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 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.

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.

The small intestine of rats was divided into twenty sections in a reproducible manner in order to study the distribution of Nippostrongylus brasiliensis by stretching it under a tension of 5g in adrenaline saline.

A small but significant difference between the distribution of parasites in male and female rats was observed.

As larvae had virtually ceased to reach the intestine by the fifth day all changes in distribution after that day were due to movements of the established adult population.

Up to the twelfth day of a primary infestation the majority of the worms were found between the third and tenth sections, the population mode being in the fifth or sixth section. After the thirteenth day the number of worms in this region fell sharply.

The female worms had not ceased from egg-laying by the time most of the worms were being rejected.

The posterior half of the small intestine, i.e. the eleventh to twentieth sections, was not heavily parasitized, many of the worms seen being in passage to the anus.

The first section was not parasitized until the seventh day, but thereafter remained parasitized until long after worms had disappeared from the more posterior sections.

The relative number of male worms present increased as the infestation aged.

Throughout the experiment the relative number of male worms present at the anterior end of the smaller intestine was higher than that at the posterior.

Fourth-stage larvae were found chiefly in the sections that were later most heavily parasitized by adult worms.

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.

The combination of pyrimethamine and sulfadoxine (PSD or Fansidar) represents one of the most important chemo-therapeutic agents currently used to treat falciparum malaria. To investigate the molecular basis of resistance to PSD, reliable in vitro drug assays are required to permit correlation of resistance levels with different genotypes. We describe here protocols that permit accurate evaluation of IC50 values for sulfadoxine (SDX) inhibition of Plasmodium falciparum. Historically, tests for this drug have suffered from poor reproducibility and extreme variability in reported values. We have examined a series of variables, including serum-containing versus serum-free media, erythrocyte source, pre-test growth conditions, test components and post-test processing. We define conditions which better control the levels of the drug antagonists folate and p-aminobenzoate, yielding reproducible differences between lines of P. falciparum with differing alleles of the dihydropteroate synthetase gene, which encodes the target enzyme of SDX. We also use this assay to demonstrate a marked difference in the response of different parasite lines to antagonism of SDX inhibition by exogenous folate. The ability to measure reliable IC50 values for SDX inhibition should greatly facilitate further experiments to explore the molecular basis of Fansidar resistance.

Gut symbionts can augment resistance to pathogens by stimulating host-immune responses, competing for space and nutrients, or producing antimicrobial metabolites. Gut microbiota of social bees, which pollinate many crops and wildflowers, protect hosts against diverse infections and might counteract pathogen-related bee declines. Bumble bee gut microbiota, and specifically abundance of Lactobacillus ‘Firm-5’ bacteria, can enhance resistance to the trypanosomatid parasite Crithidia bombi. However, the mechanism underlying this effect remains unknown. We hypothesized that the Firm-5 bacterium Lactobacillus bombicola, which produces lactic acid, inhibits C. bombi via pH-mediated effects. Consistent with our hypothesis, L. bombicola spent medium inhibited C. bombi growth via reduction in pH that was both necessary and sufficient for inhibition. Inhibition of all parasite strains occurred within the pH range documented in honey bees, though sensitivity to acidity varied among strains. Spent medium was slightly more potent than HCl, d- and l-lactic acids for a given pH, suggesting that other metabolites also contribute to inhibition. Results implicate symbiont-mediated reduction in gut pH as a key determinant of trypanosomatid infection in bees. Future investigation into in vivo effects of gut microbiota on pH and infection intensity would test the relevance of these findings for bees threatened by trypanosomatids.

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 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.

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.

Neuronal lesions have been considered the hallmark of chagasic megaesophagus, but the role of Trypanosoma cruzi and the participation of the inflammatory cells in this process are still debated. In the present study we counted neurons in the oesophagus from patients with and without megaesophagus and further examined these samples for the presence of parasite kDNA and cells with cytolytic potential (Natural Killer cells, cytotoxic lymphocytes and macrophages). The presence of parasite kDNA was demonstrated in 100% of cases with megaesophagus and in 60% of patients without megaesophagus. When analysed for the number of neurons, the patients without megaesophagus could be classified into 2 groups, as having normal or a decreased number of neurons. The former group did not show any inflammatory process, but interestingly, all patients without megaesophagus presenting decreased number of neurons also presented both parasite kDNA and inflammatory process in the organ. We further observed that the numbers of cytotoxic cells in the myenteric plexus region inversely correlate with the number of neurons. These data together strongly suggest that chronic lesions in chagasic megaesophagus might be a consequence of immune-mediated mechanisms, that last until the chronic phase of infection, and are dependent on the persistence of parasite in the host's tissue.

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.

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.

The present report is an account of observations made in Bagdad during the year 1910 (March to November) on the Oriental Sore as it occurs in this part of the world. Though the sore of Bagdad may not differ very markedly from that of other places, it is so common here that all stages and types of the sore may easily be studied, and such points as the early age of infection, immunity, and duration of the disease are very clearly exemplified. Accordingly, a more or less complete account of this disease of Bagdad, known locally as the Date boil or Arabic “Uchut,” will be given, though descriptions of the sore as it occurs in several parts of the world have been published by other observers. During the investigations various side issues arose, and as these suggest certain interesting points, three sections have been added dealing with (1) the life history of Lankesteria culicis (Ross) a gregarine of Stegomyia fasciata, (2) Haemogregarina canis and its development both in the dog and the tick Rhipicephalus sanguineus, and (3) Her-petomonas muscae domesticae, and other flagellates of the house-fly.

Infection and inflammation in the gastrointestinal (GI) tract induces a number of changes in the GI physiology of the host. Experimental infections with parasites represent valuable models to study the structural and physiological changes in the GI tract. This review addresses research on the interface between the immune system and GI physiology, dealing specifically with 2 major components of intestinal physiology, namely mucin production and muscle function in relation to host defence, primarily based on studies using the mouse-Trichinella spiralis system. These studies demonstrate that the infection-induced T helper 2 type immune response is critical in generating the alterations of infection-induced mucin production and muscle function, and that this immune-mediated alteration in gut physiology is associated with host defence mechanisms. In addition, by manipulating the host immune response, it is possible to modulate the accompanying physiological changes, which may have clinical relevance. In addition to enhancing our understanding of immunological control of GI physiological changes in the context of host defence against enteric infections, the data acquired using the mouse-T. spiralis model provide a basis for understanding the pathophysiology of a wide range of GI disorders associated with altered gut physiology.

A series of line drawings of the unsporulated and sporulated oocysts of the species of Eimeria found in cattle and sheep in Britain has been compiled.

The incidence of the different species in faecal samples from animals, of which only a minority were known to be suffering from enteritis or diarrhoea, has been recorded. Samples from sheep frequently contained five or six different species among which those that are believed to be pathogenic (E. arloingi, E. crandallis, E. ninaekohlyakimovae) were the most common.

The samples from cattle most frequently contained two or three species. E. bovis and E. zuerni, which are associated with acute disease, were the most common.

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.

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.

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.