Ecological and physiological aspects of helminth--host interactions in the mammalian gastrointestinal canal

Vertebrates as uninfected disseminators of helminth eggs and larvae

The passive dispersal of non-mobile organisms by vertebrates (zoochory) is a common mechanism used to explain their often widespread distribution. Transport occurs either internally via the vertebrate digestive tract (endozoochory), or externally be adhering to skin, feathers or fur (ectozoochory), and its success is due to both physiological and ecological factors associated with the disseminating 'hosting' animal. Helminth eggs and larvae are generally non-mobile stages that are largely dependent on the movement of another animal, typically a host, for geographical dissemination. Studies on the zoochory of helminths by vertebrates are extensive and particularly long-standing, stretching back to the 19th century, although this literature is often overlooked when considering the biogeography of parasites. This review assesses the potential of helminths to be dispersed passively by zoochory examining evidence from both laboratory and field studies. The physiological dynamics of the vertebrate intestines and skin surface as hostile environments, as well as the characteristics of eggs and larvae which may facilitate successful transport are evaluated. The various mechanisms of helminth endo- and ectozoochory are presented and the likelihood of long-distance dispersal determined. It is concluded that zoochory is a potentially important means of disseminating parasites.

Workshop no. 2. Parasitic infection and host nutrition

Even if we do not always acknowledge the fact, nutrition is a fundamental aspect of symbiosis and parasitism. (1) The significance of nutrition often forms a basic feature in schemos of classification of the various associations between living organisms (see Read, 1908; Whitfield, 1979). (2) The growth and reproduction of different parasites appear to Vary in response to the nutrition of the host (see Mettrick & Podesta, 1974; Nesheim, Crompton, Arnold & Barnard, 1977; 1978; Parshad, Crompton & Nesheim, 1980). (3) The course of a parasitic infection may also vary in response to the nutritional status of the host and perhaps such variations are the result of the affocts of nutrition on the host's immune response (Chandra & Nowberne, 1977; Chandra, 1980). (4) Finally, parasitic disease is well known to be much more scrious in undernourished hosts (see Chandra & Newberne, 1977); when man's the deprived host, the impact of infections and parasitic disease on young children is Particularly severe and distressing (Latliam, 1975).

Biology and Systematics of Echinococcus

The biology of Echinococcus, the causative agent of echinococcosis (hydatid disease) is reviewed with emphasis on the developmental biology of the adult and metacestode stages of the parasite. Major advances include determining the origin, structure and functional activities of the laminated layer and its relationship with the germinal layer; and the isolation, in vitro establishment and characterization of the multipotential germinal cells. Future challenges are to identify the mechanisms that provide Echinococcus with its unique developmental plasticity and the nature of activities at the parasite-host interface, particularly in the definitive host. The revised taxonomy of Echinococcus is presented and the solid nomenclature it provides will be essential in understanding the epidemiology of echinococcosis.

Symbiotic bacteria of helminths: what role may they play in ecosystems under anthropogenic stress?

Symbiotic bacteria are a common feature of many animals, particularly invertebrates, from both aquatic and terrestrial habitats. These bacteria have increasingly been recognized as performing an important role in maintaining invertebrate health. Both ecto- and endoparasitic helminths have also been found to harbour a range of bacterial species which provide a similar function. The part symbiotic bacteria play in sustaining homeostasis of free-living invertebrates exposed to anthropogenic pressure (climate change, pollution), and the consequences to invertebrate populations when their symbionts succumb to poor environmental conditions, are increasingly important areas of research. Helminths are also susceptible to environmental stress and their symbiotic bacteria may be a key aspect of their responses to deteriorating conditions. This article summarizes the ecophysiological relationship helminths have with symbiotic bacteria and the role they play in maintaining a healthy parasite and the relevance of specific changes that occur in free-living invertebrate-bacteria interactions under anthropogenic pressure to helminths and their bacterial communities. It also discusses the importance of understanding the mechanistic sensitivity of helminth-bacteria relationships to environmental stress for comprehending the responses of parasites to challenging conditions.

Sexual segregation of Echinorhynchus borealis von Linstow, 1901 (Acanthocephala) in the gut of burbot (Lota lota Linnaeus)

Helminths often occupy defined niches in the gut of their definitive hosts. In the dioecious acanthocephalans, adult males and females usually have similar gut distributions, but sexual site segregation has been reported in at least some species. We studied the intestinal distribution of the acanthocephalan Echinorhynchus borealis von Linstow, 1901 (syn. of E. cinctulus Porta, 1905) in its definitive host, burbot (Lota lota Linnaeus). Over 80% of female worms were found in the pyloric caeca, whereas the majority of males were in the anterior two-thirds of the intestine. This difference was relatively consistent between individual fish hosts. Worms from different parts of the gut did not differ in length, so site segregation was not obviously related to worm growth or age. We found proportionally more males in the caeca when a larger fraction of the females were found there, suggesting mating opportunities influence gut distribution. However, this result relied on a single parasite infrapopulation and is thus tentative. We discuss how mating strategies and/or sexual differences in life history might explain why males and females occupy different parts of the burbot gut.

