Viren haben als Ursache lebensmittelassoziierter Infektionen eine große Bedeutung. Sie können vor allem über rohe oder unzureichend erhitzte Lebensmittel übertragen werden. In diesem Zusammenhang werden grüner Salat, Erdbeeren, Himbeeren, Frühlingszwiebeln, Muscheln, halbgetrocknete Tomaten, fäkal verunreinigtes Trinkwasser, Backwaren und Rohwürste als häufige Infektionsquellen genannt. Vor allem kurzgereifte Rohwürste gehören aus mikrobiologischer Sicht zu Risikoprodukten. Um eine gleichbleibende Qualität der Produkte zu gewährleisten, ist die Verwendung von Starterkulturen unerlässlich. Als sogenannte Schutzkulturen sollen sie gleichzeitig die Vermehrung unerwünschter bakterieller Pathogene unterbinden. Bisher ist allerdings nicht bekannt, inwieweit diese zur Virusinaktivierung in kurzgereiften Rohwürsten führen bzw. beitragen. Aus diesem Grund war es das Ziel dieser Arbeit, den Einfluss von rohwurstrelevanten Starter- und Schutzkulturen sowie deren Metabolite (Bacteriocine, Milchsäure) auf die Tenazität und Inaktivierungskinetik von Viren zu prüfen. Die Untersuchungen erfolgten mit dem murinen Norovirus (MNV) S 99 sowie dem humanen Influenzavirus H1N1 (A/WSN/33). Antivirale Effekte wurden zum einen anhand von in-vitro-Studien, zum anderen anhand von experimentell mit Viren kontaminierten kurzgereiften Rohwürsten (Mettwurst/Teewurst) geprüft. Die Bacteriocine Sakacin A und Nisin zeigten in phosphatgepufferter Salzlösung (PBS) keine viruzide Wirkung gegenüber MNV S 99 und H1N1 (pH 6,2; 24 °C; Exposition: 3 Tage). Weiterhin wurden anhand von in-vitro-Untersuchungen 29 verschiedene zellfreie Kulturüberstände [Milchsäurebakterien, Staphylococcus spp. (S.), Kocuria (K.) varians] hinsichtlich ihrer antiviralen Wirkung geprüft. Dabei konnte eine signifikante Titerreduktion von MNV S 99 bei Exposition mit dem Kulturüberstand eines Lactobacillus (Lb.) curvatus-Isolates festgestellt werden (p < 0,05). In mit dieser Kultur fermentiertem Tee- und Mettwurstbrät zeigte sich jedoch kein Effekt. Die Virustenazität von H1N1 und MNV S 99 konnte mit D,L-Milchsäure unter rohwurstrelevanten Bedingungen (pH 5,0 bis 6,2) sowohl in-vitro als auch im frischen Mettwurstbrät beeinflusst werden. In-vitro erzielte Titerreduktionen lagen bei 2,5 (H1N1) bzw. 3,25 log-Stufen (MNV S 99) nach drei Tagen (24 °C) Lagerung. Im Gegensatz dazu war MNV S 99 im Vergleich zu H1N1 im Mettwurstbrät stabiler. H1N1 konnte unterhalb von pH 5,5 bereits direkt nach dem Einmischen der Influenzaviren in das Wurstbrät nicht mehr nachgewiesen werden. MNV S 99 wurde hingegen erst nach einem Tag Lagerung (22 °C) maximal um 0,7 log-Stufen reduziert (pH 5,2). Die verwendeten Starter- und Schutzkulturen (Lb. sakei, Lb. curvatus, Lb. paracasei, Lb. plantarum, S. carnosus, S. xylosus, K. varians) zeigten im Mett- und Teewurstbrät im Vergleich zur Kontrolle (ohne Starterkultur) keinen zusätzlichen viruziden Effekt auf MNV S 99. Zunehmende Virustiterreduktionen konnten mit pH-Wert-Erniedrigung beobachtet werden. Nach der Reifung (1 Tag, 22 °C, pH 4,9) von Mettwurst mit Starterkulturen wurde das Virus um maximal 1,65 log-Stufen reduziert. In mit Einzel- beziehungsweise Mehrstamm-Mischkulturen fermentierter Teewurst (7 Tage, 22 °C, pH 4,9) betrug die Titerreduktion maximal 1,10 log-Stufen. Das Influenzavirus H1N1 konnte im Rohwurstbrät mit Starterkulturen auch nach Verwendung hoher Ausgangstiter bereits zu Beginn der Untersuchungen nicht mehr nachgewiesen werden. Aus den erzielten Daten kann geschlussfolgert werden, dass die Bacteriocine Sakacin A und Nisin nicht als antivirale Zusatzstoffe in Lebensmitteln (z. B. Rohwürste) geeignet sind. Das antivirale Potential von zellfreien Kulturüberständen war Bakterienstamm-spezifisch und nur in-vitro ersichtlich. Daher muss die Nutzung des Lb. curvatus 1-Stammes nicht anderen rohwurstrelevanten Starterkulturen vorgezogen werden. Die Verwendung von Milchsäure als Zusatzstoff im Rohwurstbrät eignet sich nur zum Ausschluss einer viralen Exposition im Zusammenhang mit H1N1. Frische Mettwurst muss allerdings hierzu adäquat gesäuert (pH < 5,5) werden. Neben dem antiviralen Effekt durch gebildete Säure, konnte keine weitere spezies-spezifische antivirale Wirkung verwendeter Starter- und Schutzkulturen auf MNV S 99 festgestellt werden. Die Säureleistung einzelner Kulturen ist demzufolge für eine Virusinaktivierung entscheidend. Das antivirale Potential verwendeter Starter- und Schutzkulturen in Rohwürsten ist im Zusammenhang mit MNV S 99 als gering einzuschätzen. Unter der Annahme, dass murine und humane Noroviren eine ähnliche Tenazität in kurzgereiften Rohwürsten aufweisen, sollten diese Produkte im Zusammenhang mit Noroviren als Risikoprodukte eingestuft werden.

