Dissertations / Theses on the topic 'Macroparasites'

Bats (Chiroptera) are one of the most successful and diverse of mammalian orders, with an estimated 1100 species worldwide. Due to protected species legislation, studies that focus upon bat endoparasites are limited. As such, many fundamental questions concerning bat-parasite relationships remain unanswered, including evolutionary aspects of such associations, hostparasite interactions and factors that may influence the composition of bat parasite communities. To further knowledge of bat parasitology, one hundred bats, that had either died of natural causes, or had been euthanized due to severity of injury, were acquired across Greater Manchester and Lancashire between September 2005 and September 2008. Molecular typing methods confirmed 93 specimens to be common pipistrelle (Pipistrellus pipistrellus), six to be soprano pipistrelle (P. pygmaeus) and one to be a whiskered bat (Myotis mystacinus). Development of PCR-based methodologies, coupled when possible with morphological analyses, confirmed the presence of the following microparasites (prevalence data in parenthesis): Babesia vesperuginis (23%), Trypanosoma spp (36%), Bartonella sp. (2%) and Eimeria sp. (20%), and the following macroparasites: Lecithodendrium linstowi (80.4%), Lecithodendrium spathulatum (19.6%), Prosthodendrium sp. (35.3%), Plagiorchis koreanus (29.4%) and Pycnoporus heteroporus (9.8%). Potential factors affecting the parasite community composition including host sex and age, season, year, geographic location and parasite co-infection are explored. The detection of Eimeria sp. would appear to be the first record of coccidia in British bats, and also the first global record of Eimeria sp. from the common pipistrelle. Phylogenetic analysis of bat-associated Bartonella sp. ITS region, clusters the isolate in a well supported clade with B. grahamii, B. elizabethae and B. queenslandensis, all known to infect rodents, in addition to B. grahamii and B. elizabethae being recognised human pathogens. The first molecular sequence data for L. spathulatum is presented, and sequence data for Prosthodendrium specimens is also novel; both are incorporated into a phylogenetic analysis of the Lecithodendriidae, which questions the current taxonomic status of Prosthodendrium. Lastly, in an attempt to assist the evolutionary study of haemosporidian parasites, ectoparasitic bat flies were collected in the field from Puerto Rican bats and additional samples were acquired from Germany. Dissection and cytochrome b-specific PCR analysis of DNA extracted from insect digestive tract tissue confirmed the presence of haemosporidian DNA within two of the German samples. Phylogenetic analysis of the order Haemosporidia, incorporating the novel cytochrome b gene sequence derived from these German samples, showed the latter to cluster strongly with samples isolated from Madagascan bats and illustrates likely host-switching between birds and mammals.

This thesis primarily addresses environmental influences, in particular exposure to macroparasite infection, on immunoregulatory expression in wild and laboratory murid rodents. Experimental studies in laboratory mice demonstrated that Heligmosomoides bakeri infection was generally associated with upregulation of systemic toll-like receptor (TLR) expression and TLR-mediated cytokine production at times of peak standing worm burden. TLR function and patterns of expression of TLR and other immunoregulatory genes were also monitored in a time series of wild mice (Apodemus sylvaticus) from a natural population exposed to a range of macroparasites, including Heligmosomoides polygyrus. Differences between wild and laboratory mice in the pattern of coexpression of immunoregulatory and TLR genes and in the transcriptional responses of immunoregulatory genes to TLR-stimulation suggested a stronger regulatory bias in the wild compared to laboratory mice. Perhaps most strikingly, wild mice constitutively express relatively very much more TGF-Bl, TLR2 and TLR4, but not other immunoregulatory genes such as FoxP3, IL-l0 or TNF-a. This indicates that immunoregulatory differences between wild and laboratory mice may be linked to differences in TGF-B1 producing cells, rather than IL-10-producing or FoxP3+ cells. Immunoepidemiological analyses indicated a substantial association of macroparasitic infection (principally due to the louse Polyplax serrata and Heligmosomoides polygyrus) with TLR-mediated cytokine responsiveness in wild mice. Given the primary role of TLRs in anti-bacterial responses, the consistent experimental and epidemiological links between macroparasites and TLRs in this study are interpreted as a possible effect of exposure of the host to bacteria co-localizing in macroparasite infection foci. The identity of genes differentially upregulated in wild vs. laboratory mice might also relate to bacterial exposures (possibly influenced by macroparasite infection, given the associations with TLRs described above?). Thus, TLR2 and TLR4 are key innate anti- bacterial receptors and TGF-B1 is prominently secreted by Th3-type T-regulatory cells which are associated with mucosal tolerance.

Thirty-two specimens of the sixgill sawshark, Pliotrema warreni, were trawled near Bird Island in Algoa Bay on the Eastern coast of South Africa in April and May 2015. The specimens were examined for anatomical proportions, reproductive characteristics, diet, and parasite assemblages. Several external measurements were collected including mass, total length, standard length, girth, rostrum length, interoccular to pre-caudal length, first dorsal origin to second dorsal origin, first dorsal origin to pre-caudal origin, and mouth width. The equation for mass (g) vs. total length (mm) was ln(Mass)=0.2997*ln(TL)+2.0383 for females and ln(Mass)=0.3321*ln(TL)+1.941 for males. 1st Dorsal to 2nd dorsal origin length (DD) to total length equations for females and males were DD=0.2451*TL-26.677 and DD=0.2598*TL-34.535, respectively. Mean lengths and masses were 11.5% greater and 50.3% heavier in females than males, respectively. Females were on average, 994 mm (759 mm – 1283 mm) in length while males were 891.8 mm (763 mm – 1015 mm). Average mass for females was 1702.5 g (602.5 g – 3478.5 g) whereas males it was 1132.6 g (687 g – 1593.5 g). Based on these data both sexes display isometric growth. Males were determined to reach sexually maturity around 850 mm which is similar to that reported by Ebert et al., (2013) around 830 mm. Females were found to reach sexual maturity at 1000 mm which is 100 mm smaller than what is reported by Ebert et al., (2013). Stomach mass increased with total mass and total length regardless of sex (female R² = 0.507; male R² = 0.213 for length and female R² = 0.6123; male R² = 0996 for mass). Females consumed larger prey items in terms of mass and length as well as a higher quantity of prey than males presumably because they are the larger sex and have an increased need for nourishment to provide for pregnancy. Prey items were redeye round herring, Etrumeus whiteheadi (64.96% of the diet), a benthic shrimp species not identified (7.69%), and Cape horse mackerel, Trachurus trachurus capensis (0.85%). Despite strict adherence to the guidelines for age determination for elasmobranchs provided in the literature, the conventional method used which involved extensive cleaning of the vertebral centra with an array of chemicals, setting and cutting in an epoxy resin, and staining for microscopy, did not yield readable results which could be used to determine the ages of these sharks. The highest abundance of parasites were found in the stomachs. Three specimens of a cymothoid isopod was found externally. Two specimens of Ascaris sp. nematode were found in the visceral cavity. The remaining 18 parasites consisted of three Neoechinorhynchidae sp. of acanthocephalan and 15 Proleptus obtusus nematodes all of which were found inside the stomachs. Given the results of the parasite survey, males and females do not have the same parasites as females have four different species while males only have one. More collections from other areas and times of year are necessary to obtain a better description of the species.