Histological patterns of the intestinal attachment of Corynosoma australe (Acanthocephala: Polymorphidae) in Arctocephalus australis (Mammalia: Pinnipedia)

The mucosal attachment pattern of Corynosoma australe in the intestines of Arctocephalus australis is described. Normal and abnormal tissue were sampled from 32 hosts to be submitted to histological routine protocol to embedding in paraffin and permanent mounting in balsam. Corynosoma australe shows three different degrees of body depth intestinal attachment (BDINA-1-3). BDINA-1: it is exclusive of the small intestine and the parasite attaches on the villi; BDINA-2: parasite affects the Lieberkühn crypts in several depth levels and, BDINA-3: the parasite reaches the submucosa. These attachment patterns alter the mucosa by degeneration and dysfunction due to necrosis of mucosal structure, great quantities of cellular debris and significant reduction of the mucosal thickness. Other aspects are crater-like concave holes (CLCHs) as sites where C. australe could be attached-detached several times according to adult migratory processes within luminal intestine space. The submucosa shows edema probably due to the local mucosal alterations resulting in homeostatic break. There is no severe inflammatory response by host but BDINA-1 to BDINA-3 and CLCH could represent foci to secondary opportunistic infections and significant areas of malabsorption in severally infected hosts contributing to increase clinical signs of preexistent pathologies.

Parasites of Rattus colletti (Rodentia:Muridae) from the Adelaide River floodplain, Northern Territory, and comparison with assemblages in other Rattus species

This study documents the parasite assemblage of Rattus colletti (Thomas, 1904) from the Adelaide River flood plain, Northern Territory, Australia. In total, six species of helminth (comprising two cestodes, one trematode and three nematodes), and four species of arthropod (comprising one tick, one mite, one flea (identified to family level) and one louse (identified to generic level)) were found. In spite of the hosts being present in high numbers the helminth assemblage was depauperate, characterised by low prevalence and abundance, both being higher in wet seasons. More helminths were found in larger animals. The most prevalent helminth was from the Trichostrongylina, Nippostrongylus typicus (Mawson, 1961). The assemblage was characterised as having two heirloom species (N. typicus and Hymenolepis diminuta (Rudolphi, 1819)), a host capture (Raillietina celebensis (Janicki, 1902) and a cosmopolitan species (Mastophorus muris (Gmelin, 1790)) as well as occasional infections. When compared with the helminths from a single population of Rattus sordidus (Gould, 1858) a similar number of species were found, three species being in common, and both were depauperate when compared with the more extensively surveyed faunas of Rattus fuscipes (Waterhouse, 1839) and Rattus leucopus (Gray, 1858).

Intestinal helminth parasites in flounderPlatichthys flesusfrom the River Thames: an infracommunity analysis

An analysis was undertaken of intestinal helminth communities in flounderPlatichthys flesusfrom two sites on the River Thames. A comparison was made between helminth community richness and diversity from these sites at the component and infracommunity levels. At the component community level, a richer and more diverse parasite community was found in flounder from the Tilbury location (marine influence) than that from the Lots Road location (freshwater influence). At the infracommunity level, more parasite species and parasite individuals per host were found at Lots Road and the percentage of similarity values were low at both locations. Helminth species with high prevalence values in the parasite communities of the flounder are the dominant species in any individual fish, harbouring multi-specific infections. The presence of more invertebrate species, which are intermediate hosts in the helminth life cycle in the Thames, fish vagility and the high prevalence and abundance values ofPomphorhynchus laevisin the flounder, may explain the differences between the two locations.

GEOGRAPHIC ANALYSIS OF HOST USE, DEVELOPMENT, AND HABITAT USE OF AN ACANTHOCEPHALAN SPECIES, LEPTORHYNCHOIDES THECATUS

Leptorhynchoides thecatus (Linton, 1891), an acanthocephalan parasite of freshwater fishes, varies in host use, development, and habitat use throughout North America. Spatial structure of these characteristics was examined from data extracted from the literature. Geographic patterns were inferred from point comparisons using correllograms and then tested with Moran's I statistic for global and local significance, and visually from regional means within major river drainages. Species of Micropterus Lacepède, 1802 (black basses) were common hosts in most regions, except the Lower Mississippi and South Atlantic regions where species of Lepomis Rafinesque, 1819 (sunfishes) were common hosts. Development, described as the proportions of adults relative to cystacanths (extraintestinal juveniles), decreased with latitude. Habitat use of L. thecatus showed marked geographic patterns. Leptorhynchoides thecatus occurred in the intestine of sunfishes in the South Atlantic and Lower Mississippi regions, in the ceca in fish of all species included in the study in the Missouri and Texas-Gulf regions, and both in ceca and intestines in fish of all species in northern regions. Leptorhynchoides thecatus showed geographic patterning within the variable traits across the range of the species. These patterns may be the result of ecological factors or of genetic differences that might indicate L. thecatus comprises multiple cryptic species.

Detection of the rodent tapeworm Rodentolepis (=Hymenolepis) microstoma in humans. A new zoonosis?

