Experimental Infections of Wild Birds with the Viruses of Eastern Equine Encephalitis, Newcastle Disease and Vesicular Stomatitis

Abstract

Received for publication April 7, 1959. * On leave from the Central Institute of Hygiene, Zagreb, Yugoslavia. Paper NS 270 from the Department of Veterinary Science, University of Wisconsin, Madison, published with the approval of the director of the Wisconsin Agricultural Experiment Station_ sin. The crows, hawks and owl were captured in southern Wisconsin by personnel of the Wisconsin Conservation Department. All birds appeared healthy at the beginning of the experiments. The eastern equine encephalitis virus (EEEV) used was originally isolated in 1956 from the brain of a horse which died during an encephalitis epizootic in southeastern Georgia. Allantoic fluids from the thirteenth and twenty-third serial passages in chicken embryos were used in these experiments. The vesicular stomatitis virus (VSV) used was the Wisconsin strain (New Jersey serotype) isolated from a cow in 1949 and transmitted serially in chicken embryos. The Newcastle disease virus (NDV) was Texas GB strain isolated from an outbreak of severe nervous-respiratory disease in chickens in 1948 and maintained by serial passage in chicken embryos. The routes of viral exposure used in the experiments were oral, subcutaneous, intracardial and intracerebral. Dosage varied according to the route of exposure employed and the estimated susceptibility of the individual bird. Birds were visually examined at least once daily after viral exposure to record clinical signs of illness. Body temperatures were not measured, since it was felt that the excitement produced by handling would greatly influence thermometer readings. Blood was drawn on alternate days after infection and examined for evidence of viremia. Fecal samples obtained by cloacal washing were collected daily from crows exposed to the viruses by ingestion of infected chicken embryos. Immune response was judged on the basis of virus neutralization (VN) tests on paired pre-exposure and convalescent serums. Convalescent serums were usually collected on the fourteenth day post exposure. Neutralization indices of 50 or higher in convalescent serums were considered indicative of infection and in birds which possessed no antibody before experimental exposure, this was recorded as a positive immune response. Most of the birds which did not die as a result of the infections were killed by bleeding on the fourteenth day post exposure and tissues, usually brain, lung, liver and spleen, were examined for histopathology and viral content. Tissues were prepared for histopathological examination by