniquely or jointly recognized by IgG and IgE antibodies. CONCLUSION: Infection with N americanus induces increased levels of total and specific IgE to Na-ASP-2 that result in generalized urticaria on vaccination with recombinant Na-ASP-2. These data advance knowledge of vaccine development for helminths given their propensity to induce strong T(H)2 responses. Study data highlight the important differences between the immune responses to natural helminth infection and to vaccination with a recombinant helminth antigen.

Molecular detection of Ancylostoma duodenale, Ancylostoma ceylanicum, and Necator americanus in humans in northeastern and southern Thailand.

The 2 principal species of hookworms infecting humans are Necator americanus and Ancylostoma duodenale. Case studies on zoonotic hookworm infections with Ancylostoma ceylanicum and/or Ancylostoma caninum are known mainly from Asian countries. Of these 2 zoonotic species, only A. ceylanicum can develop to adulthood in humans. In the present study, we report a molecular-based survey of human hookworm infections present in southern and northeastern Thailand. Thirty larval hookworm samples were obtained from fecal agar plate cultures of 10 patients in northeastren Thailand and 20 in southern Thailand. Partial ITS1, 5.8S, and ITS2 regions of the ribosomal DNA genes were amplified using PCR. The amplicons were sequenced, aligned, and compared with other hookworm sequences in GenBank database. The results showed that, in Thailand, N. americanus is more prevalent than Ancylostoma spp. and is found in both study areas. Sporadic cases of A. ceylanicum and A. duodenale infection were seen in northeastern Thailand.

Hookworm infection in central China: morphological and molecular diagnosis.

BACKGROUND: Necator americanus is one of the major etiological agents of human ancylostomiasis. Historically, the epidemiology of ancylostomiasis in Henan Province of central China and the molecular characteristics of N. americanus have been poorly understood. METHODS: In this study, we report a case of ancylostomiasis in Zhengzhou city of Henan Province. We also review the epidemiology of ancylostomiasis in Henan Province from 1949 to 2020. In addition, the complete mitochondrial (mt) genome of one clinical isolate is fully characterized using Illumina sequencing. All available mt genomes of hookworms in GenBank were included to reconstruct the phylogeny using both maximum likelihood (ML) and Bayesian inference (BI) methods. RESULTS: A total of three worms were collected from the patient. These worms were identified as N. americanus based on morphological characteristics as well as confirmed by genotyping with the barcoding gene cox1. Although ancylostomiasis cases have dropped substantially in recent years, hookworm infection is still a public health problem in underdeveloped areas and remote rural areas in Henan Province. The mt genome features of the N. americanus contained 12 protein-coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and a major non-coding region. The nad1 gene showed high sequence variability among isolates, which is worth considering for future genetic studies of N. americanus. Phylogenetic analyses support the monophyly of hookworm isolates from different hosts and distinct geographical locations. CONCLUSIONS: The mt genome of N. americanus presented here will serve as a useful data set for studying population genetics and phylogenetic relationships of hookworms. Positive measures for preventing and controlling ancylostomiasis are required by both health services and individuals in Henan Province.

Genotypic profile of benzimidazole resistance associated with SNP F167Y in the beta-tubulin gene of Necator americanus helminths obtained from Brazilian populations.

Necator americanus is a worm that parasites the small intestine of humans and is highly prevalent in regions with poor sanitary conditions. The main strategy to control this helminth is by mass benzimidazole administration, however, periodic use of these drugs can select strains of parasites resistant to treatment. Single nucleotide polymorphisms (SNPs) in the beta-tubulin isotype 1 gene located at codons 167, 198 and 200 have been associated with benzimidazole resistance in some nematodes. Previously, our group detected the presence of some of these SNPs in populations of soil-transmitted helminths collected in different locations in Brazil. Here, we evaluated the SNP at codon 167, which has recently been shown to be associated with failure of benzimidazoles to treat N. americanus. Our ARMS-PCR analyses were performed using 524 single N. americanus eggs from 48 patients' feces collected in six Brazilian states; however, we did not detect any mutated samples at codon 167. This study builds on previous work, helping us monitor the presence of resistance-related genotypes in Brazilian helminth populations. The data presented here can assist in the implementation of future control strategies.

Egg genotyping reveals the possibility of patent Ancylostoma caninum infection in human intestine.

