Academic literature on the topic 'Parasitism/host resistance'

Host-parasite interactions are often seen as an arms race, with parasites attempting to overcome host resistance to infection. Herbivory is a common route of transmission of parasites that represents the most pervasive challenge to mammalian growth and reproduction. The present paper reviews the foraging skills of mammalian herbivores in relation to their ability to exploit plant properties to combat parasites. The starting point is that foraging behaviour may ameliorate the impact of parasitism in three ways; hosts could: (1) avoid foraging in areas contaminated with parasites; (2) select diets which increase their resistance to parasites; (3) select for foods containing anti-parasitic properties (self-medication). Details are given of the pre-requisite skills needed by herbivores if they are to combat parasitism via behaviour, i.e. herbivores are able to: (a) determine their parasitic state and alter their behaviour in relation to that state (behaviours 1, 2 and 3); (b) determine the environmental distribution of parasites (behaviour 1); (c) distinguish plant species or plant parts that increase their resistance to parasites (behaviour 2) or have anti-parasitic properties (behaviour 3). Mammalian herbivores cannot detect the presence of the parasites themselves and must rely on cues such as faeces. Despite the use of these cues contacting parasites may be inevitable and so mechanisms to combat parasitism are necessary. Mammalian herbivores have the foraging skills needed to exploit the heterogeneous distributions of nutrients and parasites in complex foraging environments in order to avoid, and increase their resistance to, parasites. Current evidence for the use of plant secondary metabolites (PSM) by herbivores for self-medication purposes remains equivocal. PSM have both positive (anti-parasitic) and negative (toxic) effects on herbivores. Here details are given of an experimental approach using tri-trophic (plant-herbivore-parasite) interactions that could be used to demonstrate self-medication in animals. There is strong evidence suggesting that herbivore hosts have developed the foraging skills needed to take advantage of plant properties to combat parasites and thus use behaviour as a weapon in the host-parasite arms race.

Tolerance and resistance to parasites are defense strategies of host organisms. Here, we tested the development-dependent tolerance and resistance of Polypedates cruciger Blyth, 1852 tadpoles to trematode infection. We exposed the tadpoles at Gosner stages 27, 28–29, and 30–31 to two types of cercariae (furcocercous and pleurolophocercous cercariae of Acanthostomum burminis (Bhalerao, 1926)) under laboratory conditions. To determine tolerance (the ability of a host to limit health effects of a given parasite load), we exposed the tadpoles until all cercariae penetrated the host. As a measure of determining resistance, we exposed tadpoles to cercariae for a limited time and counted the number of cercariae penetrating the tadpoles. The survival of tadpoles exposed at early stages was significantly lower than that of tadpoles exposed at later stages (mixed-effect model, p < 0.05), suggesting an age-dependent tolerance to parasitism. Tadpoles exposed at early stages were also smaller, took longer to metamorphosis, showed lower resistance to parasitism (ANOVA, p < 0.001), and developed axial malformations. In the resistance experiment, fewer parasites penetrated later stage tadpoles than early stage tadpoles. Tadpoles of P. cruciger showed a development-dependent tolerance and resistance to parasitism, resulting in greater survival and fewer malformations when parasitism occurs at late stages.

Parasitic relationships between Neotropical bats and their ectoparasites are not well known, even though parasitism is one of the factors that can affect the fitness of a host population. This study characterized parasite-host relationships in relation to sex, age, body size and reproductive status in a population of Anoura geoffroyi using the indices of Prevalence, Mean Intensity and Mean Abundance. Total prevalence for 93 sampled bats was 94.6%. Two species of streblid flies that are considered primary parasites of A. geoffroyi, Exastinion clovisi (n = 203) and Anastrebla modestini (n = 152), were the most abundant ectoparasites, followed by Trichobius sp. (n = 7). Two mite species, Periglischrus vargasi (Spinturnicidae) (n = 98) and Spelaeorhynchus praecursor (Spelaeorhynchidae) (n = 11), were also found. We recorded higher mean abundance and intensity of parasitism in pregnant females compared to reproductive males and reproductively inactive females, for different specific associations of ectoparasites. Host age and body condition had no effect on the parasitological indices. Even with high rates of parasitism, parasitic load did not influence host body condition, but infestation rates by mites were higher in reproductive males and higher by flies in reproductive females, showing that ectoparasites can have variable influences between the different stages of the life history of these host bats. Thus, the reproductive activity of the hosts could be an adverse factor for resistance to parasite infestations.

Brood parasites exploit their host in order to increase their own fitness. Typically, this results in an arms race between parasite trickery and host defence. Thus, it is puzzling to observe hosts that accept parasitism without any resistance. The ‘mafia’ hypothesis suggests that these hosts accept parasitism to avoid retaliation. Retaliation has been shown to evolve when the hosts condition their response to mafia parasites, who use depredation as a targeted response to rejection. However, it is unclear if acceptance would also emerge when ‘farming’ parasites are present in the population. Farming parasites use depredation to synchronize the timing with the host, destroying mature clutches to force the host to re-nest. Herein, we develop an evolutionary model to analyse the interaction between depredatory parasites and their hosts. We show that coevolutionary cycles between farmers and mafia can still induce host acceptance of brood parasites. However, this equilibrium is unstable and in the long-run the dynamics of this host–parasite interaction exhibits strong oscillations: when farmers are the majority, accepters conditional to mafia (the host will reject first and only accept after retaliation by the parasite) have a higher fitness than unconditional accepters (the host always accepts parasitism). This leads to an increase in mafia parasites’ fitness and in turn induce an optimal environment for accepter hosts.

