Humans and great apes cohabiting the forest ecosystem in central african republic harbour the same hookworms

Background

Hookworms are important pathogens of humans. To date, Necator americanus is the sole, known species of the genus Necator infecting humans. In contrast, several Necator species have been described in African great apes and other primates. It has not yet been determined whether primate-originating Necator species are also parasitic in humans.

Methodology/Principal Findings

The infective larvae of Necator spp. were developed using modified Harada-Mori filter-paper cultures from faeces of humans and great apes inhabiting Dzanga-Sangha Protected Areas, Central African Republic. The first and second internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal DNA and partial cytochrome c oxidase subunit 1 (cox1) gene of mtDNA obtained from the hookworm larvae were sequenced and compared. Three sequence types (I–III) were recognized in the ITS region, and 34 cox1 haplotypes represented three phylogenetic groups (A–C). The combinations determined were I-A, II-B, II-C, III-B and III-C. Combination I-A, corresponding to N. americanus, was demonstrated in humans and western lowland gorillas; II-B and II-C were observed in humans, western lowland gorillas and chimpanzees; III-B and III-C were found only in humans. Pairwise nucleotide difference in the cox1 haplotypes between the groups was more than 8%, while the difference within each group was less than 2.1%.

Conclusions/Significance

The distinctness of ITS sequence variants and high number of pairwise nucleotide differences among cox1 variants indicate the possible presence of several species of Necator in both humans and great apes. We conclude that Necator hookworms are shared by humans and great apes co-habiting the same tropical forest ecosystems.

We conducted analyses of DNA sequences obtained from the infective larvae of Necator spp. from humans and great apes inhabiting Dzanga-Sangha Protected Areas, Central African Republic. Three sequence types (I–III) were recognized in the in the ITS region, and 34 cox1 haplotypes represented three phylogenetic groups (A–C). I-A, II-B, II-C, III-B, III-C combinations were determined. Combination I-A, corresponding to Necator americanus, was demonstrated in humans and western lowland gorillas; II-B and II-C were observed in humans (local inhabitants and researchers), western lowland gorillas and chimpanzees; III-B and III-C were found only in humans. Pairwise nucleotide difference in the cox1 haplotypes between the groups was more than 8%, while the difference within each group was less than 2.1%, suggesting that each type represents a distinct species. This is the first molecular evidence that Necator species found in great apes can infect humans and vice versa.

Rapid detection and identification of human hookworm infections through high resolution melting (HRM) analysis

Background

Hookworm infections are still endemic in low and middle income tropical countries with greater impact on the socioeconomic and public health of the bottom billion of the world's poorest people. In this study, a real-time polymerase chain reaction (PCR) coupled with high resolution melting-curve (HRM) analysis was evaluated for an accurate, rapid and sensitive tool for species identification focusing on the five human hookworm species.

Methods

Real-time PCR coupled with HRM analysis targeting the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA as the genetic marker was used to identify and distinguish hookworm species in human samples. Unique and distinct characteristics of HRM patterns were produced for each of the five hookworm species. The melting curves were characterized by peaks of 79.24±0.05°C and 83.00±0.04°C for Necator americanus, 79.12±0.10°C for Ancylostoma duodenale, 79.40±0.10°C for Ancylostoma ceylanicum, 79.63±0.05°C for Ancylostoma caninum and 79.70±0.14°C for Ancylostoma braziliense. An evaluation of the method's sensitivity and specificity revealed that this assay was able to detect as low as 0.01 ng/µl hookworm DNA and amplification was only recorded for hookworm positive samples.

Conclusion

The HRM assay developed in this study is a rapid and straightforward method for the diagnosis, identification and discrimination of five human hookworms. This assay is simple compared to other probe-based genotyping methods as it does not require multiplexing, DNA sequencing or post-PCR processing. Therefore, this method offers a new alternative for rapid detection of human hookworm species.

