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Co-infection with hookworm and schistosomes is a common phenomenon in sub-Saharan Africa, as well as in parts of South America and southeast Asia. As a first step towards understanding the metabolic response of a hookworm-schistosome co-infection in humans, we investigated the metabolic consequences of co-infection in an animal model, using a nuclear magnetic resonance (NMR)-based metabolic profiling technique, combined with multivariate statistical analysis. Urine and serum samples were obtained from hamsters experimentally infected with 250 Necator americanus infective L(3) and 100 Schistosoma japonicum cercariae simultaneously. In the co-infection model, similar worm burdens were observed as reported for single infection models, whereas metabolic profiles of co-infection represented a combination of the altered metabolite profiles induced by single infections with these two parasites. Consistent differences in metabolic profiles between the co-infected and non-infected control hamsters were observed from 4 weeks p.i. onwards. The predominant metabolic alterations in co-infected hamsters consisted of depletion of amino acids, tricarboxylic acid cycle intermediates (e.g. citrate and succinate) and glucose. Moreover, alterations of a series of gut microbial-related metabolites, such as decreased levels of hippurate, 3-hydroxyphenylpropionic acid, 4-hydroxyphenylpropionic acid and trimethylamine-N-oxide, and increased concentrations of 4-cresol glucuronide and phenylacetylglycine were associated with co-infection. Our results provide a first step towards understanding the metabolic response of an animal host to multiple parasitic infections., ((c) 2009 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Background: Epidemiological studies suggest that hookworm infection protects against asthma, and therefore that hookworm infection may have a direct or an indirect therapeutic potential in this disease. We now report the first clinical trial of experimental hookworm infection in people with allergic asthma., Objectives: To determine the effects of experimental hookworm infection in asthma., Methods: Thirty-two individuals with asthma and measurable airway responsiveness to adenosine monophosphate (AMP) were randomized and double blinded to cutaneous administration of either ten Necator americanus larvae, or histamine solution (placebo), and followed for 16 weeks. The primary outcome was the change in provocation dose of inhaled AMP required to reduce forced expiratory volume in 1 s by 20% (PD(20)AMP) from baseline to week 16. Secondary outcomes included change in several measures of asthma control and allergen skin sensitivity and the occurrence of adverse effects., Results: Mean PD(20)AMP improved in both groups, more in the hookworm [1.49 doubling doses (DD)] than the placebo group (0.98 DD), but the difference between groups was not significant (0.51 DD; 95% confidence interval: -1.79 to 2.80; P=0.65). There were no significant differences between the two groups for other measures of asthma control or allergen skin sensitization. Infection was generally well tolerated., Conclusions: Experimental infection with ten hookworm larvae in asthma did not result in significant improvement in bronchial responsiveness or other measures of asthma control in this study. However, infection was well tolerated and resulted in a non-significant improvement in airway responsiveness, indicating that further studies that mimic more closely natural infection are feasible and should be undertaken.

Hookworms (Ancylostoma duodenale and Necator americanus) are blood-feeding intestinal nematodes that infect approximately 700 million people worldwide. To further our understanding of the systems metabolic response of the mammalian host to hookworm infection, we employed a metabolic profiling strategy involving the combination of (1)H NMR spectroscopic analysis of urine and serum and multivariate data analysis techniques to investigate the biochemical consequences of a N. americanus infection in the hamster. The infection was characterized by altered energy metabolism, consistent with hookworm-induced anemia. Additionally, disturbance of gut microbiotal activity was associated with a N. americanus infection, manifested in the alterations of microbial-mammalian cometabolites, including phenylacetylglycine, p-cresol glucuronide, 4-hydroxy-3-methyl-phenylpropionic acid, hippurate, 4-hydroxyphenylactate, and dimethylamine. The correlation between worm burden and metabolite concentrations also reflected a changed energy metabolism and gut microbial state. Furthermore, elevated levels of urinary 2-aminoadipate was a characteristic feature of the infection, which may be associated with the documented neurological consequences of hookworm infection.

