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SUMMARYGastrointestinal nematodes represent important sources of economic losses in farmed ruminants, and the increasing frequency of anthelmintic resistance requires an increased ability to explore alternative strategies. Theoretical approaches at the crossroads of immunology and epidemiology are valuable tools in that context. In the case of Teladorsagia circumcincta in sheep, the immunological mechanisms important for resistance are increasingly well-characterized. However, despite the existence of a wide range of theoretical models, there is no framework integrating the characteristic features of this immune response into a tractable phenomenological model. Here, we propose to bridge that gap by developing a flexible modelling framework that allows for variability in nematode larval intake which can be used to track the variations in worm burdens. We parameterize this model using data from trickle infection of sheep and show that using simple immunological assumptions, our model can capture the dynamics of both adult worm burdens and nematode fecal egg counts. In addition, our analysis reveals interesting dose-dependent effects on the immune response. Finally, we discuss potential developments of this model and highlight how an improved cross-talk between empiricists and theoreticians would facilitate important advances in the study of infectious diseases.

SUMMARYCystic echinococcosis is a significant parasitic disease in Iran, where a variety of animals act as intermediate hosts. In this study, 25 isolates of Echinococcus granulosus obtained from water buffalo from various parts of Iran were characterized on the basis of the morphology of the metacestode and the adult worm. The characteristics of protoscoleces from the different studied areas were nearly similar. They showed 2 rows of alternating large and small hooks and their shapes were smooth in outline. In contrast to the protoscoleces, the adult rostellar hooks showed a rough outline. The results showed that the total length, the blade lengths of the large and small hooks and the number of hooks are almost similar to those isolated from sheep but significantly different from those isolated from camels. The growth rates of adult E. granulosus (total worm length, segmentation and maturation) of buffalo origin, at 35 and 41 days post-infection of dogs, were nearly comparable to the common sheep strain. The form of the strobila and the morphology of the reproductive system were also similar to those of sheep origin. This suggests that the common sheep strain (G1) of E. granulosus may also use buffaloes as its intermediate host.

SUMMARYRegular distribution of ivermectin reduces onchocerciasis transmission and morbidity by killing, within humans, the microfilarial stage of the parasite (microfilaricidal effect). In addition, ivermectin exerts a so-called embryostatic effect by which microfilarial production by the adult female worm becomes suppressed during a number of weeks after treatment. To assess the overall effect of ivermectin on onchocerciasis transmission and evaluate the likelihood of local elimination of the infection it is important to estimate the magnitude of the anti-fertility effect over the course of a treatment programme. Estimates of the effect of repeated drug treatments on the production of microfilariae by adult Onchocerca volvulus were obtained by developing a model that was fitted to data collected from three hyperendemic communities in Guatemala, where eligible residents received ivermectin twice per year for two and a half years. The data consist of microfilarial load measurements in the skin, collected just before each six-monthly treatment during the programme. The model that is developed describes the dynamics of an individual host's expected microfilarial load over the 30-month study period. We adopt a Bayesian approach and use Markov chain Monte Carlo (McMC) techniques to fit the model to the data. Combining estimates from the three villages, average microfilarial production in the first six months post-treatment was reduced by ~64% of its pre-treatment level, regardless of values chosen for the pre-ivermectin fertility rate within plausible ranges. Increased adult worm death rate after treatment (to mimic removal of macrofilariae via nodulectomy during the programme) resulted in a smaller estimated magnitude of the embryostatic effect (rate of microfilarial production was reduced by ~58% of pre-ivermectin value). After subsequent treatments, the rate of microfilarial production appeared to be similarly decreased. The data and analyses therefore do not support the hypothesis of a cumulative effect of multiple ivermectin treatments on microfilarial production by female worms.