A longitudinal survey of gastro-intestinal parasites was conducted over a 3-year period in remote communities in the north-west of Western Australia where, based on diagnosis by microscopy of faecal samples, Rodentolepis (=Hymenolepis) nana was found to be the most common enteric parasite. In the present study, using molecular tools, we describe the unexpected discovery, of a mixed infection with a second hymenolepidid species, Rodentolepis (=Hymenolepis) microstoma in four of the surveyed individuals. In the absence of any reliable earlier reports we believe this is to be the first instance of the detection of R. microstoma from human hosts. The development of a diagnostic restriction fragment polymorphism has enabled the study of R. microstoma in human populations and will greatly facilitate a more thorough understanding of the epidemiology of this parasite in the future.

The life cycle of Nematodiroides zembrae (Nematoda, Trichostrongylina) in the rabbit

The morphogenesis and the chronology of the life cycle of Nematodiroides zembrae (Bernard, 1965), a parasite of Oryctolagus cuniculus from Spain, were studied in detail in its natural host. For each experiment a morphological description of the different stages of the life cycle is provided. The free-living larvae developed in eggs until infective stage. First hatching began at 10 days. Twenty-one, worm-free rabbits were each infected per os with N. zembrae larvae and killed 3 days after infection (DAI) and every day from 4 to 22 DAI. By 3 DAI all recovered larvae were exsheathed and present in the small intestine. The third moult occurred between 6 and 7 DAI. The last moult occurred between 11 and 19 DAI. The prepatent period lasted for 21-22 days. The distribution of N. zembrae along the small intestine of the rabbit is described. Significantly different distributions of the parasite along the small intestine indicated that migrations occurred during the development of N. zembrae in the rabbit. The life cycle of N. zembrae is compared with the 5 known life cycles of Nematodirus spp. in ruminants. The biological data are very similar in both groups except for the prepatent period.

Localization and migration of benzimidazole resistant and susceptible adult Cooperia curticei in the small intestine of sheep after treatment with thiabendazole

Four groups of three lambs per group were experimentally infected with Cooperia curticei susceptible (two groups) or resistant (two groups) to benzimidazoles, and distributions of adult worms in the small intestine were studied. For each Cooperia isolate, one group was treated with thiabendazole (TBZ) (5 or 50mg/kg bodyweight) 28 days after infection. In the two untreated groups, the population of C. curticei were present from the second to the tenth meter of intestine from the pylorus with a maximum in the sixth meter for both isolates. After treatment with TBZ, the size of the resistant worm population did not significantly decrease but a large number of worms were found towards the proximal sections of the intestine. In contrast, the susceptible population was reduced by about 40% but the surviving worms remained at this same site of predilection after treatment. Measurements of the concentration of TBZ and 5OH-thiabendazole (5OH-TBZ) in the intestinal segments do not indicate a clear relationship between the localization of worms and TBZ or 5OH-TBZ concentrations at least 12h after the anthelmintic treatment. The hypothesis of an enhanced expression of the mechanisms of resistance in the first few meters of small intestine is suggested.

Integumental amino acid uptake in a carnivorous predator mollusc (Sepia officinalis, Cephalopoda)

The epithelial cells of the integument of body, arms and tentacles of Sepia officinalis present on their apical membrane a well-organised brush border and show the morphological and histochemical characteristics of a typical absorptive epithelium. The ability of the integument to absorb amino acids was investigated both in the arms incubated in vitro and in a purified preparation of brush border membrane vesicles (BBMV). Autoradiographic pictures of the integument after incubation of the arms in sea-water with or without sodium, showed that proline intake was Na+-dependent, whereas leucine intake appeared to be a largely cation-independent process. Time course experiments of labelled leucine, proline and lysine uptakes in BBMV evidenced that these amino acids are accumulated within the vesicles in the presence of an inwardly directed sodium gradient. The sodium-driven accumulation proves that cationic and neutral amino acids are taken up by the apical membrane of the epithelium of Sepia integument through a secondary active mechanism. For leucine, a 90% inhibition of the uptake was recorded in the presence of a large excess of the substrate. In agreement with the autoradiography results, an analysis of the cation specificity transport in BBMV showed that leucine uptake had a low cation specificity, whereas lysine and proline uptakes were Na+-dependent. An excess of lysine and proline, which share with alanine two different transport systems in the gill epithelium of marine bivalves, reduced eucine uptake. The possible role of the absorptive ability of the integument in a carnivorous mollusc is discussed.

Experimental investigation of physiological factors that may influence microhabitat specificity exhibited by Leptorhynchoides thecatus (Acanthocephala) in green sunfish (Lepomis cyanellus)

Representatives of Leptorhynchoides thecatus (Acanthocephala) inhabit ceca of green sunfish but cannot survive in the anterior intestine. The influence of elevated cecal protein concentrations, pH, and amounts of lumenal materials on the microhabitat specificity of L. thecatus was investigated. An attempt was made to alter the distribution of worms in starved fish, in fish of which cecal pH was reduced, and in fish of which intestinal protein concentration was elevated. Protein concentration and pH showed no effect on worm distribution. Starving hosts had no effect on worm number or distribution but resulted in retardation of worm growth and development, providing a mechanism by which worms may overwinter and by which peak egg production may coincide with abundance of the amphipod intermediate host. None of the factors investigated is solely responsible for the microhabitat specificity of L. thecatus. It is suggested that helminth site specificity is characterized by long histories of adaptation to specific habitats with many physiological adaptations being facilitated synergistically. Maximization of sexual congress may exert an important selective pressure favoring this establishment of microhabitat specificity.