Potential alterations of host and parasite ranges are likely with climate change so an understanding of the host traits and ecological factors that can influence host-parasite interactions is vital for the effective protection of ecosystems. Accidental introductions of non-native species can place elevated stress on native ecosystems so that the examination of key species can act as early warning systems. The Eurasian otter, Lutra lutra¸ is a top predator and sentinel species for the health of European freshwater ecosystems and is therefore a suitable model for exploring parasite fauna introductions. In this PhD, the patterns and processes that define macro-parasitic infections were explored using evidence from post-mortems of 587 otters. Specifically, the invasive status of two helminths (Pseudamphistomum truncatum and Metorchis albidus: Trematoda; Opisthorchiidae) was investigated, both species having been identified in the UK otter populations for the first time within the last 10 years. Genetic variation, however, was similar across Europe indicating neither helminth is likely to have been a recent introduction to the UK., The distribution of both helminths as well as the only ectoparasite, Ixodes hexagonus (Arthropoda; Ixodidae), recovered from UK otters, were associated with abiotic factors, particularly temperature. The complexity of the parasite life cycles was investigated; otters act as a definitive host for both helminth species considered in this thesis and early stage intermediate hosts were identified for P. truncatum as the snail Radix balthica and the roach Rutilus rutilus. Metacercariae of M. ablidus were detected on chub (Leuciscus cephalus), rudd (Scardinius erythrophthalmus) and roach. Parasite aggregation and parasite fecundity of the P. truncatum populations were influenced by abiotic factors, region and season, whilst P. truncatum abundance was defined better by the biotic factors host age-class and condition demonstrating how multiple factors combine to produce parasite population dynamics in wild fauna. Ultimately, the data collated throughout this PhD was used to parameterise a susceptible-infected Susceptible-Infected (SI) model describing the host population dynamics of opisthorchiid trematodes. This model is applied to the P. truncatum system to examine which factors might determine the proportion of hosts that become infected.

Même si la majorité des études théoriques ou empiriques se sont essentiellement focalisées sur des interactions impliquant un seul hôte et un seul parasite, le polyparasitisme est la règle en milieu naturel chez les mammifères. Les déterminants potentiels de la richesse parasitaire (nombre d'espèces de parasites hébergés par un hôte), mais aussi les possibles impacts de ces multiples espèces de parasites sur les hôtes sont encore largement méconnus. En effet, les nombreuses études préexistantes sur les déterminants ont souvent été réalisées dans un cadre conceptuel trop étroit avec des données souvent restreintes à certaines zones faunistiques. Nous avons donc étendu les données et reconsidéré certains déterminants « classiques » (tels la latitude, la taille du groupe ou encore la taille du domaine vital pour l'ensemble des mammifères). Nous en avons également proposé de nouveaux, tels la socialité chez les rongeurs ou la nature des gîtes chez les chauves souris. Les travaux relatifs aux impacts de la diversité en tant que telle sont par contre peu nombreux et récents. Nous avons donc tenté de les appréhender à différents niveaux (immunité, métabolisme et traits de vie). En établissant les effets cumulatifs des infestations multiples, tels une augmentation de l'investissement immun ou du métabolisme basal, notre travail renforce l'idée récente et encore largement sous estimée que la diversité parasitaire puisse être un facteur de pression par elle-même sur les hôtes
Despite most sudies related to host- parasite relationships have focused on single host /single parasite systems, polyparasitism (i. E. Multiple parasitic infestations or polyparasitism) is the law in natural systems at individual, populational or species level. Importantly however, may open questions arise from the reality of polyparasitism. Among them, those related to the potential impacts of parasitic diversity per se but also to the determinants of this parasitic diversity need to be furtfher explored. Infortunately, studies related to the impacts or coinfectiosn are still scarce. Moreover, the numerous available investigations of determinants may have largely suffered from a too narrow conceptual framework, leading to erroneous or naive predictrions. Focusing on macroparasites and using comparative phylogenetic approach across wild mammal species, we have then reinvestigated the determinants of parasitic diversity, notably revisiting “classical” determinants such as group size home range size or latitude but also exploring understudied ones such as roosting ecology of bats or sociality of rodents. The impacts of parasitic diversity have mainly been approached in our study by focusing on mammals' responses at immune, metabolic or life history trait levels. We have then found strong support for cumulative effects of polyparasitism at metabolic and immune levels

Les maladies tropicales négligées sont un groupe de maladies infectieuses rencontrées surtout dans les zones rurales ou dans les zones urbaines et pauvres des pays à revenu faible et intermédiaire, et qui constituent elles-mêmes des facteurs aggravants de pauvreté. Comparés à des maladies comme le sida, la malaria et la tuberculose, l'étude et l'effort de lutte contre ces maladies infectieuses sont beaucoup moins développés en termes de fonds investis, de programmes de recherche et de politiques de santé publique. Cette thèse vise à apporter une contribution à l'étude des maladies tropicales négligées, par le biais de travaux théoriques situés à l'interface entre la modélisation et l'écologie, l'évolution et le contrôle de ces maladies. Les résultats obtenus et discutés portent plus particulièrement sur la transmission des maladies vectorielles, et sur l'évolution des macro-parasites. Cette thèse permet ainsi d'illustrer l'intérêt des approches de modélisation en recherche fondamentale pour mieux comprendre et lutter contre ce groupe de maladies infectieuses, des maladies qui chaque année affectent encore des centaines de millions de personnes à travers le monde.