The present study was designed to assess the role of inulin and sugar beet fibres (SBF) on adult O. dentatum in growing pigs. Four experimental diets were formulated based on barley flour with added insoluble fibre from oat husk (Diet 1), a pure carbohydrate source inulin (Diet 2), soluble fibre from sugar beet fibre (SBF) with a high proportion of soluble fibre components (Diet 3) or inulin plus SBF (Diet 4). Thirty-two 10-week-old pigs were divided randomly into 4 groups each of 8 pigs. After 3 weeks adaptation on Diet 1 all pigs were infected with a single dose of 6000 L 3 O. dentatum . At week 7 p.i. one group was switched to Diet 2, another group to Diet 3 and another group to Diet 4. The remaining 8 pigs continued on Diet 1 until the end of the experiment and served as controls. At week 13, all pigs were necropsied and their worm burdens determined. The worm recoveries from the pigs on the inulin supplemented diet (Diet 2) were reduced by 97% compared to the controls (Diet 1). Further, the inulin-fed pigs exhibited markedly reduced faecal egg counts. The pigs on inulin plus SBF diet (Diet 4) and on SBF diet (Diet 3) had 86% and 70% adult worm reductions compared with the controls, respectively. The results from this study indicate that highly degradable and rapidly fermentable carbohydrates such as dietary inulin have a profound deworming effect on O. dentatum infection.

SUMMARYThe morbidity and transmission dynamics of geohelminthiases are determined by the patterns of infection intensity in the community. Understanding the determinants of these patterns requires a combination of field, laboratory and theoretical study. Studies of age-specific reinfection, and of the phenomenon of predisposition, indicate that the major determinant of convex age-intensity profiles and of heterogeneity in infection intensity is the rate of establishment of infection, rather than the rate of adult worm mortality. The rate of establishment is, in turn, determined by exposure to, and protection from, infection. The evidence indicates that exposure, at least to the orally-transmitted geohelminths, varies with age and is highly heterogeneous between hosts. The immune response in geohelminthiasis is vigorous, parasite-specific, hetero geneous between hosts, and both age and infection dose dependent, but has yet to be convincingly shown to be protective. Since the immune response is itself a function of exposure, unravelling the interaction between ecology and immunology as determinants of geohelminth worm burden will require simultaneous assessment of both processes via immuno epidemiological study.

SUMMARYThe host–parasite relationship of the Chinese mainland strain of Schistosoma japonicum in CBA mice is described and compared to previous reports on this parasite in mice. S. japonicum took under 2 weeks to complete its migration to the portal system of mice, and peak passage of schistosomula through the lungs occurred 5–6 days after infection. The mean percentage establishment of worms, which was independent of the infecting inoculum, was 46%. The adult worm burdens remained constant over a 28-week period of infection. Male and female worms reached maximum mean lengths of 13 and 19 mm, respectively. Egg laying commenced 30 days after infection. The number of ova deposited in the liver stabilized at some 55000 by 12 weeks of infection with 30 cercariae, but the intestinal egg burden rose from 132000 at 12 weeks to 430000 at 28 weeks. Faecal eggs were first observed 6 weeks after mice were exposed to 100 cercariae and 7 weeks after lighter exposures. Faecal egg output also stabilized 12 weeks after infection. The formation of granulomas in the liver occurred within 2 weeks of egg deposition and encompassed a maximum area 14 weeks after infection. Fifty per cent mortality occurred 15 weeks after exposure, but only in hosts infected with 100 cercariae.

SummaryFourteen 9-month-old zebu calves were immunized with 10000 irradiatedSchistosoma bovisschistosomula given in 1–3 intramuscular or subcutaneous doses, and 4 more calves were immunized with 10000 irradiated cercariae administered percutaneously in a single dose. Eight weeks after the beginning of the experiment these calves, together with four non-immunized controls were challenged percutaneously with 10000 normalS. boviscercariae/calf. Comparative clinical, parasitological, pathological and pathophysiological observations subsequently revealed significant differences between the vaccinated and non-vaccinated calves. The vaccinated calves showed significantly higher growth rates, and a superior body composition as indicated by their lower total body water content. The beneficial effects of vaccination were also shown by significantly lower faecal egg outputs in the vaccinated calves and by their lower tissue egg and adult worm counts. The reduced tissue egg counts were also reflected in the milder histopathological changes seen in the vaccinated calves. The vaccinated calves had significantly higher packed cell and circulating red blood cell volumes than the challenged controls, longer red blood cell half lives, and somewhat lower blood volumes and rates of red blood cell synthesis. No untoward clinical effects that could be attributed to vaccination were recorded. These results indicate that zebu cattle can be effectively protected againstS. bovisby vaccination with irradiated organisms. We are now evaluating this type of vaccine in a field trial in an enzootic area in the Sudan.

