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The public health significance of hookworm disease is briefly reviewed. The latest evidence confirms that blood loss caused by the worms' feeding activity in the gut is a contributing factor in the development of poor iron status leading to iron-deficiency anaemia. The World Health Organization has identified adolescent girls and women of child-bearing age as high-risk groups regarding the impact of hookworm disease. The merits of treating pregnant women with anthelminthic drugs after the first trimester are discussed.

SUMMARYA longitudinal investigation on natural populations of Ascaris in humans and pigs and an investigation of soil contamination with Ascaris eggs were carried out from June 1993 to June 1994 in 2 villages, Manhu area, Xinjian County, Jiangxi Province, China. Results from these studies indicate that although human ascariasis is endemic there is significant fluctuation in both prevalence and the mean number of eggs/g faeces (epg) of the communities. Fluctuation of age-stratified prevalence and mean epg was detected in children but not in most adult groups. Most cases of human ascariasis were judged to involve low intensities of infection and a typical overdispersion distribution pattern was observed through the year. It was estimated that during the year, nearly half of the eggs discharged in the environment came from infections in children aged between 2 and 15 years which accounted for about 30% of the total population. Soil in and around houses and in vegetable gardens was found to be contaminated by Ascaris eggs and this situation remained relatively stable throughout the year. Monthly developmental rate of Ascaris eggs in soil was detected and the results suggest that the fluctuation in prevalence observed during the year should be directly attributed to the effect of seasonality of egg development. Features of Ascaris infection in pigs were found to be similar to those in humans except for a lower mean intensity of infection. The possibility of cross-infection of Ascaris between human and pig hosts is discussed.

SummaryWe exposed 19 species of cockroaches to Moniliformis moniliformis by administering shelled acanthors orally and by injecting hatched acanthors directly into the body cavity. The exposure method had little influence on susceptibility: with one exception, species that were susceptible to oral exposure were also susceptible to injected acanthors and, in no case, did acanthors develop in injected animals when they did not develop in orally exposed conspecifics. We found no support for the hypothesis that the intestine may be a barrier to M. maniliformis establishment in cockroaches. There is, however, clear interspecific variation in susceptibility to M. moniliformis infection.

SUMMARYAncylostoma 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.

SUMMARYA study to compare the effects of different frequencies of targeted chemotherapy with levamisole (Ketrax: JAGAL Pharma, Lagos, Zeneca Pharmaceuticals UK) as an action for the control of Ascaris lumbricoides was carried out in 3 communities in rural Oyo State, Nigeria. The targeted group comprised children, aged 5 to 15 years, attending primary school within their village. Treatment was provided within the school with the assistance of the school teachers. Three frequencies of targeted treatment were offered. In one village targeted treatment was provided on 1 occasion in 1 year, in another village at two 6-monthly intervals and in the third village every 4 months. Prevalence and intensity (e.p.g.) of A. lumbricoides infection were determined immediately before and after the period of intervention using a modified Kato–Katz technique. In the villages which received treatment once and at 6-monthly intervals, a reduction in post-treatment intensity of A. lumbricoides was observed in the total population but this failed to attain statistical significance. In contrast, within the village which received 4-monthly targeted chemotherapy, a significant reduction in post-treatment intensity of A. lumbricoides was observed in the total population and in the targeted children. In general, reductions in the intensity of A. lumbricoides after intervention were not particularly pronounced in untreated children (aged 0–4 years) even in the 4-monthly targeted village, whereas in untreated adults, reductions approached statistical significance in villages which received targeted treatment once and at 4-monthly intervals.