Strongyloides venezuelensis: adhesion of adult worms to culture vessels by orally secreted mucosubstances

Adults worms of Strongyloides venezuelensis were cultured in vitro. After overnight incubation, about 60% of the worms adhered firmly to the bottom of culture vessels by secreting adhesive substances from the mouth. A single worm produced 24.5 +/- 10.1 of the adhesion spots overnight. When they were transferred to new culture vessels, they still produced new spots comparable to those produced for first 24 hr. The adhesion spots were positively stained with Coomassie brilliant blue and also with mucicarmine, periodic acid-Schiff, and alcian blue, pH 2.5, but not with alcian blue, pH 0.3, indicating their glycoprotein nature. The substances were amorphous and did not contain cells or nuclei. Histologic staining with a panel of lectins showed that the adhesive substances were rich in mannose, N-acetyl galactosamine, and N-acetyl glucosamine, but devoid of sialic acid. These characteristics were distinct from those of jejunal goblet cell mucins of rats. Adhesive substances contained antigenic components recognized by sera from infected rats. Thus, the adhesive substances secreted from the mouth of S. venezuelensis were clearly of parasite origin. We consider the production/secretion of the adhesive substances by S. venezuelensis adult worms a key step for the parasites to invade and establish the host epithelial layer.

Lung-worms (Nematoda: Pseudaliidae) of harbour porpoises (Phocoena phocoena) in Norwegian waters: patterns of colonization

We studied the component community of lung-worms of the harbour porpoise, attempting to establish the relative importance of ecological and evolutionary factors on its development. The lungs of 64 porpoises by-caught in Norwegian waters were examined for helminths. Three pseudaliid species were detected. The porpoises appear to be readily colonized by lung-worms, the structure of the component community of calves being fairly similar to that of the remainder. Prenatal and/or transmammary infections might partly account for these early infections. However, host age was correlated with the number of lung-worm species, suggesting that the lung-worms may have heteroxenous cycles similar to other metastrongyloids. The lung-worm species tended to co-occur more often than expected by chance. This pattern is commonly observed in communities formed by phylogenetic relatives. Mean species richness of lung nematodes differed significantly among mammalian orders. However, species richness of marine species seemed very similar to those of most terrestrial species. This evidence suggests that phylogenetic factors seem more important than ecological ones in determining the number of lung-worm species in mammals.

Intestinal contractions and migration behaviour in Hymenolepis diminuta

The aim of this study was to determine if intestinal contractions were important in the migration behaviour of the rat tapeworm Hymenolepis diminuta. The objectives were to investigate the intestinal motility responses of the host to a meal which initiates worm migration, and the worms' responses to an artificial peristaltic contraction. A 1 g glucose meal elicited a significant orad migration by H. diminuta in the small intestine of the rat host when compared to water-fed controls (P less than 0.05). The glucose meal also significantly increased the transit rate, and thus, frequency of intestinal contractions in the small intestine of the rat, when compared to water-fed controls (P less than 0.05). Application of a circumintestinal ligature (6.3 g) (simulating an intestinal peristaltic contraction) resulted in significant worm migration when the ligature was applied in regions containing the worm's strobila as compared to controls where loose ligatures were tied in regions containing the strobila, or to controls where tight ligatures were tied ahead of the worm's strobila. These results suggest that H. diminuta migrates in an orad direction in response to the mechanical pressure produced by intestinal contractions induced by host feeding. It is concluded that contractions of the small intestine are an important cue in the migration behaviour of this cestode.

Hymenolepis diminuta: effects of decerebration on thermal response behavior

Hymenolepis diminuta propels itself with unidirectional peristaltic-like waveforms. When intact adult H. diminuta are placed in a thermal gradient, with the anterior proglottids hot relative to the posterior proglottids, the worms migrate up the gradient toward the hot side. When the anterior is cold, relative to the posterior, the worms moved slightly or little. These behaviors in a thermal gradient represent true thermokinetic responses for an organism with undirectional locomotion. Removal of the scolex, containing the worm's cerebral ganglia, did not significantly alter these thermal responses. These data suggest that the peripheral nervous system is capable of integrating sensory input over the length of the strobila and coordinating locomotory behavior, in the absence of the central nervous system.

Behavioural adaptation of the tapeworm Hymenolepis diminuta to its environment

Hymenolepis diminuta migrates up the small intestine in response to feeding the host 1 g of glucose. Locomotion during migration may result from fixed patterns of retrograde peristaltic-like waves in the strobila of the tapeworm which propel the organism against the normal expulsive forces in the small intestine. The peristaltic-like locomotory waves occur in a gradient along the strobila with a frequency of 24.9 +/- 0.9 cycles/min in the anterior segments of the worm, decreasing linearly to 6.6 +/- 1.4 cycles/min in the posterior segments of the worm. Chemical signals, isolated from the small intestine of fed hosts, which stimulate migration behaviour in vivo do not alter the behaviour of the scolex or strobila in vitro. Removal of the scolex containing the cerebral ganglia does not alter the frequency or pattern of locomotory activity in the strobila. After the worm is cut into pieces, each region generates the pattern of locomotory activity that is appropriate for that region. These data suggest that the peripheral nervous system, and not the central nervous system, is responsible for the coordination of the fixed patterns of locomotory activity in these tapeworms.