Cells capable of transferring immunity toTrichinella spiralis, i.e. of accelerating adult worm expulsion, were present in the mesenteric lymph nodes of mice infected for 4, 6 or 8 days, but not in mice infected for only 2 days. The time-course of worm expulsion in mice infected on the day of transfer was similar in recipients of day 8 cells, expulsion becoming marked only when the recipients had been infected for at least 6 days. Transfer of cells 4 or 6 days after infection did not result in an accelerated worm expulsion; transfer 1 or 2 weeks before infection did not enhance the level of immunity in recipient mice. In contrast to the results obtained with mesenteric lymph node cells (MLNC) no immunity was trsnsferred when recipients were given spleen cells taken from donors infected for 8 days. It is suggested that MLNC do not cause worm expulsion directly, but cooperate with another component of the host's defence mechanism. Accelerated expulsion in recipients of cells was accompanied by a premature decline in fecundity of female worms. Evidence is presented to show that worm expulsion and impaired reproduction may represent independent aspects of the immune response toT. spiralis.

Of the 39 most common helminth parasites of man listed by Peters & Gilles (1977), 30 may be detected and often diagnosed by finding their eggs or larvae in the faeces of infected people. The preferred habitat of many of these helminths is the alimentary tract itself and the continual flow of material through the food tube provides a simple, passive and reliable means of transport and eventual exit from the host for the reproductive stages of a worm. Helminth eggs are generally less than 150 μm in diameter and although individually comprise a small material investment by the adult worm in the propagation of the species, the chances of infecting a host are so slim (though this may be a teleological inference) that adult worms are often highly fecund: a female Ascaris lumbricoides is estimated to release daily into the intestine approximately 200,000 eggs (WHO, 1967). Yet numbers should not always be equated with great substance or bulk – an equally important determinant of the chances of finding an egg in faeces: assuming a spherical diameter of 60 μm and a specific gravity of 1·2 (Sawitz, 1942) then a female Ascaris is estimated to produce only about 25 mg of eggs each day, which is 0·01% of a moderate daily output of 250 g of faeces.

SummaryThe host—parasite relationships of two geographical isolates ofSchistosoma haematobiumin CBA mice are described and compared to previous reports on this parasite in other experimental hosts and in man. The mean percentage establishment of worms in mice was 17% and was not affected by the age or sex of the host. Adult worm burdens remained constant over 20 weeks, but were reduced after 18 months of infection. Male and female worms reached mean maximum lengths of 4·78 and 5·9 mm respectively. Egg laying commenced 9·5 weeks after infection and eggs accumulated in the tissues throughout the period of infection. A large increase in the rate of egg accumulation occurred coincidental with the appearance of eggs in the bladder of some mice. Faecal eggs were first observed in some mice at 12·5 weeks and most mice excreted a few eggs by 17 weeks p.i. (post-infection). Eggs were not found in the urine of infected mice. Excreted eggs and eggs isolated from the livers of infected mice hatched, but the resulting miracidia were unable to infect appropriate snail hosts. The development of hepatic granulomas and egg-induced pathology in the bladder of mice is described.

My attention was first directed to this Cestode in 1906 when I was asked to examine several specimens of edible fish which had been exposed for sale in the public markets and had been condemned as human food on account of the presence of obvious, intrusive bodies in the flesh. In three of these cases the muscles of the flesh of the fishes—a Halibut, a Megrim and a Hake—contained cysts which enclosed the larvae of a Tetrarhynchid, and on examination the latter was identified as T. erinaceus from the peculiar nature of the armature of the proboscides. In another case the wall of the stomach of a Halibut was also infected with the same larvae. Acting on an obsolete principle of Border Law the Fish Inspectors promptly condemned the fishes and then caused them to be examined. I do not think there was any valid reason for the condemnation of the articles of food, for I can find no reference in the literature to the presence of Tetrarhynchids in the human alimentary canal, and there does not appear to be any question of a possible communication of a parasite by the consumption, as food, of such infected flesh. Further the number of larvae present was far too few to lead to any emaciation of the fish, or to the likelihood of the production of toxic substances in the flesh of the animal. Nevertheless the Inspectors probably acted in the interests of the public health in condemning such articles of food as contained obvious cyst-like structures in the flesh, as to the precise nature of which they were ignorant, since there is always the possibility that these bodies might be detrimental to the health of those eating them.