The effect of polyparasite infections on cytokine and chemokine responses as well as the effect of antiparasite treatment was studied in children without parasite infection (the G0 group), in children singly infected with Schistosoma haematobium (the G1 group), and in children multiply infected with S. haematobium/Schistosoma mansoni, Entamoeba histolytica/Entamoeba dispar, and Necator americanus (the G3+ group). Linear regression analysis disclosed a significant risk for coinfection with hookworm and Schistosoma species. Polyparasite infections detected in 23% of children before treatment were present in 5% at 15 months after treatment. Chemokine responses to S. mansoni adult worm antigen (SmAg) diminished after treatment for macrophage inflammatory chemokine (MIP)-1alpha/chemokine (C-C motif) ligand (CCL)-3 (among G3+ children, by a factor of 200 [95% confidence interval {CI}, 33-1111]) and for MIP-1beta/CCL-4 (among G3+ children, by a factor of 26 [95% CI, 6-117]) but were enhanced for thymus- and activation-regulated chemokine/CCL-17 (among G3+ children, by a factor of 10 [95% CI, 3-32]) (P < .001 for all). In response to E. histolytica antigen, interleukin (IL)-13 levels increased after treatment among G1 children by a factor of 138 (95% CI, 12-1569) and among G3+ children by a factor of 21 (95% CI, 7-64) (P < .001 for both). Cellular production of interferon (IFN)-gamma in response to SmAg decreased 4 weeks after treatment among G3+ children, whereas T helper cell type 2 (Th2) IL-13 production was enhanced among G1 and G3+ children. In summary, polyparasite infections with S. haematobium/S. mansoni, E. histolytica/E. dispar, and N. americanus generated prominent proinflammatory cytokine and chemokine responses, and, after antihelminth treatment, the inflammatory chemokine response lessened as the Th2 responsiveness in coinfected children increased.

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.

The recommended control option against onchocerciasis is repeated ivermectin treatment, which will need to be implemented for decades, and it remains unknown how repeated ivermectin therapy might affect immunity against Onchocerca volvulus in the long term. O. volvulus-specific antibody reactivity and cellular cytokine production were investigated in onchocerciasis patients receiving ivermectin (150 microg/kg) annually for 16 years. In treated patients, the T helper type 2 (Th2) cytokine interleukin (IL)-5 and T regulatory IL-10 in response to O. volvulus antigen (OvAg) and bacteria-derived Streptolysin O (SL-O) diminished to levels found in infection-free endemic controls; also, cellular release of Th1-type interferon (IFN)-gamma at 16 years post initial ivermectin treatment (p.i.t.) approached control levels. In ivermectin-treated onchocerciasis patients, IL-5 production in responses to the mitogen phytohaemagglutinin (PHA) decreased, but IL-10 in response PHA increased, and neither attained the cytokine production levels of endemic controls. At 16 years p.i.t., O. volvulus-specific IgG1 and IgG4 subclass reactivity still persisted at higher levels in onchocerciasis patients than in O. volvulus exposed but microfilariae-free endemic controls. In addition, cytokine responses remained depressed in onchocerciasis patients infected concurrently with Mansonella perstans and Necator americanus or Entamoeba histolytica/dispar. Thus, long-term ivermectin therapy of onchocerciasis may not suffice to re-establish fully a balanced Th1 and Th2 immune responsiveness in O. volvulus microfilariae-negative individuals. Such deficient reconstitution of immune competence may be due to an as yet continuing and uncontrolled reinfection with O. volvulus, but parasite co-infections can also bias and may prevent the development of such immunity.

Background: We wanted to quantify the impact that polyparasite infections, including multiple concurrent low-intensity infections, have on anemia., Methods: Three stool samples were collected and read in duplicate by the Kato-Katz method in a cross-sectional sample of 507 children from Leyte, The Philippines. The number of eggs per gram of stool was used to define 3 infection intensity categories--uninfected, low, and moderate/high (M+)--for 3 geohelminth species and Schistosomiasis japonicum. Four polyparasite infection profiles were defined in addition to a reference profile that consisted of either no infections or low-intensity infection with only 1 parasite. Logistic regression models were used to quantify the effect that polyparasitism has on anemia (hemoglobin level <11 g/dL)., Results: The odds of having anemia in children with low-intensity polyparasite infections were nearly 5-fold higher (P = .052) than those in children with the reference profile. The odds of having anemia in children infected with 3 or 4 parasite species at M+ intensity were 8-fold greater than those in children with the reference profile (P < .001)., Conclusion: Low-intensity polyparasite infections were associated with increased odds of having anemia. In most parts of the developing world, concurrent infection with multiple parasite species is more common than single-species infections. This study suggests that concurrent low-intensity infections with multiple parasite species result in clinically significant morbidity.