A study to compare effects of mass, targeted and selective chemotherapy with levamisole (Ketrax) as an action for the control of Ascaris lumbricoides was carried out in three communities in rural Oyo State, Nigeria. Selective treatment was applied in one village by treating the most heavily infected 20% of the inhabitants, targeted treatment in the second village involved children aged 2–15 years, while mass treatment was offered to all inhabitants excluding infants under 1 year and pregnant women in the third village. Recommended doses of levamisole were given in the villages, as described above, at 3-monthly intervals during a period of 1 year. Prevalence and intensity (epg) of A. lumbricoides infection were determined immediately before and 3 months after the period of intervention using a modified Kato-Katz technique. In the selective treatment village, no significant differences were found between the pre- and post-treatment egg counts (mean(±S.D.) epg 6776±10791 versus 4259±10909 respectively) of A. lumbricoides in the total population. In the targeted treatment village, significant differences were recorded in pre- and post-treatment egg counts for the total population (9057 ± 15 797 versus 2579±6529) among the children alone (10935±20094 versus 992±3175) and among the untreated adults (7742±9782 versus 4561±8798). In the mass treatment village, significant differences in pre- and post-treatment egg count values were also recorded (11 907±17220 versus 1489±5165). The intensity of Trichuris trichiura and hookworm infections among the villagers before and after intervention were not observed to have changed significantly regardless of selective, targeted or mass treatment.

Field observations at one site on brown trout (Salmo trutta) and three-spined sticklebacks (Gasterosteus aculeatus) concurrently infected with mature Neoechinorhynchus rutili, together with the knowledge that large trout can be piscivorous in habit led to the proposition that the post-cyclic transmission of N. rutili may occur between these fish species. This route of transmission has been suggested for a number of acanthocephalan species. A laboratory experiement was conducted and it was demonstrated that uninfected rainbow trout (Salmo gairdneri) can acquire a N. rutili infection as a result of feeding on sticklebacks already carrying established worms in their intestines. This finding may help to explain how N. rutili is found in a wide range of fish definitive hosts throughout the northern holarctic region. More generally this example provides further evidence of the flexibility within acanthocephalan life-history patterns.

During the course of a primary infection of Nippostrongylus brasiliensis in protein-malnourished rats, plasma concentrations of corticosterone were found to decrease from 0.89 +/- 0.03 at the start of the infection to 0.28 +/- 0.08 mumol/l, 9 days post-infection (p.i.). Similarly, adreno-corticotrophic hormone levels were also observed to fall from 62.09 +/- 12.06 to 20.54 +/- 1.81 by 5 days p.i. and to 35.12 +/- 16.61 nmol/l by 9 days p.i. However, no significant changes were seen in the dry weight of the adrenal glands other than those expected in relation to changes in body weight. Concentrations of both plasma tri-iodothyronine and thyroxine were also severely depleted over the same period from 5.33 +/- 0.34 to 1.09 +/- 0.42 and 104.43 +/- 10.4 to 34.12 +/- 8.95 nmol/l respectively. This was considered not to be due to any change in the capacity of the plasma to bind these hormones. Results for insulin were highly variable, but overall were lower from protein-malnourished rats than results documented for well-nourished rats and a reduction from 18.07 +/- 3.17 to 6.08 +/- 2.18 mu units/ml, 9 days p.i. was observed. The results are discussed in relation to the role of these hormones in protein metabolism in a protein-malnourished animal.

Experiments to investigate the metabolism of glycine, L-glutamic acid and L-aspartic acid byMoniliformis moniliformiswere carried out by incubating adult worms aerobically for 3 h at 37°C in Tyrode's solution containing either [U-14C]glycine, L-[U-14C]glutamic acid, L-[U-14C]aspartic acid or L-[4-14C]aspartic acid. Much of the glycine and glutamic acid was absorbed by the worms, but little of either was metabolized. Aspartic acid was readily taken up and metabolized. After incubating with L[U-14C]aspartic acid, most radioactivity was found in ethanol and a volatile compound, presumed to be carbon dioxide, with smaller amounts in lactate, alanine, acetate, malate, glucose and succinate. After incubating with L-[4-14C]aspartic acid, most radioactivity was found in lactate and the presumed CO2with small amounts in alanine, malate and succinate. No radioactivity was found associated with ethanol or acetate. Possible metabolic pathways and suggestions for a relationship between the metabolism of aspartate with that of alanine and serine in this parasite are discussed.