Platelet parameters in subjects infected with hookworm

Hookworm is an important intestinal parasite infection with high prevalence in tropical countries. In addition to iron deficiency anaemia, the human hookworm appears to have evolved a number of complementary strategies to overcome the host's haemostatic processes. These include the inhibition of blood coagulation, platelet aggregation and mediator release, and the secretion of fibrinogenolytic enzymes. In this work, we studied the platelets in the subjects with detection of hookworm infection from screening stool examination comparing to those without. One hundred subjects were included, studied for stool parasite and platelet parameters. Of our 100 subjects, hookworms were identified in stools of six cases, giving an infection rate equal to 6%. The platelet parameters of the subjects showed a statistically significant lowering of mean platelet volume (MPV) in the subjects with hookworm infection. Also, we detected a non-significant lower platelet count in subjects with hookworm infections. Of interest, the alteration in platelet size, identified by platelet parameters, has never been documented in the literature. This observation might be a pathological process or might be an accidental finding in our study.

Hookworm infections of schoolchildren in southern Thailand

A study of hookworm infections of schoolchildren was conducted in Nakhon Si Thammarat Province, southern Thailand. Of the 2,940 hookworms that were recovered from the children, almost all (99.9%), were Necator americanus, only three (0.1%) were identified as Ancylostoma duodenale, and all were female worms. An estimation of the worm burden of and the worm expulsion from the schoolchildren indicated there were 17 cases of light intensity hookworm infection. Fifteen cases (88.2%) expelled worms in numbers that corresponded with the worm burden that was estimated from the number of eggs per gram of feces. Two cases (11.8%) expelled more worms than predicted. In 16 moderate intensity cases, five (31.3%) expelled worms in a quantity that corresponding with the estimated worm burden. Eleven cases (68.7%) expelled fewer worms than predicted. All cases of heavy intensity infection expelled fewer worms than predicted.

A novel method for the isolation of nematode larvae using pluronic F-68-treated cellulose strips

A new method is described for the isolation of cultured nematode larvae. This allows effective separation of larvae from fecal contamination, exsheathed larvae from cast sheaths, and viable larvae from nonviable larvae. The method involves the use of cellulose strips and has been assessed using larvae from 2 hookworm species, Necator americanus and Ancylostoma ceylanicum. Pretreatment of the cellulose strips with 1.0% (w/v) of the nonionic surfactant, Pluronic F-68, significantly increased larval recovery of both species.

Influence of intestinal parasitism on lactose absorption in well-nourished African children

Hydrogen breath tests were performed in Gabon (Central Africa) after a loading dose of lactose in 67 well-nourished African children (50 with intestinal parasites and 17 unparasitized) and in 18 unparasitized young adults. All had normal nutritional status, and none had diarrhea or digestive symptoms. Parasites that were found included Ascaris lumbricoides in 76% of the parasitized children, Trichuris trichiura in 58%, Giardia in 24%, Entamoeba histolytica in 20%, Schistosoma intercalatum in 16%, and Necator Americanus in 14%. A similar proportion of parasitized (64%) or unparasitized (62.8%) subjects were lactose malabsorbers. Giardia infection was associated with a higher, but not significantly different, proportion of lactose intolerance (10 of 12, 83.3%). The presence of infection with A. lumbricoides or T. trichiura did not increase the percentage of lactose malabsorption. These data indicate that a decrease of lactase activity in well-nourished African children is not related to the presence or the importance of Ascaris or other intestinal parasites if the nutritional status is normal.

The epidemiology and population biology of Necator americanus infection in a rural community in Zimbabwe

Baseline data from an epidemiological study of hookworm infection in a rural community in Zimbabwe are presented. The infection status of an age-stratified sample of the community was assessed using anthelmintic expulsion techniques. Necator americanus was the only helminth parasite found to be present. The age-prevalence and intensity profiles rose asymptotically to an adult prevalence of about 80% and adult mean burden of 7.7 worms per host. The overall mean burden was 4.8 worms per host. The frequency distribution of N. americanus was overdispersed and well described by the negative binomial distribution with a value for the aggregation parameter, k, of 0.346. Separate estimates of k were lower in males and older hosts. The distribution patterns were difficult to reconcile with any simple process of age-dependent acquisition of an effective immune response. A significant negative correlation was recorded between per caput fecundity and worm burden, providing evidence for a density-dependent regulation of female worm fecundity. The basic reproductive rate (R0 congruent to 2) was found to be similar to estimates from other geographical areas.