SUMMARYThis paper describes sensitivity analyses and expectations obtained from a mathematical model developed to account for the effects of host nutrition on the consequences of gastrointestinal parasitism in sheep. The scenarios explored included different levels of parasitic challenge at different planes of nutrition, for hosts differing only in their characteristics for growth. The model was able to predict the consequences of host nutrition on the outcome of parasitism, in terms of worm burden, number of eggs excreted per gram faeces and animal performance. The model outputs predict that conclusions on the ability of hosts of different characteristics for growth to cope with parasitism (i.e. resistance) depend on the plane of nutrition. Furthermore, differences in the growth rate of sheep, on their own, are not sufficient to account for differences in the observed resistance of animals. The model forms the basis for evaluating the consequences of differing management strategies and environments, such as breeding for certain traits associated with resistance and nutritional strategies, on the consequences of gastrointestinal parasitism on sheep.

Gastrointestinal parasitism in lambs is usually manifested as a sub-clinical infection and causes significant losses in performance. Its control through the use of chemoprophylaxis is no longer sustainable due to the development of parasitic resistance to anthelminthics, but also due to environmental and consumer concerns. There is thus an urgent need to develop alternative, sustainable methods of controlling gastrointestinal parasitism. These include dietary supplementation of host with protein. The aim here is to develop a mathematical simulation model for the description of the joint effects of nutrition and host performance genotype on the outcome of sub-clinical challenge by gastrointestinal parasitism for growing lambs.

A genetic analysis of parasitic ability in the soybean cyst nematode Heterodera glycines was performed. To identify and characterize genes involved in parasitism, we developed three highly inbred H. glycines lines, OP20, OP25 and OP50, for use as parents for controlled crosses. Through these crosses, we have identified genes in the inbred parents that control reproduction of the nematode on hosts that carry resistance genes. These genes, designated as ror-* for reproduction on a resistant host, segregate in a normal Mendelian fashion as independent loci. Host range tests of F1 generation progeny indicated that at least one parasitism gene in both the OP20 and OP50 lines for host PI 88788 was dominant. Parasitism genes in OP50 for hosts “Peking” and PI 90763 are recessive. Two types of single female descent populations, a single backcrossed BC1F2-derived and a double backcrossed BC2F1-derived, were established on the susceptible soybean cultivar “Lee 68.” Host range tests for parasitism in these lines demonstrated the presence of two independent genes in OP50, one for host PI 88788 designated ror-1 and one for host PI 90763 designated ror-2. OP20 carries two independent genes for parasitism on PI 88788, designated as alleles kr3 and kr4.

Parasitic weeds represent a major threat to agricultural production across the world. Little is known about which host genetic pathways determine compatibility for any host–parasitic plant interaction. We developed a quantitative assay to characterize the growth of the parasitic weed Phelipanche aegyptiaca on 46 mutant lines of the host plant Arabidopsis thaliana to identify host genes that are essential for susceptibility to the parasite. A. thaliana host plants with mutations in genes involved in jasmonic acid biosynthesis/signaling or the negative regulation of plant immunity were less susceptible to P. aegyptiaca parasitization. In contrast, A. thaliana plants with a mutant allele of the putative immunity hub gene Pfd6 were more susceptible to parasitization. Additionally, quantitative PCR revealed that P. aegyptiaca parasitization leads to transcriptional reprograming of several hormone signaling pathways. While most tested A. thaliana lines were fully susceptible to P. aegyptiaca parasitization, this work revealed several host genes essential for full susceptibility or resistance to parasitism. Altering these pathways may be a viable approach for limiting host plant susceptibility to parasitism.

Host-parasite interactions are believed to exert strong selection in natural communities. Most notably, parasites should select for increased resistance in hosts, while hosts should select for increased infectivity in parasites (Koskella & Lively, 2007; Koskella, Vergara, & Lively, 2011; Lohse, Guiterrez, & Kaltz, 2006). Under this coevolutionary process, can host populations evolve resistance to their rapidly evolving parasite populations? This experiment was designed to determine if hosts rapidly adapt to resist parasites that are themselves under selection to infect their hosts. The New Zealand freshwater snail, Potamopyrgus antipodarum, is naturally infected by the trematode Microphallus. Microphallus is a castrating parasite and is thus likely to impose strong selection on its snail host (Hechinger, 2012). Snails and parasites were collected from a natural lake in summer 2013. These hosts constitute the parental generation of the experiment: they were either exposed to parasite eggs (Exposed) or not exposed (Control). Parental snails matured and reproduced over the course of a year. Their offspring were then exposed to parasites collected from the same lake in summer 2014. These parasites would have had one to a few additional generations of evolution relative to 2013 parasites. After parasite development (~3 months), the offspring were dissected to determine infection status and thereby their resistance to infection. The offspring of Control parents had a significantly higher mean infection rate (35%: less resistant) than the offspring of Exposed parents (30%: more resistant). This result indicates that increased resistance to parasitism evolved in a single host generation. Our finding provides evidence that a host population can rapidly evolve resistance to a parasite population that is itself rapidly co-evolving to infect its host. We predict that the evolution of host resistance would be far greater after multiple generations of parasite selection, and this could be the subject of future study.

The consumption of plants rich in plant secondary metabolites has been associated with improved resilience of parasitised hosts, i.e. their ability to perform under parasitic infection, compared to animals fed conventional feeds (Athanasiadou et al., 2007). Furthermore, such bio-active plants can improve host resistance, which refers to the host ability to regulate gastrointestinal nematode establishment, development, fecundity and survival (Athanasiadou et. al. 2008). Chichorium intybus L. (chicory) is such a bio-active forage and its potential anthelmintic activity is currently investigated as an alternative means to control parasitism in sheep production systems. In the present study we employed an in vitro assay to study a possible mechanism of anti-parasitic action arising from chicory, and to test whether this anthelmintic activity is affected by the vegetative stage of the plant.