SUMMARYThe daily food intake and related changes in body weight were measured in young rats which were fed on synthetic diets containing 1% (3 experiments), 2% (4 experiments) and 20% (1 experiment) casein respectively. Some rats were infected with Nippostrongylus brasiliensis and allowed to feed ad libitum, some remained uninfected and were allowed to feed ad libitum while others, which were matched by initial weight with rats from the infected group, remained uninfected and were given only the same amount of food as that consumed during the previous 24 h by their infected partners. No significant differences were detected between the rats before the start of the infection. Thereafter, the food intake of the infected undernourished rats was usually found to be significantly lower and the loss of body weight significantly greater than those of the uninfected rats. In infection periods of relatively long duration, the pair-fed uninfected rats did not lose as much weight as their infected partners even though their food intake (1% and 2% casein) was the same. Although the food intake, and consequently the weight, of infected rats fed on the diet containing 20% casein were significantly less than in their uninfected partners, no significant differences were observed between the weights of the infected and pair-fed rats fed on this diet.

SUMMARYAn epidemiological survey of intestinal parasitic infections was conducted in a sample of 203 children aged 3–5 years from a semi-urban and a rural community in Chiriqui, Panama, in 1983–4. On the basis of stool examinations, the prevalences of Ascaris lumbricoides, Trichuris trichiura, hookworm, Giardia intestinalis, Entamoeba spp. and Strongyloides stercoralis were found to be 27, 34, 14, 15, 5 and 4% respectively. The results from children from the two communities were compared. Polyparasitism occurred significantly more often in rural than semi-urban children. Following anthelmintic treatment with levamisole, the numbers of A. lumbricoides passed/child were recorded and the frequency distribution of the parasite was observed to be highly aggregated with a variance to mean ratio of 10·2. For A. lumbricoides, relationships between worm burden, worm biomass and egg production were investigated. In the data analysis, an attempt was made to explore the influence of numbers of male worms on egg production. The results are compared with those obtained during other recent studies on the epidemiology of A. lumbricoides infection in other countries.

SUMMARYIn 1977, a parasitological survey was undertaken of stool samples collected from 335 people from 5 villages in semi-arid regions of peninsular India. Stools, which were collected from various individuals in a stratified sample of 40 matched households from each village, were examined by standard diagnostic procedures. Eggs ofAscaris lumbricoidesand protozoan cysts, which were identified on morphological grounds as belonging toEntamoebaspp., were most common. Other protozoan cysts were considered to be those ofBalantidium coli, and eggs of hookworm andHymenolepis nanawere also observed in some of the stool specimens. The prevalence of parasitic infections varied between villages. The village with the highest prevalence ofAscaris(70%) appeared to have the greatest demands made on its meagre drinking-water supply. This village is located in a dry, windy and dusty region and it is speculated that, in addition to well-established transmission mechanisms, the villagers may be exposed, perhaps through contamination of uncovered drinking-water wells and inhalation, to wind-borneAscariseggs. In 1967, a WHO Expert Committee Report on the Control of Ascariasis pointed out that information on the frequency of dust-borne infection withAscarisin man was inadequate.

SUMMARYExperiments to investigate the linked metabolism of L-serine and L-alanine by Moniliformis moniliformis in vitro were carried out by incubating adult worms aerobically for 3 h at 37 °C in Tyrode’s solution containing L-[U-14C]alanine and other amino acids. When present in the medium alone, alanine was totally removed by the worms and metabolized almost entirely to ethanol and a compound identified as carbon dioxide. When present in the medium with serine and no other amino acids, alanine was largely metabolized as before but additional alanine, believed to originate from serine, was excreted. The same results were obtained with serine and 16 other amino acids in the incubation medium.

Some effects of insemination onMoniliformis dubiuswere studied by means of a surgical technique involving the transplantation of worms of known age, sex and reproductive state from one male rat to another. Insemination resulting in the development of eggs was found to have occurred in femaleM. dubiusaged 16 days. An individual maleM. dubiuswas found to be capable of inseminating as many as 17 females of the same age. The duration of the patent period appeared to be related to the length of the period of contact between male and female worms at the start of the course of infection. The evidence indicated that the patent period of a female worm was curtailed in cases where the female was isolated from males sooner than 5 weeks after the start of the infection. Male worms estimated to be not more than 21 days old were found to be capable of inseminating females older than 100 days; in these cases, the patent period was brief. Evidence was obtained to suggest that insemination is followed by further growth of the somatic tissues of the female worms. These results apply to experimental infections, and caution should be exercised in applying them directly to natural infections.