The human environment, occupation, and possible water-borne transmission of the human hookworm, Necator americanus, in endemic coastal communities of the Niger Delta, Nigeria

A 15-month longitudinal study was carried out in four riverine communities of the Niger Delta to ascertain the impact of the environment and occupation on the transmission and infection pattern of the human hookworm Necator americanus. A total of 925 (50.10%) individuals were found to be infected. Male and female infection rates were 54.26% and 47.96% respectively. The difference was statistically significant (P less than 0.05). The prevalence of infection, the egg counts, and the seasonal incidence were related to the occupations and mode of transmission. The highest occupation prevalence of 60.92% occurred among the fishermen through water-borne transmission, while prevalence rates of 52.96% and 52.4% were recorded respectively through soil transmission. The difference between fishermen's prevalence and farmers' prevalence was statistically significant (P less than 0.01). Farmers' egg counts varied from 1,500 eggs per gram (epg) in the dry season to 7,500 epg in the rainy season. Fishermen's egg counts ranged from 3,000 epg in the rainy season to 8,000 epg in the dry season. The difference was not significant (P greater than 0.05). Among farmers the highest monthly incidence of 25% occurred in June, while the highest incidence of 35% occurred in fishermen in April. Incidence of infection among fishermen remained significantly higher (P less than 0.05) than in other occupation groups during the dry season months. Water-borne transmission of hookworm probably increases the incidence and egg counts among fishermen during the dry season.

A modified agar plate method for detection of Strongyloides stercoralis

The agar plate method is a new technique with high detection rates for coprological diagnosis of human strongyloidiasis. This report details modifications of the technique and establishes a standardized procedure. We recommend that all plates should be carefully observed using a microscope because macroscopic observation can lead to false negative results. It is also advisable to pour formalin solution directly into microscopically positive dishes to collect worms by sedimentation. This procedure enables one to observe worms otherwise hidden. Sealing dishes with adhesive tape prevents larvae from crawling out of the dishes, eliminating any possibility in the reduction of detection rates, and greatly improves the safety conditions for the technician performing the procedure. We consider the agar plate method to be superior to the filter paper method in detecting Strongyloides, and we believe that it will eventually become the technique of choice.

Hookworm (Necator americanus) infection and storage iron depletion

The relationship between iron status and the intensity of infection with hookworm was investigated in a rural population on Karkar Island, Mandang Province, Papua New Guinea. There was a significant negative correlation between plasma ferritin level and hookworm burden, which was strongest in males. In contrast, there was no correlation between plasma ferritin and hookworm egg count, and no consistent correlation between haemoglobin level or haematocrit and either measure of hookworm intensity. The results suggest that the role of hookworm in the aetiology of anaemia may be difficult to assess without the accurate measurement of hookworm burden.

Identification of human hookworm in failed-treatment cases using Chinese hamsters (Cricetulus griseus) and scanning electron microscopy

An attempt was made to identify the human hookworm involved in failed-treatment cases using abnormal hosts and scanning electron microscopy. Thirty-seven, 2 to 6 month old Chinese hamsters (Cricetulus griseus) from a closed, outbred, conventional colony, were each given between 20 and 120 filariform larvae per os. The larvae were cultured from faeces from mebendazole (Vermox) 500 mg single-dose, failed-treatment cases living in the lowveld farming area of the Transvaal Province, South Africa. About 60 to 78 days after inoculation, the animals were killed and adult worms were removed from their small intestines. Eleven (30%) of the 37 hamsters harboured a total of 31 adult worms (19 males and 12 females), while 26 hamsters were refractory to infection. The greatest number of worms recovered from a single animal was six. A total of 27 worms (17 males and 10 females) were subjected to examination by scanning electron microscopy. Micrographs showed male and female worms to be morphologically all of the Necator americanus species, as identified by a pair of ventral and dorsal cutting plates, a dorsal tooth and the fused terminus of spicules in the male bursa. The transverse cuticular striations were distinct and smooth. Several points of interest arose from the results of this study and are discussed.