Gastrointestinal parasitism in grazing lambs adversely affects animal performance and welfare, causing significant production losses for the sheep industry. Control of gastrointestinal parasitism using chemotherapeutic treatment is under threat due to the emergence of anthelmintic resistance, thus stimulating research into alternative control strategies. Whilst investigating control strategies experimentally can be costly and time consuming, using a mathematical modelling approach can reduce such constraints. A previously developed model which describes the impact of host nutrition, genotype and gastrointestinal parasitism in a growing lamb, provided an appropriate starting point to explore control strategies and their impact on host-parasite interactions. Two contrasting mechanisms have previously been proposed to account for the occurrence of anorexia during parasitism. These were reductions in either intrinsic growth rate or relative food intake. Thus, the existing individual lamb model was modified to evaluate these mechanisms by exploring the relationship between anorexia and food composition (Chapter 2). For foods that did not constrain food intake, published data was found to be consistent with the predictions that arose from anorexia being modelled as a reduction in relative food intake. Reported genetic parameter estimates for resistance and performance traits appear to vary under differing production environments. In order to explore the impact of epidemiological effects and anthelmintic input on genetic parameter estimates the model was extended to simulate a population of lambs in a grazing scenario (Chapter 3). Whilst estimates of heritabilities and genetic correlations for drenched lambs remained constant, for lambs given no anthelmintic treatment, the heritability of empty body weight (EBW) reduced and the genetic correlation between faecal egg count (FEC) and EBW became increasingly negative with increasing exposure to infective larvae. Thus differences in anthelmintic input and pasture larval contamination (PC) may provide plausible causes for the variation in genetic parameter estimates previously reported. To investigate the interactions between host resistance and epidemiology (Chapter 4) a population of 10,000 lambs were simulated and FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to ‘susceptible’ (S) and ‘resistant’ (R) groups, respectively. R and S groups were then simulated to graze separate pastures over 3 grazing seasons. The average FEC and PC predictions of these groups diverged during the first 2 grazing seasons and stabilised during the third, such that the difference in FEC predictions between R and S groups were double those predicted when grazed with the population. This was found to be consistent with experimental data. Further, anthelmintic treatment and grazing strategies were predicted to have no impact on the EBW of resistant lambs, suggesting that control strategies should be targeted towards susceptible animals. Targeted selective anthelmintic treatment (TST) has been proposed to reduce risks of anthelmintic resistance with minimal impacts on performance. To describe the short- and long-term impacts of TST and drenching frequency on sheep production and the emergence of anthelmintic resistance, the model was extended to include a description of anthelmintic resistance genotypes within the nematode population (Chapter 5). Reducing the proportion of treated animals was predicted to increase the duration of anthelmintic efficacy, whilst reducing the drenching frequency increased the long-term benefits of anthelmintic on sheep production. Various determinant criteria for use in TST regimes were compared (Chapter 5) including performance traits such as live weight and growth rate, and parasitological traits such as FEC. Using FEC as the TST criterion was predicted to allow the greatest reduction in the number of anthelmintic treatments administered whilst maintaining the highest average EBW, whilst live weight and growth rate were predicted to give little to no improvement in comparison to selecting animals at random for TST. Using estimated breeding values (EBVs) for FEC as the determinant criterion for TST regimes was compared to using measured FEC (Chapter 6). The EBV for true FEC across the entire growth period, akin to perfect genomic selection, was predicted to be a better criterion than measured time-specific FEC (including a sampling error) for a TST regime. EBVs calculated using measured time-specific FEC showed little benefit compared to measured FEC. The information gained from these simulation studies increases our understanding of control strategies and their impact on host-parasite interactions under various scenarios that may not have been possible using experimental methods. It is important to remember that the aim of alternative or complimentary control strategies is to maintain the sustainability of sheep production systems, and as such the production gain of any control strategy needs to be weighed against the financial, labour and time costs involved in implementation.

Roughly one-third of cattle in sub-Saharan Africa are at risk of contracting "Nagana" - a disease caused by Trypanosoma parasites similar to those that cause human "Sleeping Sickness". Laboratory mice can also be infected by trypanosomes, and different mouse breeds show varying levels of susceptibility to infection, similar to what is seen between breeds of cattle. We have applied next-generation technologies to identify shared polymorphisms between susceptible mice, and annotated these for potential function alongside publicly available SNP data sets. By so doing, short lists of genes at the QTL have been created to aid functional testing in cattle. This includes two promising 'candidate genes': Pram1 and Cd244, which can now be tested to confirm their effect on response to trypanosome infection. The human-infective parasite Trypanosoma brucei rhodesiense generally causes an acute form of "sleeping sickness" across Eastern Africa, compared to the more chronic T b. gambiense infections found in Western Africa. The 1988-1993 Ugandan T b. rhodesiense outbreak constituted infections by parasites with differences in their clinical manifestation. Two such sub types, termed Busoga 17 (B 17) and Zambesi 310 (Z31O), caused more acute, and more chronic infections, respectively. In order to investigate whether the major QTL that regulates survival in T congolense infections (Tir 1) does so in a similar manner in T b. rhodesiense, mice congenic for the C5 7BL/ 6 allele (Tirl CC) at Tir 1 were infected with Z310 and B 1 7 zymodeme T b. rhodesiense parasites. Whilst Tir 1 was not found to have a significant effect on survival, all mice had a significantly shorter mean survival time when infected with B 17 (~1O. 7 days) than those infected with Z31 0 (~15.6 days), in line with previous observations of human infections. In order to identify genetic loci that might underlie differences in virulence between T b. rhodesiense zymodemes, cluster analysis was performed on the microsatellite genotypes of 31 T b. rhodesiense isolates that represented nine different zymodemes. Despite STRUCTURE identifying three population clusters, the Z310 and B 17 parasite populations could not be distinguished, suggesting that either multiple genes control virulence, that there is gene flow between similar parasite populations, or that the microsatellite genotyping is insufficient to distinguish between different parasite populations. Finally, we present the first whole-genome sequences of T b. rhodesiense field isolates, one each of Z310 and B 1 7. Genomic analysis of east African T b. rhodesiense and west African T b. gambiense has suggested that recombination may be occurring between them. SNP genotyping of 32 T b. rhodesiense isolates showed that differences in clinical phenotypes were associated with differences in alleles on chromosome 8. The genome sequence suggests that chromosome 8 is heterozygous for alleles of west African origin in the more virulent strain, suggesting that recombination may be associated with parasite virulence. This suggests that the human subspecies of T brucei are not genetically distinct, which has major implications for the control of the parasite, the spread of drug resistance and understanding the variation in virulence and the emergence of human infectivity. Further genetic analysis of T b. brucei populations from Western, central and Eastern Africa may be necessary to ascertain whether recombination is occurring directly between human-infective subspecies, or in the underlying animal-infective population.