Os vírus da influenza aviária, ou vírus da influenza A, podem acometer inúmeras espécies de aves e mamíferos, e são conhecidos pelos relevantes impactos gerados na economia e Saúde Pública. As aves pertencentes às ordens Anseriformes (patos, marrecos e cisnes) e Charadriiformes (maçaricos, gaivotas e trinta-réis) são consideradas reservatórios, sendo que o comportamento migratório de muitas destas espécies pode favorecer a disseminação viral entre países. Existem poucos estudos sobre a circulação dos vírus da influenza aviária na América do Sul, dificultando a compreensão da ecologia e epidemiologia destes patógenos no Brasil. Este trabalho tem como objetivo monitorar as aves migratórias, em áreas de descanso e invernada na região Amazônica brasileira, por meio da detecção e caracterização dos vírus da influenza A. Através de seis expedições científicas ao norte do estado do Pará entre 2008 e 2010 foram colhidos swabs orotraqueais e cloacais de 1093 aves silvestres, principalmente Anseriformes e Charadriiformes. Pela técnica de Real time RT-PCR, nove aves foram positivas: 2 Actitis macularius, 4 Arenaria interpres, 1 Calidris pusilla, 1 Charadrius semipalmatus e 1 Dendrocygna viduata. Destas, o isolamento viral foi realizado com sucesso a partir das amostras de três Arenaria interpres, corroborando estudos que demonstram uma elevada prevalência do vírus da influenza A nesta espécie. As reações de inibição da hemaglutinação e de inibição da neuraminidase revelaram tratar-se do subtipo viral H11N9, considerado de baixa patogenicidade e relativamente comum nestas aves. O sequenciamento genético indicou estreita relação filogenética entre as estirpes virais deste estudo e aquelas isoladas na América do Norte, evidenciando um vínculo epidemiológico entre estas populações. Assim, é essencial a contínua vigilância epidemiológica dos vírus da influenza aviária em aves silvestres nesta região, visando a obtenção de informações sobre a prevalência do vírus, subtipos circulantes e suas características patogênicas, para subsidiar medidas apropriadas de prevenção e controle caso ocorram surtos no país. / Avian influenza viruses infect a variety of birds and mammals and are known for their relevant enconomic and public health impacts. Anseriformes (ducks, mallards and geese) and Charadriiformes (shorebirds, seagulls and terns) are natural reservoirs of avian influenza viruses, and the migratory behaviour of many of these species can result in the spread of the virus among countries. There are few studies investigating the occorrence of these viruses in South America, hindering understanding of their ecology and epidemiology in Brazil. This study aims to detect and characterize avian influenza viruses in migratory birds in wintering areas on the Amazon coast. Orotracheal and cloacal swabs were obtained from 1093 wild birds, mostly Anseriformes and Charadriiformes, during six expeditions between 2008 and 2010 to the state of Pará, Brazil. Samples from nine birds were positive to Real time RT-PCR: 2 Actitis macularius, 4 Arenaria interpres, 1 Calidris pusilla, 1 Charadrius semipalmatus e 1 Dendrocygna viduata. Virus isolation was successfully carried out for the samples from three Arenaria interpres, in agreement with previous studies reporting high prevalence in this species. Hemaglutinin and neuraminidase inhibition assays indicated these strains belonged to subtype H11N9, considered low pathogenic and relatively common in shorebirds. Gene sequencing demonstrated close phylogenetic relationship between the strains isolated in this study and those found in North America, revealing the existence of epidemiological conectivity among these populations. It is therefore vital to maintain active epidemilogical surveillance of wild birds in this region, collecting information on virus prevalence, subtype and pathogenicity that may in turn be used to implement prevention and control policies for avian influenza outbreaks.

