Les invasions biologiques sont de plus en plus fréquentes, avec des conséquences importantes sur la biodiversité et la santé humaine. Étudier les mécanismes qui les expliquent permet simultanément (i) d’envisager des stratégies efficaces de contrôle et de prévention et (ii) d’étudier divers processus écologiques et évolutifs sur des échelles de temps contemporaines. Plusieurs hypothèses basées sur le parasitisme et l’immunité des hôtes sont proposées pour expliquer le succès des espèces envahissantes. Ainsi, au cours de l’invasion, les hôtes exotiques (1) perdraient leurs parasites naturels (Enemy Release, ER), (2) transfèreraient leurs parasites exotiques aux hôtes natifs (Spill-Over, SO) et/ou (3) amplifieraient les cycles des parasites natifs au sein des hôtes locaux (Spill-Back, SB). En relation avec ces changements dans les interactions hôtes-parasites, l’hypothèse EICA (Evolution of Increased Competitive Ability) prédit une modulation des ressources de l’hôte envahissant via un investissement moins important dans les réponses immunitaires coûteuses (inflammation) au profit de réponses immunitaires beaucoup moins coûteuses (réponses médiées par les anticorps) et de capacités de reproduction et de dispersion des populations sur le front d’invasion. Le but de ma thèse est de tester ces prédictions dans le cadre de deux invasions actuellement en cours au Sénégal : celles du rat noir Rattus rattus et de la souris domestique Mus musculus domesticus, deux espèces envahissantes majeures tant par leurs impacts (économique, sanitaire, écologique) que par leur distribution quasiment mondiale. Mes travaux se basent sur un dispositif d’échantillonnage en populations naturelles et sur le développement d’approches comparatives le long d’un gradient d’invasion pour chacune des deux espèces exotiques. Les patrons de structure (prévalence, abondance, richesse) de deux communautés de parasites (helminthes gastro-intestinaux, bactéries pathogènes) et les profils immunitaires (réponses médiées par les anticorps naturels, inflammation) des rongeurs commensaux exotiques (M. m. domesticus, R. rattus) et/ou natifs (Mastomys spp.) ont été comparés pour des localités situées dans des régions anciennement envahies (depuis plus de 100 ans), récemment envahies (depuis moins de 30 an : front d’invasion), et non envahies. Mes résultats montrent des variations dans la structure des communautés de parasites et les réponses immunitaires des hôtes natifs et exotiques. Les tendances observées, aussi bien pour les communautés de parasites que pour les composantes immunitaires étudiées le long des deux routes d’invasion, attestent de patrons globalement plus complexes qu’attendu sous les hypothèses de départ, suggérant l’existence de relations complexes entre caractéristiques des communautés d’hôtes et de parasites, investissement immunitaire, conditions environnementales et invasions biologiques. Des approches expérimentales doivent être envisagées afin de déterminer les conséquences et les mécanismes sous-jacents aux différents phénomènes observés. / Biological invasions are increasingly phenomenon worldwide having deleterious impacts on biodiversity and human health. Studying the mechanisms explaining them allows both (i) to define efficient strategies for controlling and preventing invaders and (ii) to study ecological and evolutionary processes at contemporary scales. Some major hypotheses rely on parasitism and host immunity to explain invasion success. Thus, exotic host populations (1) may benefit of an " Enemy Release " (ER) through impoverishment of their original parasite communities, and may affect native hosts by (2) transferring exotic parasites (Spill-Over, SO) and/or (3) by increasing transmission risk of native parasites (Spill-Back, SB). In turn, according to the refined “Evolution of Increased Competitive Ability” (EICA) theory, invasive populations should experience immune trade-offs by favouring less expensive antibody-mediated responses over costly inflammation, to increase their competitive ability (dispersion, reproduction). The aim of my thesis is to test these predictions along the invasion routes of two commensal exotic species in Senegal, the domestic mouse (Mus musculus domesticus) and the black rat (Rattus rattus). These rodent species are considered to be major invasive species worldwide inducing high economic, sanitary and ecological damages. My research is based on comparative analyses along one invasion route for each invasive species. We focused on gastrointestinal helminths and pathogenic bacteria as parasite communities, and inflammation and natural antibody-mediated responses as immune estimates. Comparisons were performed for invasive and/or native (Mastomys spp.) rodents between localities of long-established invasion (100-200 years ago), recent invasion (10-30 years ago; invasion front), and non-invaded localities. My findings showed variations along both invasion routes in parasite community structure and immune patterns, but in a more complex way than expected under the initial predictions. The heterogeneity of changes observed highlights the existence of particular relations between host and parasite traits, host immune investment, environmental conditions and biological invasions. Further experimental works are needed to assess the consequences and mechanisms underlying the changes observed along both invasion routes.

