A field trial was conducted to evaluate the potential of the nematode-destroying fungus Duddingtonia flagrans to control free-living stages of horse strongyles. In late Spring 2 groups of horses (yearlings) with mixed infections of strongyles were allowed to contaminate 2 equal-sized pastures. One of the groups (F) received a daily dose of D. flagrans mixed in a feed supplement, while the other (C) received a similar amount of supplement without fungus. During a 3-month contamination period strongyle egg counts in faeces and number of infective strongyle larvae harvested from faecal cultures were determined. Grass samples were collected fortnightly. After the contamination period the yearlings were removed and 2 groups of young tracer foals (TF and TC) grazed the fungus and control pastures respectively for 4 weeks, housed for another 15 weeks and then killed to determine their worm burdens. The number of larvae in cultures from group TF was significantly lower than that in TC and herbage infectivity was reduced to a very low level on the pasture grazed by horses fed fungi. The number of Strongylus vulgaris and Strongylus edentatus larvae was also significantly lowered in group TF. Cyathostome larvae recovered from the mucosa of the ventral and dorsal colon and from the caecum were significantly lowered in group TF foals. Also, the number of strongyles found in the gut contents of group TF foals were significantly reduced in the dorsal colon, but numbers of worms in the ventral colon and in the caecum were similar to those of the controls.

The pattern of oocyst production of 8 inbred lines of chickens was compared for each of the 7 species of Eimeria which infect this host. Both the overall numbers and the pattern of oocyst production differed in the inbred lines, but there was no evidence of prolonged cycling of schizogenic developmental stages. Comparison of the numbers of oocysts produced by the different lines indicates that there may be common genetic factors affecting susceptibility to 6 of the 7 species. Surprisingly there appears to be an inverse relationship between susceptibility to E. tenella and susceptibility to the other species: lines which produced most oocysts of E. tenella produced least oocysts of the other species and vice-versa.

Echinococcus granulosus antigen B (AgB) is encoded by a gene family and is involved in the evasion of the host immune response. E. granulosus exists as a number of strains (G1–G10) that differ in biological characteristics. We used PCR-SSCP followed by DNA sequencing to evaluate sequence variation and transcription profile of AgB in 5 E. granulosus strainsNucleotide sequence data reported in this paper are available in the GenBankTM database under the Accession numbers AY569341-AY569371, AY159484, AY159485, AY608606, AY608607, AY614001.. Twenty-four genomic sequences were isolated and clustered in 3 groups related to 2 of the 5 reported AgB genes. AgB4 genes were present in almost all strains, whereas AgB2 were present as functional genes exclusively in G1/G2 cluster, and as non-functional genes in G5 and the G6/G7 cluster, suggesting inter-strain variation. The AgB transcription patterns, analysed by RT-PCR, showed that AgB2 and AgB4 genes were transcribed in G1, while only the AgB4 gene was transcribed in G7 strain. Cysts from the same strain or cluster shared more genomic and cDNA variants than cysts from different strain or cluster. The level of nucleotide and deduced amino acid sequence variation observed is higher than that reported so far for coding genes of other helminths. Neutrality was rejected for AgB2 genes. These data show the genetic polymorphism of antigen-coding genes among genetically characterized strains of E. granulosus.

The epidemiological and ecological processes which govern the success of multiple-species co-infections are as yet unresolved. Here we investigated prior versus late residency within hosts, meaning which parasite contacts the host first, to determine if the outcomes of intra-host competition are altered. We infected a single genotype of the waterflea Daphnia galeata with both the intestinal protozoan Caullerya mesnili and the haemolymph fungus Metschnikowia sp. (single genotype of each parasite species), as single infections, simultaneous co-infections and as sequential co-infections, with each parasite given 4 days prior residency. Simultaneous co-infections were significantly more virulent than both single infections and sequential co-infections, as measured by a decreased host life span and fecundity. Further, in addition to the Daphnia host, the parasites also suffered fitness decreases in simultaneous co-infections, as measured by spore production. The sequential co-infections, however, had mixed effects: C. mesnili benefited from prior residency, whereas Metschnikowia sp. experienced a decline in fitness. Our results show that multiple-species co-infections of Daphnia may be more virulent than single infections, and that prior residency does not always provide a competitive advantage.