Parasitological, malacological and anthropological studies were performed to assess the prevalence of Schistosoma haematobium and S. mansoni in schoolchildren living in the suburban area of Bamako. A total of 1017 schoolchildren aged 6-14 years were selected in two different areas between September 1997 and December 1999. In Djikoroni, the prevalence of S. haematobium and S. mansoni was 80.7% (339/420) and 22.8% (85/372) respectively. There was no significant difference of prevalence and intensity of infection with S. haematobium between schools, gender and age (p > 0.05), whereas, those of S. mansoni were higher in the vicinity of (+/- 100 m from) major sites where infected Biomphalaria pfeifferi were found (p < 0.001). In Niomirambougou, S. haematobium was prevalent in 46.7% (279/597) and S. mansoni in 28.2% (134/475). Boys and children aged 11-14 years were more infected (p < 0.001). Associated intestinal helminths (Hymenolepis nana, Necator americanus and Ascaris lumbricoides) were relatively scarce (prevalence < 1%). The prevalences of schistosome infected snails intermediate host were relatively high, 49.3% (100/203) in B. pfeifferi, 20.6% (88/138) in B. truncatus and 24.1% (7/29) in B. globosus. We recorded a total of 2514 water contacts about which 1130 in December and 1384 in January. Most of the children, 42.9% (1077/2511) were attracted to water bodies for bathing, swimming and playing, suggesting the lack of recreational facilities in these areas. Developing local control programmes in schools located in the vicinity of water bodies would contribute to break the parasite transmission cycle in Bamako.

Passage of helminth larvae through the lungs can cause pulmonary eosinophilia that may have evolved as a means of parasite attrition. If allergic responses represent a misdirected activation of this arm of the immune system, then mechanisms governing eosinophil recruitment during infection would be expected to be closely related to those seen in allergy. We studied primary Necator americanus infection and compared this to multiply-infected or vaccinated mice. The arrival of larvae in the lungs triggered rapid eosinophil recruitment, which was greatly enhanced in previously sensitized mice. Interestingly, the presence of larvae in the lung was sufficient to trigger eosinophil chemoattractant production, including the chemokines eotaxin and MIP-1alpha, and was not enhanced by prior exposure to the parasites. Infection stimulated IL-5 production in all groups; however, this and IgE production were greatly enhanced in sensitized animals. Elevated IL-5 increased bone marrow production of eosinophils, and eosinophilia was abrogated by treatment with anti-IL-5 antibody. Therefore, trapping of larvae in the pulmonary vasculature is sufficient to trigger eosinophil recruitment, by induction of chemokines and IL-5. Primed cognate Th2 immunity does not increase local chemokine production, but does increase IL-5 production, which greatly enhances the availability of eosinophils for recruitment to the lung.

In this study parasite-specific antibody, cellular reactivity and Thl-type or Th2-type cytokine responses were investigated in humans concurrently infected with Necator americanus and Oesophagostomum bifurcum. The prospects for O. bifurcum-specific serodiagnosis based on IgG4 and IgE were evaluated. IgG4 showed low specificity for O. bifurcum due to antigen cross-reactivity with N. americanus, while IgE specifically distinguished between hookworm and O. bifurcum, and, in doubly infected patients, levels of O. bifurcum-specific as well as N. americanus-specific IgE were significantly elevated compared to those with N. americanus mono-infections. Cellular immunity was not strictly dominated by a Thl- or Th2- type reactivity. In co-infected patients cellular unresponsiveness to parasite antigens was observed, while cellular production of tumour necrosis factor alpha (TNF-alpha) and gamma-interferon (IFN-gamma) was greater in those doubly infected. Th2-type cytokines (interleukin-5 and interleukin-10) were produced in equal amounts by peripheral blood mononuclear cells from individuals with mono- and coinfections. Such mixed Thl-type and Th2-type immune responsiveness associated with persisting gastrointestinal parasitic nematodes may reflect a state of infection at which parasite-induced inflammatory and enteropathogenic responses co-exist, and furthermore, helminth coinfection will not only suppress parasite-specific cellular responsiveness but may also direct cytokine production towards a "permissive Th1-type cytokine profile" that favours parasite persistence.

