Le titre de la thèse concernant le succès des nématodes peut sembler extremement vaste. Notre projet était pourtant bien d’avoir une vue d’ensemble de l’ensemble des acteurs, à savoir les nématodes parasites du tube digestif mais également l’hôte et certains aspects de sa réponse, et enfin l’éleveur qui est celui qui décide du mode d’élevage et des traitements antiparasitaires. Nous avons essentiellement travaillé en conditions expérimentales et sur une espèce de ces strongles. En ce qui concerne les traits de vie des nématodes plusieurs grands phénomènes conditionnent leur succès : a) leur capacité assez variable selon les isolats à infester un hôte, b) l’interaction entre résistance aux antiparasitaires et cette capacité à infester, c) enfin leur aptitude à survivre aux stress climatiques au cours de leur phase non-parasitaire. / The success of gastrointestinal nematodes in their sheep hosts is so extensive that they present one of the leading threats to ruminant health and production throughout the globe. This thesis research identified three key factors which influence their success including the gastrointestinal nematode biology, the sheep host protective response and the farmers control decisions. Using Haemonchus contortus as a model species, we demonstrated that the success of GIN biology is aided by their capacity to overcome numerous selective pressures that target both parasitic and free-living stages in their life cycle. This was achieved by amplifying life-history traits following challenge to recoup any costs in survival and reproduction. In turn, high levels of fitness were maintained and they remained stable in the face of numerous selective pressures. Sheep have the capacity to exert almost perfect control over GIN success by blocking their life cycle through via protective responses.

Orientador: Elizabeth Moreira dos Santos Schmidt / Resumo: Este trabalho encontra-se dividido em três capítulos. O capítulo 1 versa sobre uma revisão de literatura que teve como objetivo a realização de um levantamento retrospectivo sobre os endoparasitas em bovinos no Brasil, que também incluiu dados mundiais. No capítulo 2, objetivou-se investigar os nematódeos gastrintestinais (GI) e pulmonares que parasitam bovinos jovens. Para isso, foram utilizados 140 bezerros mestiços, de dois a 12 meses de idade, clinicamente saudáveis, de duas propriedades leiteiras nos municípios de Botucatu e Manduri, estado de São Paulo. Durante um ano, trimestralmente, amostras de fezes foram coletadas diretamente da ampola retal para a realização da contagem de OPG pela técnica de McMaster modificada e pesquisa de L1 de Dictyocaulus viviparus pela modificação da técnica de Baermann. Além disso, coproculturas foram realizadas em pool de amostras para a observação das larvas infectantes. Na propriedade de Manduri, houve um aumento significativo da contagem de OPG no inverno. Na propriedade de Botucatu, os animais com até três meses de idade apresentaram maiores contagens de OPG quando comparados aos animais mais velhos. Em geral, foram observados ovos de estrongilídeos, Strongyloides spp., Moniezia spp., Trichuris spp. e oocistos de Eimeria spp. Nas coproculturas, em ordem de prevalência, foram recuperadas larvas infectantes de Cooperia spp., Haemonchus spp., Oesophagostomum spp. e Trichostrongylus spp. As L1 de D. viviparus foram recuperadas somente na ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work was divided into three chapters. The chapter 1 aimed to perform a review article based on a retrospective survey of epidemiological studies examining endoparasites that affect bovine in different regions of Brazil, which also included international data. The chapter 2 aimed to determine the gastrointestinal (GI) and pulmonary parasites that affect calves. For this, we used 140 clinically healthy crossbred calves, two to 12 months old, which belonged to two private farms in the municipalities of Botucatu and Manduri, São Paulo state. The animals were monitored for 12 months. Feces were collected directly from the rectum every three months. Fecal egg counts were determined using the modified McMaster technique with a sensitivity of 50 eggs per gram of feces (EPG). Coproculture was performed on pooled samples to identify Strongylida infective larvae. First-stage larvae of Dictyocaulus viviparus were identified by a modified Baermann method. The calves from Manduri farm showed a significant increase in the fecal egg counts in the winter when to compare to other seasons. The Botucatu farm calves differed significantly in the age groups in that younger calves (2 – 3 months old) showed a higher EPG than older calves (8 – 12 months old). Generally, we found Strongyle type-eggs, Strongyloides spp., Moniezia spp., and Trichuris spp. eggs and Eimeria spp. oocysts. The most prevalent genera in all coprocultures were: Cooperia spp., Haemonchus spp., Oesophagostomum spp., and Tri... (Complete abstract click electronic access below) / Mestre

Animals acquire immunity against gastrointestinal (GI) nematode infection depending on their age and continual exposure to larvae, however, expression of this acquired immunity is often penalized during pregnancy and lactating period. This is described as periparturient relaxation in immunity (PPRI), and suggested to have nutritional basis. Although dietary protein has positive effect on immunity against GI nematode infection in mammalian host, we have not fully achieved to characterise the detailed interaction between PPRI and dietary protein. Therefore, this PhD aimed to further investigate this interaction in a well-established Nippostrongylus brasiliensis re-infected lactating rat model. Feeding high protein diet (HP) as opposed to low protein diet (LP) during pregnancy was necessary in maintaining sufficient maternal performances and systemic immune response (Chapter 2 and 3). Accumulation of host’s body protein reserve during pregnancy was significantly higher in HP fed animals compared to LP fed counterparts, which led to improvement in both maternal performances and immunity during the early stage of lactation. However, as lactation period progressed and re-infection of N. brasiliensis took place, importance of current dietary status, rather than the accumulated protein reserve, became evident for maternal performances and immunity. Indeed, animals fed HP during lactation showed significantly heavier pup weight compared to LP fed animals; HP animals showed higher serum immunoglobulin levels and reduced worm burden compared to LP. N. brasiliensis, however, goes through systemic migration, entering host’s skin and migrating to lung parenchyma through blood vessels before reaching the intestine. In Chapter 4, a detailed lung pathology study following N. brasiliensis infection was performed to generate data on the effects of the nematode in the lung of the rat host as such data were scarce. Rat host showed similar lung pathology to that of mice; up-regulation of genes related to type 2 immunity and development of emphysema-like pathology were observed following N. brasiliensis re-infection. In Chapter 5, the effect of dietary protein supplementation on lung and intestinal histology and gene expression analysis was investigated. It was shown that HP fed animals showed higher expression of genes related to type 2 immunity compared to LP in the lung. This effect of protein supplementation in the lung may have contributed to fewer worm burdens in HP fed rats compared to LP in the intestine. Dietary protein supplementation significantly affected the expression of genes related to goblet cells; it resulted in up-regulation of the expression of Retnlb and down-regulation of Agr2 and Tff3 in HP fed animals compared to LP. It is evident that dietary protein is modulating intestinal immunity, and this may be targeted towards specific pathways. In addition, the effect of dietary protein supplementation on immune cell populations of secondary lymphoid organs was analysed. Marked increase in the percentage of macrophage in the spleen and T cell in the mesenteric lymph node was observed following protein supplementation, highlighting the importance of dietary protein on systemic immunity during the parasite infection. These results demonstrate that dietary protein supplementation is effective for improving both maternal performances and immune responses, not only at the intestinal phase but also at the migrating phase, when animal is undergoing PPRI during N. brasiliensis infection. Such information is expected to define strategic utilisation of nutrient supply and to result in development of sustainable parasite control strategies in mammals.