Understanding the ecological processes that impact parasite abundance and distribution is critically important for epidemiology and predicting how infectious disease dynamics may respond to future disturbance. Digenean trematodes (Platyhelminthes: Trematoda) are parasitic flatworms with complex, multi-host life cycles that include snail first-intermediate hosts and vertebrate definitive hosts. Trematodes cause numerous diseases of humans (e.g. schistosomiasis) and livestock (e.g. fascioliasis), and impact the ecology of wildlife systems. Identifying the ecological mechanisms that regulate these complex, multi-host interactions will advance both our understanding of parasitism and the dynamics of infectious disease. By examining patterns of infection in Elimia (= Oxytrema = Goniobasis) proxima snails, my dissertation research investigated the environmental factors and ecological processes that structure trematode communities in streams. First, I examined temporal variation in trematode infection of snails in five headwater streams. Over a three year period, I found no consistent seasonal patterns of trematode infection. There was consistency across sites in trematode prevalence, as sites with high prevalence at the beginning of the study tended to remain sites of high infection, relative to lower prevalence sites. Second, I examined landscape level variation in trematode infection by characterizing the regional distribution, abundance and diversity of E. proxima infections in 20 headwater streams. I found a broad scale spatial pattern in trematode communities due to regional turnover in dominant species. This pattern was correlated with elevation, but there were no significant relationships with other environmental variables. Additionally, molecular characterization of trematodes indicated the presence of cryptic (morphologically indistinguishable) species complexes within this system, and variation in genetic diversity among trematode types may reflect differences in host dispersal abilities. Third, I examined trematode infection within a single stream network across multiple headwaters and the mainstem. I found a decreasing downstream gradient of trematode prevalence related to several environmental variables including elevation, snail density, conductivity, and stream depth. Additionally, headwater communities were nested subsets of the communities found in the mainstem. By combining approaches at different temporal and spatial scales, my dissertation research increases our understanding of the processes that impact the abundance and distribution of parasites. / Ph. D. / Understanding the ecology of wildlife parasite infection is critical both for public health and the conservation of global biodiversity. Digenean trematodes (Phylum: Platyhelminthes, Class: Trematoda) are parasitic flatworms that cause numerous diseases of humans (e.g. schistosomiasis) and livestock (e.g. fascioliasis), and can impact wildlife ecology. Trematodes have complex life cycles that involve multiple hosts. A typical trematode life cycle includes a series of three hosts: (1) a snail first-intermediate host; (2) an aquatic invertebrate or vertebrate second-intermediate host; and (3) a vertebrate final host. By identifying the ecological processes that are important in these complex, multi-host interactions, we can advance our understanding of parasites and infectious disease. Freshwater ecosystems serve as the transmission channels for many types of parasites, including trematodes, but we know relatively little about the ecology of parasites in streams. My dissertation research investigated the ecology of parasites in streams by examining patterns of trematode infection in stream snails, <i>Elimia</i> (= <i>Oxytrema</i> = <i>Goniobasis</i>) <i>proxima</i>. First, I examined seasonal changes in trematode infection of snails in five headwater streams. Over a three year period, I found no consistent seasonal patterns of trematode infection. There was consistency across sites in the level of trematode infection (i.e. sites with high levels of infection at the beginning of the study tended to remain sites of high infection, relative to sites with lower levels of infection). Second, I examined variation in trematode infection across a regional spatial scale by examining the number and types of trematodes infecting snails in 20 headwater streams in southwestern Virginia and northwestern North Carolina. Across the region, I found a broad spatial pattern in the geographic distribution of trematodes due to changes in the dominant type of trematode infection. This pattern was related to elevation, but not to any other environmental variables we measured. Additionally, I obtained genetic sequences from these trematode samples, and this revealed the existence of additional trematode species that we could not distinguish based on visual examination of morphological features. Furthermore, differences in the genetic diversity of trematode species may be related to differences in the mobility of trematode host species. Third, I examined trematode infection at eight locations within a single stream. I found that trematode infection decreased from upstream to downstream, and that this pattern was related to several environmental variables including elevation, snail density, conductivity, and stream depth. By combining examinations of infection patterns over time and at different spatial scales, my dissertation research increases our understanding of the processes that impact parasite transmission in freshwater ecosystems.

This study is focused on cercarial cysteine peptidases of the trematode Diplostomum pseudospathaceum. It follows previous research which confirmed the presence of a 24kDa cysteine peptidase in cercariae biochemically and by mass spectrometry. It was postulated, that the function of this peptidase is histolytic, when cercariae penetrate the tissues. During an attempt to purify this peptidase and characterize its peptidolytic activity, it was found out that the cercarial homogenate containsmore different peptidases varying in their pI. Tests of peptidolytic activity and inhibition have shown that these peptidases are cathepsin L-like. They are active over a broad spectrum of pH with optima of activities in weakly acidicor neutral pH. Using degenerate primers based on conserved motifs of cysteine pepridases, partial sequences of three genes for cathepsin L of D. pseudospataceum (DpCL1, 2 a 3) were obtained. Then the complete sequences of DpCL2 and 3 genes and partial sequence (without 5'end) of DpCL1 were obtained by RACE PCR. To confirm function of these peptidases we tried to immunolocalize them. We assumed that they are localized in penetration glands. Preliminary results suggested that some of the cathepsins could be also localized in the gut of cercariae. For more detailed biochemical...