Os vírus da influenza aviária, ou vírus da influenza A, podem acometer inúmeras espécies de aves e mamíferos, e são conhecidos pelos relevantes impactos gerados na economia e Saúde Pública. As aves pertencentes às ordens Anseriformes (patos, marrecos e cisnes) e Charadriiformes (maçaricos, gaivotas e trinta-réis) são consideradas reservatórios, sendo que o comportamento migratório de muitas destas espécies pode favorecer a disseminação viral entre países. Existem poucos estudos sobre a circulação dos vírus da influenza aviária na América do Sul, dificultando a compreensão da ecologia e epidemiologia destes patógenos no Brasil. Este trabalho tem como objetivo monitorar as aves migratórias, em áreas de descanso e invernada na região Amazônica brasileira, por meio da detecção e caracterização dos vírus da influenza A. Através de seis expedições científicas ao norte do estado do Pará entre 2008 e 2010 foram colhidos swabs orotraqueais e cloacais de 1093 aves silvestres, principalmente Anseriformes e Charadriiformes. Pela técnica de Real time RT-PCR, nove aves foram positivas: 2 Actitis macularius, 4 Arenaria interpres, 1 Calidris pusilla, 1 Charadrius semipalmatus e 1 Dendrocygna viduata. Destas, o isolamento viral foi realizado com sucesso a partir das amostras de três Arenaria interpres, corroborando estudos que demonstram uma elevada prevalência do vírus da influenza A nesta espécie. As reações de inibição da hemaglutinação e de inibição da neuraminidase revelaram tratar-se do subtipo viral H11N9, considerado de baixa patogenicidade e relativamente comum nestas aves. O sequenciamento genético indicou estreita relação filogenética entre as estirpes virais deste estudo e aquelas isoladas na América do Norte, evidenciando um vínculo epidemiológico entre estas populações. Assim, é essencial a contínua vigilância epidemiológica dos vírus da influenza aviária em aves silvestres nesta região, visando a obtenção de informações sobre a prevalência do vírus, subtipos circulantes e suas características patogênicas, para subsidiar medidas apropriadas de prevenção e controle caso ocorram surtos no país. / Avian influenza viruses infect a variety of birds and mammals and are known for their relevant enconomic and public health impacts. Anseriformes (ducks, mallards and geese) and Charadriiformes (shorebirds, seagulls and terns) are natural reservoirs of avian influenza viruses, and the migratory behaviour of many of these species can result in the spread of the virus among countries. There are few studies investigating the occorrence of these viruses in South America, hindering understanding of their ecology and epidemiology in Brazil. This study aims to detect and characterize avian influenza viruses in migratory birds in wintering areas on the Amazon coast. Orotracheal and cloacal swabs were obtained from 1093 wild birds, mostly Anseriformes and Charadriiformes, during six expeditions between 2008 and 2010 to the state of Pará, Brazil. Samples from nine birds were positive to Real time RT-PCR: 2 Actitis macularius, 4 Arenaria interpres, 1 Calidris pusilla, 1 Charadrius semipalmatus e 1 Dendrocygna viduata. Virus isolation was successfully carried out for the samples from three Arenaria interpres, in agreement with previous studies reporting high prevalence in this species. Hemaglutinin and neuraminidase inhibition assays indicated these strains belonged to subtype H11N9, considered low pathogenic and relatively common in shorebirds. Gene sequencing demonstrated close phylogenetic relationship between the strains isolated in this study and those found in North America, revealing the existence of epidemiological conectivity among these populations. It is therefore vital to maintain active epidemilogical surveillance of wild birds in this region, collecting information on virus prevalence, subtype and pathogenicity that may in turn be used to implement prevention and control policies for avian influenza outbreaks.