The relationship between intestinal location and fecundity in adult Trichinella spiralis

Adult female worms recovered from the jejunum of rats infected per os with 1000 larvae of Trichinella spiralis were significantly more fecund (peak jejunal fecundity = 35.7 +/- 3.1 newborn larvae per female) than females recovered from the terminal ileum (9.3 +/- 4.1 larvae per female) in the same infections. The majority of the adult worms were established in those sections of the small intestines that produced the most fecund females (r = 0.92; P less than 0.05). Worm fecundity is believed to be location-specific because adult females that were surgically implanted into the jejunum were significantly more fecund that were implanted into only the ileum. It is concluded that the physico-chemical conditions of the anterior small intestines are optimal for the parasites' reproductive fitness and this exerts a strong selective pressure on habitat selection behavior.

Effects of 5-hydroxytryptamine (serotonin) on the incorporation of 32P-inorganic phosphate into phospholipids in Hymenolepis diminuta (Cestoda)

5-Hydroxytryptamine (5-HT) (1,2 and 5 mM) significantly stimulated the incorporation of radioactive inorganic phosphate (32Pi) into phosphatidylinositol, phosphatidylethanolamine, phosphatidic acid and also total phospholipid fraction of Hymenolepis diminuta after one hour of incubation. Such effect was both time and concentration dependent. In the presence of 5-HT early labelling of phosphatidylinositol was observed. Also, the percentage stimulation by 5-HT was the highest in this fraction under all experimental conditions. The inorganic, organic, total and phosphatidylcholine-bound phosphate of H. diminuta incubated with 5-HT were not significantly different from those of the control under all incubation conditions. Results reported herein suggest that messenger molecules that are derived from phosphoinositides may be involved in the stimulatory mechanism of 5-HT in H. diminuta.

The impact of host nutrition on gastrointestinal helminth populations

Malnutrition and helminth infection are amongst the most prevalent chronic conditions affecting human health globally. It is estimated that parasitic helminths infect more than 1 billion people, and that more than 2 million clinical cases occur each year (Peters, 1978; Walsh, 1984). Estimates of the incidence of clinical malnutrition suggest that between 5 and 8 million cases occur annually. In many parts of the developing world malnutrition and infection conjointly are the most serious health problem in children, acting as primary or more often as secondary factors in mortality (Puffer & Serrano, 1973). The impact on health is exacerbated because both conditions are chronic, are most common in growing children and, most importantly, tend to occur together in the same individuals (Pawlowski, 1984; Chandra & Newberne, 1977).

Site selection by Microphallus pygmaeus Levinsen, 1881 (Trematoda: Microphallidae) in the laboratory mouse

When Microphallus pygmaeus Levinsen, 1881 was inoculated orally to laboratory mice, most specimens, failed to attach to the intestinal wall and passed out rapidly with the faeces. Those which did settle were distributed more or less evenly throughout the small intestine by 4 h after inoculation. By day 1 after inoculation the worms had developed to oviposition and most were found in the ileum. By 2 days after inoculation all worms were established, and they remained in this region where they grew and continued egg production with very little further mortality until day 6 after inoculation. Thereafter, gravid worms progressively detached and passed rapidly through the caecum, colon, and rectum with the faeces. All parasites had been voided by about day 12 inoculation. In spite of high mortality, distribution in the small intestine is also affected by the site of implantation.

The nature and action of host signals

It is clear that excystations in vitro of the coccidia so far examined involves two steps, in the first of which CO2 is important, and the second, in which an external source of chymotrypsin and surface-active agents are required. However, the details of the mechanism of excystment are not clear. We do not know how the presence of CO2 changes the permeability of the oocyst wall. We do not know whether CO2 does anything to the sporozoite or sporocyst; the circumstance that mechanically-released sporocysts readily excyst under appropriate conditions without the necessity for high concentrations of, or perhaps any, CO2 suggests it does not. Circumstantial evidence suggests that the substrate in which chymotrypsin acts is the Stieda body, but whether the enzyme has other roles we do not know. Similarly, the role of bile is ill-defined, although it does seem that the induction of activity is important--but how is this brought about? The techniques available to excyst oocysts are, for many species, very efficient. If CO2 is, as it seems to be, a fundamental stimulus, then efficiency might be enhanced if more attention was given, not so much to increasing the time of exposure and amount of CO2 in the gas phase, but rather to the pH of the medium, which is rarely stated or apparently, controlled. The pH determines the proportion of the different carbonate species in solution, which may be of greater significance than the partial pressure of CO2 in the gas phase (see also Section V A). Although high numbers of excysted sporocysts can be obtained with a particular technique, this does not necessarily mean that all the signals supplied by the host are reproduced in vitro. Jackson (1962) found it necessary to wash oocysts in water or dilute buffers between the primary phase and the secondary phase, a step which implies a deficiency in the methods he used. Commonly, oocysts are exposed to a strong solution of L-cysteine. Does this reflect a general deficiency in the technique, or a counterpart of strongly reducing conditions in ruminant and non-ruminant alike? It seems that we have only a very general outline of excystment, and that we do not understand the details. Yet the problem seems to have been put aside; the most recent relevant reference we have found is dated 1983.

