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Parasites exert substantial costs on their hosts. Thus, natural selection should favour behavioural defenses that reduce hosts’ exposure to parasites. This prediction has rarely been tested for aquatic hosts exposed to parasites. I designed experiments to test if fathead minnows could detect cercariae of the trematode, Ornithodiplostomum sp. and engage in antiparasite behaviours to avoid them. Minnows exposed to cercariae formed 20.1% tighter shoals compared to water controls. Further, minnows greatly reduced their overall activity, but only when they were exposed for a second time. The latter result is important because it provides the first indication that hosts can learn to avoid parasites. Lastly, I tested if epidermal club cells play a defensive role against cercariae. Club cells did not, but other components of the epidermis, probably mucus cells, decreased cercarial infectivity by 61-68%. My results show that fish can detect, learn, and ultimately avoid aquatic larval stages of parasites. / 105 leaves : ill. ; 29 cm.

The effect of Plagiorchis elegans cercariae on the vertical distribution of second, third, and fourth instar larvae of Aedes aegypti in the water column was studied in the laboratory. Under daytime conditions and in the absence of the parasite, larvae divided their time between the top and bottom of the water column. At night larvae spent the majority of their time at rest at the top of the column. In the presence of P. elegans cercariae larvae spent more time at rest at the surface under daytime conditions but increased their active time at the bottom under nighttime conditions. The presence of cercariae elicited escape and grooming responses and tended to reduce and fragment feeding activity.

Effects of infections with sylvatic species Trichinella, T. nativa or T. pseudospiralis, on the diel locomotory activity and locomotory activity pattern of an indigenous rodent host, the deer mouse (Peromyscus maniculatus), were assessed in a familiar environment and during the process of familiarization in a novel environment. Infection with muscle-encapsulating T. nativa severely reduced overall locomotory activity and changed locomotory activity patterns in a dose dependent fashion. In contrast, T. pseudospiralis infection had no such effects on diel locomotory activity. Infection with these nonencapsulating nematodes also changed locomotory activity patterns, but effects were independent of inoculation dose. Trichinella pseudospiralis infection almost completely reversed the locomotory exploration patterns of mice. Both T. nativa- and T. pseudospiralis-infected mice spent more time in shelter than did sham-inoculated conspecifics. Biological characterization of these infections in deer mice revealed striking departures from the conventional course of infection as typified by synanthropic trichinellosis in laboratory mice, and provided further insight into the relationship between the major phases of infection and the observed behavioral changes. Altered behaviors of infected deer mice are discussed in terms of their consequences on host fitness and survival, as well as parasite transmission. The study establishes links between behavioral observations derived from synanthropic and laboratory rodent-T. spiralis host-parasite associations and their sylvatic counterparts. It provides the behavioral underpinnings for future assessments of the role of wild rodents in the transmission of sylvatic trichinelloses.

Anthelmintic treatment of livestock is an important aspect of the control of gastrointestinal parasites. Resistance to anthelmintics is common, and an understanding of resistance requires knowledge of an anthelmintic's mode(s) of action and mechanism(s) of resistance. The parasitic nematode, Haemonchus contortus, has developed resistance to benzimidazoles and avermectins/milbemycins. Proposed mechanisms of resistance are here supported by genetic changes observed in genes whose protein products are believed to interact with these anthelmintics. Statistically significant differences in allele frequencies were observed between untreated and ivermectin- and moxidectin-treated strains in a gene encoding a putative glutamate-gated chloride channel alpha subunit, a proposed target of avermectins/milbemycins. One allele appeared to be associated with resistance. Similar changes in allele frequencies in the same strains occurred in a gene encoding a subunit of a gamma-aminobutyric acid receptor. Significant differences in allele frequencies of a gene encoding a P-glycoprotein were found in strains of H. contortus treated with ivermectin and moxidectin compared to derived, untreated strains. In all treated strains, one allele appeared to be associated with resistance. Similarly, allele frequencies of this gene were significantly different between a cambendazole-treated strain and its derived, untreated strain. These results implicate glutamate-gated chloride channels and gamma-aminobutyric acid receptors in mechanisms of resistance to avermectins/milbemycins and implicate P-glycoprotein in a mechanism of resistance to avermectins/milbemycins and benzimidazoles in H. contortus.

The effects of food availability and the presence of the parasite, Plagiorchis elegans, on the probability of Aedes aegypti preimagos to transform from one immature stage to the next over consecutive 24- or 48-hour periods of time were determined. Under conditions of low food availability, 24- and 48-hr transition probabilities of all larval instars, to the next were reduced. Increases in food availability reversed this process, causing significant decreases in same-stage transition probabilities. However, as transition to successive stages increased among first, second, third and fourth instars, there was concomitant significant increase in first and fourth preimago mortality. Addition of Plagiorchis elegans cercariae caused significant decreases in the 24 and 48-hour same-state probabilities for all pre-imago stages. Successive stage transitions for first, second and third instars were significantly increased while those of fourth instars and pupae were significantly decreased following exposure to the parasites. The mortality of all preimago stages significantly increased with exposure to parasite, but was highest among fourth instars and pupae. There were strong food-by-parasite interaction effects among first, second and third instars. Differences in transition probabilities increased with increasing food levels between controlled and parasite-exposed groups. The opposite was true for fourth instars and pupae. While there was no significant interactive effect between food and the presence of the parasite on pupae regardless of food concentration, this was not true for mortality probabilities among fourth instars. Significantly more fourth instars died in response to parasite exposure and there were significant interactive effects of food and parasites on the probability of fourth instars transformation to pupae over 48 hrs.