In den vergangenen Jahren wurde ein Anstieg der Anzahl infektiöser Gastroenteritiden beobachtet, welche durch Viren hervorgerufen wurden. In vielen Fällen ließen sich Infektionen auf den Verzehr kontaminierter Lebensmittel zurückführen. In diesem Zusammenhang wurde der Begriff der sogenannten „food borne viruses“ geprägt. Welche Bedeutung Rohwurstprodukten bei der Übertragung humanpathogener Viren zukommt, kann derzeit nur anhand weniger objektiver wissenschaftlicher Fakten eingeschätzt werden. Die vorliegende Arbeit beschäftigte sich mit Studien zu Tenazität und Inaktivierung von Viren in Rohwurstprodukten. Dabei wurde ECHO-Virus stellvertretend für die Spezies humaner Enteroviren untersucht. Enteroviren zeichnen sich durch eine hohe Tenazität aus. Als ein wichtiger Vertreter kann Polio-Virus angeführt werden, welches bekanntlich durch Lebensmittel übertragbar ist. Im Zuge der aktuellen Problematik mit aviären Influenzaviren wurden stellvertretend zwei niedrigpathogene Isolate aviärer Influenzaviren für die Versuchsreihen gewählt. Die gewonnenen Ergebnisse sollten dazu beitragen, die Rolle des Lebensmittels Rohwurst bei der Übertragung lebensmittelassoziierter Virusinfektionen besser abschätzen zu können (hinsichtlich einer Risikobewertung) und Aussagen hinsichtlich möglicher Maßnahmen zur Risikominimierung zu ermöglichen. vorgenommen werden.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2008. / Härtill 4 uppsatser.

Introdução: O surgimento de uma nova cepa do vírus Influenza A, o H1N1, determinou uma pandemia no ano de 2009, com importante repercussão global. Esse vírus infectou principalmente adultos jovens e crianças menores de dois anos com grande aumento na morbimortalidade quando comparado com as taxas anuais decorrentes do influenza. Objetivo: Avaliar as características epidemiológicas e clínicas da infecção pelo vírus influenza A (H1N1) em crianças, a fim de agregar conhecimento para melhor abordagem em futuras pandemias. Métodos: Estudo de corte transversal com revisão dos prontuários de todas as crianças, entre zero e 16 anos, hospitalizadas com quadro gripal no Hospital de Clínicas de Porto Alegre (HCPA) em 2009. A identificação do vírus H1N1 foi feita através de Reação em Cadeia da Polimerase (PCR) em laboratório de referência. Resultados: Cento e noventa e uma crianças foram internadas com suspeita de infecção pelo H1N1, destas, 83 (43%) foram submetidos à pesquisa do vírus H1N1, sendo 28 positivos (34%) e 55 negativos (66%). Os pacientes positivos para H1N1 eram mais velhos, 27 (7-108) versus sete (3-32) meses (p=0,015), todos apresentaram febre versus 70% do outro grupo (p=0,015), chegaram ao hospital com menor saturação de hemoglobina, 80% (±20%) versus 95% (±4) (p<0,001) e precisaram de maior pressão expiratória final, dez (±3) versus cinco (±1) cm H2O (p=0,001) e de maior fração inspirada de oxigênio, um (0,65-1) versus 0,4 (0,4-1) (p=0,053) quando colocados em ventilação mecânica. Não houve diferença quanto à necessidade de internação em unidade de terapia intensiva, indicação de suporte ventilatório, tempo de internação e óbito. Conclusão: As crianças acometidas pelo H1N1 apresentaram-se mais graves, embora tenham tido desfechos semelhantes às não infectadas. / Introduction: A new Influenza virus stem, H1N1, determined a pandemic in 2009 with great global repercussions. This virus infected mainly young adults and children under two years of age with marked increase in morbimortality when compared with annual rates. Objective: To analyze epidemiological and clinical characteristics of the infection by influenza A (H1N1) virus in children, in order to improve knowledge to a better approach in future pandemics. Methods: Cross section study with review of patient records for all children, between zero and 16 years, hospitalized with flu-like disease at Hospital de Clínicas de Porto Alegre (HCPA) in 2009. Identification of H1N1 virus was done through PCR technique on reference laboratory. Results: One hundred ninety-one children were hospitalized with suspected H1N1 infection. Of these, 83 (43%) patients were tested for the H1N1 virus, 28 (34%) being positive and 55 (66%) negative. H1N1 patients were older, 27 (7-108) versus seven months old (3-32) (p=0,015), all had fever versus 70% of the other group (p=0,015), they arrived at the hospital with lower oxygen hemoglobin saturation, 80% (±20%) versus 95% (±4%) (p<0,001) and when placed in mechanical ventilation they needed greater end expiratory pressures, ten (±3) to five (±1) cm H2O (p=0,001) and inspired oxygen fraction, one (0,65-1) versus 0,4 (0,4-1) (p= 0,053) . There was no difference in terms of need for hospitalization in intensive care unit, need of ventilatory support or death. Conclusion: Children infected by H1N1 were more severely ill at arrival to the hospital, although they had similar outcomes to non-infected patients.

Introdução: O surgimento de uma nova cepa do vírus Influenza A, o H1N1, determinou uma pandemia no ano de 2009, com importante repercussão global. Esse vírus infectou principalmente adultos jovens e crianças menores de dois anos com grande aumento na morbimortalidade quando comparado com as taxas anuais decorrentes do influenza. Objetivo: Avaliar as características epidemiológicas e clínicas da infecção pelo vírus influenza A (H1N1) em crianças, a fim de agregar conhecimento para melhor abordagem em futuras pandemias. Métodos: Estudo de corte transversal com revisão dos prontuários de todas as crianças, entre zero e 16 anos, hospitalizadas com quadro gripal no Hospital de Clínicas de Porto Alegre (HCPA) em 2009. A identificação do vírus H1N1 foi feita através de Reação em Cadeia da Polimerase (PCR) em laboratório de referência. Resultados: Cento e noventa e uma crianças foram internadas com suspeita de infecção pelo H1N1, destas, 83 (43%) foram submetidos à pesquisa do vírus H1N1, sendo 28 positivos (34%) e 55 negativos (66%). Os pacientes positivos para H1N1 eram mais velhos, 27 (7-108) versus sete (3-32) meses (p=0,015), todos apresentaram febre versus 70% do outro grupo (p=0,015), chegaram ao hospital com menor saturação de hemoglobina, 80% (±20%) versus 95% (±4) (p<0,001) e precisaram de maior pressão expiratória final, dez (±3) versus cinco (±1) cm H2O (p=0,001) e de maior fração inspirada de oxigênio, um (0,65-1) versus 0,4 (0,4-1) (p=0,053) quando colocados em ventilação mecânica. Não houve diferença quanto à necessidade de internação em unidade de terapia intensiva, indicação de suporte ventilatório, tempo de internação e óbito. Conclusão: As crianças acometidas pelo H1N1 apresentaram-se mais graves, embora tenham tido desfechos semelhantes às não infectadas. / Introduction: A new Influenza virus stem, H1N1, determined a pandemic in 2009 with great global repercussions. This virus infected mainly young adults and children under two years of age with marked increase in morbimortality when compared with annual rates. Objective: To analyze epidemiological and clinical characteristics of the infection by influenza A (H1N1) virus in children, in order to improve knowledge to a better approach in future pandemics. Methods: Cross section study with review of patient records for all children, between zero and 16 years, hospitalized with flu-like disease at Hospital de Clínicas de Porto Alegre (HCPA) in 2009. Identification of H1N1 virus was done through PCR technique on reference laboratory. Results: One hundred ninety-one children were hospitalized with suspected H1N1 infection. Of these, 83 (43%) patients were tested for the H1N1 virus, 28 (34%) being positive and 55 (66%) negative. H1N1 patients were older, 27 (7-108) versus seven months old (3-32) (p=0,015), all had fever versus 70% of the other group (p=0,015), they arrived at the hospital with lower oxygen hemoglobin saturation, 80% (±20%) versus 95% (±4%) (p<0,001) and when placed in mechanical ventilation they needed greater end expiratory pressures, ten (±3) to five (±1) cm H2O (p=0,001) and inspired oxygen fraction, one (0,65-1) versus 0,4 (0,4-1) (p= 0,053) . There was no difference in terms of need for hospitalization in intensive care unit, need of ventilatory support or death. Conclusion: Children infected by H1N1 were more severely ill at arrival to the hospital, although they had similar outcomes to non-infected patients.