This thesis examines the parasite dynamics and the mechanisms affecting parasite load and transmission focalising on the role played by host and habitat heterogeneities. This study is based on the gastrointestinal nematode Heligmosomoides polygyrus and the small mammal yellow necked mouse and uses data gathered from experimental field manipulations of parasites intensities and data gathered from trapping monitoring. Initially the parasite community of yellow-necked mouse (Apodemus flavicollis) was explored in North-Eastern Italian Alps with the aim to describe the major patterns and identify the factors affecting parasite community structure. Despite the observed spatial variability it has been found that differences within the host population such age and secondly sex and breeding conditions, were the major factors acting on parasite occurrence and intensity. Habitat differences had a less apparent effect on parasite community structure. The consequences of H. polygyrus infection on other parasite species infections have been analysed, in specific the infestation of the tick Ixodes ricinus in populations of A. flavicollis. H. polygyrus load and tick infestation were monitored as well as were carried out field manipulations of H. polygyrus intensity and were monitored changes in tick infestation. It has been found that H. polygyrus load was negatively related to I. ricinus infestations. Host factors mediated the H. polygyrus-I. ricinus interaction such that young and non-breeding mice exhibited higher I. ricinus to H. polygyrus intensity respect breeding adults. The role of host sex on parasite abundance was then investigated carrying out a field experiment where the H. polygyrus intensity were manipulated in relation to mice gender. In specific, H. polygyrus was removed alternately from either sexes and the parasite load was analysed in the untreated sex. It was found that males mice were responsible to drive parasite transmission in the host population and this was observed in absence of sex-bias in parasite infection, suggesting that this pattern was not a mere consequence of quantitative differences in parasite loads between sexes. To disentangle the possible mechanism causing this sex bias in parasite transmission mathematical simulations based on parameters obtained for the field experiment were used. Two non mutually exclusive hypotheses causing sex bias in parasite transmission were tested: a- males immune response is less efficient and this causes the development of more successful parasite infective stages or b-males behaviours allow them to be more efficient is spreading in more exposed areas parasite infective stages. Multi-host models were developed and simulations were compared with field results. While it was not disentangled the most dominant mechanism causing sex bias in parasite transmission this study underlined the importance of host sexes in affecting parasite dynamics and host-parasite interaction. In conclusion this thesis highlighted the importance of considering host and environmental differences when investigating host parasite interactions. This finding could be extremely important when planning measured of disease control or to avoid disease outbreak. Controlling target group of individuals host could avoid economical losses and a more effective measure of intervention.

Ce travail contribue à un modèle déterministe discret d'un système hôte-macroparasite et propose un modèle stochastique équivalent. Une application du modèle consiste en l'étude quantitative du système Bar-Diplectanum Aequans à l'aide de deux simulateurs parallèles. Une étude algorithmique détaillée est donnée pour le simulateur déterministe. L'extensibilité de très bonne qualité est évaluée théoriquement et testée. Une utilisation optimisée des mémoires caches permet d'atteindre 60 % de la puissance crête au coeur des calculs. Les temps d'exécution sont réduits et la précision des calculs améliorée, ce qui permet de reproduire des dynamiques observées sur le terrain. Le second simulateur utilise une méthode de type Monte Carlo. On donne les performances associées à une programmation hybride sur une grappe de noeuds SMP. L'étude quantitative effectuée sur les résultats des simulateurs donne un éclairage nouveau sur l'interaction des mécanismes des systèmes hôte-macroparasite.

Thesis (PhD)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: Fleas (Siphonaptera) are obligate ectoparasites of mammals and birds. Due to their economic importance as disease vectors, most contemporary studies on macroparasites now also consider the spatial variation of parasite communities and the underlying mechanisms involved in shaping current distribution patterns. Fleas differ in life history traits, such as the level of host specificity and microhabitat preferences, which can result in differential evolutionary responses to similar abiotic events. The main objectives of this study are to investigate: (1) the influence of vicariance and host association on the genetic structure of two generalist flea species, Listropsylla agrippinae, and Chiastopsylla rossi. The taxa differ in the time spent on the host (fur vs. nest) and the level of host specificity; (2) the taxonomy of Dinopsyllus ellobius to determine whether more than one species exist and if so to then elucidate the mechanisms of speciation; and (3) the influence of flea life history on species distribution model performance and see if the relative importance of predictor variables differ between species with different life histories. A total of 1423 small mammals were brushed to collect 2906 flea individuals originating from 31 geographically distinct localities throughout South Africa (SA). Phylogeographic structure of L. agrippinae and C. rossi were determined by making use of 315 mitochondrial COII (mtDNA) and 174 nuclear EF1-α (nDNA) sequences. The more host specific fur flea, L. agrippinae, displayed pronounced spatial phylogeographic structure, based on mtDNA, which was congruent with host vicariance in the region. In contrast, the more generalist nest flea, C. rossi, showed a higher level of inter-populational divergence, based on mtDNA and nDNA, and this may be attributed to comparatively higher restrictions to dispersal when compared to the more specific fur flea. In an attempt to resolve the taxonomy of D. ellobius, 151 mtDNA and 68 nDNA alleles were generated from individuals meeting the morphological description of D. ellobius. Two distinct D. ellobius lineages that corresponded to previously described species (D. ellobius and D. abaris) were recorded. The results indicate that the two species indeed differ morphologically and based on the distribution of the two species it was concluded that the diversification could be a result of climate driven vicariance and subsequent ecological segregation according to habitat use. Locality records from Segerman (1995) were digitized and used as background data in species distribution modelling. Sufficient information was obtained for 21 flea species. A total of 68 climatic and landscape feature predictor variables were obtained and through a process of elimination, 19 variables were ultimately used. Model performance was good to excellent on average and the contribution of climate and landscape feature variables differed between fleas with different life histories. Historical and contemporary climate has the most prominent effect on flea distribution at the regional scale, but the level of host association influences the phylogeographic pattern of fleas. This study provides the first evidence of congruent phylogeographic patterns between a generalist temporary parasite and its hosts. Our findings provide further support for the notion that more than one species exist within the D. ellobius complex and that speciation is a result of complex interactions. The study also provides novel data on the role of environmental variables in shaping the geographic distribution of flea species with different life histories. With the anticipated rise in flea-borne diseases worldwide, due to changes in vector distribution, the study further emphasize the need for studying the mechanisms involved in shaping flea distribution patterns.