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

Natural mortality is a poorly known aspect of fisheries biology, despite its importance in stock assessments and population analysis. Of the many potential sources of mortality and morbidity in fishes, the effect of internal parasites is perhaps the least studied. Intestinal parasites may inhibit nutrient uptake as well as stimulate an inflammatory response in fish. Intestinal parasites of several tropical pelagic elasmobranchs, including silky and night sharks (Carcharhinus falciformis and C. signatus), the pelagic stingray (Pteroplatytrygon violacea), and mesopelagic fishes including sailfin lancetfish (Alepisaurus ferox), oilfish (Ruvettus pretiosus), snake mackerel (Gempylus serpens), escolar (Lepidocybium flavobrunneum), and Atlantic pomfret (Brama brama) are described from the South Atlantic Bight in the western North Atlantic. Parasites recovered include cestodes, trematodes, acanthocephalans and nematodes. Total gastrointestinal parasite loads were compared against the size (both length and weight) of the host, showing no correlation in pelagic elasmobranchs and a small correlation in mesopelagic teleosts. Sex and parasite loads were also compared for elasmobranchs showing a weak correlation. Capture seasons were also compared, and other results of this research showed that the parasites in this study are not host-species specific. The observed parasite classes and total helminth loads are the first described for these five mesopelagic fishes and will serve as a baseline for further studies. Future research is suggested to ascertain if commercially valuable, co-occurring, co-existing pelagic fishes may also be at risk for similar intestinal parasite fauna and burdens.

Black Buffalo Ictiobus niger are a catostomid species native to the Mississippi River Basin with declining populations. Aquaculture is a common component of recovery plans, however little information is published on catostomid culture methods. This study developed culture techniques for Black Buffalo including tank acclimation, induced spawning, larval rearing, and protein requirements. Fish needed a lengthy acclimation (> 2 months) to reduce signs of stress. After, an induced-spawning protocol was described with gonadotropin-releasing hormone analogue. Swim-up fry did not readily consume zooplankton at first feeding but began selecting for cladocerans one week after stocked in a rearing pond. The juvenile growth study found diets containing 41% crude protein are optimal for growth. Finally, trematodes harm catfish production, and Black Buffalo are a potential control option for catfish producers. However, Black Buffalo did not consume snails, the trematode’s intermediate host, suggesting they would not be an effective trematode control.

Trichobilharzia spp. are avian schistosomes related to medically important human parasites of the genus Schistosoma. Penetrating cercariae are well known as causative agent of cercarial dermatitis in humans. Cercariae actively penetrate the skin of definitive hosts and transform into schistosomula. This process is preceded by cercarial tail detachment and includes emptying of penetration glands and extensive surface changes. One of these changes is the loss of highly immunogenic glycocalyx which represents a protective coat in the aquatic environment. The glycocalyx has specific composition of saccharide molecules which are bound to lipids or proteins on the membrane of cercarial tegument. There is only limited information about the mechanism of shedding. Hypotheses based on indirect evidences suggest that peptidases or (phospho)lipases from penetration glands could be involved. This work describes the changes in surface glycosylation during transformation of cercariae into schistosomula by fluorescently labelled lectins and monoclonal antibodies against Lewis X antigen. Lectins UEA-I, LTA and PNA have been chosen as markers of transformation of T. regenti. Further, our experiments have been focused on shedding of cercarial glycocalyx. During in vitro induction of penetration gland emptying and...

Fascioloides magna is a trematode originating in North America. It is a significant pathogen, especially in cervids, but it can also infect ruminants kept for agricultural purposes.Adult trematodes are found in the liver tissue of their definitive hosts, where they can survive for a long period of time and produce large quantity of eggs. Those are passed through bile ducts and intestine with feces into the external environment. This thesis is focused on the morphology of individual developmental stages of F. magna. To this date only very limited number of literary resources concerning the topic had been published. Recorded results are compared with literary resources on Fasciola hepatica, a closely related trematode. The morphological characteristics of the individual developmental stages were studied by using histological, electron-miscroscopical and other methods (fluorescent labelling). The thesis also describes pathological changes of the definitive hosts' liver tissue. By means of the stated methods, the thesis expands the existing knowledge on the morphology of F. magna especially of surface structures and the distribution of the senzoric organs, some of which have been described for the very first time. Powered by TCPDF (www.tcpdf.org)