Two hookworm parasites, Necator americanus and Ancylostoma duodenale, infect approximately one billion people worldwide. These hookworms are one of the leading causes of iron-deficiency anaemia especially in children, resulting directly from intestinal capillary blood loss following the feeding activities of fourth-stage (L(4)) larva and adult worms. If ignored, human hookworm infections can retard growth and the intellectual development of children. Another clinical manifestation often associated with hookworm infections is cutaneous larva migrans (CLM). It is a well recognised, usually self-limiting condition caused by the infectious larvae of nematodes, especially Ancylostoma spp. CLM is characterised by skin eruption and represents a clinical description rather than a definitive diagnosis. Of the hookworm parasites, the dog and cat worm A. braziliense and A. caninum are the most common nematodes causing CLM, although many other species have also been implicated. The major subject of this review article will be discussion of the evolution of therapies and treatment of human necatoriasis and the development of experimental infections with N. americanus. Difference in the clinical efficacy of mebendazole and albendazole will be discussed along with drug resistance of N. americanus.

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.

The hookworms Necator americanus and Ancylostoma duodenale infect approximately 1 billion people worldwide. The prevalence of hookworm infection increases with age in children, typically reaching a plateau in late adolescence, whereas the intensity of infection may continue to increase throughout adulthood. Hookworms cause intestinal blood loss in amounts proportional to the number of adult worms in the gut. The relationship between hookworm infection intensity and hemoglobin concentration is evident in epidemiologic studies, but may be apparent only above a threshold worm burden that is related to the iron stores of the population. Current hookworm control efforts are focused on reducing infection load and transmission potential through periodic anthelminthic chemotherapy. Several controlled trials have demonstrated a positive impact of anthelminthic treatment on hemoglobin levels, with best results obtained in settings where iron intakes were also increased. Evidence suggests that anthelminthic programs will have modest impacts on iron deficiency anemia in the short term, with greater impacts on more severe anemia. Hookworms are an important cause of anemia in women, who are often overlooked by current helminth control programs. Current WHO recommendations for use of anthelminthics in schoolchildren and women are reviewed. There is a need to clarify whether hookworms are an important etiology of iron deficiency anemia in preschool children.

This paper reviews our research on the hookworm Necator americanus over several years. Our field site for the research was on Karkar Island, Papua New Guinea, where we found a prevalence of N. americanus infection among adults of nearly 100%. The intensity of infection was related to host age and to the development of iron deficiency anaemia, which occurred at a much lower infection intensity than had been previously reported. We studied the immune response to infection and our results initially suggested that antibody responses and eosinophilia do not protect the host against infection. However, we have more recently found a negative correlation of both IgE and eosinophilia with the weight and fecundity of N. americanus which suggests that the immune response does have some effect on N. americanus and that this immunity is dependent on the Th2 subset of T lymphocytes. Following treatment for hookworm, the prevalence of N. americanus returned almost to pretreatment levels within 2 years, with the rate of acquisition of adult worms independent of host age. A significant predisposition to hookworm infection was demonstrated by individuals. Prevention will result from measures to reduce the transmission and intensity of infection, and can be achieved through improved sanitation or by vaccination. However, vaccination is not yet a viable option because of our limited knowledge about protective immunity.

T rosette cells results in patients with (Necator americanus and Ancylostoma duodenale) hookworm infection, divided into groups on the basis of the degree of anaemia (Group I had marked anaemia Hb 1-7, hypochromia ), Group II had moderate anaemia (Hb 8-11, hypochromia ++) and Group III had no signs of anaemia despite the underlying hookworm infection), were compared with results in 28 healthy controls who had no signs of other infection and excreting no ova of hookworm or other parasites. The level of sheep erythrocyte rosette-forming T-lymphocytes (SE-TL) in the patients (Group I:42 +/- 8%; Group II:45 +/- 11%; Group III:47 +/- 6%) was markedly reduced compared to controls (58 +/- 13%) (P < 0.001). The leucocyte migratory responses to purified protein derivative (P.P.D); were significantly (P < 0.05) reduced in all the subgroups as compared with the controls. The results support the hypothesis of the existence of immunosuppression in patients with hookworm infection.