AFRIKAANSE OPSOMMING: Vlooie (Siphonaptera) is verpligte ektoparasiete van soogdiere en voëls. As gevolg van hul ekonomiese belangrikheid as vektore van oordraagbare siektes, neem meeste kontemporêre studies oor makroparasiete nou die ruimtelike variasie (vikariansie) van parasiet gemeenskappe en die onderliggende meganismes betrokke by die vorming van die huidige verspreiding patrone in ag. Vlooie verskil in lewensgeskiedenis eienskappe, soos die graad van gasheer spesifisiteit en mikrohabitat voorkeur, wat kan lei tot differensiële evolusionêre patrone tot soortgelyke abiotiese gebeure. Die belangrikste doelwitte van hierdie studie is om ondersoek in te stel na: (1) die invloed van vikariansie en gasheer assosiasie op die genetiese struktuur van twee algemene vlooi spesies, Listropsylla agrippinae en Chiastopsylla rossi. Die taxa verskil in die hoeveelheid tyd wat gespandeer word op die gasheer (pels vs. nes) en die graad van gasheer spesifisiteit; (2) die taksonomie van Dinopsyllus ellobius om te bepaal of daar meer as een spesie bestaan, en indien wel, die meganismes van spesiasie voortbring; en (3) die invloed van vlooi lewensgeskiedenis op die prestasie van die spesies verspreidings model en kyk of die relatiewe belangrikheid van omgewingsvoorspellers verskil tussen spesies met verskillende lewensgeskiedenisse. 'n Totaal van 1423 klein soogdiere is geborsel om 2906 vlooi individue afkomstig van 31 geografies verskillende plekke in Suid-Afrika in te samel. Filogeografiese struktuur van L. agrippinae en C. rossi is bepaal deur gebruik te maak van 315 mitochondriale COII (mtDNA) en 174 kern EF1-α (nDNA) volgorde bepalings. Die meer gasheer spesifieke pels vlooi, L. agrippinae, het ruimtelike filogeografiese struktuur aangetoon, gebaseer op mtDNA, wat ooreenstem met gasheer vikariansie in die streek. In teenstelling hiermee het die minder gasheer spesifieke nes vlooi, C. rossi, 'n hoër vlak van inter-populasie divergensie getoon, gebaseer op mtDNA en nDNA, wat toegeskryf kan word aan relatief hoër beperkings op verspreiding teenoor die meer gasheer spesifieke pels vlooi. In 'n poging om die taksonomie van D. ellobius op te los is 151 mtDNA en 68 nDNA allele gegenereer uit individue wat voldoen aan die morfologiese beskrywing van D. ellobius. Twee afsonderlike D. ellobius afstammelinge wat ooreengestem het met voorheen beskryfde spesies (D. ellobius en D. abaris) is aangeteken. Die resultate dui daarop dat die twee spesies inderdaad morfologies verskil en gebaseer op die verspreiding van die twee spesies is daar tot die gevolgtrekking gekom dat die diversifikasie moontlik toegeskryf kan word aan klimaat gedryfde vikariansie en daaropvolgende ekologiese segregasie volgens habitat gebruik. Geografiese verspreidings rekords van Segerman (1995) was gedigitaliseerd en gebruik as agtergrond data in die spesie verspreidings modelle. 'n Totaal van 68 klimaat en landskap kenmerk voorspeller veranderlikes is verkry, en deur 'n proses van eliminasie, is 19 veranderlikes gebruik. Model prestasie was oor die algemeen goed tot uitstekend en die bydrae van klimaat en landskaps veranderlikes het verskil tussen vlooie met verskille in lewensgeskiedenis. Historiese en kontemporêre klimaat het die mees prominente effek op vlooi verspreiding by die plaaslike skaal, maar die vlak van die gasheer assosiasie beïnvloed die filogeografiese patroon van vlooie. Hierdie studie bied die eerste getuienis van ooreenstemmende filogeografiese patrone tussen 'n minder gasheer spesifieke, tydelike parasiet en sy gashere. Ons bevindinge bied verdere ondersteuning vir die idee dat meer as een spesie bestaan binne die D. ellobius kompleks en dat spesiasie 'n gevolg is van komplekse interaksies. Die studie bied ook nuwe data oor die bydrae van die omgewingsveranderlikes in die vorming van die geografiese verspreiding van vlooi spesies met verskillende lewensgeskiedenisse. Met die verwagte styging in vlooi-oordraagbare siektes wêreldwyd, as gevolg van veranderinge in vektor verspreiding, beklemtoon die studie verder die noodsaaklikheid vir die bestudering van die meganismes betrokke in die vorming van vlooi verspreiding patrone.