This study describes the effect of the root hemi-parasitic angiosperm Rhinanthus minor on the structure of the communities in which it lives and seeks to elucidate a mechanism through which the parasite acts to effect these changes in the community. Field manipulations reveal that R. minor suppressed the growth of grasses and legumes in a newly sown meadow whilst promoting the forbs within one growing season. In contrast the removal of R. minor from mature meadow plots did not influence their composition. After an additional growing season the parasite did not further influence the composition of the new meadows but removal did begin to benefit the biomass of mature plots. In isolation the parasite caused most damage to grasses whilst leaving legumes and forbs undamaged. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to the forbs. Consequently the parasite was able to moderate intra-specific competition between grasses and forbs. I thus hypothesised that forbs were able to prevent the parasite form abstracting resources where as grasses could not. Tracer experiments using isotopically e5N) labelled potassium nitrate confirmed this hypothesis showing that more of the resources taken up by the host were stolen by the parasite from grasses than from forbs. There was much variability in the translocation of resources from the legume studied. The reasons underlying the differential uptake of resources were highlighted using histological studies which showed that all of the forbs possessed successful resistance mechanisms to the parasite whilst no successful resistance was observed in the grasses or legumes. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death at the host-parasite interface and host lignification. I therefore propose that differential host resistance may underlie this parasite's community level effects as forbs possess a resistance capacity that other potential hosts do not.

Os nematoides que atualmente tem sido classificados como P. coffeae, demonstram ampla variabilidade morfológica, molecular e quanto à reação à diferentes hospedeiros. Por conseguinte, é essencial que se identifique corretamente as espécies e que se conheça a capacidade de parasitismo em alguns hospedeiros, para que se possa estabelecer medidas de controle e estimar eventuais riscos da entrada de um patógeno em uma área com hospedeiro suscetível. Neste sentido, a presente pesquisa propõe, numa primeira parte, uma medida de controle de P. jaehni (K5), que é muito agressivo à cafeeiro arábico, baseada no uso de plantas má hospedeiras. Na segunda parte deste trabalho é realizada uma caracterização da reação de diferentes espécies vegetais à quatro populações de Pratylenchus spp. Em virtude do exposto, este estudo objetivou avaliar a reação de diferentes cultivares de feijoeiro comum frente à P. jaehni (K5), visando seu possível uso no manejo de áreas cafeeiras infestadas e caracterizar a reação de diferentes espécies vegetais de importância econômica (café, porta-enxertos cítricos, banana e sorgo) frente à quatro populações de Pratylenchus spp. As populações inciais utilizadas nos experimentos variaram entre 180 e 200 nematóides. Em todos os experimentos, os nematóides foram extraídos das raízes pelo método de Coolen e D´Herde (1972) e, eventualmente, do substrato pelo método de Jenkins (1964). Foram realizados três ensaios: i) o primeiro com feijoeiro comum, onde todas as cultivares utilizadas foram resistentes à P. jaehni (K5), inclusive na réplica; ii) o segundo com porta-enxertos cítricos, no qual somente o limão-cravo foi hospedeiro de P. jaehni (K5); iii) o terceiro, no qual foi utilizado café, limão-cravo, banana e sorgo para o conhecimento das respectivas reações frente à 4 populações de Pratylenchus spp. Neste último experimento ocorreu uma reação hospedeira diferenciada para cada população. De acordo com os resultados, concluise que as cultivares de feijoeiro comum utilizadas apresentam potencial de uso em áreas cafeeiras infestadas por P. jaehni (K5), em consórcio ou em áreas de renovação de cafezal, e que as populações de Pratylenchus spp. são capazes de se reproduzir de forma diferenciada frente às espécies vegetais testadas.
Nematode populations that have been classified as P. coffeae show wide morphological, molecular and host range variability. Therefore, is essential the correct identification of the species and the knowledge about its parasitism capacity on some hosts, to ensure appropriate control measures and to estimate the entry risks of a pathogen in an area with susceptible host. In this sense, the present research report, firstly, propose a control measure of P. jaehni (K5), which is very aggressive to the arabic coffee, based on the use of poor host plants. In the second part, was carried out a host status evaluation of different plant species to four populations of Pratylenchus spp. In this context, were evaluated the reaction of different common bean cultivars to P. jaehni (K5), for its possible use in management of coffee areas infested with this nematode, and characterized the response of different economic important plant species (coffee, citrus rootstocks, banana and sorghum) to four populations of Pratylenchus spp (IB01P, IB02P, K5 e C1). The initial population used in experiments ranged between 180 and 200 nematodes. In all experiments, nematodes were extracted from roots by Coolen e D\'Herde´s method (1972) and eventually from the substrate by Jenkins´ method (1964). Three assays were conducted and results was as following: i) in the first one, with common bean, all tested cultivars were resistant to P. jaehni (K5), including the replica; ii) in the second one, with rootstocks, only rangpur lime was a good host of P. jaehni (K5); iii) in the third one, in which was used coffee, rangpur lime, banana and grain sorghum, was observed a differential host reaction for each nematode population evaluated. According to the present results, we suggest that common bean cultivars tested have great potential for use, or in intercropping or in crop rotation, in coffee areas infested by P. jaehni (K5) and populations of Pratylenchus spp. have different reproductive fitness in the plants species tested.

