En este trabajo se desarrolla un modelo matemático con parámetros difusos para el análisis de la dinámica poblacional de los parásitos gastrointestinales Ostertagia ostertagi bajo diferentes condiciones climáticas. Ostertagia es el nematode predominante en la región pampeana de Argentina. La parasitosis gastrointestinal es una de las enfermedades con mayor impacto económico, tornando ineficientes a los siste-mas de producción de carne. En la región de la Pampa Húmeda, se ha estimado que se pierden anualmente unos 22 millones de dólares por mortalidad de terneros y 170 millones de dólares en perdidas sub-clínicas. El modelo está compuesto por dos módulos. El primer módulo se compone de dos modelos para los estadios de vida libre y el otro módulo consiste de dos modelos para el estadio parasitario. Cada uno de los mo-delos está formulado en términos de ecuaciones en diferen-cias con paso diario. Los parámetros para todos los modelos son formas funcionales definidas por sistemas de inferencia difusa, los cuales incorporan información cualitativa y cuan-titativa de los procesos involucrados. Estos parámetros difu-sos tienen la suficiente flexibilidad para replicar las condicio-nes de campo, particularmente las climáticas, las cuales son fundamentales para el desarrollo de estrategias de control. El modelo completamente integrado es capaz de evaluar posibles escenarios a los que los sistemas de producción se pueden enfrentar, dando una rápida respuesta a cerca de la dinámica de la infección. También el modelo permite simular control parasitario. Se considera que el efecto de un trata-miento con antihelmínticos afecta directamente a la pobla-ción de parásitos adultos (Ad) y a la cantidad de huevos por gramos de materia fecal (HPG). Por ejemplo, se puede suponer que cuando el antihelmíntico es el más efectivo, el HPG y la población Ad, caen a casi 0. Por lo tanto es posible analizar el impacto de diferentes estrategias de control parasitario, simulado eficiencia y/o retardo de diferentes drogas sobre la dinámica de la infección en la pastura así como en la pobla-ción de parásitos dentro del hospedador. Así, es posible generar un conjunto de simulaciones en las que se modifica el momento del año en el que se produce el tratamiento anti-helmíntico y deducir cuál es el patrón de aplicación más eficiente. El modelo puede ser una buena herramienta para la generación de nuevas estrategias de desparasitación, las cuales pueden tener un impacto económico importante para las diferentes áreas de producción ganadera del país. / A mathematical model with fuzzy parameters was developed for the analysis of the population dynamics of gastrointestinal parasites Ostertagia ostertagi under different climatic con-ditions. Ostertagia spp., is the predominant nematode in the pampas region of Argentina. Gastrointestinal parasitism is one of the diseases that have the highest economic impact on the Argentinian beef production system, rendering it inefficient. In the region of the Humid Pampas, it has been estimated that some 22 million dollars are lost annually because of the death of calves and 170 million dollars are lost in sub-clinic costs. The model is composed by two modules. A first module is composed by two models for the free- living stage while the second module consists of two models for the parasitic stage. The models are formulated in terms of a system of difference equations with daily time-step. In all models, the parameters are functional forms defined through fuzzy rule based systems which incorporate both quantitative and qualitative informa-tion on the processes involved. These fuzzy parameters allow for the flexibility needed when attempting to replicate field conditions, particularly weather conditions, which are funda-mental for developing any control strategy. The completely integrated model is able to evaluate possible scenarios that a meat production system could face, giving a rapid answer about the infection dynamics. The scenarios may be as diver-se as wished. Also, the model allows simulating worm control. We can consider the effect of an anthelmintic suppression treatment on the population of adult parasits (Ad) and the series of egg per grams of dung (EPG) values by, for example, supposing that when the anthelmintic is most effective, the EPG and adult population Ad count falls almost to 0. Therefore it is possible analyze the impact of different strategies of parasite control, simulating the efficiency and/or delay of various drugs on the dynamics of pasture infection. For example, it is possible to generate a set of simulations by varying the time of year of the sequence of application of a medical treatment with drugs and to infer which pattern is more efficient. The model can be a tool for generating new strategies for deworming, which can have an important economic impact if talking into account the area of the cattle production region in our country.

In this study different molecular techniques are contrasted (RAPD's, allozyme, sequencing mtDNA, sequencing ribosomal spacers) and appropriate analytical methods (allelic and infinite-sites approaches; inbreeding and coalescent models) used for estimating population genetic parameters in parasites. A range of population genetic questions at different scales were chosen to emphasise the importance of tailoring techniques and analytical methods to the particular question being investigated. The realisation that each question formulated has a particular scale means the appropriate technique and markers must be useful at that scale to attempt to answer the question. The useful scale of a technique depends several factors including the region of DNA examined, the density of sampling of the technique, and the mode of evolution of the markers. Each technique will produce a useful range of variability. Below the lower limit there is no variation, above the upper limit the variation is too high to produce useful comparisons. Parasites are of interest for many reasons, primarily because they can cause disease and thus impact on their host's population dynamics. They are often closely associated with their hosts and may undergo co-evolution, as well as causing an ongoing immunological "arms race" with their hosts. The parasitic mode of live is found throughout nearly all taxonomic groupings and thus classical models of population genetics based on sexual, diploid vertebrates do not fit well with the entire diversity of parasite groups. Genetic diversity within and among populations of Echinococcus granulosus was examined contrasting a RAPD dataset with an allozyme dataset. Two models of variation in Echinococcus have been proposed, those of Smyth and Rausch, and the expected genetic structure from each was compared to the observed genetic structure. The premise of Smyth’s model, predominant self-fertilisation, was supported, but the resultant pattern of genetic variation followed Rausch’s model. RAPD data, being dominant, present challenges to analysis. An approach to overcome this dominance problem and allow standard allelic frequency analysis is described using the selfing rate estimated from allozyme data. The RAPD data were also analysed using both band-sharing and nucleotide diversity approaches. A population genetic study of Ostertagia ostertagi in the USA was extended to two different scales: within an Australian state and between the USA and Australian continents. Three alternative explanations for the observed discrepancy between genetic structure and differentiation in an important biological trait, hypobiosis, were explored. A number of programs and analyses were compared including coalescent geneflow estimates. Variation among multiple copies of two spacer regions of rDNA was examined within individuals of Ostertagia ostertagi. Both the intergenic spacer and internal transcribed spacer 1 regions were found to include repeat regions, with different numbers of repeats creating length differences in clones from the same worm. Multi-copy genes present extra challenges in analysis to ensure that only homologous copies are being compared. Many studies fail to look for variation within populations or within individuals. The two major conclusions from these examples are that: 1). The study of variation necessarily involves an implicit scale, and markers must be chosen that are appropriate to the question being explored. 2). Using several methods of analysis of genetic data allows contrasts to be made, and if different methods produce similar results gives much more confidence in the conclusions drawn. Incongruence in results leads to new questions and reexamination of the assumptions of each analysis.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.