National Research Foundation (NRF)

Neste trabalho, nos propomos a estudar o desenvolvimento teórico de alguns modelos matemáticos básicos de doenças infecciosas causadas por macroparasitas, bem como as dificuldades neles envolvidas. Os modelos de transmissão, que descrevemos, referem-se ao grupo de parasitas com transmissão direta: os helmintos. O comportamento reprodutivo peculiar do helminto dentro do hospedeiro definitivo, no intuito de produzir estágios que serão infectivos para outros hospedeiros, faz com que a epidemiologia de infecções por helmintos seja fundamentalmente diferente de todos os outros agentes infecciosos. Uma característica importante nestes modelos é a forma sob a qual supõe-se que os parasitas estejam distribuídos nos seus hospedeiros. O tamanho da carga de parasitas (intensidade da infecção) em um hospedeiro é o determinante central da dinâmica de transmissão de helmintos, bem como da morbidade causada por estes parasitas. Estudamos a dinâmica de parasitas helmintos de ciclo de vida direto para parasitas monóicos (hermafroditas) e também para parasitas dióicos (machos-fêmeas) poligâmicos, levando em consideração uma função acasalamento apropriada, sempre distribuídos de forma binomial negativa. Através de abordagens analítica e numérica, apresentamos a análise de estabilidade dos pontos de equilíbrio do sistema. Cálculos de prevalências, bem como de efeitos da aplicação de agentes quimioterápicos e da vacinação, no controle da transmissão e da morbidade de parasitas helmintos de ciclo de vida direto, também são apresentados neste trabalho.
The aim of this work is to study the theoretical development of some basic mathematical models of infectious diseases caused by macroparasites as well as the difficulties involved in them. The transmission models which we describe refer to the group of parasites with direct transmission: the helminths. The peculiar reproductive behavior of the helminth in the definitive host, in order to produce stages which will be infectious for other hosts, makes the epidemiology of infections by helminths fundamentally different from all other infectious agents. An important feature of these models is the form assumed for the distribution of parasites among their hosts. The worm burden (intensity of the infection) in a given host is the crucial quantity of the dynamics of the helminth transmission, and also of the morbidity caused by the parasites. By assuming that the parasites are distributed in a negative binomial form, we study the dynamics for both monoic (hermaphrodite) and dioic (male-female) polygamic with a particular mating function. Through both analytical and numerical approaches, the stability of the equilibrium points is analyzed. Prevalence computations and studies about the control of transmission and morbidity of heminthic parasites of direct life cycle, through the application of chemiotherapic agents and through vaccination, are also presented in this work.

This study examines, from a modelling point of view, the dynamics of infectious diseases in wildlife caused by macroparasites and by tick-borne infections. The overall aim was to investigate the important role played by parasite aggregation in the dynamics of both systems. For macroparasites we first developed some deterministic models that incorporate explicit mechanisms for generating aggregation in parasite distribution, specifically multiple infections and host heterogeneity. We explored the role of aggregation in host regulation and in determining a threshold value for parasite establishment. A large aggregation makes it more difficult for parasites both to regulate hosts, and to get established in a population at carrying capacity. Furthermore, the stabilization yielded by aggregation strongly depends on the mechanism that produces the aggregation. We then introduced some uncertainties into the host-macroparasite system, presenting an individual-based stochastic model that incorporated the same assumptions as the deterministic model. Stochastic simulations, using parameter values based on some real case studies, preserved many features of the deterministic model, like the average value of the variables and the approximate length of the cycles. An important difference is that, even when deterministic models yield damped oscillations, stochastic simulations yield apparently sustained oscillations. The amplitude of such oscillations may be so large as to threaten the parasites’ persistence. With respect to tick-borne diseases we presented a general model framework that incorporated both viraemic and non-viraemic routes of infections. We compute the threshold for disease persistence and study its dependence on the parameters and on host densities. The effects of tick aggregation and correlation between different tick stages on the host have both an important effect on infection persistence, if non-viraemic transmission occurred. In the case of Lyme Disease and Tick-borne Encephalitis (TBE) in Trentino (northern Italy) we showed some numerical results, using parameter estimates based on a detailed field study, and explored the effects of uncertainty on the endemic equilibrium of both diseases assuming only viraemic transmission for Lyme Disease while for TBE we permitted only non-viraemic transmission through co-feeding ticks. In conclusion we have examined the patterns and changes of aggregation in a number of contrasting systems and believe that these studies highlight both the importance of considering heterogeneities in modelling host-parasite interactions and, more specifically, modelling the biological mechanisms that produce aggregation in parasite distributions.