Introdução: O surgimento de uma nova cepa do vírus Influenza A, o H1N1, determinou uma pandemia no ano de 2009, com importante repercussão global. Esse vírus infectou principalmente adultos jovens e crianças menores de dois anos com grande aumento na morbimortalidade quando comparado com as taxas anuais decorrentes do influenza. Objetivo: Avaliar as características epidemiológicas e clínicas da infecção pelo vírus influenza A (H1N1) em crianças, a fim de agregar conhecimento para melhor abordagem em futuras pandemias. Métodos: Estudo de corte transversal com revisão dos prontuários de todas as crianças, entre zero e 16 anos, hospitalizadas com quadro gripal no Hospital de Clínicas de Porto Alegre (HCPA) em 2009. A identificação do vírus H1N1 foi feita através de Reação em Cadeia da Polimerase (PCR) em laboratório de referência. Resultados: Cento e noventa e uma crianças foram internadas com suspeita de infecção pelo H1N1, destas, 83 (43%) foram submetidos à pesquisa do vírus H1N1, sendo 28 positivos (34%) e 55 negativos (66%). Os pacientes positivos para H1N1 eram mais velhos, 27 (7-108) versus sete (3-32) meses (p=0,015), todos apresentaram febre versus 70% do outro grupo (p=0,015), chegaram ao hospital com menor saturação de hemoglobina, 80% (±20%) versus 95% (±4) (p<0,001) e precisaram de maior pressão expiratória final, dez (±3) versus cinco (±1) cm H2O (p=0,001) e de maior fração inspirada de oxigênio, um (0,65-1) versus 0,4 (0,4-1) (p=0,053) quando colocados em ventilação mecânica. Não houve diferença quanto à necessidade de internação em unidade de terapia intensiva, indicação de suporte ventilatório, tempo de internação e óbito. Conclusão: As crianças acometidas pelo H1N1 apresentaram-se mais graves, embora tenham tido desfechos semelhantes às não infectadas. / Introduction: A new Influenza virus stem, H1N1, determined a pandemic in 2009 with great global repercussions. This virus infected mainly young adults and children under two years of age with marked increase in morbimortality when compared with annual rates. Objective: To analyze epidemiological and clinical characteristics of the infection by influenza A (H1N1) virus in children, in order to improve knowledge to a better approach in future pandemics. Methods: Cross section study with review of patient records for all children, between zero and 16 years, hospitalized with flu-like disease at Hospital de Clínicas de Porto Alegre (HCPA) in 2009. Identification of H1N1 virus was done through PCR technique on reference laboratory. Results: One hundred ninety-one children were hospitalized with suspected H1N1 infection. Of these, 83 (43%) patients were tested for the H1N1 virus, 28 (34%) being positive and 55 (66%) negative. H1N1 patients were older, 27 (7-108) versus seven months old (3-32) (p=0,015), all had fever versus 70% of the other group (p=0,015), they arrived at the hospital with lower oxygen hemoglobin saturation, 80% (±20%) versus 95% (±4%) (p<0,001) and when placed in mechanical ventilation they needed greater end expiratory pressures, ten (±3) to five (±1) cm H2O (p=0,001) and inspired oxygen fraction, one (0,65-1) versus 0,4 (0,4-1) (p= 0,053) . There was no difference in terms of need for hospitalization in intensive care unit, need of ventilatory support or death. Conclusion: Children infected by H1N1 were more severely ill at arrival to the hospital, although they had similar outcomes to non-infected patients.