A prevalence of 76% and a mean intensity of 42.7 Anisakis simplex was found in harbour porpoises (Phocoena phocoena) (N = 78) by-caught in cod gill nets set by fishers from the Gaspe area in summer 1993. No young-of-the-year porpoises (N = 12) were infected. Prevalence and mean intensity among immature and adult porpoises as well as between sexes and length-classes were not significantly different. Anisakis simplex was present in the three stomach compartments of harbour porpoises. Adult stages were proportionately less abundant in the main and pyloric stomachs than the forestomach. Percent intensity of A. simplex was influenced by maturity of harbour porpoises. Gravid female A. simplex contained up to 818,000 eggs. Egg number was highly correlated with worm uttering volume. Density effects were not demonstrated, possibly due to high variability of egg number, total length, uterine and total worm volume between parasites from each stomach and between stomachs of harbour porpoise.

The objectives of this study were to determine the effect of different types and levels of dietary fiber on Heligmosomoides polygrus (Nematoda) in laboratory mice. BALB/c mice were randomly assigned to one of seven diets: no fiber, cellulose (5%, 10%, 20%), and pectin (5%, 10%, 20) and infected with H. polygyrus one week later. The length of intestine increased significantly with the concentration of pectin and was associated with longer villi, thicker mucosa and increased villus/crypt ratio. In contrast, changing concentration of cellulose had minimal effects on the gastrointestinal tract. More day 5 larvae were found in mice fed 20% pectin, but neither type nor level of dietary fiber affected worm survival or spatial distribution. An increase from 5% to 10% pectin increased per capita egg production both in vivo and in vitro, but a further increase to 20% pectin decreased per capita egg production in vivo to the low level seen in mice fed no fiber. However when the parasites from mice fed 20% pectin diet were cultured in vitro, they released very high numbers of eggs. Changing concentration of cellulose had no effect on parasite egg production in vivo or in vitro. Our study supports the hypothesis that pectin promotes the establishment and reproduction of Heligmosomoides polygyrus, and that this is closely related to the changes in gut morphology. Therefore we conclude that cellulose, not pectin, should be used to balance reduced content of macronutrients in studies on malnutrition and nematode infection.

Resistance to the avermectin/milbemycin class of anthelmintics in nematodes has become a serious problem worldwide due to their unrestricted usage. Resistance to these compounds is attributed to the over-expression of the transport protein, P-glycoprotein (P-gp). P-gp acts by pumping drug molecules out from the cell or organism, P-gp efflux activity can be blocked using multidrug resistance (MDR) modulators associated with chemotherapy to enhance their therapeutic effect. A series of experiments was undertaken to determine if the association of the anthelmintics, ivermectin (IVM) and moxidectin (MOX), and MDR modulators would increase the anthelmintics' efficacy against resistant parasites. Using an in vitro migration assay, IVM and MOX in the presence or absence of verapamil (VRP), CL347,099 and cyclosporin A (CyA) were used against IVM- and MOX-selected strains of H. contortus. The modulators alone had no effect on reducing the number of migrating larvae, IVM and MOX had a significant increase in efficacy of 52.7 and 58,3% respectively, when used in association with VRP, above that obtained with the anthelmintics alone. CL347,099 was also able to significantly increase the IVM and MOX efficacy by 24.2 and 38.9%, respectively. The effect of IVM and MOX in combination with VRP and CL347,099 was determined in jirds infected with selected strains of H. contortus. The combinations of VRP with either IVM or MOX significantly reduced worm counts of the selected strains compared with the untreated controls, whereas IVM or MOX alone did not. CL347,099 plus MOX combination was significantly more efficacious than moxidectin alone against the selected strains. To evaluate the effect of VRP on the pharmacokinetic behaviour of the anthelmintics IVM and MOX, the drug combination was given to sheep. The IVM plus VRP treatment resulted in an increase of the pharmacokinetic parameters of IVM. The peak concentration (83%) and area under the curve (54%) were significantly differen

The effect of low dietary zinc on the survival and reproduction of an intestinal nematode (Heligmosomoides polygyrus) during both primary (Experiment 1) and challenge (Experiment 2) infections was investigated. Plasma zinc concentrations were significantly lower in mice fed a 5 ppm zinc diet (ZR), compared with control mice fed a 60 ppm zinc diet (C) in both experiments. There were no significant differences between ZR and C mice in any other zinc parameter or on worm burdens or worm fecundity in either experiment. Comparisons between the primary infection and the challenge infection did suggest a possible effect of calorie restriction on worm burdens. / Parasitic infection did, however, affect the host nutritional status. Spleen weight was significantly higher in infected mice in both experiments. In the challenge infection, both liver and spleen copper concentrations were significantly higher, and spleen iron concentration significantly lower in the infected mice. That these significant results were seen only in the challenge infection may suggest the role of the host immune response.