SUMMARY Observations made with the transmission electron microscope are described from the free ovaries of sexually mature female Corynosoma semerme (Palaeacanthocephala) from the ringed seal (Pusa hispida). The structure of the inature ovaries consists of a supporting syncytium, oogonial cells and tissue and appears to be basically similar to that already described for 4 other species of Acanthocephala representing the 3 orders of the phylum. A comparison has been made between the organization of the cytoplasm of the mature oocyte and the zygote with referenee to the eonsequences of fertilization. A detailed description is presented of the heterogeneous inclusions that are observed in the cytoplasm of the mature oocyte but not in the zygote. The fate and possible function of the components of these inclusions is discussed. INTRODUCTION The palaeacanthocephalan genus Corynosoma has a worldwide distribution and includes at least 30 species which attain sexual maturity in avian and mammalian hosts (Yamaguti, 1963). Most of the work that has been done on Corynosoma seems to have been concerned with taxonomy and ecology ; virtually nothing is known about its physiology and reproductive biology. Two species of Corynosoma occur and reproduce in the alimentary tract of the ringed seal (Pusa hispida) from the Bothnian Bay of the Baltic Sea (Helle & Valtonen, 1980 ; 1981). Recently, living sexually mature female Corynosoma semerme have been obtained from ringed seals and it has been possible to prepare samples of free ovaries (= ovarian balls, see Atkinson & Byram (1976); Asaolu, Whitfield, Crompton & Maxwell (1981)) for examination by transmission electron microscopy. Some of these. observations are described in this paper. They complement observations on the ultrastructure of the ovarian tissue of Polymorphus minutus (Crompton & Whitfield, 1974), Monili-formis dubius (Crompton & Whitfield, 1974; Atkinson & Byram, 1976; Parshad, Crompton & Martin, 1980 ; Asaolu et al. 1981) and Acanthosentis tilapiae and Pallisentis golvani (Marchand & Mattei, 1976) and they provide new information about cytological changes occurring in the early embryo after fertilization.

A survey was carried out to determine values for the prevalence and intensity of infection of intestinal helminths in children living in Cocle Province, Republic of Panama. The data set consisted of the results of microscopic examinations (modified Kato Katz technique) of stool samples collected in November 1987 from 661 children attending primary schools in 4 communities in the province. The overall prevalences of Ascaris lumbricoides, hookworm and Trichuris trichiura infections were found to be 18.2, 12.0 and 27.5% respectively. There were significant differences between the infection prevalence values for children attending the different schools, but not with respect to age or sex. Positive associations were detected between particular pairs of infections and these were most evident when Trichuris trichiura was involved. The data revealed evidence of a positive association between siblings at one school only for each helminth infection. There was extreme variation in the values for intensity of infection (20-126180 epg for A. lumbricoides). Highly significant, and unexplained, differences were observed in the intensity of A. lumbricoides infection by primary school; this finding did not apply to hookworm or T. trichiura. The analysis also revealed that children heavily infected with A. lumbricoides were also likely to be heavily infected with T. trichiura. Comparisons with the results of surveys carried out in Cocle Province in 1926 and 1974 indicate that these infections are declining in this region of Panama.

SummaryBy means of conventional light microscopical and counting procedures, estimations have been made of the average number and size of ovarian balls from unfertilized and fertilized femaleMoniliformis dubius. The observations were made on worms recovered from experimental primary infections lasting 1, 2, 3, 4, 5, 8, 11, 14, 17 and 20 weeks in male rats. The number of ovarian balls rises to about 6300 per worm, with the maximum being attained more rapidly in unfertilized than in fertilized females. On average more ovarian balls were present in unfertilized than in fertilized females, but a marked decline in number occurred in both groups of worms towards the end of the experimental period. Similarly, on the basis of the area within the elliptical profiles of fixed ovarian balls, it appeared that those from unfertilized females were generally larger on average than those from fertilized worms.