Patterns in helminth communities: why are birds and fish different?

Recently, some authors (Kennedy, 1981; Price & Clancy, 1983) have argued that there are fundamental differences between the communities of helminths in fish and bird hosts. Such differences are foreshadowed by the work of Dogiel (1964) and are apparent from survey data (e.g. Threlfall, 1967; Bakke, 1972; Hair & Holmes, 1975 on birds, and compare Chubb, 1963; Mishra & Chubb, 1969; Wootten, 1973; Ingham & Dronen, 1980 on fish). Questions still remain, however, as to whether the distinctions are truly justified and whether the differences are really fundamental. In this paper, we address these questions by examining helminth diversity in a series of hosts. We then discuss and provide explanations for the observed differences.

Metabolic integration during the host associations of multicellular animal endoparasites

The nature of metabolic interaction during parasitic infection was discussed and the concept of metabolic integration outlined. The subjective nature of the integrative argument was noted. The parasite-host relationships of larval trematodes of the genus Schistosoma with their intermediate molluscan hosts, the nematode Trichnella spiralis and cestode Hymenolepis diminuta, with their definitive hosts, as well as the hymenopterous insect parasite, Hyposoter exiguae, with its insect host, Trichoplusia ni, were examined. The significance of the immune system in the establishment of the parasite-host association and the means by which parasites evade host defense were discussed. The involvement of microorganisms or "hyperparasites" during the host associations of multicellular parasites was described. The importance of evolutionary considerations in assessing the nature of metabolic interaction and its significance to the success of the parasite-host relationship was emphasized. The use of teleological assessment and anthropomorphic description was discussed.

Schistosoma mansoni: electron probe X-ray microanalysis of the elemental composition of the tegument and subtegumental tissues of adult worms

The elementary composition [Na, Mg, P, S, Cl, K, Ca and Fe] of the tegument, tegumental spines, and subtegumental tissues of adult male and female Schistosoma mansoni have been determined by electron probe X-ray microanalysis of unfixed, freeze-dried cryosections. Statistical analysis of the results suggests that there are distinct differences in the elemental composition of the tissues both between and within individual male and female worms, and between male and female worms in general. In particular, there were significant variations in the elemental contents of the tissues between individual male and female worms, which may reflect differences in the physiology and/or metabolic state of the worms. Significant differences in the elemental composition of the various tissues examined within individual worms were also found. In general, in both male and female worms, there were significantly higher elemental levels in the tegument, as opposed to the subtegumental tissues. The elemental composition of the tegumental spines in both male and female worms differed from that of the tegumental cytoplasm, although the differences in the elemental composition between spines from male and female worms reflected the differences in the elemental content between the teguments themselves. Differences in the elemental composition of the tissues between male and female worms were also found, with the female tegument containing significantly higher elemental levels (with the exception of Cl) than the male tegument. In particular, the tegument of female worms contained higher levels of calcium and, in relatively small areas, isolated calcium-containing granules. This higher tegumental calcium level in female worms may reflect a higher calcium demand by sexually mature female worms due to the presence, within the mature vitelline cells, of calcium-containing corpuscles and the production of large numbers of eggs.

Factors promoting in vitro excystation of Giardia muris cysts

Giardia muris cysts, isolated from mouse faeces, excysted routinely at levels greater than 90%, when induced in 1X Hanks' supplemented with 17 mM glutathione, 29 mM L-cysteine-HCl, and 50 mM NaHCO3 for 30 minutes at 35 degrees C, followed by washing and suspension in trypsin-Tyrode's solution at pH 8.0. Although trypsin was not required in this final step, it enhanced the escape of the trophozoites from their cysts. G. muris excystation was dependent upon the length of the induction period, pH, oxidation-reduction potential and temperature. Optimal induction conditions for excystation were: an induction period of 5 to 30 min; pH of 2; 120 mV oxidation-reduction potential; and a temperature around 35 degrees C. A gradual decline in excystation occurred as pH and oxidation-reduction potential were changed to 7 and 57 mV, respectively. There was a pronounced increase in excystation percentages with increasing temperatures between 0 and 37 degrees C. At 40 degrees C and above, the G. muris cysts showed signs of inactivation. The thermal death point of G. muris cysts was determined to be about 54 degrees C. G. muris cysts showed no polarity; however, the tail or posterior trophozoite portion always emerged through one end of the cyst first. Cytokinensis began within the first hour after excystation. This method always produced extremely active, normal-looking G. muris trophozoites.

Parasite population biology and host nutrition: dietary fructose and Moniliformis (Acanthocephala)

Experiments were carried out to investigate the possible influence of host-dietary fructose concentration on the relationship between worm burden and the fecundity of Moniliformis dubius. Worm length was found to be dependent both on the fructose concentration of the host's diet and on worm burden. The number of free ovaries/female worm was found to increase linearly with increasing dietary fructose concentration but was independent of worm burden. The length of the ovaries increased with increasing dietary fructose concentration and decreased in response to increases in worm density. The magnitude of the density-dependent reduction in the volume of ovarian tissue/female was decreased in worms from rats fed on diets containing low concentrations of fructose. The numbers of eggs present in the body cavities of the female worms was found to be positively correlated with dietary fructose concentration. At 5 weeks post-infection, mature eggs (containing fully developed acanthor larvae) were found in the body cavities of female worms from rats whose diets contained 3 and 12% fructose, but not in those from rats whose diets contained 1 and 2% fructose (w/w). The experimental results are discussed in the wider context of the influence of host nutrition on parasite population biology.