Species of Argulus are macro-, ecto-parasites known to infect a wide variety of fish, but in the UK mainly cause problems in rainbow (Oncorhynchus mykiss) and brown trout (Salmo trutta). Argulus foliaceus is estimated to have caused problems in over 25% of stillwater trout fisheries in the UK. While A. foliaceus does not usually cause high levels of mortality, the parasite affects fish welfare, and also makes fish harder to catch due to morbidity and reduced appetite. This can cause severe economic problems for the fishery, resulting in reduced angler attendance due to poor capture rates and the reduced aesthetic appearance of fish; in the worst-case scenario this can result in the closure of the fishery. Current methods of control include chemical treatment with chemotherapeutant emamectin benzoate (Slice), physical intervention with egg-laying boards which are removed periodically and cleaned in order to reduce the number of parasites hatching into the environment, and the complete draining and liming of the lake to remove all free-living and egg stages of the parasite. While these treatments have all been shown to reduce parasite numbers, none are known to have resulted in permament eradication of the parasite. There is evidence to suggest that A. foliaceus will eventually develop resistance to Slice - the only currently available chemical treatment against the infection - and egg-laying boards and the draining and liming of the lake are both time- and labour-intensive. Previous studies have shown that slow fish turnover is a risk factor with respect to A. foliaceus infections, and with a wide variety of stocking practices occurring in the UK one of the first aims of this project was to determine their impact on the host-parasite dynamics. Mathematical models provide a cost-effective way of examining the impact of such practices, and after a literature review (chapter one), in chapter two a three-compartment mathematical model was adapted for use in the A. foliaceus-trout system. Four generalised stocking methods were then incorporated and analysed, and a minimum threshold host density was found to be necessary to sustain the parasite. Including a function which reduced the capture rate as the parasite burden increased allowed the parasite to survive at a lower host density, as susceptible fish were removed from the water at a slower rate, and attached parasites also remained in the water for longer. This resulted in hysteresis in the model, as the invasion threshold for the parasite remained the same, but once established the parasite became harder to eradicate, requiring significant reductions in the host density. In chapter three the model was further developed in order to improve its biological real- ism. Several features were added and these included: natural host mortalities, a separate compartment for the parasite egg population, and parasite survival after the natural or parasite-induced mortality of its host. In chapter four seasonality was added by incorporating temperature-dependent egg-laying rates and an over-wintering period during which the parasite was unable to reproduce. The model was then fit to the available data, and estimates for the rate of parasite-induced host mortalities and the parasite’s rate of attachment to a host were found. In chapter five we returned to stocking methods, this time looking at the frequency and timing of stocking events and the impact of imposing a rod limit (whereby anglers are only permitted to capture four fish per visit); it was concluded that while current guidelines suggest that very frequent trickle stocking is recommended when dealing with Argulus spp. infections, monthly stocking does not appear to worsen the infection, and if the fish capture rate is high then less-frequent stocking may also be permissable - particularly if stocking occurs towards the end of the year when the parasite is no longer active. This practice may, however, be detrimental to the fishery due to low fish densities in the summer months. In chapter six treatment with Slice was included in the model, and it was demonstrated that with constant treatment, and in the absence of reservoir hosts and a withdrawal period from the drug prior to stocking treated fish into the fishery, the parasite was eradicated. Under current veterinary cascade guidelines, however, trout are required to undergo a withdrawal period of 500 degree days prior to being made available for human consumption. When this was included in the model the drug still decreased parasite abundance, but did not eradicate it - this is in agreement with results reported by communications with fishery managers currently treating fish with Slice. A reduction in the withdrawal period of 25% was shown to further decrease parasite abundance, but still did not result in parasite extinction. As constant treatment with Slice is not advisable due to the potential for resistance build-up, we then sought to find time at which to apply a single treatment of Slice, and found that this was in August when the temperature was highest and the parasite was reproducing and attaching to hosts quickly. Egg-laying boards were also incorporated into the model and similarly to findings by Fenton et al. [11] the success of this treatment was mostly dependent on the proportion of eggs being laid on the boards (as opposed to natural substrates). In contrast with the A. coregoni system, however, the boards would have to be cleaned and replaced more frequently that once per year, as several cohorts of A. foliaceus emerge during a single year.

Die Einschleppung gebietsfremder Parasiten durch den Menschen ist einer der Hauptgründe für das Auftreten neuer Krankheiten in the letzten Jahrzehnten. Neue Wirte sind oftmals anfälliger für diese invasiven Parasiten als die ursprünglichen Wirte. In schwerwiegenden Fällen können invasive Parasiten zu Massensterben und zum Aussterben ihrer neuen Wirte führen. Der ursprüngliche Wirt des Aalparasiten Anguillicola crassus ist der Japanische Aal. In den frühen 1980er Jahren wurde der Parasit in die Population des Europäischen Aals eingeschleppt. Er ist einer der Faktoren, die für den Populationsrückgang des Europäischen Aals verantwortlich sind. Die molekularen Prozesse, die zur stärkeren Anfälligkeit des Europäischen Aals im Vergleich zum Japanischen Aal führen, sind noch nicht zureichend bekannt. Die Analyse transkriptomweiter differenzieller Genexpression von Immungewebe ergab, dass im Europäischen Aal sowohl Immun- als auch Nichtimmungene differenziell exprimiert waren. Dies war im Japanischen Aal nicht der Fall und deutet darauf hin, dass der Europäische Aal eine ineffiziente und kostspielige Immunantwort auslöst. Die Resultate ensprechen jenen die schon in anderen Wirbeltierwirt-invasiven Parasiten-Systemen beobachtet wurden. Ausserdem stützen diese Resultate die Hypothese, dass neuen Wirten eine wirksame Immunantwort fehlt und sie deuten darauf hin, dass Nichtimmunprozesse wesentlich zur höheren Anfälligkeit von neuen Wirten beitragen. Als Reaktion of die negativen Fitnesseffekte können neue Wirte Abwehrmechanismen entwickeln. Im Europäischen Aal entspricht das der Einkapselung von A. crassus. Einkapselung führte zu eine niedrigere Abundanz adulter A. crassus. Dies deutet darauf hin, dass das Einkapseln sich positiv auf die Gesundheit infizierter Aale auswirkt. Jedoch war die Abundanz zweier nativer Parasiten höher in Aalen, die A. crassus einkapselten. Eine verbesserte Abwehr des eingeschleppten Parasiten könnte daher die Abwehr nativer Parasiten beeinträchtigen.
The human-mediated translocation of non-native parasites into foreign regions is one of the primary factors for the emergence of new diseases in recent decades. Novel hosts are often more susceptible to these invasive parasites than the native host. In severe cases, invasive parasites can lead to population declines and extinctions of their novel hosts. The eel parasite Anguillicola crassus is native to the Japanese eel. In the early 1980s it was introduced into the European eel population and is now considered to be one factor contributing to the population decline of its novel host. The underlying molecular processes determining higher susceptibility in the European eel compared to the Japanese eel are not well understood. Using whole-transcriptome differential gene expression analysis of immune organs, I found that genes involved in both immune and non-immune processes were differentially expressed in the European eel but not the Japanese eel, suggestive of an ineffective and costly immune response in the former. These results are in line with those observed between susceptible and resistant hosts in other vertebrate host-invasive parasite systems. Furthermore, the results support the hypothesis that novel hosts lack an effective immune response. The results also suggest that alteration of non-immune processes contributes substantially higher susceptibilities of novel hosts. In response to the negative fitness effects of invasive parasites, novel hosts can evolve coping mechanisms. The European eel has the capacity to encapsulate and kill A. crassus. Using natural infections, I found a lower abundance of adult A. crassus, the most costly parasitic stage in those eels encapsulating the parasite, suggesting that encapsulation can potentially improve health of infected eels. At the same time, the abundance of two native parasites was higher in those eels encapsulating A. crassus. Thus, coping with A. crassus may come at the expense of coping with native parasites.