Un milieu de culture in vitro est mis au point pour la multiplication du rosier, valable pour 7 clones. Quatre sont utilisés pour l'étude des relations hôte-parasite dans le cas de sphaerotheca pannosa var. Rosae. Une différence de sensibilité est constatée chez ces clones à la suite de l'infection par l'agent pathogène. Deux sont sensibles sur lesquels le parasite sporule abondamment, un est résistant ou la sporulation du champignon est faible et un est très résistant sur lequel la sporulation est absente. Des points nécrotiques apparaissent sur tous les clones étudiés ils jouent un rôle très important dans la régression de la croissance et la disparition de l'agent pathogène chez les clones résistant et très résistant. Les observations histologiques et ultrastructurales ont montré que la formation d'appressoriums n'est pas obligatoire à la pénétration de s. Pannosa dans les cellules épidermiques. Le champignon, après sa pénétration forme un haustorium enveloppe par une membrane extrahaustoriale qui a pour origine le plasmalemme de l'hôte. Au sein de l'haustorium, on observe de nombreux lobes formes à partir du corps haustorial central par bourgeonnement. Les hôtes résistants sont riches en composes phénoliques qui encapsulent l'haustorium et provoquent sa nécrose. Au contraire, chez l'hôte sensible, et en l'absence de composes phénoliques, l'haustorium envahit une grande partie de la cellule épidermique, en particulier in vitro. Chez tous les hôtes, l'infection des cellules épidermiques provoque un ensemble de modifications au sein des cellules attaquées et des cellules adjacentes et sous-jacentes.