Hookworms are intestinal parasites that cause major public health problems, especially in developing countries. To differentiate eggs from different hookworm species, it is necessary to use molecular methodologies, since the eggs are morphologically similar. Here, we performed the molecular identification of single hookworm eggs from six Brazilian states. Of the 634 eggs individually analyzed, 98.1% (622/634) represented Necator americanus, and surprisingly, 1.9% (12/634 eggs from the same patient) represented Ancylostoma caninum. DNA analysis of the A. caninum-positive stool sample revealed no contamination with animal feces. This is the first report of the presence of A. caninum eggs in human feces, which may have a direct implication for the epidemiology of hookworm infection caused by this species. This suggests the need for special attention regarding prophylaxis, as different reservoirs, previously not described, may have great relevance for the spread of A. caninum.

Risk factors for infection with soil-transmitted helminths during an integrated community level water, sanitation, and hygiene and deworming intervention in Timor-Leste.

Water, sanitation and hygiene interventions have been advocated as important complements to deworming programs to improve soil-transmitted helminth control. Evidence for the impact of water, sanitation and hygiene on soil-transmitted helminth infections is mixed, and based mainly on cross-sectional studies. In this study, we assessed associations between individual- and household-level water, sanitation and hygiene variables and soil-transmitted helminth infections, using data collected during the 2 year follow-up study period of the WASH for WORMS randomised controlled trial in Timor-Leste. Data were collected across four surveys, conducted at 6 monthly intervals in 23 communities. We analysed water, sanitation and hygiene and sociodemographic variables as risk factors for infection with Necator americanus, Ascaris spp., and undifferentiated soil-transmitted helminth infection, using generalised linear mixed models to account for clustering at community, household and participant levels. Water, sanitation and hygiene risk factors were examined both concurrently and with a 6 month lag period that coincided with the most recent deworming. The analysis included 2333 participants. Factors associated with N. americanus infection included age group, male sex (adjusted odds ratio (aOR) 3.1, 95% confidence interval (CI) 2.4-4.2), working as a farmer (aOR 1.7, 95% CI 1.2-2.4), and completing secondary school or higher (aOR 0.29, 95% CI 0.16-0.53). Risk factors for Ascaris spp. infection included age group, living in a dwelling with more than six people (aOR 1.6, 95% CI 1.1-2.3), having a tube well or borehole as the household water source (aOR 3.7, 95% CI 1.3-10.8), and using a latrine shared between households 6 months previously (aOR 2.3, 95% CI 1.2-4.3). Handwashing before eating was protective against infection with any soil-transmitted helminth (aOR 0.79, 95% CI 0.65-0.95). In the context of regular deworming, few water, sanitation and hygiene-related factors were associated with soil-transmitted helminth infections. Future research examining the role of water, sanitation and hygiene in soil-transmitted helminth transmission is required, particularly in low transmission settings after cessation of deworming. Identifying improved indicators for measuring water, sanitation and hygiene behaviours is also a key priority.

Use of quantitative PCR to assess the efficacy of albendazole against Necator americanus and Ascaris spp. in Manufahi District, Timor-Leste.

BACKGROUND: Soil-transmitted helminths (STHs) including Ascaris lumbricoides, Necator americanus, Ancylostoma spp. and Trichuris trichiura are cause of significant global morbidity. To mitigate their disease burden, at-risk groups in endemic regions receive periodic mass drug administration using anthelmintics, most commonly albendazole and mebendazole. Assessing the efficacy of anthelmintic drugs is important for confirming that these regimens are working effectively and that drug resistance has not emerged. In this study we aimed to characterise the therapeutic efficacy of albendazole against Ascaris spp. and N. americanus in Timor-Leste, using a quantitative polymerase chain reaction (qPCR) method for parasite detection and quantification. RESULTS: A total of 314 participants from 8 communities in Timor-Leste provided stool samples before and 10-14 days after the administration of a single 400 mg dose of albendazole. Helminth infection status and infection intensity (measured in Ct-values and relative fluorescence units) were determined using qPCR. Efficacy was determined by examining the cure rates and infection intensity reduction rates. Albendazole was found to be highly efficacious against Ascaris spp., with a cure rate of 91.4% (95% CI: 85.9-95.2%) and infection intensity reduction rate of 95.6% (95% CI: 88.3-100%). The drug was less efficacious against N. americanus with a cure rate of 58.3% (95% CI: 51.4-64.9%) and infection intensity reduction rate of 88.9% (95% CI: 84.0-97.0%). CONCLUSIONS: The observed cure rates and infection intensity reduction rates obtained for Ascaris spp. and to a lower extent N. americanus, demonstrate the continued efficacy of albendazole against these species and its utility as a mass chemotherapy agent in Timor-Leste. Furthermore, this study demonstrates the usefulness of qPCR as a method to measure the efficacy of anthelminthic drugs. Additional research is necessary to translate Ct-values into eggs per gram in a systematic way. TRIAL REGISTRATION: Australian and New Zealand Clinical Trials Registry 12614000680662 (registered 27 June 2014).