The purpose of this study was to determine under laboratory conditions over a period of 311 days if infection with the nematode Anguillicola crassus induces stress in European eels (Anguilla anguilla), and stimulates the endocrine stress axis as measured by serum cortisol levels. Eels were experimentally infected with 3rd-stage larvae (L3) in different doses to simulate natural conditions with varying infection pressures. Blood samples were drawn from the caudal vein every 2 weeks and serum cortisol concentrations were determined by radioimmunoassay (RIA). The results showed that the application of L3 resulted in a significant increase in the cortisol levels. The period of time at which elevated cortisol values were observed was consistent with the time of larval development and the appearance of adult A. crassus. Thus, there is a stress response to the larval and young adult stages, but no chronic response to older adults. Therefore, it is likely that infection of eels under natural conditions especially with a high number of larvae may be a considerable stressor, in combination with different environmental factors like water temperature, pH, oxygen concentration, pollution and inter-individual relationships.

Effects of heavy metal pollution on the cercariae of the marine trematode Cryptocotyle lingua (Creplin) were studied by measuring horizontal swimming rate (HSR) and longevity. These factors are important for transmission to the next host, a fish. Cercariae released by Littorina littorea (L.) collected from polluted and unpolluted sites were compared. Both HSR and longevity were significantly reduced in cercariae from the polluted environment. Cercarial quality was therefore reduced, directly or indirectly, by development within a metal-accumulating host. Cercariae released by hosts from a clean environment were subjected to nominal concentrations of 2 and 3 mg/l copper, 1 and 2 mg/l zinc, 2 and 5 mg/l iron and 2 and 4 mg/l manganese in artificial seawater. In all cases the HSRs and longevity were reduced. The effect was more pronounced in the higher concentrations. The significant HSR tests indicate that the absorption and effect of metals occurred within 1 min. The cercarial tegument, specialized for absorption in endoparasitic environments, is possibly responsible. Cercariae may therefore be excellent indicator organisms for pollution. The pollution-induced reductions in cercarial quality seem capable of producing transmission failure. Heavy metal pollution could therefore alter parasite populations and communities.

Blastocystis infection has a worldwide distribution especially among the disadvantaged population and immunocompromised subjects. This study was carried out to determine the prevalence and the association of Blastocystis infection with the socio-economic characteristics among 300 primary schoolchildren, living in rural communities in Lipis and Raub districts of Pahang state, Malaysia. Stool samples were collected and examined for the presence of Blastocystis using direct smear microscopy after in vitro cultivation in Jones' medium. The overall prevalence of Blastocystis infection was found to be as high as 25·7%. The prevalence was significantly higher among children with gastrointestinal symptoms as compared to asymptomatic children (x2=4·246; P=0·039). Univariate and multivariate analyses showed that absence of a piped water supply (OR=3·13; 95% CI=1·78, 5·46; P<0·001) and low levels of mothers’ education (OR=3·41; 95% CI=1·62, 7·18; P<0·01) were the significant predictors of Blastocystis infection. In conclusion, Blastocystis is prevalent among rural children and the important factors that determine the infection were the sources of drinking water and mothers' educational level. Interventions with provision of clean water supply and health education especially to mothers are required.

An M13 phage random 12-mers peptide library was used to screen cathepsin L mimotopes of Fasciola hepatica and to evaluate their immunogenicity in sheep. Seven clones showed positive reactivity to a rabbit anti-cathepsin L1/L2 antiserum in ELISA, and their amino acid sequences deduced by DNA sequencing were tentatively mapped on the protein. Twenty sheep were randomly allocated into 4 groups of 5 animals each, for immunization with 1×1014 phage particles of clones 1, 20, a mixture of 7 clones and PBS, without adjuvant at the beginning, and 4 weeks later. All groups were challenged with 300 metacercariae at week 6 and slaughtered 16 weeks later. The mean worm burdens after challenge were reduced by 47·61% and 33·91% in sheep vaccinated with clones 1 and 20, respectively; no effect was observed in animals inoculated with the clone mixture. Also, a significant reduction in worm size and burden was observed for those sheep immunized with clone 1. Animals receiving clone 20, showed a significant reduction in egg output. Immunization induced a reduction of egg viability ranging from 58·92 to 82·11%. Furthermore, vaccinated animals produced clone-specific antibodies which were boosted after challenge with metacercariae of F. hepatica.