[ES] La producción en acuicultura se ha visto menguada por aparición de enfermedades en los sistemas de cría de peces. En concreto, en la dorada (Sparus aurata), hay dos parásitos destacados: Enteromyxum leei (Myxozoa) y Enterospora nucleophila (Microsporidia). Hasta la fecha, para ninguno de los dos se ha establecido un cultivo in vitro, y solo para E. leei se ha conseguido establecer un modelo de mantenimiento de la infección in vivo. La presente tesis pretende incrementar el conocimiento sobre estos parásitos y sus relaciones con el hospedador, sentando las bases para generar soluciones que puedan ser aplicadas en la acuicultura. El objetivo con E. leei fue estudiar la inmunidad adquirida inducida en la dorada y la posibilidad de generar herramientas de diagnóstico y vacunas frente a esta enfermedad. Para ello, primero se demostró la resistencia del pez al parásito tras una segunda exposición, la cual duró hasta 16 meses. Además, la resistencia parece estar correlacionada con altos niveles de inmunoglobulina (Ig) M específica en sangre, y una alta expresión de Igs, incluso antes de la re-exposición al parásito. El siguiente paso fue afinar el protocolo de infección con E. leei. Los resultados mostraron que una semana es suficiente para transmitir la infección de E. leei por efluente, independientemente de la temperatura. Tras la demostración de la respuesta adaptativa eficaz frente a E. leei, y al disponer de un modelo de infección refinado, se realizó un ensayo de inmunización pasiva. Aquí, los resultados mostraron que los anticuerpos especi'ficos efectivamente consigue ralentizar la invasión del intestino por el parásito y disminuir los síntomas de la enfermedad. Paralelamente, el resultado del análisis del repertorio de las regiones variables de la IgM e IgT del intestino peces resistentes mostró la inducción de una respuesta policlonal en las ce'lulas B. En base a estos resultados, se realizó una búsqueda de antígenos de E. leei que pudieran ser utilizados como candidatos para la producción de vacunas (análisis proteómico) o herramientas de diagnóstico (análisis in silico). Para ello, se ensambló un transcriptoma de novo utilizando una muestra mixta de intestino de dorada y parásito. Los resultados dieron lugar a 7 y 12 candidatos en la búsqueda in silico y proteómica, respectivamente. En los estudios de E. nucleophila, debido a que fue descrita muy recientemente, el punto de partida fue más básico. Las muestras de este parásito solo se pueden obtener de brotes naturales en piscifactorias. Por ello, primero se realizó un estudio de caracterización de la patología de la infección a partir de peces infectados naturalmente. En etapas tempranas de la infección, el parásito se localiza principalmente en el intestino, pero meses después, la prevalencia en intestino baja e incrementa en los órganos hematopoyéticos y el esto'mago. Los signos clínicos de la infección consistieron en una reducción significativa del crecimiento, emaciación, y palidez de las paredes intestinales. A nivel celular, en los casos ma's graves se observó hipercelularidad en el epitelio intestinal y proliferación de ce'lulas rodlet, un elevado número de linfocitos en la base del epitelio e infiltración de granulocitos acidófilos en el epitelio intestinal. Finalmente se probaron varias formas de transmisión horizontal de E. nucleophila (cohabitación, efluente, intubación oral y anal) con para desarrollar un modelo de mantenimiento in vivo. Se consiguió la transmisión el parásito por todas las vías, pero con una disminución de prevalencia a lo largo del tiempo. Variables como la temperatura, la dosis, y el estado de los peces donantes parecen ser más determinantes que la ruta seleccionada para la transmisión. Entre las rutas probadas, la intubación anal parece ser la más prometedora, pero ninguna de ellas fue capaz de reproducir los signos clínicos observados en las infecciones naturales.
[CA] La producció en aqüicultura s'ha vist minvada per aparició de malalties en els sistemes de cria de peixos. En concret, en l'orada (Sparus aurata), hi ha dos paràsits destacats: Enteromyxum leei (Myxozoa) i Enterospora nucleophila (Microsporidia). Fins avui, per a cap dels dos s'ha establert un cultiu in vitro, i només per a E. leei s'ha aconseguit establir un model de manteniment de la infecció in vivo. La present tesi pretén incrementar el coneixement sobre aquests paràsits i les seves relacions amb l'hoste, establint les bases per a generar solucions que puguin ser aplicades en l'aqüicultura. L'objectiu amb E. leei va ser estudiar la immunitat adquirida induïda en l'orada i la possibilitat de generar eines de diagnòstic i vacunes enfront d'aquesta malaltia. Per a això, primer es va demostrar la resistència del peix al paràsit després d'una segona exposició, la qual va durar fins a 16 mesos. A més, la resistència sembla estar correlacionada amb alts nivells d'immunoglobulina (Ig) M específica en sang, i una alta expressió de Igs, fins i tot abans de la re-exposició al paràsit. El següent pas va ser afinar el protocol d'infecció amb E. leei. Els resultats van mostrar que una setmana és suficient per a transmetre la infecció de E. leei per efluent, independentment de la temperatura. Després de la demostració de la resposta adaptativa eficaç enfront de E. leei, i en disposar d'un model d'infecció refinat, es va realitzar un assaig d'immunització passiva. Aquí, els resultats van mostrar que els anticossos específics efectivament aconsegueix alentir la invasió de l'intestí pel paràsit i disminuir els símptomes de la malaltia. Paral·lelament, el resultat de l'anàlisi del repertori de les regions variables de la IgM i IgT de l'intestí peixos resistents va mostrar la inducció d'una resposta policlonal en les cèl·lules B. Sobre la base d'aquests resultats, es va realitzar una cerca d'antígens de E. leei que poguessin ser utilitzats com a candidats per a la producció de vacunes (anàlisis proteómico) o eines de diagnòstic (anàlisi in silico). Per a això, es va assemblar un transcriptoma de novo utilitzant una mostra mixta d'intestí d'orada i paràsit. Els resultats van donar lloc a 7 i 12 candidats en la cerca in silico i proteòmica, respectivament. En els estudis de E. nucleophila, pel fet que va ser descrita molt recentment, el punt de partida va ser més bàsic. Les mostres d'aquest paràsit només es poden obtenir de brots naturals en piscifactorias. Per això, primer es va realitzar un estudi de caracterització de la patologia de la infecció a partir de peixos infectats naturalment. En etapes primerenques de la infecció, el paràsit es localitza principalment en l'intestí, però mesos després, la prevalença en intestí baixa i incrementa en els òrgans hematopoètics i l'estómac. Els signes clínics de la infecció van consistir en una reducció significativa del creixement, emaciació, i pal·lidesa de les parets intestinals. A nivell cel·lular, en els casos més greus es va observar hipercelularidad en l'epiteli intestinal i proliferació de cèl·lules rodlet, un elevat nombre de limfòcits en la base de l'epiteli i infiltració de granulòcits acidòfils en l'epiteli intestinal. Finalment es van provar diverses formes de transmissió horitzontal de E. nucleophila (cohabitació, efluent, intubació oral i anal) amb per a desenvolupar un model de manteniment in vivo. Es va aconseguir la transmissió el paràsit per totes les vies, però amb una disminució de prevalença al llarg del temps. Variables com la temperatura, la dosi, i l'estat dels peixos donants semblen ser més determinants que la ruta seleccionada per a la transmissió. Entre les rutes provades, la intubació anal sembla ser la més prometedora, però cap d'elles va ser capaç de reproduir els signes clínics observats en les infeccions naturals.
[EN] Aquaculture production is hampered by the emergence of parasite diseases in fish farming systems. Among them, in Sparus aurata, there are two important enteric parasites described: Enteromyxum leei (Myxozoa) Enterospora nucleophila (Microsporidia). To date, no in vitro culture has been established for either parasite, and only for E. leei was it possible to establish a model for maintaining the infection in vivo. The aim of this thesis is to gain new knowledge about these parasites and their relationship with the host, also the basic foundations for generating solutions that can be applied in aquaculture. The general objective for E. leei was to study the acquired immunity induced in gilthead bream and the possibility of generating diagnostic tools and vaccines against this disease. To this end, resistance against the parasite was assessed with a second exposure against the parasite, which showed a resistance for at least 16 months. Besides resistance seemed to be correlated with high levels of specific immunoglobulin (Ig) M in blood, and a high expression of Igs, in particular, the soluble forms, even before re-exposure to the parasite. The next step was refining the protocol for effluent infection with E. leei by studying infection at different exposure time points, temperatures and population densities. The results showed that one week of exposure is sufficient to spread E. leei infection by effluent, regardless of temperature. After demonstrating the resistance against E. leei, and with a refined infection model, a passive immunization assay was performed. The results showed that the serum with specific antibodies effectively slows down the invasion of the gut by the parasite and reduces the symptoms of the disease. At the same time, the analysis of the repertoire of the variable regions of intestinal IgM and IgT showed an induction of a polyclonal response in B cells. On the basis of these results, a research was carried out for E. leei antigens that could have use as candidates for the production of vaccines (proteomic study) or diagnostic tools (in silico study) using the parasite transcriptomic data. To do this, a de novo transcriptome was assembled using a mixed sample of gilthead sea bream and parasite, with a posterior filtrate of the sequences. The In silico and proteomic analysis search resulted in 7 and 12 transcripts, respectively, which are being used for diagnostic and vaccine production. The starting point was more basic in E. nucleophila studies, since this is a recently described disease. The samples of this parasite can only be obtained from natural outbreaks in fish farms. Therefore, first study was carried out to characterize the pathology of the infection of naturally infected fish. In the early stages of the infection, the parasite is mainly located in the intestine, but months later, the prevalence is lower in the intestine and increases in the hematopoietic organs and the stomach. Clinical signs of infection were significant reduction in growth, wasting, and intestinal walls paleness. At the cellular level, in the most severe cases hypercellularity in the intestinal epithelium, proliferation of rodlet cells, high number of lymphocytes at the base of the epithelium and infiltration of acidophilic granulocytes in the intestinal epithelium were observed. Finally, horizontal transmission of E. nucleophila was tried using different transmission methods: cohabitation, effluent, and oral and anal intubation. Transmission of the parasite was achieved with all routes, but there was a decrease in prevalence over time in all cases except for the anal route. Variables such as temperature, dose, and the status of the donor fish appear to be more important than the selected route. Among the routes tested, anal intubation seemed to be the most promising, as it was sustained over a longer period of time, but none of them was able to reproduce the same clinical signs of infection observed in natural infections.
The authors kindly acknowledge the collaboration of anonymous fish farming companies allowing access to the animals during the disease outbreaks. We thank J. Monfort and L. Rodríguez (IATS-CSIC) for the technical assistance on histological processing.This work has been carried out with financial support from the European Union and the Spanish Ministry of Economy and Competitiveness (MINECO) under grant projects ParaFishControl (H2020-634429) and AGL2013-R-48560-C2-2-R, respectively. APS was contracted under ParaFishControl project. Primer sequences and access to the gilthead sea bream transcriptomic database were kindly provided by Prof. J. Pérez-Sánchez of the IATS- Nutrigenomics group. The authors thank I. Vicente for fish maintenance and technical assistance during samplings. The authors thank P. Boudinot (INRAE) for his help in designing and interpreting the immunoglobulin repertoire study and results, J. Pérez-Sánchez (IATS-CSIC) for providing access to the gilthead sea bream genome sequences to perform the repertoire analysis.This work was funded by the European Research Council (ERC Consolidator Grant 2016 725061 TEMUBLYM).
Picard Sánchez, MA. (2021). Control of enteric parasitic diseases of farmed gilthead sea bream: New insights into Enteromyxum leei (Myxozoa) and Enterospora nucleophila (Microsporidia) infections [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167035
TESIS