The commercial production of channel catfish (Ictalurus punctatus) is major industry in Mississippi. Infections of channel catfish with the digenetic trematode Bolbophorus damnificus have often been associated with heavy economic losses in the industry. To efficiently control transmission of this trematode, the avian hosts need to be identified. In the first study, two American white pelicans, two double-crested cormorants, two great blue herons, and two great egrets were fed channel catfish infected with B. damnificus metacercariae. The presence of Bolbophorus damnificus ova in pelican feces at three days post infection (dpi) indicated the pelicans had patent infections. Mature B. damnificus were recovered from the intestines of both pelicans at 21 dpi. No B. damnificus infections were observed in the other bird species. In a second study, 33 American white pelicans, 34 double-crested cormorants, 35 great blue herons, and 32 great egrets were collected in the Mississippi Delta. The prevalence of B. damnificus in the American white pelican was 93.9%, with an average of 158 B. damnificus found per bird (range 0-681). Bolbophorus damnificus was not found in any of the other bird species. The results of these two studies confirm that the AWPE is the only proven natural host for B. damnificus. In a third study, two previously undescribed cercariae were found infecting rams-horn snails in commercial catfish ponds. In challenge studies, channel catfish were exposed to both cercariae types. Only one type of cercariae (type I) was infective to channel catfish. The first evidence of type I metacercariae was seen histologically at 14 dpi and grossly at 21 dpi. Development continued until 120 dpi, when both gross examination and histology suggested that the metacercariae were mature. The type I metacercariae appeared to cause little host damage. Molecular analysis of the 18S rRNA gene region indicated that the type I cercariae and metacercariae may be a species of Clinostomum. The data generated in these three studies provides additional information that can be used in the development of efficacious management schemes to control digenetic trematodes infecting commercial catfish.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Nos estuÃrios tropicais, naturalmente complexos devido à dinÃmica de marÃs, perÃodos de precipitaÃÃo pluviomÃtrica atuam como distÃrbio intermediÃrio. As caracterÃsticas ambientais sÃo imprescindÃveis na histÃria de vida da biota da regiÃo, resultando no estabelecimento de padrÃes de reproduÃÃo ou interferindo no metabolismo dos organismos podendo tornÃ-los mais suscetÃveis ao acometimento por parasitas. O bivalve Lucina pectinata (Gmelin, 1791), apesar de apreciado no litoral brasileiro, foi pouco estudado no paÃs atà o momento. Este trabalho teve como objetivo caracterizar a biologia reprodutiva de Lucina pectinata (Mollusca: Bivalvia, Lucinidae) do estuÃrio do rio CearÃ, Fortaleza, CE, Brasil, e efetuar consideraÃÃes sobre parasitismo por trematÃides nesta populaÃÃo, em funÃÃo das variaÃÃes ambientais do local. Os exemplares coletados tiveram as gÃnadas e brÃnquias analisadas histologicamente. Para determinar a maturaÃÃo sexual dos indivÃduos, empregou-se escala gametogÃnica com quatro estÃdios de desenvolvimento gonadal. Lucina pectinata apresentou ciclo reprodutivo contÃnuo, com picos de desova na estaÃÃo seca. O nÃvel de parasitismo na populaÃÃo foi baixo, e a mesma nÃo està sendo prejudicada pela presenÃa de parasitas. Observaram-se semelhanÃa das variÃveis abiÃticas do local durante a mesma estaÃÃo, distinguindo-se nitidamente os perÃodos secos dos chuvosos. O distÃrbio pluviomÃtrico à discutido como fator regulador da populaÃÃo de Lucina pectinata, contribuindo tanto para sua renovaÃÃo quanto para controlar a incidÃncia dos parasitas trematÃides / In tropical estuaries, environments naturally complex due to the tidesÂs dynamics, the rainfall periods act as an intermediate disturbance. The environmental characteristics are important in the biotaâs life history of the region, resulting in the establishment of reproduction patterns or interfering at organisms metabolism making them more susceptible to being affected by parasites. The bivalve Lucina pectinata (Gmelin, 1791), although appreciated in the Brazilian coast, was little studied in the country so far. This study aimed to characterize the reproductive biology of Lucina pectinata (Mollusca: Bivalvia, Lucinidae) from the Cearà river estuary, Fortaleza, CE, Brazil, and make considerations on trematode parasitism in this population, according to local environmental variations. Specimens collected had the gonads and gills assessed histologically. To determine the individuals sexual maturity, was employed gametogenic scale with four stages of gonadal development. Lucina pectinata presented continuous reproductive cycle, with peak spawning at dry season. The level of parasitism in the population was low, and the same is not being affected by the presence of parasites. Were observed proximity of the abiotic variables during the same season, distinguishing clearly the dry periods of rainy. Disturbance rainfall is discussed as a factor regulating the population of Lucina pectinata, contributing to its renewal and to control the incidence of trematode parasites

A novel clinical assay for the assessment and subsequent treatment of Haemonchus infection in sheep to slow down the development of anthelmintic resistance – the FAMACHA / Dissertation (MSc)--University of Pretoria, 2001. / Veterinary Tropical Diseases / unrestricted