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 L3O. 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.

Echinococcus species are important parasites of wildlife, domestic animals and people worldwide; however, little is known about the prevalence, intensity and genetic diversity of Echinococcus tapeworms in Canadian wildlife. Echinococcus tapeworms were harvested from the intestines of 42% of 93 wolves (Canis lupus) from five sampling regions in the Northwest Territories, Manitoba and Saskatchewan, and visually identified to genus level by microscopic examination. Genetic characterization was successful for tapeworms from 30 wolves, and identified both Echinococcus canadensis and Echinococcus multilocularis in all sampling locations. Mixed infections of E. canadensis/E. multilocularis, as well as the G8/G10 genotypes of E. canadensis were observed. These findings suggest that wolves may be an important definitive host for both parasite species in western Canada. This represents the first report of wolves naturally infected with E. multilocularis in North America, and of wolves harbouring mixed infections with multiple species and genotypes of Echinococcus. These observations provide important information regarding the distribution and diversity of zoonotic species of Echinococcus in western North America, and may be of interest from public health and wildlife conservation perspectives.

The results are presented of an experimental study of the population biology of chronic Trichuris muris (Nematoda) infection in cortisone-treated CBA/Ca mice. Attention is focused upon both the validity of the common use of faecal egg counts to demonstrate density dependence in helminth fecundity, and the identification of other possible density-dependent mechanisms that may regulate worm numbers in chronic trichuriasis. The results show that faecal egg counts, although demonstrating high daily variation, are not an artefact of host faecal output but a significant density-dependent function of worm burden. This finding contrasts with the observations on Heligmosomoides polygyrus infection in outbred MF1 mice, but accords with similar studies in a wide variety of host - helminth systems. Worm establishment in the murine host is found to be a density related function of infection dose. This is attributed to the probable existence of a physical gut-carrying capacity in the murine host for T. muris. Worm distribution in the gut is also shown to be density dependent, with worms being displaced from the caecum to the colon at increasing intensities of infection. The sex ratio of the adult parasites, however, is found to be both unitary and independent of worm burden. Evidence for a significant density-dependent decline in female T. muris growth or size is presented. The results also show a significant positive association between female T. muris weight and per capita fecundity. These findings indicate that the stunted growth of individual worms at high parasite densities may be a potential mechanism underlying density dependence in helminth fecundity.

The nodule worm Oesophagostomum bifurcum (Nematoda: Strongylida) is a parasite of major human health importance predominantly in northern Togo and Ghana. Currently, it is estimated that 0·25 million people are infected with this nematode, and at least 1 million people are at risk of infection. Infection with this parasite causes significant disease as a consequence of encysted larvae in the wall of the large intestine. In spite of the health problems caused by O. bifurcum, there have been significant gaps in the knowledge of the biology, transmission and population genetics of the parasite. This review provides an account of some recent insights into the epidemiology and genetics of the parasite from human and non-human primate hosts in specific regions of Africa using molecular tools. Recent research findings are discussed mainly in relation to non-human primates being reservoirs of infection, and the consequences for the prevention and control of oesophagostomiasis in humans are briefly discussed.