Age-related changes in hookworm infection, anaemia and iron deficiency in an area of high Necator americanus hookworm transmission in south-eastern Brazil.

Surprisingly few detailed age-stratified data exist on the epidemiology of hookworm and iron status, especially in Latin America. We present data from a cross-sectional survey examining 1332 individuals aged 0-86 years from a community in south-east Brazil for hookworm, anaemia and iron deficiency. Sixty-eight percent of individuals were infected with the human hookworm Necator americanus. The force of infection (lambda=0.354) was similar to estimates from other areas of high hookworm transmission. Individuals from poorer households had significantly higher prevalence and intensity of infection than individuals from better-off households. The prevalence of anaemia, iron deficiency and iron-deficiency anaemia was 11.8%, 12.7% and 4.3%, respectively. Anaemia was most prevalent among young children and the elderly. Univariate analysis showed that haemoglobin and serum ferritin were both significantly negatively associated with hookworm intensity among both school-aged children and adults. Multivariate analysis showed that, after controlling for socio-economic status, iron indicators were significantly associated with heavy hookworm infection. Our results indicate that, even in areas where there is a low overall prevalence of anaemia, hookworm can still have an important impact on host iron status, especially in school-aged children and the elderly.

A study on the prevalence of hookworm infection in four districts of West Bengal and its linkage with anaemia.

Stool samples collected from the districts of Darjeeling, Jalpaiguri, Hooghly and Calcutta in West Bengal were examined for hookworm and associated parasites. It was found that maximum prevalence of hookworm was in Hooghly district (24.8%). N. americanus appeared to be more prevalent species in all the districts studied. The load ofhookworm infection appeared to be mostly in the mild range. Ascaris lumbricoides appeared to the most common accompanying infection. In the affected population, the degree of anaemia was mostly mild.

First Molecular Identifications of Necator americanus and Ancylostoma ceylanicum Infecting Rural Communities in Lower Myanmar.

Hookworms are enteric parasitic roundworms infecting an estimated 400 million persons worldwide. Herein, we provide the first molecular identifications of human hookworms from certain parts of rural Lower Myanmar. DNA was extracted from hookworm-positive stool samples, as determined by microscopy. DNA sequences of the partial internal transcribed spacer 1, full length 5.8S gene, and partial internal transcribed spacer 2 were determined and compared with available hookworm sequences from public databases. Of the 11 polymerase chain reaction-positive samples, eight (Bago Region, N = 4; Mon State, N = 4) yielded sequences with high similarity to those of Necator americanus A further three sequences (Mon State, N = 2; Bago Region, N = 1) showed high similarity with those of Ancylostoma ceylanicum The latter is primarily a parasite of dogs and represents a zoonosis. Given that different species of hookworms exhibit different epidemiological and biological characteristics, accurate identification is essential for the planning and execution of effective control programs for hookworm infections.

An environmental assessment and risk map of Ascaris lumbricoides and Necator americanus distributions in Manufahi District, Timor-Leste.