SUMMARYAn analysis of the frequency distribution of numbers of Moniliformis dubius in rats of an outbred strain of Wistar origin (CFHB) and feeding ad libitum on Oxoid 41B diet, showed that over-dispersion occurred regardless of the age and sex of the rats and the infective dose given (12, 20 or 40 cystacanths/rat). Over-dispersion was also shown to be independent of variability in the age and sex of the cystacanths given. The analysis demonstrated that the over-dispersion declined as the course of the infection proceeded. As expected, parasite survival was found to be age-dependent with female worms living longer, on average, than males, and both male and female worms living longer in rats given 12 as opposed to 20 cystacanths. Possible mechanisms for generating the over-dispersion observed during this work are discussed and a tentative hypothesis, invoking host heterogeneity with regard to carbohydrate availability in the small intestine, is proposed for further experimental investigation.

SUMMARYThe prevalence of Taenia saginata (Cestoda) among 146 predominantly Pokot tribesmen in western Kenya was studied in an attempt to assess the reliability of detecting infections by faecal examinations. Firstly, a single faecal sample was microscopically examined after being processed by a standard ether sedimentation technique. Secondly, all subjects were treated with niclosamide and a purgative and the tapeworms were recovered. In this way the efficiency of diagnosing infections by faecal examinations was estimated. T. saginata eggs were found in the faeces of 68% of the men who were eventually found to be infected. Information was collected by interview from all subjects about whether they were or ever had been infected with tapeworms and about the form of treatment previously sought or taken. Eleven out of 25 men were apparently unaware of their tapeworm infections while no evidence of infection was found among 10 of the 24 reportedly infected men. A change in the pattern of treatment for tapeworms was reported which may have resulted in a recent decline in the prevalence of infection.

General nutritional effects on female CFLP mice harbouring larval Taenia crassiceps were investigated using groups of mice fed ad libitum on purified diets containing 2%, 4%, 8% and 16% (w/w) protein respectively. When uninfected and infected mice were compared over an experimental period of 20 weeks, it was established that a significantly higher proportion of uninfected mice survived the course of the experiment than infected mice. There was no evidence of the presence of the parasites having any effect on the overall food intake of the mice. Infected mice, however, were found to be significantly heavier, on a fresh weight basis, than their uninfected partners, but the pattern was reversed when the dry weights of mouse carcasses were compared following the removal of parasites. In general, more parasite tissue was recovered from mice feeding on the higher protein diets (8% and 16%).

SUMMARYThe morphology of the mucosal surface of samples from the small intestine of young protein-deficient pigs was examined by scanning electron microscopy. Three pigs had been infected with Ascaris suum for at least 58 days while 1 had remained uninfected; all pigs were housed and maintained under the same conditions, at the same time. The tissue samples collected at post mortem examination from pigs which contained A. suum showed varying degrees of villous atrophy and fusion. In addition, unusual small craters and as yet unidentified objects were observed at the surfaces of the enterocytes of Ascaris-infected pigs. These changes in mucosal morphology were not seen in the tissue taken from the uninfected pig. The possible association between the mucosal lesions and lactose maldigestion in young, protein-deficient pigs infeceted with A. suum is discussed.

SUMMARYThe structure of the ovarian tissue in juvenile Corynosoma semerme and C. strumosum from a fish paratenic host and in the cystacanth stage of Echinorhynchus gadi from an amphipod intermediate host was investigated by means of transmission electron microscopy. The species were obtained from hosts living in the Baltic Sea. The observations indicate that ovarian development was more advanced in cystacanths of E. gadi than in juveniles of C. semerme and C. strumosum. Free ovaries were present in E. gadi with an obvious supporting syncytium and surface microvilli. The biological significance of the different stages of ovarian development in these species is discussed briefly in relation to either reproductive strategies and host specificity in definitive hosts or to the attainment of infectivity by cystacanths in intermediate hosts.