Spermatogenesis and the fine structure of the mature spermatozoon of Fasciola hepatica have been studied by transmission electron microscopy. The primary spermatogonia display a typical gonial morphology and occupy the periphery of the testis. They undergo 3 mitotic divisions to give rise to 8 primary spermatocytes forming a rosette of cells connected to a central cytophore. The primary spermatocytes undergo 2 meiotic divisions, resulting in 32 spermatids that develop into spermatozoa. Intranuclear synaptonemal complexes in primary spermatocytes confirm the first meiotic division. The onset of spermiogenesis is marked by the formation of the zone of differentiation which contains 2 basal bodies and a further centriole derivative, the central body. The zone extends away from the spermatid cell to form the median process; into this migrates the differentiated and elongate nucleus. Simultaneously, 2 axonemes develop from the basal bodies. During development, they rotate through 90° to extend parallel to the median process. The migration of the nucleus to the distal end of the median process coincides with the fusion of the axonemes to the latter to form a monopartite spermatozoon. The mature spermatozoon possesses 2 axonemes of the 9 + ‘1’ pattern typical of parasitic platyhelminths, 2 elongate mitochondria and a variable array of peripheral microtubules. The nuclear region of the spermatozoon is immotile. The value of sperm ultrastructure as a taxonomic tool in platyhelminth phylogeny is discussed.

Sex ratio theory usually predicts an equilibrium sex ratio and equal proportions of males and females in a population, including the progenitors of the reproductive cells of protozoans. This proposal was tested with three species of malarial parasites of lizards, Plasmodium mexicanum of the western fence lizard, and P. agamae and P. giganteum of the African rainbow lizard, using single samples from naturally infected lizards, repeated samples from free-ranging lizards (P. mexicanum only), and repeated samples from laboratory maintained animals. Macrogametocytes were usually more abundant than microgametocytes, and were slightly larger, revealing a typically greater investment of resources by the progenitors of female reproductive cells. However, the proportion of microgametocytes varied among the three species and among infections within each species of Plasmodium. The sex ratio of gametocytes often remained constant within infections followed over time even if the absolute number of gametocytes was changing. However, the equilibrium sex ratio of gametocytes varied among those infections that had an unchanging microgametocyte proportion. Thus, although an equilibrium sex ratio apparently occurs for most infections, there appears to be no characteristic proportion of microgametocytes for any of the species. Potential explanations for this conflict with theory are presented.

The fine-structure of the epimastigote forms of Trypanosoma lewisi in the rectum of the flea, Nosopsyllus fasciatus is described.

The parasites are attached to the rectal wall by penetration of the flagella between the highly folded wall of the rectum, by the wedging of the expanded flagella in these folds and irregularities of the wall and by a zonula adherens functional complex between the flagellar membrane and the cuticle of the rectum.

The parasites remain associated with each other by their flagella. The daughter axonemes produced during division are retained within the parent flagellar membrane; this delayed division of the flagella results in up to four axonemes being found within a single flagellar membrane. The parasites accumulate together in masses in the lumen of the rectum and their surfaces interdigitate resulting in the mass of parasites being retained together.

The financial assistance of the Agricultural Research Council is gratefully acknowledged. My sincere thanks are due also to my supervisor Dr Tate for his help, encouragement and enthusiasm through the course of this work.

In Plasmodium gallinaceum, parasitic in domestic fowls, in addition to the schizogony in red blood corpuscles, schizogony also occurs in monocytes and cells of the reticulo-endothelial system. This schizogony in cells other than erythrocytes may be termed, for convenience, exo-erythrocytic schizogony.

Exo-erythrocytic schizonts are characterized by never having malarial pigment (as they live in cells devoid of haemoglobin), by growing to a large size and forming numerous merozoites, up to 50 or 60 or even more.

Exo-erythrocytic schizonts are not confined to leucocytes of the blood stream, but can also develop in fixed endothelial cells of organs such as the brain, lung, liver and spleen.

The brain is an especially important focus of development and, after sporozoite infection, it is the first organ in which exo-erythrocytic schizonts develop. These schizonts may be found in capillaries of the brain as soon as parasitized erythrocytes are present in the peripheral circulation, but as yet they have not been found before parasites-are present in the peripheral blood.

In the brain rows of schizonts may develop and ultimately occlude most of the capillaries in the brain. This blockage of capillaries results in symptoms of general paralysis in the infected birds and death follows in a few days; and it frequently occurs in birds which apparently have been cured of the peripheral infection by treatment with quinine.

The exo-erythrocytic stages of P. gallinaceum occur in birds which have been inoculated with blood or with sporozoites.

During growth, the body of the schizont breaks up into a number of masses or cytomeres, on the periphery of which the merozoites are developed on regularly arranged rows of digitiform processes. A mass of chromatin migrates to the distal end of each process and is cut off to form a merozoite.