BACKGROUND: In Timor-Leste there have been intermittent and ineffective soil-transmitted helminth (STH) deworming programs since 2004. In a resource-constrained setting, having information on the geographic distribution of STH can aid in prioritising high risk communities for intervention. This study aimed to quantify the environmental risk factors for STH infection and to produce a risk map of STH in Manufahi district, Timor-Leste. METHODOLOGY/PRINCIPAL FINDINGS: Georeferenced cross-sectional data and stool samples were obtained from 2,194 participants in 606 households in 24 villages in the Manufahi District as part of cross sectional surveys done in the context of the "WASH for Worms" randomised controlled trial. Infection status was determined for Ascaris lumbricoides and Necator americanus using real-time quantitative polymerase chain reaction. Baseline infection data were linked to environmental data obtained for each household. Univariable and multivariable multilevel mixed-effects logistic regression analysis with random effects at the village and household level were conducted, with all models adjusted for age and sex. For A. lumbricoides, being a school-aged child increased the odds of infection, whilst higher temperatures in the coolest quarter of the year, alkaline soils, clay loam/loam soils and woody savannas around households were associated with decreased infection odds. For N. americanus, greater precipitation in the driest month, higher average enhanced vegetation index, age and sandy loam soils increased infection odds, whereas being female and living at higher elevations decreased the odds of infection. Predictive risk maps generated for Manufahi based upon these final models highlight the high predicted risk of N. americanus infection across the district and the more focal nature of A. lumbricoides infection. The predicted risk of any STH infection is high across the entire district. CONCLUSIONS/SIGNIFICANCE: The widespread predicted risk of any STH infection in 6 to 18 year olds provides strong evidence to support strategies for control across the entire geographical area. As few studies include soil texture and pH in their analysis, this study adds to a growing body of evidence suggesting these factors influence STH infection distribution. This study also further supports that A. lumbricoides prefers acidic soils, highlighting a potential relatively unexplored avenue for control. TRIAL REGISTRATION: ClinicalTrials.gov ACTRN12614000680662.

Adult hookworms (Necator spp.) collected from researchers working with wild western lowland gorillas.

BACKGROUND: In general, studies on the diversity of strongylid nematodes in endangered host species are complicated as material obtained by non-invasive sampling methods has limited value for generic and species identification. While egg morphology barely allows assignment to family, the morphology of cultivated infective third stage larvae provides a better resolution at the generic level but cannot be used for exact species identification. Morphology-based taxonomic approaches greatly depend on the examination of adult worms that are usually not available. METHODS: Hookworm parasites in two European researchers, who participated in gorilla research in the Central African Republic, were expelled after anthelmintic treatment to the faeces, collected and morphologically examined. A male worm discharged naturally from a wild bonobo (Pan paniscus) in Congo was also examined for comparison. RESULTS: Two species of Necator were identified in researchers' faecal material: Necator americanus (Stiles, 1902) and N. gorillae Noda & Yamada, 1964; the latter species differed in having a smaller body, smaller buccal cavity and shorter spicules with spade-shaped membranes situated distally. Males of N. gorillae also possessed unusual cuticular thickenings on the dorsal side of the prebursal region of the body. These characters, shared with the male worm from the bonobo, correspond well to the description of N. gorillae described from gorillas in Congo. CONCLUSIONS: Based on the morphology of the hookworms recovered in this study and previous molecular analyses of larvae developed from both humans and western lowland gorillas (Gorilla gorilla gorilla) from this locality, we conclude that the researchers became infected with gorilla hookworms during their stay in the field. This is the first report of infection with a Necator species other than N. americanus in humans.

Emerging patterns of hookworm infection: influence of aging on the intensity of Necator infection in Hainan Province, People's Republic of China.

We examined risk factors associated with Necator americanus infection among persons aged > or =50 years in Hainan Province, People's Republic of China. Age and sex made the most important contributions to the variation in infection intensity (28%-30%), with age alone responsible for 27% of this variation. When stratified by 20-year age intervals, the influence of shared residence was 23% for persons aged > or =50 years and 27% for those aged <20 years, who had the highest and lowest levels of infection intensity, respectively. This points to shared residence as a means of capturing the complex relationship between aging and shared socioeconomic, environmental, and behavioral factors that influence transmission of Necator infection. None of the other 26 personal or 32 household risk factors were found to be significant. The importance of aging in Necator infection reveals an emerging public health problem among the elderly population of developing countries.

Epidemiological evidence for a differential effect of hookworm species, Ancylostoma duodenale or Necator americanus, on iron status of children.