An epidemiological survey of intestinal helminthiases was conducted on 766 primary school children aged 5-16 years from Ile-Ife, Nigeria. On the basis of stool examinations, the prevalence of Ascaris lumbricoides, Trichuris trichiura, hookworm and Strongyloides stercoralis was 88.5, 84.5, 33.1 and 3% respectively. Intensity of infection was measured indirectly by egg counts for each species of helminth and also by counting worms passed after chemotherapy in the case of A. lumbricoides. The influence of host age and sex on infection levels was assessed. Relationships between the intensities of A. lumbricoides, T. trichiura and hookworm in individual children were identified. After anthelmintic treatment with levamisole, the frequency distribution of A. lumbricoides per host and the relationship between parasite fecundity and worm burden were investigated. Reinfection patterns of A. lumbricoides were assessed at two 6-monthly intervals and even within the narrow age range described, differences were found. In addition, evidence was obtained for predisposition of individuals to heavy or light infection with A. lumbricoides.

1. Certain aspects of the general morphology ofPolymorphus minutusare described together with a detailed description of the body wall.2. An additional layer of the body wall, the epicuticle, has been demonstrated. It appears to consist of acid mucopolysaccharide and may have a function of protecting the parasite from the enzymes of its host.3. A histochemical investigation has been made of the layers of the body wall and it is concluded that lipoprotein is one of the main structural components.4. The distribution of the activity of the two enzymes, non-specific esterase and alkaline phosphatase, has been studied throughout the animal and the activity of a third enzyme, leucine aminopeptidase, has been detected in the body wall.5. It is suggested that all the layers of the body wall, with the exception of the cuticle and epicuticle, are of metabolic importance. The striped layer may be connected with absorption and the felt and radial layers may be involved in the further metabolism of absorbed compounds.6. The results obtained are used to formulate a possible structure of the surface of the parasite which would facilitate the absorption of nutrient substances through the body wall.I am grateful to Dr P. Tate for advice and encouragement during this work, Dr R. J. Tatchell for helpful discussions, and Dr D. L. Lee for criticising the manuscript and Mr T. M. Warwick, Department of Zoology, University of Edinburgh for providing material.

Crompton & Harrison (1965) complied from the literature a list of 84 species of bird which have been reported to be final hosts ofPolymorphus minutusand since then, the parasite has been found in the American White-winged Scoter (Melanitta deglandi) and the Chestnut Teal (Anas castanea) by Schmidt (1965) and Avery (1966) respectively. Unless detailed investigations are undertaken, there is no way of knowing how many of these birds from true hosts in whichP. minutuscan reproduce successfully.P. minutushas also been reported from the muskrats (Ondata zibethica) which Golvan (1961) considered to be an accidental host and I have recovered seven living specimens ofP. minutus48 h after forcibly feeding 20 cystacanths of the parasite contained inGammarus pulexto a female Wistar rat. The seven worms were firmly attached to the rat's intestinal wall and all were located in the posterior half of the intestine.

The distribution of glycogen has been studied in P. minutus by means of histochemical methods. The strongest staining for glycogen was detected in the proboscis, the radial layer of the body wall and the non-contractile parts of the muscles.Histochemical methods have also been used to study the localization of the activity of ten oxidoreductase enzymes. The enzymes are situated in the mitochondria of P. minutus, the distribution of which corresponds closely with that of glycogen.I am grateful to Dr P. Tate for helpful discussions, and to Drs D. L. Lee and F. P. B. Wooding for criticizing the manuscript. Thanks are also due to Mr D. Barnard for technical assistance.

An electron microscope study has been made of some of the events which occur during the beginning of the relationship between Moniliformis dubius and its intermediate host, Periplaneta americana. The acanthor penetrates through the intestinal wall and is encapsulated by host haemocytes. This encapsulation is typical of the haemocytic reaction of insects to foreign bodies. A proliferation of the acanthor's surface membrane then takes place and forms a coat of microvilli. The formation of this coat by the parasite is accompanied by the dispersion or disintegration or both of the encapsulating haemocytes. The coat of microvilli constitutes a major component of the envelope surrounding early larval stages of M. dubius. There is no evidence for the presence of host connective tissue in the envelope.We are grateful to Dr A. V. Grimstone, Department of Zoology, for use of the electron microscope, and to Mr David Barnard and Miss Valerie Furber for technical assistance. We thank Dr George Salt, F.R.S. for his criticism of the manuscript.