Parasites are ubiquitous and shape almost every aspect of their hosts, including physiology, behaviour, life histories, the structure of the microbiota, and entire communities. Hence, parasitism is one of the most potent forces in nature and, without parasites, the world would look very different. The book gives an overview over the parasite groups and the diversity of defences that hosts have evolved, such as immune systems. Principles of evolutionary biology and ecology analyse major elements of host–parasite interactions, including virulence, infection processes, tolerance, resistance, specificity, memory, polymorphisms, within-host dynamics, diseases spaces, and many other aspects. Genetics is always one of the key elements in these topics. Modelling, furthermore, can predict best strategies for host and parasites. Similarly, the spread of an infectious disease in epidemiology combines with molecular data and genomics. Furthermore, parasites have evolved ways to overcome defences and to manipulate their hosts. Hosts and parasites, therefore, continuously co-evolve, with changes sometimes occurring very rapidly, and sometimes requiring geological times. Many infectious diseases of humans have emerged from a zoonotic origin, in processes governed by the basic principles discussed in the different sections. Hence, this book integrates different fields to study the diversity of host–parasite processes and phenomena. It summarizes the essential topics for the study of evolutionary parasitology and will be useful for a broad audience.

Cryptosporidium species represent a genus of parasitic protozoa (Apicomplexa) that are transmitted via the faecal-oral route and commonly infect the epithelial tissues of the gastric or intestinal (or sometimes the respiratory) tract of many vertebrates, including humans. Infection occurs following the ingestion of viable and resistant oocysts, through direct host-to-host contact or in contaminated food, drinking or recreational water. Infection can be transmitted via anthroponotic (human-to-human, human-to-animal) or zoonotic (animal-to-human or animal-to-animal) pathways, depending upon the species of Cryptosporidium. Although infection can be asymptomatic, common symptoms of disease (cryptosporidiosis) include diarrhoea, colic (abdominal pain), nausea or vomiting, dehydration and/or fever. In humans, cryptosporidial infection in immunocompetent patients is usually short-lived (days to weeks) and eliminated following the stimulation of an effective immune response. However, infection in immunodeficient individuals (e.g., those with HIV/AIDS) can be chronic and fatal (in the absence of immunotherapy), as there are few effective anti-cryptosporidial drugs and no vaccines available. The present chapter provides an account of the history, taxonomy and biology, genomics and genetics of Cryptosporidium, the epidemiology, pathogenesis, treatment and control of cryptosporidiosis and the advances in tools for the identification and characterisation of Cryptosporidium species and the diagnosis of cryptosporidiosis.

Abstract This chapter provides information on geographical distribution; host plants; symptoms; biology and life cycle; economic importance; movement and means of dispersal; pest risk analysis; invasiveness rating; management measures, including cultural, host resistance, biological, and chemical control; and detailed account of diagnosis procedures, such as morphological, biochemical, and molecular characterization, of Achlysiella, Hirschmanniella, Nacobbus, Pratylenchus, Radopholus and Zygotylenchus species.

Abstract This chapter provides information on geographical distribution; host plants; symptoms; biology and life cycle; economic importance; movement and means of dispersal; pest risk analysis; invasiveness rating; management measures, including cultural, pest resistance, biological, and chemical control; and detailed account of diagnosis procedures, such as morphological and molecular characterization, of Tylenchulus species.

Parasitic plants are among the most problematic pests of agricultural crops worldwide. They are found worldwide in all plant communities except aquatic. Parasitic plants are the organisms that settle in the host plant by means of the special organs they have developed and penetrate the vascular tissues of the hosts and meet their nutritional, water and mineral needs from the host plant. This particular body they have is called a haustorium. The discovery and investigation of the haustorium structures led to the evaluation of many heterotrophic plant species previously defined as parasitic plants in different groups. Host organisms are very important in completing the life cycle of parasitic plants. In general, the parasite weakens the host, so it produces fewer flowers and viable seeds or the value of the timber is reduced. However, some parasites, mostly annual root parasites belonging to the Orobanchaceae, can kill the host and cause significant economic damage while attacking monocultures in agriculture, and much effort is put into controlling these harmful parasites. Parasitic weeds are difficult to control because there are few resources for crop resistance and it is difficult to apply sufficiently selective control methods to kill weeds without physically and biochemically damaging the crop to which they are attached.