Parasite detection efficiencies of five stool concentration systems

Fresh fecal material that was free of ova and parasites was pooled with 10% Formalin in a 1:4 ratio to prepare a standard specimen. Portions of 100 ml of this specimen were individually seeded with Cryptosporidium oocysts, Entamoeba coli, Entamoeba histolytica, and Giardia lamblia cysts; ova of Necator americanus; and Strongyloides larvae. Appropriate volumes of each parasite suspension were used to evaluate the Fecal Concentrator Kit (Remel, Lenexa, Kans.), Fecal Parasite Concentrator (Evergreen Scientific, Los Angeles, Calif.), Para-Pak Macro-Con (Meridian Diagnostics, Inc., Cincinnati, Ohio), and Trend FeKal CON-Trate (Trend Scientific, Inc., St. Paul, Minn.). A standardized gauze filtration method was used as the reference procedure. Tests were performed in triplicate with each individual parasite-concentrator combination, with three slides examined from each sediment. All of the systems effectively concentrated parasites compared with direct examination of unconcentrated fecal material. The Fecal Concentrator Kit provided the best overall performance. Clarity of sediment, lack of debris, and uniformity of background material were found to be important considerations for microscopic detection of parasites in concentrated specimens.

A simple method for the collection of Necator americanus larvae

A simple method for the collection of third-stage larvae of Necator americanus has been described. This technique provides repeated recovery of very clean larvae from cultures in moderate numbers.

An investigation of hookworm infection and reinfection following mass anthelmintic treatment in the south Indian fishing community of Vairavankuppam

Hookworm infections, as assessed by counting worms expelled following anthelmintic treatment and by egg output, were found to be of low prevalence and intensity in a South Indian fishing community. The initial overall prevalence of infection in the community was 43%, and the average burden was estimated at 2.2 hookworms per person. The age profiles of prevalence and intensity differed between males and females, with the latter harbouring significantly higher levels of infection. Children of both sexes under 10 years of age rarely harboured hookworms. Treatment with pyrantel pamoate was estimated to be 91% effective in clearing hookworm infections. Egg counts made on stools collected during an 11-month period of reinfection indicated that female patients became reinfected soon after treatment, while little hookworm egg excretion was observed in males during the observation period following treatment. Females acquired a significantly higher number of worms during the reinfection period compared with males, although the average burden in females reached only 28% of the initial, pre-treatment level. The hookworm population consisted of predominantly Necator americanus, and less than 10% of Ancylostoma duodenale. The parasites were highly aggregated within the host population with 10% of the community harbouring over 65% of the total hookworms. Low values of the negative binomial aggregation parameter, k, (indicating extreme over-dispersion) were recorded in groups stratified by age and sex. Highly significant positive correlations were observed between the initial (pre-treatment) and reinfection worm burdens of female (but not of male) patients. It is suggested that occupational practices related to walking through areas contaminated with hookworm larvae play an important role in generating the observed patterns of infection within this community.

Necator americanus in neonatally infected hamsters. The time-course of infection and antibody response to the surface antigens of L4 and adult worms

Neonatal hamsters were infected with a hamster-adapted strain of Necator americanus, and the time-course of infection was followed by worm and faecal egg counts. Parasite eggs were first recorded during the 6th week of infection, increasing rapidly thereafter to peak in weeks 7-10. Male hamsters excreted more eggs than females, but both sexes were equally susceptible to infection and harboured comparable worm burdens. Faecal egg counts declined from week 10 onwards and this was associated with a loss of worms from animals with heavy infections. Low level infections were stable over the first 114 d of infection but worm fecundity nevertheless still declined over this period. Both hamster sexes responded similarly to surface antigens on adult worms, the antibody levels rising from week 5 onwards to reach a plateau in weeks 6-7, which persisted until the experiments were terminated. The major antigens recognised on the surface of adult worms had molecular masses corresponding to 25 kDa, 32 kDa, a doublet with the heaviest polypeptide resolving at 46 kDa, and a triplet with the heaviest at 67 and 93kDa. In contrast L4 had only 2 major cuticular antigens resolving at 41 and 93kDa. The 93kDa molecule on L4 and adult worms may be antigenically related.

Population biology of hookworms in west Bengal: analysis of numbers of infective larvae recovered from damp pads applied to the soil surface at defaecation sites