Les virus influenza comptent parmi les agents pathogènes les plus importants à l'origine d'infections respiratoires graves. Les antiviraux jouent un rôle important dans les infections grippales sévères. Cependant, un usage monothérapeutique de l'oseltamivir (OS), un inhibiteur de la neuraminidase (INA), chez les personnes immunosupprimées (IS) favorise l'émergence fréquente de résistance à ce médicament, ce qui entraîne une mortalité importante chez les individus IS. En revanche, les inhibiteurs du complexe polymérase (baloxavir marboxil (BXM) et/favipiravir (FA)) n'ont pas été bien étudiés en tant que traitement chez les hôtes IS. Par conséquent, une nouvelle stratégie thérapeutique permettant d'éradiquer rapidement les virus influenza chez les patients IS est nécessaire. La combinaison d'antiviraux ciblant différentes étapes du cycle de vie viral peut augmenter l'efficacité antivirale et réduire la fréquence de la résistance aux médicaments par rapport à la monothérapie. Nous avons, dans un premier temps, adapté une souche contemporaine A/Switzerland/9715293/2013 (H3N2) chez des souris C57BL/6 après 15 passages. La caractérisation moléculaire du variant adapté a démontré que la combinaison des mutations dans les gènes PA (K615E) et HA (N122D, N144E, N246K et A304T) constituent des marqueurs important de virulence dans ce modèle. Dans un second temps, nous avons évalué l'efficacité de la combinaison d'OS avec des inhibiteurs de polymérase (BXM et/ou FA) contre le virus influenza A/H3N2 chez des souris pharmacologiquement IS. Nous avons trouvé que les approches de monothérapies avec l'OS ou le FA ont seulement retardé la mortalité, alors qu'un effet synergique sur la survie (80 % de survie) et une réduction des titres viraux pulmonaires ont été observés dans le groupe de la thérapie combinée (OS/FA) comparativement à l'OS. Le BXM simple ou en combinaison avec l'OS et/ou FA a engendré une protection complète (100 % de survie) et une réduction significative des titres viraux pulmonaires. Nous avons également observé que les traitements monothérapeutiques avec l'OS et le BXM ont induit les mutations E119V dans et I38T dans les gènes de la neuraminidase et de la polymérase acide (PA), respectivement, alors que les combinaisons n'ont pas induit de mutation de résistance. Mon projet de thèse démontre que le régime thérapeutique à doses multiples du BXM seul offrait des avantages supérieurs à ceux des monothérapies à base d'OS et de FA contre les virus A/H3N2. De plus, nous avons confirmé le potentiel de la thérapie combinée pour réduire le risque d'émergence de la résistance au sein des populations IS. Le BXM, approuvé en octobre 2018 par la FDA, est un antiviral ciblant la PA des virus influenza. La substitution I38T dans la PA est le marqueur moléculaire de résistance au baloxavir le plus répandu chez les virus de la grippe saisonnière. Le risque pour la santé publique posé par les variants présentant une sensibilité réduite au baloxavir dépend de leur capacité à se répliquer et à se transmettre dans la communauté par rapport aux virus sensibles. Nos objectifs étaient d'étudier : (1) L'impact de la mutation PA/I38T sur la capacité réplicative et la virulence des virus A/Québec/144147/09 (H1N1) et A/Switzerland/9715293/2013 (H3N2) in vitro et in vivo. (2) Le potentiel de transmission par contact direct des virus A/H3N2 de type sauvage (PA/I38) et mutant (PA/I38T) dans un modèle de cochon d'inde afin de prédire la transmissibilité dans la communauté. Nous avons trouvé que la substitution PA/I38T ne modifiait pas la capacité de réplication in vitro dans les cellules ST6GalI-MDCK et A549 dans les deux backgrounds génétiques. Chez les souris, les virus A/H1N1pdm09 et A/H3N2 recombinants portant la mutation PA/I38T ont induit des titres viraux pulmonaires et des pertes de poids comparables au virus sauvage. La substitution PA/I38T-H3N2 a également induit des titres comparables à ceux des virus sauvages dans les lavages naseaux des cochons d'inde et les deux virus se sont transmis de manière équivalente par contact direct. Nous avons trouvé une légère dominance du génotype sauvage (I38) par rapport au génotype