[Studies On The Bladder Worm, Cysticercus Cellulosae: The Ultrastructure Of C. Cellulosae]

An electron microscopic study was performed to know the basic tegumental structure of Cysticercus cellulosae. The scolex and bladder portions of cysticerci (human and porcine strains) were prepared for transmission and scanning electron microscopy by conventional procedures. In general, the tegument of C. cellulosae showed the basic ultrastructure of cestode tegument on electron micrographs. The teguments of both scolex and bladder portions consisted of such components i.e., an outer vesicular layer with numerous microtriches and inner fibrous layer. Below the fibrous layer, there were layers of muscle bundles and tegumental cells. The microtriches which covered the surface of cysticercus revealed two distinctly different shapes. The characteristic bladder-like, elongated pyramid shaped 'tetrahedral form' was observed on the surface of the scolex portion, whereas the elongated cylindrical 'filamentous form' was distributed on the surface of bladder portion. In spite of the difference of isolated host and location, the cysticerci showed the same result. But dimensional variations of the tegument according to topography of the worm were observed. The possibility of application in making differential diagnosis from other larval cestodes and possible functions of this larval tegument were discussed.

Biochemical and physiological effects of metazoan endoparasites on their host species

1. The integrative nature of the parasite-host association was discussed, specifically with regard to the metabolic effects of parasitization as well as the physiological manifestation of infection in relation to the host's nutritional physiology. Endocrine interactions were also considered. 2. Relationships involving parasitic insects, including members of the orders Diptera, Hymenoptera and Strepsiptera, parasitic helminths, including members of the phyla Acanthocephala and Nematoda and the classes Cestoidea and Trematoda of the Platyhelminthes, as well as parasitic crustaceans in association with their invertebrate and/or vertebrate, intermediate, paratenic as well as definitive hosts were considered. 3. A broad conceptual or "topic" approach to understanding symbiotic relationships was emphasized. De-emphasis of descriptive categorization and the use of benefit/harm as criteria characterizing parasitic relationships was suggested. 4. The hypothetical concept of host regulation was briefly examined and the use of anthropometric descriptors such as "beneficial" and "harmonious" in parasitology discussed.

The adverse consequences of heavy Trichuris infection

Sixty-seven children with heavy Trichuris trichiura infection (Group A) were compared to 73 control children of similar socio-economic status but with light or no T. trichiura (Group B), for nutritional status, rates of concomitant bacterial and protozoal, and symptoms and clinical signs associated with heavy T. trichiura infection. Anoscopy was used to determine heavy T. trichiura infection. Measurements and physical examination were done on Group A on admission to and discharge from hospital; 46% were seen on follow-up visit two to eight months later. Children in Group B were seen only once. There were significant differences for nutritional status (p less than 0.01) and rates of bacterial and protozoal co-infection (p less than 0.01) and a significantly greater rate of invasive amoebiasis in Group A. After treatment, nutritional parameters of Group A children improved significantly, symptoms and clinical signs decreased and there was also a significant decrease in the rate of concomitant bacterial and protozoal infection. Subgroups of Group A children, with and without concomitant enteropathogens, revealed that infection with Entamoeba histolytica and bacterial enteropathogens had had no significant impact on clinical and nutritional status.

Two-dimensional electrophoretic separation and fluorographic analysis of the gene products synthesized by Hymenolepis diminuta with particular reference to the parasite-specific polypeptides in the brush border membrane

This study is the first demonstration of individual gene products synthesized by Hymenolepis diminuta. To identify proteins synthesized specifically by H. diminuta, we radiolabeled adult worms with [14C]leucine in vitro. Subsequent one- and two-dimensional gel electrophoretic separation and staining of the protein constituents from lysates of whole worms, brush border denuded worms, and brush border fractions extracted from whole worms demonstrates the diversity of the proteins in each of these lysates. Fluorographic analysis of the radioactivity in the same polyacrylamide gels identified the protein constituents synthesized by H. diminuta. The results from this study disclose and characterize, by molecular weight and isoelectric point, 17 polypeptides which are synthesized by H. diminuta and associated with its surface brush border.

Vitamin A deficiency and the development of Litomosoides carinii (Nematoda, Filarioidea) in cotton rats

This paper demonstrates that vitamin A deficient (A-) cotton rats are more susceptible to infection with Litomosoides carinii than normal (A+) cotton rats. However, embryogenesis is frequently retarded in female worms from A- hosts. Groups of young cotton rats were depleted of their liver stores of vitamin A by feeding them a vitamin A free diet from weaning. From 6 weeks of age this diet was supplemented with either 2, 5, 10, 25 or 100 IU vitamin A per 100 g body weight per day and half the animals in each group were infected with L. carinii. At autopsy, 51 days post-infection, serum vitamin A levels were proportional to vitamin A intake but were unaffected by infection (P less than 0.05). A+ cotton rats grew more rapidly and gained more weight than A- ones; infected animals gained less weight than their uninfected controls. More parasites developed in rats fed either 2 or 5 IU vitamin A than those fed either 10, 25 or 100 IU (P less than 0.02) and parasites from the 5 IU group were significantly longer than those from all other groups (P less than 0.02). However, microfilarial development was retarded in female worms from A- animals as compared with A+ ones.

