The aim of this research was to determine the influence of iron deficiency on both the efficacy and metabolic patterns of albendazole in mice infected with Heligmosomoides polygyrus. Anthelmintic efficacy was markedly decreased in iron-deficient mice; the deficiency was also associated with a decrease in body weight, altered hematological parameters and a decreased net egg output; worm establishment in the deficient group was not affected by the deficiency. Although anthelmintic efficacy was significantly decreased by the iron deficiency, plasma concentration profiles of the main metabolites, albendazole sulphoxide and albendazole sulphone, were not changed by the deficiency. Levels of intestinal cytochrome P-450, the main metabolizing enzyme of albendazole however, was significantly depressed in iron-deficient mice. These observations suggest that although pharmacokinetic parameters are not affected by iron deficiency, nutritional status has the potential to influence anthelmintic efficacy and thus warrants further study.

In the past 20 years, boron has been identified as an essential trace element for animals and humans but also as an increasingly important industrial pollutant. We examined first whether boron influenced survival of the gastrointestinal nematode Heligmosomoides bakeri. Female Balb/c mice were fed deficient (0.1 mug B/g), marginal (2.0 mug B/g) or control (12.0 mug B/g) diets, and infected with third-stage larvae. Although liver boron concentrations did not differ among diet groups, dietary boron deficiency impaired survival of the parasite and modulated a broad range of cytokines and chemokines. On the other hand, infection history altered liver mineral concentrations. Second, we examined whether elevated boron concentrations would exert toxic effects on H. bakeri in vitro. Boron toxicity was evidenced by reduced motility, fecundity, infectivity and survival. Feeding stages and free-living stages were more sensitive than non-feeding stages and parasitic stages respectively in a dose-dependent manner.

The rate of recombination and parasite load of species of anuran from Peruvian Amazonia were examined to test the idea that recombination functions to diversify progeny in order to resist the continual counter-adaptation of parasites. The anurans were found to be hosts to over 32 species of macroparasite, as well as a wide variety of protistan and moneran parasites. It was found that a combination of three variables (diet, habitat, abundance), together with host body size accounted for a substantial proportion of the variation in mean parasite richness and parasite species distribution among host species. The relationship between parasites and ecology was found to be independent of host phylogeny. The demonstration of substantial environmental heterogeneity in parasitization predicates that a positive relationship between parasite richness and recombination should be found in this case. This prediction was supported by the data: highly parasitized species of anuran had higher rates of recombination. This is the first study to demonstrate a direct positive relationship between recombination (rather than sex) and parasites.

This research investigated the effects of waterborne zinc (Zn) on the interactions between guppies, Poecilia reticulata (Peters), and Gyrodactylus turnbulli Harris, 1986, a monogenean parasite of its skin and fins. The first objective was to determine if sublethal concentrations of waterborne Zn (up to 240 mug/L added to artificial freshwater) exerted a concentration-dependent effect on the population dynamics of Gyrodactylus on isolated guppies. Whereas survival of uninfected fish was unaffected, mortality of infected fish increased linearly with increasing Zn concentration. In addition, the improved parasite population growth at concentrations up to 120 mug Zn/I suggested either that the elevated Zn promotes survival and/or reproduction of the parasite, or impairs host defense mechanisms. Analysis of lifetime survival and reproduction of individual parasites on and off the fish revealed Zn toxicity to the parasite as survival of detached parasites decreased linearly with increasing Zn concentration and parasite survival on the host was also lower at the highest Zn concentrations. Also, all morphological parameters decreased linearly in response both to increasing concentration and duration of exposure to waterborne Zn. The guppy epidermis responded rapidly to both infection and waterborne Zn, and the cumulative effects of these combined stressors were synergistic for epidermal thickness and mucous cell numbers, but antagonistic in terms of mucin composition. Both Zn and infection induced mucous production, but at elevated Zn concentrations and/or at high parasite burdens, the capacity for continued mucous production was apparently exceeded. I hypothesize that this condition is favorable for parasite survival because of the impaired host response; but unfavorable for host survival because of the high numbers of pathogenic parasites and the inability to control entry of Zn into host tissues. In conclusion, sublethal concentrations of waterborne Zn are more detrimental to the infected host than to the parasite.

The following studies were done to identify factors that influence the virulence of Xenorhabdus nematophilus and the interactions of the bacterium with the nonself defence systems of nonimmune Galleria mellonella. Isolates of X. nematophilus that are qualitatively similar in biochemical properties differed significantly in virulence for G. mellonella larvae. The production of enzymes such as proteases could not account for differences in the virulence of the isolates. / Growth conditions, influenced the growth rate and the interactions of the bacterium with nonimmune G. mellonella larvae. In general, X. nematophilus cells grown under aerobic conditions were more susceptible to the nonself defences of G. mellonella larvae than those grown under less than ideal conditions, resulting in increased clearance of the bacteria from the hemolymph (blood) of the insects. Clearance of the bacteria from the hemolymph of the insect was positively correlated with culture condition, culture age, and attachment to insect hemocytes in vitro. / Isolates of X. nematophilus produced flagella and fimbriae when grown under microaerobic and aerobic conditions. The type of fimbriae produced was influenced by culture conditions. The injection of both flagella and fimbriae in picogram quantities into nonimmune G. mellonella caused an increase in total hemocyte counts within these insect larvae. The injection of fimbrial and flagellar antigens into G. mellonella larvae caused changes in the hemocyte types found in circulation in the insect's hemolymph. (Abstract shortened by UMI.)