mutant (38T) chez des cochons d'inde co-infectés par des mélanges de virus de type sauvage et mutant. Cependant, chez les souris, le génotype mutant a plutôt dominé le génotype sauvage. Collectivement, les virus influenza A contemporains portant la mutation PA/I38T peuvent conserver un niveau significatif de fitness viral, ce qui justifie la surveillance de leur dissémination. / Influenza viruses are among the most important pathogens causing severe respiratory diseases. Antiviral agents are recommended for treatment of severe influenza infections. Virus clearance is usually delayed among high-risk populations, including immunosuppressed (IS) patients. To inhibit virus replication in these individuals, the prolonged use of Oseltamivir (OS), a NA inhibitor (NAI), is required, which frequently leads to the emergence of drug-resistant viruses. In contrast, polymerase inhibitors (baloxavir marboxil (BXM) and favipiravir (FA)) have not been well studied as treatment in IS individuals. Therefore, a new therapeutic strategy to rapidly eradicate influenza viruses in IS patients is needed. Combination therapy with compounds targeting multiple steps in the viral life cycle may improve treatment outcomes and prevent the emergence of resistance. First, we generated a mouse-adapted A/H3N2 virus (A/Switzerland/9715293/2013 (H3N2) by 15 serial passages of mouse lungs. Molecular characterization of the adapted variant demonstrated that the combination of PA (K615E) and HA (N122D, N144E, N246K and A304T) mutations were critical markers of virulence in this model. In a second step, we evaluated the efficacy of OS and polymerase inhibitors (BXM and/or FA) combinations against influenza virus A/H3N2 infections in pharmacologically IS mice. We found that all untreated animals died. OS and FA monotherapies only delayed mortality, while we observed a synergistic improvement on survival (80 %) and lungs viral titers reduction in the OS/FA group compared to OS. BXM alone or in double/triple combination provided a complete protection and significantly reduced lungs viral titers. OS and BXM monotherapies induced the NA/E119V and PA/I38T substitutions, respectively, while we did not detect mutation with combinations. Our study confirms that the multiple dose regimen of BXM alone provided superior benefits compared to OS and FA monotherapies and suggests the potential for drug combinations to reduce the incidence of resistance. BXM, licensed in 2018 by the FDA, is an antiviral targeting the highly conserved cap-dependent endonuclease region of the PA gene. The PA/I38T substitution is the most common molecular marker of BXM resistance in seasonal influenza viruses. The public health risk posed by viruses with reduced susceptibility to BXM depends on their potential capacity to replicate and transmit in the community compared to susceptible viruses. We have two principal objectives: (1) To evaluate the impact of the PA/I38T substitution on the replicative capacity and virulence of A/Quebec/144147/09 (H1N1) and A/Switzerland/9715293/2013 (H3N2) viruses in vitro and in vivo. (2) To evaluate direct contact transmission of wild-type (PA/I38) and mutant (PA/I38T) A/H3N2 viruses in a guinea pig model to predict transmission in the community. We found that the PA/I38T substitution did not alter the in vitro replication capacity in ST6GalI-MDCK and A549 cells in both genetic backgrounds (A/H1N1pdm09 and A/H3N2). In mice, recombinant A/H1N1pdm09 and A/H3N2 viruses carrying the PA/I38T substitution induced viral titers and weight losses comparable to wild-type virus. The PA/I38T-H3N2 substitution also induced titers comparable to wild-type viruses in guinea pig nasal wash samples and both viruses were transmitted equivalently by direct contact. We found a slight dominance of the wild type (I38) over the mutant (38T) genotype in guinea pigs co-infected with mixtures of wild type and mutant viruses. However, in mice, the mutant genotype rather dominated the wild type virus. Collectively, contemporary influenza A viruses carrying the PA/I38T mutation may retain a significant level of viral fitness, warranting their monitoring in the community.