The mature schizont consists of a mass of irregular merozoites enclosed in a sac-like membrane which may be the remains of the host cell. The merozoites are composed almost entirely of chromatin and when they are fully developed practically no cytoplasm of the schizont remains.

A study was carried out to investigate the frequencies of abortion and congenital Toxoplasma gondii infection within 27 families (765 individuals) of a pedigree Charollais sheep flock maintained on a working farm in Worcestershire, UK, since 1992. Pedigree lambing records were analysed to establish the frequency of abortion for each family. The frequency of congenital infection was determined for each family by PCR analysis of tissue samples taken from newborn lambs. A total of 155 lambs were tested for congenital T. gondii infection, which were all born during the study period 2000–2003. Significant differences in the frequency of abortion between sheep families within this flock were observed with frequencies ranging between 0% and 48% (P<0·01). Significantly different infection frequencies with T. gondii were also observed for different families and ranged between 0% and 100% (P<0·01). Although the actual cause of each abortion was not verified, a highly significant positive correlation was found to exist between the frequency of abortion and the frequency of T. gondii infection in the same families (P<0·01). The data presented here raise further questions regarding the significance of congenital transmission of T. gondii within sheep populations, the possible successive vertical transmission of T. gondii within families of sheep, and the potential role of inherited genetic susceptibility to abortion with respect to T. gondii infection. This work invites further study into the epidemiology of ovine toxoplasmosis and may have implications for sheep husbandry methods in the future.

Photorhabdus sp. are entomopathogenic bacteria which, upon experimental infection, interact with the insect immune system, but little is known about the roles of their symbiotic nematode partners Heterorhabditis sp. in natural infections. Here, we investigated the respective contributions of nematodes and bacteria by examining humoral and cellular immune reactions of the model lepidopteran insect Manduca sexta against Heterorhabditis carrying Photorhabdus, nematodes free of bacteria (axenic nematodes) and bacteria alone. Insect mortality was slower following infection with axenic nematodes than when insects were infected with nematodes containing Photorhabdus, or the bacteria alone. Nematodes elicited host immune responses to a lesser extent than bacteria. Transcription of certain recognition and antibacterial genes was lower when insects were naturally infected with nematodes carrying no bacteria compared to insects that received bacteria, either with or without nematodes. Axenic nematodes also did not elicit such high levels of phenoloxidase activity and haemocyte aggregates as did treatments involving Photorhabdus. By contrast, the phagocytic capability of host haemocytes was decreased by both axenic and bacteria-associated nematodes, but not by Photorhabdus alone. These results imply that both bacteria and nematodes contribute separately to the pathogenic modulation of host immune responses during natural infections by the mutualistic Heterorhabdus-Photorhabdus complex.

The weight gain and growth rate of Trichoplusia ni larvae were severely depressed following parasitization by the insect parasite, Hyposoter exiguae. The development of the host was also delayed and juvenile hormone esterase activity present at the normal time of moulting was absent in parasitized insects. Similar effects on growth and development were achieved by rearing host insects on nutrient-deficient media. Accompanying the above effects of parasitization were alterations in dry/wet weight ratio and host haemolymph osmolality. Parasitization resulted in immediate increases in the concentrations of haemolymph non-glycogen carbohydrate (composed of trehalose, maltose and glucose) and protein. The concentration of fat body glycogen also increased following parasitization. In contrast, the concentration of haemolymph non-glycogen carbohydrate and protein, as well as fat body glycogen, decreased in nutrient-deprived larvae. The significance of the above results as they relate to the insect parasite–host relationship is discussed.

The maturation of female Schistosoma mansoni depends on pairing with a male which induces mitotic activities in the reproductive organs of the female worm. Since in other organisms cell proliferation is regulated by well-conserved signal transducing molecules, we looked for such molecules on immunoblots of schistosomes, using antibodies against conserved epitopes of Ras, GAP and MAP kinases. We identified all 3 molecules in schistosomes and found that they are developmentally regulated. Furthermore, there is evidence for their involvement in the male-directed maturation of the female.