Membrane transport of aromatic amino acids by Hymenolepis diminuta (Cestoda)

Aromatic amino acids (phenylalanine, tryptophan and tyrosine) are absorbed by Hymenolepis diminuta through a combination of mediated (non-Na+-sensitive) transport and diffusion. All 3 amino acids are accumulated against an apparent concentration difference during a 30-min incubation of tapeworms in 0.1 mM 3H-labelled amino acid. Inhibitor studies demonstrate that phenylalanine, tryptophan and tyrosine are mutually competitive inhibitors of the uptake of each other, and the uptake of these amino acids is inhibited by aliphatic amino acids but not by basic or dicarboxylic amino acids. The D- and L-isomers of aromatic amino acids are equally effective in inhibiting aromatic amino acid uptake. The data indicate that at least 3 amino acid transport loci are involved in aromatic amino acid transport by H. diminuta.

The growth of Moniliformis (Acanthocephala) in rats fed on various monosaccharides and disaccharides

Aspects of the course of infection, growth and reproductive activity of Moniliformis were studied in adult male and female rats fed on isoenergetic purified diets containing various sugars. When rats were infected and fed on experimental diets containing either 3% glucose or 3% galactose for 5 weeks, very little growth of worms and no signs of reproduction were observed. In contrast, Moniliformis grew well and showed many signs of normal reproduction when the rats were fed on diets containing either 3% fructose or 3% mannose. The ability of the worms to grow and reproduce was not lost by maintaining them first for 5 weeks in rats fed on diets containing 3% glucose and 3% galactose. When the diets of such rats were changed to ones containing 3% starch and 3% fructose, respectively, for a further 5 weeks, the worms grew and normal reproduction occurred. Similar experiments were carried out in which groups of infected rats were fed for 5 weeks on diets containing gradually increasing amounts of glucose (6-36%). It was not until the rats were fed on diets containing 24% glucose that the mean dry mass of the worms approached that of worms from rats fed on the diet containing 3% fructose; no host diet was found to be as effective a supporter of worm growth as 3% mannose. Under no circumstances, not even when the host's diet contained 36%, was galactose found to be a suitable sugar for supporting the growth and reproduction of Moniliformis. Results consistent with those recorded for worms from rats fed on the diets containing monosaccharides were obtained when infected rats were fed for 5 weeks on diets containing 3% of various disaccharides. Considerable growth and reproduction of Moniliformis occurred when sucrose was included in the host's diet, but not when lactose, maltose or trehalose was present. Several of these observations may be related to the fact that different sugars are absorbed at different rates from the intestinal tract. It is suggested that all of a given sugar, when present in the diet at a low concentration, may be removed rapidly from the anterior part of the small intestine with the result that none will be available to the parasites. Significant amounts, however, of those sugars that are absorbed more slowly may reach the region of the intestine in which the parasite normally lives.

An ultrastructural study of the microtriches of adult Proteocephalus tidswelli (Cestoda: Proteocephalidea)

Ultrastructural observations on adult Proteocephalus tidswelli revealed a marked microtrichial polymorphism. Structural and dimensional variations of microtriches between different regions of the strobila and scolex, as well as within the same region, were observed. The authors suggest that microtriches are involved in a diversity of functions, and possible functional activities are discussed.

Parasites ana malabsorption

Intestinal parasites not only cause diarrheal illnesses but may also cause significant malabsorption in man. Separation of true malabsorption caused by a particular parasite from other factors that may coexist with and even mimic malabsorption, such as malnutrition may be very difficult. Despite these problems, it appears that giardiasis, coccidiasis, strongyloidiasis and capillariasis cause malabsorption of many important nutrients. D. latum interfere with vitamin B12 absorption.

Hymenolepis diminuta: the role of the tail in determining the position of the worm in the intestine of the rat

One-worm infections of Hymenolepis diminuta in rats had their strobila severed surgically, in the neck region, on day 14 of an infection. The scolex and remaining strobila survived but were recovered from a more posterior region of the intestine where small worms are attached during development. The movement to the new region was usually not complete in 24 h, but was complete by 72 h, and probably by 48 h. The operation, involving laparotomy and an incision in the duodenal wall which avoided severing the strobila, had no effect on the position of the worm but did depress the growth of the worm during the ensuing 24 h. It is suggested that (1) the preferred site for H. diminuta is 30-50% down the small intestine, (2) the worm monitors information about its position from all over its strobila and (3) as the worm grows, its position is determined by balancing the input of adverse information from its tail and head ends. The slowness with which surgically shortened worms return to the preferred site may be due either to delay in the worm "realising" it has no tail, or to the location stimuli in the intestine being disturbed for 24 h by the operation.