Large number of fishes of the family Cryprinodontidae collected from a stream at Hastings, Sierra Leone, were found with a diplostomulum encysting on the skin and in the musculature.Infected pieces of fish were fed to day-old chicks and cattle-egrets, and adult stages of a worm, considered to be new species and namedDiplostomum(Dolichorchis)leonensis, were obtained.Morphological details of the diplostomulum and the adult worm are described.The author wishes to express his gratitude to Dr G. Dubois for his interest and advice in connexion with the study, to Miss M. R. Coker who prepared the diagrams; and to Messrs F. Deen, T. Alhassan and M. Seisay for technical help.

Although the common Filariid parasite of the Camel was identified as a distinct species more than forty years ago (Lewis, 1882), the recent memoir on Indian Nematodes by Baylis and Daubney (1923) contains the first intelligible account of the structure of the adult worm. Their description of the species, which they refer to the genusAcanthocheilonema, is based partly on some rather fragmentary material received from the Zoological Survey of India, and partly on notes and drawings supplied by Major F. H. Stewart, I.M.S.

1. The anatomy of the male and female genitalia ofParorchis acanthusis described in detail. An extensive receptaculum uterinum occurs in the female system.2. The chromosome number inP. acanthusis twenty-two.3. Spermatogenesis, oogenesis, and fertilization, are described in the adult worm. The chromosome number in both male and female cells is reduced to eleven at the first meiotic division.4. Maturation in the female takes place in the “receptaculum uterinum”.5. Cleavage of the ovum to the three cell stage has been followed.6. The probable synonymy ofP. acanthusandP. avitusis discussed.

One of a large number ofLymnaea peregra(Mull.) from a pond near Glasgow was found to be infested withCercaria diplostomi gasterostei.C. d. gastrosteihas been found to penetrateGasterosteus aculeatusand develop into a diplostomulum in the retina of the eyes.Large numbers ofG. aculeatusfrom the pond have been found withDiplostomulum gasterosteioccurring in the retina.Infested heads of fish were fed to domestic ducklings and pigeons, and adult stages of a worm considered to be a new species and namedD. gasterosteiwere obtained.Morphological details of the cercaria, diplostomulum and the adult worm are described.The author wishes to thank Dr C. A. Hopkins for reading and criticising the manuscript, Dr D. A. Erasmus and Dr G. Rees for valuable suggestions. My thanks are due also to the technical staff of the Department who assisted me in the collection of snails and fishes, and to Mr Francis Deen who did the sectioning of the specimens. This work was in part supported by a grant from Shell Oil Company (London).

SummaryRats were treated with betamethasone at different stages of infection withStrongyloides ratti. Treatment caused a diminution in the number of adult worms recovered but this residual population was not expelled as were worms from untreated rats. If treatment was started after expulsion had already begun adult worm numbers increased – suggesting that auto-infection occurred. Treatment throughout a primary infection prevented the development of an immune response which expelled, or killed, a challenge infection. Treatment, just before and just after challenge, prevented the expulsion of the challenge infection. Worm expulsion up to day 35 was prevented by treating rats with betamethasone 4, 6, 8 and 10 days after infection.

SUMMARYAvailable data in the literature pertaining to the life-history characteristics of all known species of mammalian schistosomes have been gathered, and correlations between such variables as length of pre-patent period, adult worm size, rate of progeny production and progeny size have been explored. Accommodation of the schistosome life-cycle to the constraints imposed by certain host characteristics such as life-expectancy and size is discussed. Of the 23 known species of mammalian schistosomes, 20 species apparently rely to a major extent on relatively large-bodied and long-lived mammals such as primates, ungulates and proboscideans for their transmission. Only 1 species,Schistosomatium douthitti, is exclusively dependent on rodents for its transmission.S. douthittiattains maturity within its definitive host faster than any other mammalian schistosome, and is the only species known to be capable of producing viable eggs by facultative parthenogenesis. For all species of mammalian schistosomes, adult worm size, as estimated by female length, is positively correlated with the number of uterine eggs contained within the female (r= 0·682). For the 7 species for which data exist, rate of egg production/worm pair/day is positively correlated with uterine egg counts (r= 0·873) and inversely correlated with egg length (r= −0·787) and miracidium length (r= −0·953). Length of the pre-patent period is positively correlated with egg length (r= 0·503). With respect to the molluscan host, the number of cercariae produced by snails is positively correlated with the shell size of the snail (r= 0·657). For the 5 species for which data exist, the rate of egg production is inversely correlated with shell size of the intermediate host (r= −0·955) and the common logarithm of the number of cercariae produced (r= −0·893). Comparisons between species suggest that exceptionally low rates of cercariae production in the intermediate host may be compensated for by rapid rates of egg production in the definitive host, implying a degree of integration in the schistosome life-cycle not previously appreciated. Most species of mammalian schistosomes have long-lived definitive hosts, and snail hosts capable of producing many cercariae; compensatory relationships are therefore less obvious in such species. Additional quantitative data on all aspects of schistosome life-histories, particularly rate and duration of egg production, are needed to confirm or refute the relationships discussed above.

