RESUMEN
Mice and lambs were infected with the LI/I, LI/31 or MA54 strain of louping ill virus (LIV) to provide information relevant to testing the efficacy and biosafety of a new generation of flavivirus vaccines based on a Semliki Forest virus (SFV) vector. Whereas clinical signs and neuropathological lesions were consistently severe in mice, the majority of lambs showed lesions of moderate severity and only lambs with severe lesions were clinically affected. For both species, dispersal of viral antigen occurred along neuronal cell processes, and neuronal degeneration and death were confirmed as central events after infection with LIV. In contrast to lambs, in which most lesions remained localized, mice showed widely dispersed lesions which were associated with less intense leucocytic infiltrates. Among the infiltrating cells, histiocytes predominated and apoptotic forms were prominent in severely affected animals. The intranasal route of infection provided an efficient avenue for entry of LIV into the brain and resulted in lesions which were more severe than those produced by subcutaneous or intraperitoneal inoculation.
Asunto(s)
Virus de la Encefalitis Transmitidos por Garrapatas/patogenicidad , Meningoencefalomielitis Ovina/patología , Enfermedades de los Roedores/patología , Animales , Antígenos Virales/metabolismo , Encéfalo/metabolismo , Encéfalo/patología , Encéfalo/virología , Modelos Animales de Enfermedad , Virus de la Encefalitis Transmitidos por Garrapatas/clasificación , Virus de la Encefalitis Transmitidos por Garrapatas/inmunología , Técnicas para Inmunoenzimas/veterinaria , Etiquetado Corte-Fin in Situ , Meningoencefalomielitis Ovina/metabolismo , Meningoencefalomielitis Ovina/mortalidad , Ratones , Ratones Endogámicos BALB C , Neuronas/metabolismo , Neuronas/patología , Neuronas/virología , Enfermedades de los Roedores/mortalidad , Enfermedades de los Roedores/virología , Ovinos , Tasa de SupervivenciaRESUMEN
The epidemiology of louping-ill in red grouse was studied in northern Britain concentrating on the possible role of other species and mechanisms of disease persistence. This tick borne viral disease caused heavy mortality in red grouse, particularly chicks. Louping-ill induced mortality reduced the strength of the density dependence that generates the tendency of grouse populations to cycle and in some populations may cause population sinks. Four routes of transmission were examined and non-viraemic transmission of virus between ticks cofeeding on hares was considered significant. Field data supported the hypothesis that disease dynamics is influenced greatly by mountain hares, both as passive amplifiers and as hosts for the tick vector. Genetic variation in louping-ill within Britain was small.
Asunto(s)
Vectores Arácnidos/virología , Enfermedades de las Aves/epidemiología , Aves/virología , Meningoencefalomielitis Ovina/epidemiología , Infestaciones por Garrapatas/veterinaria , Garrapatas/virología , Animales , Enfermedades de las Aves/mortalidad , Enfermedades de las Aves/transmisión , Enfermedades de las Aves/virología , Aves/parasitología , Reservorios de Enfermedades , Femenino , Flavivirus/genética , Flavivirus/aislamiento & purificación , Lagomorpha/parasitología , Meningoencefalomielitis Ovina/mortalidad , Meningoencefalomielitis Ovina/transmisión , Meningoencefalomielitis Ovina/virología , Dinámica Poblacional , Prevalencia , ARN Viral/genética , Escocia/epidemiología , Ovinos/virología , Especificidad de la Especie , Infestaciones por Garrapatas/virología , Factores de TiempoRESUMEN
Studies were made to find evidence of louping-ill virus infection in free-living red grouse and relate this to their breeding success. In areas where ticks were abundant 61 (84%) adult grouse had antibody to the virus compared with 1 (10%) in areas where ticks were relatively scarce. Of 162 chicks tested 25 were shown to be viraemic. Infected chicks were of significantly less weight than comparably aged uninfected birds and the probability that they died was much greater than that of uninfected birds. It is concluded that the relatively poor breeding success in areas of high tick numbers was principally due to infection with louping-ill virus. The susceptibility of the red grouse to infection is discussed.