Experiments were carried out to ascertain whether the acute inflammatory phase of the intestinal response of hamsters to infection with Trichinella spiralis would adversely affect hookworms in concurrently infected animals. The survival and growth of hookworms were unaffected. However, the presence of hookworms reduced the establishment of T. spiralis, the initial growth of female worms and their fecundity. The expulsion of T. spiralis was also significantly slower in concurrently infected animals and there was significant depression of the serum IgG antibody response to muscle stage and adult worm antigens of T. spiralis in concurrently infected animals. These results are discussed in relation to the chronicity of human hookworm infections.

Reinfection with hookworm (Necator americanus) following chemotherapy was studied over 2 years in a rural village in Madang Province, Papua New Guinea. The prevalence of hookworm infection had returned to pre-treatment levels after 2 years, and the geometric mean hookworm burden had returned to 58% of the pre-treatment value. The rate of acquisition of adult worms was independent of host age, and was estimated as a geometric mean of 2.9-3.3 worms/host/year (arithmetic mean 7.9-8.9 worms/host/year). There was significant predisposition to hookworm infection; the strength of this predisposition did not vary significantly between age or sex classes.

Ancylostoma duodenale and Necator americanus are extremely common species of soil-transmitted helminth which flourish where poverty and malnutrition prevail. Hookworms contribute significantly to iron-deficiency anaemia, which remains one of the world's major nutritional problems, through the feeding activities of intestinal stages leading to chronic blood loss into the gut. In this article, a mathematical model is proposed to explain how human iron metabolism may respond to hookworm infection of varying intensity. The model draws attention to the importance of the regulation of stored iron levels in the process. The results from the model are presented for the effects of hookworm infection on the iron metabolism of a healthy adult male. Calculations are also presented in which the effects of hookworms on the iron metabolism of a non-pregnant woman are compared with those of a pregnant woman. Use of the model may help develop a better understanding of the pathology of hookworm disease.

Poly-parasitism is common in endemic communities and reactivity of sera from hookworm-infected patients against schistosomular antigens has been reported. Protective cross-immunity between N. americanus and S. mansoni was investigated in NIH and BALB/c mice. Protective resistance to homologous challenge with both parasites was confirmed in this model, however, functional immunity to heterologous challenge was not demonstrated. Sera from animals which had received homologous challenge with N. americanus and from hookworm-infected mice, which had previously been exposed to radiation-attenuated S. mansoni, exhibited an enhanced IgGAM response to infective stage N. americanus somatic antigens. The implications of these results with respect to serodiagnosis are discussed.

Between November and December 1987, 201 subjects from three communities of the Cordillera Province, Santa Cruz Department, South-East Bolivia (Camiri, Boyuibe, and Gutierrez) were examined for serum iron levels. Sixty-three (31.3%) were iron deficient. There were no significant differences between males and females (37.2% and 26.9%, respectively) and among the three localities studied. Iron deficiency was highest in the 3- to 9-year-old age group and lowest in the 30- to 39-year-old group. Considering the prevalence in the same localities of infections by hookworms, Trichuris trichiura, Strongyloides stercoralis, and Trichostrongylus, it is suggested that hookworms and possibly other intestinal parasites may be an important cause of the observed iron deficiency.

In order to determine the main clinical and laboratory manifestations associated with the infestation by an uncinaria during the first year of life, 42 children were studied from a group hospitalized between the years 1980 and 1985 in whom the main diagnosis at their time of leave from the hospital was parasitosis. Over 31 patients (74%) showed some degree of malnutrition, and severe in 24 of them (57% of the total). Clinical manifestations were mainly related to anemia (paleness, lack of air) and active intestinal bleeding (enterorrhagia, melena). Among the laboratory findings, 80% of the patients were shown to have anemia and in 24% of them, their hemoglobin levels were less than 5 g/dL, in more than half the anemia was normocytic normochromic. Also included are particularities concerning uncinariasis in the breast-feeding infant and some differences with the infection in the adult.