BACKGROUND: The hookworms, Ancylostoma duodenale and Necator americanus, cause significant gastrointestinal blood loss. In clinical studies, greater blood losses have been reported with A. duodenale. However, there has been no evidence that endemic A. duodenale infection has greater impact than N. americanus infection on the iron status of populations. METHODS: In a sample of 525 school children in Pemba Island, Tanzania, we compared the degree of anaemia and iron deficiency associated with the two hookworm species at the individual and community (i.e. school) levels. Multiple regression was used to control for infection intensities and other child characteristics. RESULTS: In the 492 children with hookworm positive faecal cultures, haemoglobin and ferritin concentrations decreased with increasing proportions of A. duodenale. Among children with only N. americanus larvae, the prevalence of anaemia was 60.5 % and the prevalence of ferritin <12 microg/l was 33.1%, while in children with > or =50% A. duodenale larvae, the respective prevalences were 80.6% and 58.9%. When children were grouped by the prevalence of A. duodenale at the school level, children from high prevalence (> or =20%) schools had significantly worse iron deficiency and anaemia than children from low prevalence schools. CONCLUSIONS: The species of hookworm being transmitted in a community influences the burden of iron deficiency anaemia in the community, and should be considered in prioritizing and planning programmes for hookworm and anaemia control.

PIP: Hookworms infect 1.3 billion people annually. Iron-deficiency anemia caused or exacerbated by intestinal blood loss is the major feature of hookworm infection, with such loss caused by the feeding of hookworms upon the intestinal mucosa. The hookworms Ancylostoma duodenale and Necator americanus cause major gastrointestinal blood loss. While relatively greater blood loss has been reported in clinical studies due to infection with A. duodenale, there has been no evidence that endemic A. duodenale infection has a greater impact than N. americanus infection upon the iron status of populations. The authors compared the degree of anemia and iron deficiency associated with these 2 hookworm species at the individual and community levels using a sample of 525 school children in grades 1-4 in Pemba Island, Tanzania, and controlling for infection intensities and other child characteristics through multiple regression. In the 492 children with hookworm-positive fecal cultures, hemoglobin and ferritin concentrations decreased with increasing proportions of A. duodenale. Among children with only N. americanus larvae, the prevalence of anemia was 60.5% and the prevalence of ferritin under 12 mcg/l was 33.1%. In children with 50% or higher proportions of A. duodenale larvae, the respective prevalences were 80.6% and 58.9%. Children from schools with high prevalences of A. duodenale infection had significantly worse iron deficiency and anemia than did children from low prevalence schools.

Transmission patterns and the epidemiology of hookworm infection.

BACKGROUND: This paper presents a suite of models of hookworm transmission dynamics which vary the mixing patterns and rates of contamination and infection between children and adults. In this context mixing refers to the degree of epidemiological communication between children and adults, for example, whether adults are likely to get infected from infective material passed by children. METHODS: Three models are described which represent random mixing, no mixing and restricted mixing respectively. Child, adult and population targeted chemotherapy programmes are examined and compared between these models. Data from a hookworm control programme in Zimbabwe were analysed with respect to their fit to the various models. RESULTS: The analysis suggests that some mixing does occur and that in this study location, the sites where adults deposit faeces are more likely to lead to subsequent contamination than the sites children use. CONCLUSIONS: Mixing patterns may have a profound effect on transmission dynamics and should be considered in relation to design of control programmes.

Transmammary passage of Strongyloides sp. larvae in the human host.

The prevalence of infection with Strongyloides fuelleborni and hookworms (Ancylostoma duodenale and Necator americanus), and the possible transmammary passage of these parasites, was studied in the people of a village in Bulapé, Zaire, Africa. Stool examinations revealed that 34% of 76 infants under 200 days of age were infected with S. fuelleborni and 8% were infected with hookworms. Infection rates in the general population were 44% for S. fuelleborni and 90% for hookworms. The examination of milk from nursing mothers revealed the presence of Strongyloides larvae in one case. The finding suggests that S. fuelleborni may be transmitted via the milk in humans.

The effect of the availability of latrines on soil-transmitted nematode infections in the plantation sector in Sri Lanka.

The relationship of soil-transmitted nematode infections to the availability of latrines was studied among 1,614 children 3-12 years of age living on plantations in Sri Lanka. The majority (89.7%) of the children had at least one type of soil-transmitted nematode. There was a significantly lower mean count of hookworm eggs for children coming from plantations with good sanitary facilities. For Ascaris and Trichuris, a similar association was observed between the mean egg count and the availability of latrines for children from the low-country plantations, where people live in more scattered settlements, but not in the up-country area, where worker settlements are larger and more crowded. Congested living conditions in themselves consequently seem to be a major determinant for ascariasis and trichuriasis, and the provision of latrines and safe water does not substantially change that situation. However, improvements of sanitary facilities will probably have a more immediate effect on the prevalence of hookworm infection.

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.