The aims of this study were to analyze the seasonal distribution of infective larvae on the soil surface, to determine whether numbers of infective larvae near faeces were related to the faecal egg count of individuals, and to relate the distribution of larvae to environmental characteristics. Larvae were recovered from damp pads, applied to the soil surface in an annulus around fresh, identified stools of individuals who were participating in a larger epidemiological study. This provided an estimate of exposure to infection at the time of defaecation. Transmission was restricted to the rainy season and large aggregations of larvae were encountered earlier rather than later in the rainy season. Frequency distributions for the number of larvae extracted from each pad showed a high degree of aggregation, with most monthly counts showing good fits to the negative binomial probability distribution. Despite variations in monthly sampling means, the degree of aggregation in the population of larvae was remarkably stable over the 18 month sampling period (k of negative binomial = 0.01 to 0.08). Estimates of the degree of aggregation of the parasites in the human population were also available, and comparisons suggest that the infective larvae were much more aggregated than the parasitic stages. There was no relationship between the mean daily egg output of individuals and the number of larvae which developed and were recovered from the soil surface near the faeces. Thus, people who contribute large numbers of eggs to the environment are not necessarily those who are the greatest source of infection for others.(ABSTRACT TRUNCATED AT 250 WORDS)

Hookworm infection in a rural community in south India and its association with haemoglobin levels

Faecal samples were obtained from 1113 persons living in a rural area in South India, and the hookworm ova load (Necator americanus) was determined using Kato's thick smear method. Evidence of hookworm infection was present in 92%, 77% having a count of under 100 epg, 11% a count of 1000 to 1999 epg, and 4% having counts between 2000 and 12,000 epg. Females had significantly higher ova counts than males on the average, but age did not appear to have any effect. Haemoglobin was also estimated: 80% of adult males, 87% of adult females and 90% of children were anaemic. There was a significant negative association between ova load and haemoglobin level, and the decrease in haemoglobin for a doubling of the ova load was estimated by regression analysis to be 0.18, 0.29 and 0.16 g/dl in adult males, adult females and children, respectively. There was nearly perfect agreement in the ranking of 10 clusters by mean ova count and mean haemoglobin level or percentage with anaemia.

The growth and migration of Necator americanus following infection of neonatal hamsters

Necator americanus was studied in neonatally infected hamsters in order to determine precisely the growth and migration of the parasite in this laboratory host. Most larvae stayed at the skin infection site for at least 48 hours following administration of larvae and the movement to the lungs commenced on day 3. There was no significant growth at the skin site or during the first two days in the lungs. 98% of the larvae were recovered from the lungs by day 6 and showed signs of some growth and development. Moulting larvae were seen in the lungs on days 7 and 8, but intestinal worms, which were first detected on day 7, were all L4 larvae. These worms were significantly longer than the lung stages and henceforth grew rapidly. Over 80% of the worms were recovered from the intestine on day 9, only small numbers of larvae persisting in the lungs until day 12. Moulting worms were observed in the intestine on days 17 to 21, after which growth continued and did not slow until about the fifth week. Small quantities of eggs were occasionally detected as early as day 34 and continuous egg production commenced in the seventh week of infection reaching a peak by about the 10th week.

[Epidemiology of intestinal helminthiasis (necatoriasis, taeniasis, ascariasis, trichuriasis) in the Kaya Region (Upper-Volta)]

Prevalence of intestinal helminthiasis: 1 223 stool specimens are examined in Louda and 690 in Damesma (Kaya, Upper-Volta). In this sample eggs of N. americanus are seen in 14,7% of the specimens in Louda and 9,3% in Damesma. Eggs of H. nana are seen in 10% of the specimens, for the two villages. Eggs of T. saginata are seen in 7.4% of the specimens of the two villages. And eggs of A. lumbricoides, T. trichicera are found inters then 0.5% of the specimens.

Endoscopic discovery and capture of Necator americanus in the stomach

We report a case of the endoscopic discovery and removal of a specimen of Necator americanus hooked into the gastric mucosa of a black woman from Zaire. We extracted the parasite by means of biopsy forceps. Signs of previous bites were seen in the antrum. This exceptional localization might be due to a jejuno-duodeno-gastric reflux.

[Necator americanus uncinariasis in an infant born and residing in Mexico City]

A six-month-old infant is reported with the unquestionable diagnosis diagnosis of Necator americanus uncinariasis. The mother was also infected with the same hookworm. The patient was born and has always dwelt in Mexico City, where helminthiasis is considered extremely rare. The epidemiologic studies determined that the dwelling conditions were inadequate for the transmittal of the agent through the soil. The authors emphasize the importance of the presumptive diagnosis in those cases suggesting the disease and to carry out studies to confirm the existence of other infectious means

[Formol-gasoline concentration technique for eggs and cysts (author's transl)]

Modification of the formol-ether concentration technique was made by substituting gasoline for ether and omitting Triton from the formula. Parallel examination of hundred (100) stool samples by the original and by the modified technique resulted in identical distribution of negative, light, medium and heavy positive slides. The same samples examined by the direct smear and by the Kato's technique gave lower rates of positives. The modified technique is useful in laboratories with limited material resources.