In order to determine the prevalence of the nutritional situation in children under six years of age and to study the relation with malaria and intestinal parasitism an epidemiological study of a cross sectional was carried out in Cordoba locality, Buenaventura Municipality in the Colombian Pacific Coast. One hundred and twenty eight children were studied to whom a questionnaire, a thick smear examination, and a serological test through the indirect immunofluorescence reaction was practiced. Coproparasitoscopic examination were also done in addition to medical and clinical anthropometric examinations, the latter consisting of the measurements of weight and height. The results of this investigation showed a prevalence of the nutritional state, according to Waterlow classification, of 0.81 percent, 17 percent and 2 percent for the first, second and third degree of malnutrition respectively. Instead, according to the Gómez classification it was 49 percent, 14 percent and 2 percent for the slight, moderate and severe degrees of malnutrition. When the geometric mean of the antibody titles for P. falciparum and for P. vivax were compared, using the methodology of the Waterlow classification, statistical associations were discovered and it was found that the geometric mean for P. falciparum were higher in those children that didn't have any malnutrition. Nevertheless, the geometric mean for P. vivax was higher for those children with a certain degree of malnutrition. Nevertheless, when the intensity of infection of the intestinal helminths, the quality of the dwelling and the breast-fed time duration were compared, no significant differences were detected, therefore we believe it convenient to keep on with this type of investigation, specially with those longitudinal-type studies so as to detect causal association in the relation nutrition/malaria.

In 345 apparently healthy Papua New Guinea male subjects, predominantly highlanders, 89% of whom were infected with hookworm (Necator americanus), there was a statistically significant inverse correlation of hookworm egg count with haemoglobin and serum ferritin level, but no significant correlation with serum albumin, folate or B12 values. A sub-group of 128 was chosen for a six-month study on the effect of treatment with the anthelmintic mebendazole and/or parenteral iron on haemoglobin and serum ferritin levels. Mebendazole-treated subjects remained worm-free and the hookworm egg counts of the controls decreased during the study period. Parenteral iron treatment had the expected effect of raising haemoglobin to a normal level. There was a statistically significant improvement in haemoglobin level in all treated groups but not in the control. Serum ferritin levels decreased significantly in all groups, but more in the control than in the treated groups, although treatment groups were not significantly different. Although probable inadequate uptake of iron by the subjects and blood donation by some subjects was apparently more detrimental to iron status than hookworm infection, the results of this study support the view that hookworm infection in this country contributes to lowered haemoglobin levels and iron status.

A case of Necator americanus infection associated with massive intestinal hemorrhage is reported. This is believed to be the first report in Thailand.

A total of 1,623 stool specimens from different individuals were examined to assess the infection prevalence and the pattern of occurrence of Necator americanus and Ancylostoma duodenale in a riverine community in Nigeria. 56.3% of 823 males and 52.63% of 800 females were positive for both species of hookworm, 25.1% of infected males, and 26.1% of infected females had A. duodenale while 46.7% of infected males and 51.2% of infected females had N. americanus. 28.2% of males and 22.7% of females had mixed infections of both species. The occurrence of each species was independent of the other. The distribution of infection was age-dependent, while sex had no effect on infection pattern. In A. duodenale infection, egg counts rose between 15 and 25 years of age, but declined with increasing host age. Egg counts in N. americanus infection were more stable with increasing age of the host. The probability of recovering N. americanus eggs in the faeces was higher than that of A. duodenale. In mixed infections, egg out put of N. americanus was higher than that of A. duodenale as indicated by the higher conditional probability of recovering N. americanus eggs in the presence of A. duodenale. The egg production of A. duodenale seems to be suppressed by N. americanus when both co-occur.

Faecal egg counts were compared in three groups in an area of universal hookworm infestation. Egg counts were lower in asthmatic and atopic non-asthmatic subjects than in a non-atopic population. The atopic population was defined by skin testing for immediate hypersensitivity responses. It is suggested that the atopic state may confer increased resistance to helminth infestation.

Iron-deficiency anemia resulting from intestinal blood loss is the major consequence of hookworm infection. Development of the anemia can be prevented, and it can be treated by administration of iron. Hypoproteinemia, often associated with hookworm infection, may be the result of either protein malnutrition or increased intestinal loss of protein. It is unlikely that the worms cause diffuse morphologic or functional alterations of the intestine. Fortification or supplementation with iron is a practical method to control hookworm disease in endemic areas.