Tese de mestrado. Biologia (Biologia da Conservação). Universidade de Lisboa, Faculdade de Ciências, 2014
As invasões biológicas por espécies não-nativas constituem uma das principais ameaças aos ecossistemas naturais e à biodiversidade. Milhares de espécies foram extintas ou estão em risco devido a espécies introduzidas, em resultado de interações directas, competição ou transmissão de parasitas e agentes patogénicos. A maior parte das espécies consegue escapar dos seus parasitas quando são introduzidas em novos habitats, contudo alguns parasitas persistem nos seus hospedeiros e podem afectar seriamente as comunidades nativas. Várias têm sido as introduções de anfíbios por todo o mundo. A sua inconspicuidade e o facto de muitas vezes não afectarem directamente o Homem fazem com que pouca atenção lhes seja dada. Um anuro com grande difusão mundial é Xenopus laevis, sendo muitas vezes apontado como vector da quitridiomicose (doença resultante da infecção por Batrachochytrium dendrobatidis), e hospedeiro de parasitas originários do continente africano. A sua parasitofauna nativa caracteriza-se pela extraordinária riqueza, incluindo mais de 25 géneros de 7 grandes grupos de invertebrados. Já foi documentada a presença de alguns dos seus parasitas nativos em populações introduzidas, assim como de parasitas adquiridos nos novos habitats. Com a descoberta de X. laevis em duas ribeiras em Oeiras (Portugal), tornou-se importante a realização de um estudo que caracterizasse a sua parasitofauna e possíveis impactos nas espécies nativas, neste caso a rã-verde Pelophylax perezi. A amostragem decorreu durante o Verão. Foram procurados e capturados X. laevis e Pelophylax perezi com pesca eléctrica, tendo depois alguns sido aleatoriamente selecionados para dissecação (80 X. laevis e 18 P. perezi). Antes da dissecação, cada animal foi anestesiado numa solução de MS222 (0,1%) durante 15–30 minutos, seguindo a sua pesagem e medição (comprimento focinho-uróstilo - SUL). O sexo foi determinado pela observação directa das gónadas. Posteriormente, vários órgãos e tecidos foram removidos e examinados. Os macroparasitas encontrados foram medidos e identificados com recurso a bibliografia e à opinião de um especialista. Foram encontradas três espécies de helmintes (Protopolystoma xenopodis, Opisthodiscus cf. nigrivasis e uma espécie não identificada) em Xenopus laevis, e cinco em Pelophylax perezi (Opisthodiscus cf. nigrivasis, Sonsinotrema tacapense, Rhabdias bufonis e 2 espécies não identificadas). Protopolystoma xenopodis, a única espécie de parasita característica de X. laevis presente na população invasora, foi encontrada com uma prevalência de 55% e uma intensidade média de 2,59 parasitas adultos por hospedeiro. Valores tão elevados poderão ter resultado de um confinamento de uma grande quantidade de X. laevis em corpos de água com caudal reduzido, facilitando altos níveis de invasão por P. xenopodis durante as épocas mais quentes e secas do ano. Houve uma relação negativa entre as dimensões de P. xenopodis e o decorrer dos meses de amostragem (r=-0,44, P<0,05), surgindo indivíduos mais pequenos em Agosto do que em Julho, o que indicia o aparecimento de parasitas jovens, recém-migrados dos rins de X. laevis à medida que o Verão avança. O sexo do hospedeiro não parece ser um factor determinante na ‘primeira abordagem’ deste parasita, tendo machos e fêmeas apresentado semelhantes taxas de infecção (χ2=2,423, df=3, P=0,489), bem como semelhantes cargas parasitárias quando infectados (t42=-0,609, P>0,05). Da mesma forma, o SUL de X. laevis parece não ter nenhuma relação com o número destes parasitas (machos: r=0,07, P>0,05; fêmeas: r=0,04, P>0,05). Contudo, existiram diferenças nas dimensões de P. xenopodis entre machos e fêmeas (t92=2,271, P<0,05), tendo-se verificado as maiores diferenças em Agosto (t57=2,227, P<0,05). Verificou-se uma redução nas dimensões de P. xenopodis à medida que o SUL dos machos de X. laevis aumentava (r=-0,284, P<0,05). Por outro lado, a dimensão destes helmintes aumentou proporcionalmente ao SUL das fêmeas de X. laevis (r=0,336, P<0,05), indicando uma maior probabilidade de novas infecções em fêmeas X. laevis mais novas e relações parasita-hospedeiro mais estáveis e duradouras em X. laevis mais velhas. Foi também encontrado uma espécie de paranfistomatídeo, Opisthodiscus cf. nigrivasis em X. laevis, com uma prevalência de 33% e uma intensidade média de 2,23 parasitas por hospedeiro. Não existiu variação no número (t24=0,582, P>0,05) nem nas dimensões (t49=1,177, P>0,05) de O. cf. nigrivasis ao longo dos meses, apontando para uma não sincronização entre os ciclos de vida de parasita e anfíbio. Assim como em P. xenopodis, machos e fêmeas não apresentaram diferenças ao nível da taxa de infecção por O. cf. nigrivasis (χ2=4,413, df=2, P=0,111) nem do número de parasitas por indivíduo infectado (t24=-0,059: P>0,05). O sexo do hospedeiro também não pareceu influenciar as dimensões destes parasitas (t50=-0,415, P>0,05). O tamanho das rãs não desempenhou um factor determinante no número de O. cf. nigrivasis que parasitam X. laevis (machos: r=-0,004, P>0,05; fêmeas: r=0,05, P>0,05); contudo foi observada uma correlação positiva entre o SUL das fêmeas de X. laevis e o comprimento de O. cf. nigrivasis (r=0,417, P<0,05). Nos machos não existiu qualquer relação (r=-0,051, P>0,05), sugerindo que estes parasitas encontrem condições de vida mais favoráveis e/ou uma mais fácil adaptação em fêmeas mais velhas, e por isso maiores. Considerando todos os helmintes, 