SUMMARYOf the surface antigens identified by radio-iodination, two-dimensional gel analyses showed no similarities between those ofSchistosoma haematobiumandSchistosoma mansoni, thus providing a basis for the species specificity of these antigens described previously (Simpson, Knight, Hagan, Hodgson, Wilkins & Smithers (1985)Parasitology90, 499–508). The surface antigens ofS. haematobiumwere glycosylated and comprised an acidic polypeptide ofMr17000 as well as a complex set of polypeptides of approximate pI 6–7, which resolved in theMrrange 20000–30000. At least one of the lowerMrforms of this complex is also present in the adult worm. Limited cross-reaction was observed withS. mansoniinfection sera and this may be due to a shared carbohydrate epitope. In contrast, extensive cross-reaction was observed using sera from mice immunized withS. bovis.This pattern parallels the species-specificity of vaccine-induced immunity. Extensive cross-reaction was also observed within cell-free translation products of m-RNA from adult worms ofS. haematobiumandS. mansoniby use of heterologous human infection sera. The few antigens which were species-specific may represent surface antigens.

The design of mass and targetted community-based chemotherapy programmes for the control of the major helminth infections of man is discussed in relation to the population and transmission dynamics of the parasites. Rapid reinfection following a single mass or targetted anthelmintic application is shown to be a universal feature of helminth transmission, as a consequence of the regulatory or feed-back mechanisms controlling population abundance within both individuals and the community as a whole. Control of reinfection requires repeated community treatment where the intensity of application and the interval between treatments are dependent on the reproductive life-expectancy of the adult worm, the net force of transmission prior to control (the basic reproductive rate) and the factors which create aggregation in the distribution of parasite loads within the population. Selective or targetted treatment is shown to be most effective for the control of morbidity as opposed to the control of transmission. The impact of targetted treatment depends critically on the factors that generate heterogeneity in parasite burdens and on whether or not selectivity is based on a single or repeated identification of the ‘wormy’ fraction of the community. Monte Carlo simulation studies are employed to assess the likely impacts of different control strategies on average parasite abundance/person and the distributions of parasite loads within populations. Future epidemiological research needs are discussed in relation to theoretical work and recent field studies of predisposition to heavy infection.

It has been shown that the 5th or adult stage ofTrichinella spiralisstimulates strong immunity in mice. This was shown using a transfer technique and irradiated worms. A comparison between the immunity produced by a normal infection and one which has been irradiated is made and explanations offered to explain the fact that less immunity is stimulated by irradiated larvae.I would like to express my gratitude to H.M. Treasury and to the Agricultural Research Council for financial support during the time that this work was conducted. I would also like to thank Professor W.I.B. Beveridge, within whose department this work was conducted, for the facilities provided. I would also like to record my gratitude to Dr W. C. Campbell for the many stimulating discussions we have had on the subject ofTrichinella.

The phenomenon of self-cure, as it occurred under field conditions in East Africa, was studied in Merino sheep infected with Haemonchus contortus. The onset of self-cure, as judged by a dramatic fall in faecal egg counts, was found to be simultaneous in sheep grazing on infected pasture and in sheep grazing on parasite-free pasture. Furthermore the results of autopsies carried out before and after self-cure showed that a marked and equal loss of adult worm burdens had also occurred. These results indicate that self-cure of H. contortus infections under natural conditions occurs in the absence of reinfection and is apparently non-immunological in origin. Since the phenomenon was always associated with a period of significant rainfall, it is suggested that new growth of pasture may be a significant aetiological factor.