Made available in DSpace on 2016-12-23T13:56:00Z (GMT). No. of bitstreams: 1 Dissertacao Dra Roberta Fragoso.pdf: 511749 bytes, checksum: f17edb83d59dac38e65babef8d7d4403 (MD5) Previous issue date: 2006-07-13 / Background. High prevalence of anti-Toxocara antibodies has been reported in inpatients at one reference pediatric hospital in Vitoria, but there was not any report of this prevalence in healthy children. Objectives. (a)To study the prevalence and incidence of Toxocara infection by searching anti Toxocara antibodies in schoolchildren seven to nine years old; (b) to investigate associated factors and to perform physical examination, including ophthalmologic examination, blood eosinophil counts and stool examinations for helminthes. Methods. A commercial ELISA IgG test for Toxocara was performed in 394 children (first series from elementary school).One year later the test was done again in all children with negative result in the first test (optical density under 0.250 ). Stool examination and blood counts were performed at a routine laboratory from the municipality of Vitoria. It was applied a questionnaire for information on hygiene and socioeconomic conditions. Ophthalmologic examination included eye grounds examinations. Results. Considering OD>>500 as a positive result, the serum prevalence was 51.6% (202/394) without gender differences. Eighteen, out of 92 children (19.5%) with negative result in the first test, presented a positive test one year later. At least one intestinal helminth was detected in 68/308 (22%) without gender differences. No significant differences were observed in the prevalence of positive serology in children with or without intestinal helminthes. Eosinophilia (blood ophils >400/mm3) was observed in 181/394 (45,9%) ,higher in children with positive serology, bearing or not intestinal helminthes Owning pets, low incomes, onycophagia and use of non filtered water were significantly associated with positive serology. No signs or symptoms related to Toxocara infection were observed in children with positive serology, except two cases of retinal lesions suggestive of ocular larva migrans. Conclusion. It was confirmed he high prevalence and it was demonstrated high incidence of positive serology in children in our county. Owning pets, low incomes, onycophagia and use of non filtered water were significantly associated factors. The absence of clinical manifestations and the low frequency of ocular lesions indicate that or Toxocara infection frequently is a benign, asymptomatic infection or the high prevalence observed was due to cross reaction with intestinal helminthes infections. / Introdução. Alta prevalência de anticorpos anti-Toxocara (Ac anti-T) tem sido relatada em crianças internadas em Hospital pediátrico de Vitória, mas nenhuma observação foi feita em amostra de crianças saudáveis. Objetivos. Verificar a prevalência e a incidência anual da infecção pelo Toxocara, pela pesquisa de Ac anti-T em escolares (7-9anos), investigar fatores associados e realizar exame físico, incluindo o oftalmológico, contagem dos eosinófilos no sangue periférico e exame parasitológico de fezes. Métodos. 394 escolares (primeira série em oito escolas localizadas em bairros de baixa renda) foram submetidos a um teste ELISA IgG para Toxocara (Toxocara IgG CELISA, Cellabs Pty Ltda. Brookvale, Austrália) . Um ano após, os que apresentavam DO < 0,250, foram novamente testados para Ac anti-T .Exame parasitológico de fezes e hemograma foram realizados em laboratório de rotina da Prefeitura de Vitória. Foi aplicado um questionário para informações sobre hábitos e condições de vida. O exame oftalmológico incluiu o exame de fundo de olho e quando necessário a retinografia. Resultados: Das 391 amostras, 202 (51,6%) tiveram densidades ópticas acima de 0,500 (considerada positiva para infecção com Toxocara), sem diferença entre sexos. Das 92 crianças com a sorologia negativa, 18 (19,5%) tiveram a reação positiva no ano seguinte. Pelo menos um helminto intestinal foi identificado em 68/308 (22%) crianças, sem diferença entre sexos. Não houve diferença na freqüência de Ac anti-T em crianças com ou sem helminto intestinal. Eosinofilia (>400 eosinófilos/mm3) foi observada em 181/394 (45,9%) crianças, maior nas crianças com sorologia positiva associada ou não à presença de helminto intestinal. Possuir cão, renda familiar < 2 salários mínimos, onicofagia e beber água sem filtrar se correlacionaram com Ac anti-T. Não havia manifestação em nenhuma das crianças com sorologia positiva e apenas duas (1,2%; 2/171,) tinham lesões oculares compatíveis com Larva Migrans Ocular. Conclusão: Confirma-se ser alta a prevalência e demonstra-se ser alta a incidência anual da infecção pelo Toxocara em crianças de baixa renda em Vitória. Possuir cão, renda familiar <2 salários, onicofagia e beber água sem filtrar foram significativamente associados a Ac anti-T. A ausência de manifestações clínicas e a baixa freqüência de lesões oculares indicam que a infecção pelo Toxocara ou é benigna e assintomática ou os resultados positivos da sorologia se devem, na sua maioria, às reações cruzadas com helmintos intestinais.

Les strongyloses vétérinaires constituent l’une des principales causes de gastroentérites et d’anémie des ovins et caprins à l’origine de lourdes pertes économiques. Cependant, leurs prise en charge par les anthelminthiques existants, est confrontée à la prolifération d’une pharmacorésistance des nématodes incriminés. La première partie de ce travail de thèse présente l’ampleur du problème que pose la résistance des helminthes impliqués dans les strongyloses des petits ruminants. Elle révèle également le profil novateur des imidazo[1,2-a]pyridinyl-phénylacrylonitriles qui est proposé pour parer à l’inefficacité croissante des anthelminthiques. / Veterinary strongylosis is one of the main causes of gastroenteritis and anemia in sheep and goats causing major economic losses. However, their management by existing anthelmintics, is confronted with the proliferation of drug resistance of the nematodes incriminated. The first part of this thesis presents the magnitude of the problem posed by the resistance of helminths involved in strongylosis of small ruminants. It also reveals the innovative profile of imidazo[1,2-a]pyridinyl-phenylacrylonitriles that are proposed to counter the increasing ineffectiveness of anthelmintics.