A comparative study of the relative efficacy of pyrantel pamoate, bephenium hydroxynaphthoate and tetrachlorethylene in the treatment of Necator americanus infection in Ceylon

The clearance of hookworm (Necator americanus) ova by a single dose of tetrachlorethylene (T.C.E.) was compared with that produced by single and multiple dose regimes of bephenium hydroxynaphthoate and pyrantel pamoate. Single doses of bephenium and pyrantel were inferior to T.C.E. Three daily doses of bephenium or pyrantel produced effects comparable with a single dose of T.C.E. Because of the low cost and lack of side effects, T.C.E. remains the drug of choice in the treatment of N. americanus in infections; the only disadvantage of T.C.E. is its unnoticed deterioration under tropical conditions.

The topographic distribution of Necator americanus and Ancylostoma duodenale in the human intestine

During an investigation in Dar es Salaam, Tanzania, 28 human intestinal tracts were systematically inspected on the presence of hookworms. In total, 643 hookworms (508 Necator americanus and 135 Ancylostoma duodenale) were isolated from 19 intestinal tracts. The localization of these hookworms was determined. N. americanus worms were concentrated in the duodenum and jejunum, whereas A. duodenale worms rather prefer the jejunum and proximal ileum. Some preference of hookworms for the antimesenteric site of the intestinal wall was found. The relative distance between adjoining worms in the observed hookworm populations was 3.8 cm on the average for Necator and 5.5 cm for Ancylostoma. The distribution of the sexes in the worm-population revealed no monosexual or bisexual prevalence of the hookworms.

Evaluation of the skin test for hookworm as an epidemiological tool

The usefulness of a skin test with larval Necator americanus antigen for assessment of hookworm prevalence was evaluated in an endemic area of Costa Rica. In comparison with standard coprologic techniques employed to survey the population, the skin test detected 83% of infections, showing a fairly satisfactory sensitivity. The overall specificity of the test was 50%, i.e., random. No correlation was found between skin reactivity and hookworm burden. The sensitivity of the test increased moderately with age, but its specificity decreased significantly at the same time. False positive reactions were more numerous among persons formerly infected with hookworm who had been negative for as long as 5 years. There was an indication of cross reactivity with intestinal nematodes other than hookworm. The test was used to detect hookworm infected persons in the community for selective treatment, in comparison with mass treatment of all the people in another village. The selective administration of an anthelminthic drug to only skin test positive persons did not achieve the same drop in community hookworm prevalence as did the indiscriminate treatment of the whole population.

[Coprologic survey in Bilharzia infected children of the Adzope region (Ivory Coast)]

During a stool examination survey on 174 bilharzia attained children living in a rural area of Ivory Coast, 93% were found to have intestinal parasites mainly Entamoeba coli, Necator americanus and Ascaris lumbricoides. The prevalence of the cysts of Entamoeba histolytica (4,7%) is lower than the one found in France (7%). Concerning the other intestinal parasites, their respective occurrence have been compared with those noted in other regions of Ivory Coast and of Africa.

A comparison of post-mortem analysis of helminths with faecal egg counts

Intestinal helminth infections are very common amongst residents of the Colombo area. Most common by post-mortem examination of 104 cases of sudden death were Trichuris trichiura (97.1%), Necator americanus (88.5%), Enterobius vermicularis (77.9%) and Ascaris lumbricoides (40.4%). Trematode and cestode infections were not encountered except a single case of H. diminuta infection. A comparison of the results obtained by the direct smear method for examining stools missed cases harbouring gravid females of up to 3 Ascaris lumbricoides, 29 Trichuris trichiura and 66 Necator americanus. The direct smear revealed all the helminths present except threadworms in only 30% of the cases. The correlation between worm loads calculated from ova counts and actual numbers harboured was fairly close in 19 out of 35 cases for Ascaris and 37 out of 78 cases for Necator americanus. Highly erroneous results were obtained in many instances when worm loads were calculated from the results of ova counts.