Several parasites that require two or more hosts to complete their life cycles are known to manipulate host behaviour, enhancing their transmission to the next host. The intertidal snail, Littorina sitkana, is host to a diverse assemblage of parasites dominated by trematodes. Trematodes often use snails as first intermediate host and vertebrates as definitive host. Trematode infections can affect host behaviours such as dispersal and foraging. I identified four sites in Barkley Sound that varied in trematode prevalence and species richness. I measured dispersal of snails at these sites and in the laboratory to assess effects of trematode infection on behaviour. I measured feeding rate under laboratory conditions. Trematode effects lowered snail grazing activity at three of the four sites studied, suggesting trematode infection lowers feeding rate of L. sitkana, potentially affecting algal composition of the intertidal zone. Infected male snails travelled longer distances in some sites but shorter distances in others. There was an almost significant effect of trematode infection on vertical displacement of L. sitkana in the field. I estimated survival rates on each site through intensive capture-mark-recapture experiments. There was differential survival among sites, but no negative correlation between survival estimates and trematode prevalence. / Graduate / 0718 / 0329 / 0472 / mayala@uvic.ca

Parasites are thought to have large effects on their host populations, driving genetic change, population density changes, speciation and be a major selective force maintaining sexual reproduction. Indirect signatures of parasite-mediated selection are common, but explicit examples of parasite-mediated selection in nature are lacking. In this thesis I examine parasite-mediated dynamics in a natural population of Daphnia magna that experiences an annual epidemic of the bacterial pathogen Pasteuria ramosa. I also test a novel hypothesis investigating the relationship between parasitism and the production of resting eggs. In chapter 2 a combined field study and laboratory infection experiment illustrates one of the best examples of parasite-mediated selection in a natural population, with Daphnia collected after a parasite epidemic having higher levels of parasite resistance than those collected before. This chapter also explored the relationship between parasitism and resting eggs, which are only produced during the sexual phase of reproduction. Daphnia that were reproducing sexually in the field prior to the parasite epidemic were more susceptible, supporting higher levels of parasite growth, than their asexual counterparts. This supports the idea that some genotypes invest in sex at the expense of parasite resistance. In chapter 3 I used molecular markers to investigate genotype frequency changes in the same population in relation to the parasite epidemic. The parasite epidemic was found to be associated with genetic change in the population, and a laboratory infection experiment revealed that the genotype most resistant to the parasite was also most common following the peak of the parasite epidemic. While chapter 2 explored a genetic relationship between susceptibility and resting eggs, chapter 4 explores whether crowding conditions, cues indicating parasite prevalence in the population, or direct exposure to parasite spores can induce resting egg production. I found that crowding conditions or parasite prevalence enhance levels of male and resting egg production, but patterns were entirely dependent on Daphnia genotypes. There was no indication that exposure to parasite spores affects levels of sexual reproduction.

In the summer of 1997, 217 fishes of different species (Raja erinacea, R. radiata, R. ocellata, Malacoraja senta, and Squalus acanthias) were collected from the West Isles of the Bay of Fundy, New Brunswick. / Parasites belonging to 13 species were found: 10 Cestoda; 2 Nematoda; and 1 Acanthocephala. Of the 10 cestodes, five are described as new species. The remaining five re-described in detail and compared to similar worms reported in the literature. None of the eight tetraphyllidean cestodes was found in more than one host species, thereby supporting current dogma that the Tetraphyllidea are species specific with respect to their definitive hosts. / There is a close relationship between the topography of the spiral-valve mucosa of the preferred attachment-site and that of the inner-bothridial tegument. This provides further evidence supporting the strict morphological specificity proposed by Williams (1960).

The Arctic charr (Salvelinus alpinus) is a top predator in northern lakes and accumulates persistent lipophilic contaminants. Toxaphene, a major organochlorine contaminant in Arctic charr, is known to be acutely toxic to fish but the effects of dietary exposure have not been examined. Furthermore, lake-resident Arctic charr are frequently infected with larvae of the cestode, Diphyllobothrium dendriticum. The objective of this study was to investigate the effects of toxaphene exposure on Arctic charr growth, nutritional quality, physiology, and susceptibility to infections of D. dendriticum. A preliminary experiment found no effect of toxaphene on charr visceral organ and fat weights, plasma Vitamin A and E and plasma cortisol, although dominance hierarchies within groups may have masked treatment effects. For the main experiment, hatchery-reared Arctic charr were subjected to one of four treatments: (i) a single oral dose of corn oil (control); (ii) a single oral dose of 10 mug/g wet weight toxaphene dissolved in corn oil; (iii) exposure to 15 larval D. dendriticum; and (iv) a combination of both. (Abstract shortened by UMI.)

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1975. / Bibliography: leaves 155-163. / xvi, 163 leaves ill. (some col.), map