69% dos Xenopus laevis amostrados estavam infectados com pelo menos 1 indivíduo, com uma intensidade média de 3,25 parasitas por hospedeiro, num total de 179 parasitas. Não existiu diferenças entre o número de parasitas encontrados ao longo dos meses de amostragem (t50=-0,855: P>0,05); contudo em Agosto houve níveis de infecção ligeiramente superiores, possivelmente devido ao aumento de parasitas recém-migrados de, pelo menos, uma das espécies. Também as taxas de infecção (χ2=2,258, df=3, P=0,521) e o número de parasitas não variaram com o sexo (t53=-0,130: P>0,05) e o SUL dos hospedeiros (machos: r=0,17, P>0,05; fêmeas: r=0,06, P>0,05). Em Pelophylax perezi, todos os 18 indivíduos estavam infectados (prevalência de 100%), com uma média de 25 parasitas por hospedeiro, num total de 452 parasitas. O sexo do hospedeiro pareceu não exercer qualquer influência na biologia dos parasitas, sendo que as taxas de infecção foram semelhantes (χ2=1,862, df=3, P=0,602), bem como o número total de parasitas entre machos e fêmeas (t15=0,568: P>0,05). A espécie nativa, Pelophylax perezi, é naturalmente mais parasitada (maior número de parasitas de um maior número de espécies) que Xenopus laevis, seja pelo longo período de coexistência nestas ribeiras, seja pela ausência em Portugal de várias espécies de parasitas típicas de X. laevis. A única espécie de parasita exótica que se conseguiu estabelecer em Portugal, juntamente com X. laevis, foi P. xenopodis, e a sua estrita especificidade parasita-hospedeiro minimiza a possibilidade de infecção da rã nativa. Assim, não se verificou indícios de transmissão de espécies de parasitas originárias de África para a única espécie de anfíbio cujo habitat se sobrepõe com a área de distribuição de X. laevis em Portugal. Contudo, ocorreu um padrão inverso de infecção, tendo existido a transmissão de parasitas de P. perezi para X. laevis. As outras 2 espécies encontradas em X. laevis terão sido adquiridas posteriormente à introdução no novo habitat. Comuns em P. perezi, Opisthodiscus cf. nigrivasis ocorreram em 50% das rãs-verdes amostradas, e na sua maioria bem desenvolvidos. O mesmo não aconteceu em X. laevis, em que estes helmintes estiveram presentes mas em número reduzido e em estádios menos desenvolvidos. No rectum de alguns indivíduos foram encontradas o que aparentou ser metacercárias enquistadas, sugerindo que X. laevis pode estar a ser parasitado através da ingestão de estádios larvares deste parasitas ou de um hospedeiro intermédio portador destes. Mesmo sem os níveis de sucesso com que parasita P. perezi, O. cf. nigrivasis parece estar a usar X. laevis como vector ou hospedeiro. Dado que esta espécie invasora é bastante abundante em certas zonas das ribeiras, suplantando largamente os números de P. perezi, a população de O. cf. nigrivasis pode actualmente depender mais de X. laevis que de P. perezi. Xenopus laevis é um forte competidor e um predador voraz. Para além dos impactos já conhecidos, temia-se que pudesse ser portadora de parasitas originários de África, capazes de pôr em causa a actividade e/ou a sobrevivência das espécies nativas, perturbando ainda mais o equilíbrio do ecossistema. Contudo, isto não foi verificado, tendo sido esta espécie invasora a ser infectada por parasitas autóctones. Ainda assim, a carga parasitária que apresenta não é tão elevada nem variada como a de espécies com que co-habita, ou tão alta como nos habitats onde é nativa, o que pode tornar esta espécie mais apta a dominar os ambientes onde foi recentemente introduzida.
Biological invasions by non-native species constitute one of the leading threats to natural ecosystems and biodiversity. Most of the animals can escape from its parasites when they are introduced into new habitats, however some persist in their hosts and may seriously affect the native communities. Xenopus laevis, an anuran with large world diffusion, is often a carrier of parasites originating from the African continent. With the recent discovery of X. laevis in two streams in Oeiras (Portugal), it became important to characterize its parasite fauna and its possible impacts on native species. In this study, we searched for macroparasites in 80 X. laevis and 18 native P. perezi living in the same stream sections. We found 3 species of helminths in X. laevis: Protopolystoma xenopodis, Opisthodiscus cf. nigrivasis and one unidentified species. Protopolystoma xenopodis had a prevalence of 55%, with an average of 2,59 parasites per infected host. Opisthodiscus cf. nigrivasis had a prevalence of 33% and a mean intensity of 2,23 parasites per host. P. perezi was found to be parasitized by 5 helminths: Opisthodiscus cf. nigrivasis, Sonsinotrema tacapense, Rhabdias bufonis and two unidentified species. O. cf. nigrivasis was the only species shared between the two hosts, and had a higher prevalence (50%) and a higher mean intensity (4,67 parasites per host) in P. perezi. Considering all the helminths, 69% of the sampled X. laevis were infected with at least one species, with a mean intensity of 3,25 parasites per host. On the other hand, all the 18 individuals of P. perezi were infected with an average of 25 parasites per host. In Portugal, X. laevis was the species that was found to be infected by autochthonous parasites, probably proceeding from P. perezi. Still, the parasite burden was not as high as in the species they co-exist with, or as high as in the habitats where it is native, which could enable this species to dominate the streams where it was recently introduced.