Malaria is a leading public health problem in tropical and subtropical countries of the world. In 2019, there were an estimated 229 million malaria cases and 409, 000 deaths due malaria in the world. The objective of this chapter is to discuss about the different Plasmodium parasites that cause human malaria. In addition, the chapter discusses about antimalarial drugs resistance. Human malaria is caused by five Plasmodium species, namely P. falciparum, P. malariae, P. vivax, P. ovale and P. knowlesi. In addition to these parasites, malaria in humans may also arise from zoonotic malaria parasites, which includes P. inui and P. cynomolgi. The plasmodium life cycle involves vertebrate host and a mosquito vector. The malaria parasites differ in their epidemiology, virulence and drug resistance pattern. P. falciparum is the deadliest malaria parasite that causes human malaria. P. falciparum accounted for nearly all malarial deaths in 2018. One of the major challenges to control malaria is the emergence and spread of antimalarial drug-resistant Plasmodium parasites. The P. vivax and P. falciparum have already developed resistance against convectional antimalarial drugs such as chloroquine, sulfadoxine-pyrimethamine, and atovaquone. Chloroquine-resistance is connected with mutations in pfcr. Resistance to Sulfadoxine and pyrimethamine is associated with multiple mutations in pfdhps and pfdhfr genes. In response to the evolution of drug resistance Plasmodium parasites, artemisinin-based combination therapies (ACTs) have been used for the treatment of uncomplicated falciparum malaria since the beginning of 21th century. However, artemisinin resistant P. falciparum strains have been recently observed in different parts of the world, which indicates the possibility of the spread of artemisinin resistance to all over the world. Therefore, novel antimalarial drugs have to be searched so as to replace the ACTs if Plasmodium parasites develop resistance to ACTs in the future.

Plant parasitic nematodes are damaging pests on all crops grown across the world. They exploit plants using a range of strategies, ranging from simple browsing ectoparasitism to highly complex biotrophic endoparasites. Some nematodes induce the formation of complex feeding structures in the roots of their hosts that require extensive reprogramming of host gene expression. These changes include changes in fundamentally important plant processes, including the cell cycle. Natural resistance can be used to control plant nematodes, and great progress has been made in mapping and identifying resistance genes against nematodes. Recent work has shown that the dependence of nematodes on a feeding structure has allowed plants to evolve new mechanisms of resistance that target this structure with a toxic response.

Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors and other electronic components, have lead to the emergence of severe on-chip “hot spots,” with heat fluxes approaching — and at times exceeding — 1 kW/cm2. The cost-effective thermal management of such chips requires the introduction and refinement of novel cooling techniques. Mini-contact enhanced, miniaturized thermoelectric coolers (TECs) have been shown to be a viable approach for the remediation of on-chip hot spots, but their performance is constrained by the thermal resistance introduced by the attachment of this thermal management device. This paper uses a detailed finite-element package-level model to examine the parasitic effects of the thermal contact resistance (at the interfaces of the mini-contact and TEC) on the cooling efficacy of this thermal solution. Particular attention is devoted to the deleterious effect of contact resistance on the thermoelectric leg height and the mini-contact size required to achieve the greatest hot spot temperature reduction on the chip. Data from experiments with TECs (with a leg height of 130 μm) combined with several sizes of mini-contact pads, are used to validate the modeling approach and the overall conclusions.

Driven by shrinking feature sizes, microprocessor “hot-spots” — with their associated high heat flux and sharp temperature gradients — have emerged as the primary “driver” for on-chip thermal management of today’s IC technology. Solid state thermoelectric micro-coolers offer great promise for reducing the severity of on-chip “hot-spots”, but the theoretical cooling potential of these devices, fabricated on the back of the silicon die in an IC package, has yet to be determined. The results of a three-dimensional electro-thermal finite-element modeling study of such a micro-cooler are presented. Attention is focused on the hot-spot temperature reductions associated with variations in micro-cooler geometry, chip thickness, and chip doping concentration, along with the parasitic Joule heating effects from the electrical contact resistance and current flow through the silicon. The modeling results help to define the optimum solid-state cooling configuration and reveal that, for the conditions examined, nearly 80% of the hot-spot temperature rise of 2.5°C can be removed from a 70μm × 70μm, 680W/cm2 hot-spot on a 50μm thick silicon die with a single micro-cooler.

Due to shrinking feature size and increasing transistor density, combined with the performance demanded from next-generation microprocessors, on-chip hot spots, with their associated high heat fluxes and sharp temperature gradients, have emerged as the primary driver for thermal management of today’s IC technology. This paper describes the novel use of thermoelectric coolers for on-chip hot spot cooling through the use of a copper mini-contact pad, which connects the thermoelectric cooler and the silicon chip thus concentrating the thermoelectric cooling power. A package-level numerical simulation is developed to predict the local on-chip hot spot cooling performance which can be achieved with such mini-contacts. Attention is focused on the hot spot temperature reduction associated with variations in mini-contact size and the thermoelectric element thickness, as well as the parasitic effect of the thermal contact resistance introduced by the mini-contact enhanced TEC. This numerical model and simulation results are validated by comparison to spot cooling experiments with a uniformly heated chip serving as the test vehicle. The experimental results demonstrate that a copper mini-contact pad can improve spot cooling performance by 80 ∼ 115% on a 500μm thick silicon chip under optimum operating conditions and that larger power dissipation on the chip leads to better spot cooling performance.

Impedance method has been explored for damage detection and identification. Typically, when the impedance sensor is integrated onto the mechanical structure to be monitored, its electrical impedance is directly related to the mechanical impedance of the host structure. Thus the change of impedance measurement before and after damage occurrence can be used as the damage indicator. Since the impedance information may be measured at relatively high frequency range, the impedance method could be sensitive to small-sized damage. Generally, piezoelectric transducers are employed in the impedance approach, which can serve as actuator and sensor simultaneously. In this research, a magnetic transducer approach is investigated for impedance based damage detection. To provide design guidelines, the analytical model of the resistive magnetic impedance measurement circuit is formulated. During the formulation, the two-way magneto-mechanical coupling between the transducer and the structure is systematically studied by using the Maxwell’s equations. The preliminary sensor enhancement is achieved by selecting the number of turns of wire in the electrical coil. Moreover, in order to reduce the negative effects of the high inherent inductance and large parasitic resistance of the coil with a large number of turns of wire, a new measurement circuitry is proposed, in which a negative resistive element and a capacitor are introduced to be serially connected with the original resistive circuit. Correlated numerical and experimental studies are carried out to validate the magnetic transducer in impedance based damage detection.