Characterization of field isolates of Newcastle disease virus using antipeptide antibodies.

A recent Australian field isolate of Newcastle disease virus (NDV) was analyzed with antipeptide antibodies capable of differentiating between the sequences at the cleavage activation sites of fusion proteins of different NDV pathotypes. The isolate was found to have the same fusion protein cleavage activation signal as the V4 isolate of the Queensland strain of NDV. However, the isolate failed to react with an antibody specific for the carboxyl-terminal extension on the hemagglutinin/neuraminidase (HN)-protein precursor (HNo-protein) of the V4 isolate and other similar strains (e.g., Ulster and D26). Identity of the fusion protein cleavage activation motif of the isolate was confirmed by chemical analysis of purified fusion protein subunits of the isolate. The combination of a V4-like fusion protein cleavage activation motif but lack of an HNo-protein has not been described before, and the findings indicate that the isolate is a distinct strain of NDV. Analysis of a range of isolates from the state of Victoria, Australia, indicated that similar strains have been present in Australia since at least 1976. Other isolates examined appeared to have fusion protein cleavage activation motifs that could not be defined with the fusion-protein-targeted antibodies. These isolates also appeared to lack the HNo-protein characteristic of the Queensland strain.

Pathogenicity studies with a strain of fowl adenovirus serotype 8 (VRI-33) in chickens.

Experiments were undertaken to study the pathogenesis of VRI-33, a strain of fowl adenovirus serotype 8 isolated from the liver of a broiler chicken with inclusion body hepatitis. A 30% death rate resulted from oral infection of one-day-old specific pathogen free chickens with 10(6) plaque forming units of VRI-33. Chickens 10, 14, 21 and 28 days of age did not die following infection via natural routes but there were some motalities following infection via parenteral routes. Immunodepression by neonatal cyclophosphamide treatment, followed by infection with VRI-33 via non-parenteral routes, caused varying degrees of hepatitis with basophilic intranuclear inclusion bodies in hepatocytes. The mortality rate of cyclophosphamide-treated, VRI-33 infected chickens, was not significantly altered by post-infection temperature stress. Infection with infectious bursal disease virus, followed by infection with VRI-33 via natural routes at 14 days of age, was not associated with mortalities.

The application of the ELISA to the diagnosis and control of avian encephalomyelitis.

An ELISA for measuring serum antibody against avian encephalomyelitis virus (AEV) was evaluated for its application to the diagnosis and control of avian encephalomyelitis (AE). A scoring system was developed for this ELISA (AE ELISA-Index) so that the overall level of antibody in the flock could be presented in a single, convenient number. During suspected outbreaks of disease thought to have been caused by AEV infection, the AE ELISA-Index increased in sequential serum samples. High levels of antibody against AEV were measured in 13 flocks experiencing egg productivity problems. Variable levels of antibody activity against infectious bronchitis virus (IBV) were also observed in 11 of these flocks. The AE ELISA-Index was correlated with the embryo susceptibility test. Application of the AE ELISA has indicated that natural exposure to the virus does not occur in all flocks, and vaccination failures were detected sufficiently early for revaccination to be administered before the onset of lay.

An unusual case of inclusion body hepatitis in a cockerel.

This report describes inclusion body hepatitis in a 12-week-old leghorn-type cockerel. The cockerel had come from a specific-pathogen-free flock and was reared in a positive-pressure isolator until 6 weeks old. Grossly, the cockerel was jaundiced, and the liver was swollen and had small white foci throughout. Histologically, there were foci of hepatic necrosis and basophilic inclusion bodies in the nuclei of numerous hepatocytes. A fowl adenovirus, isolated from the liver, was found to belong to serotype 2/12. The bursa of Fabricius had some degenerative changes, but these were not consistent with infectious bursal disease, nor was there evidence of seroconversion to infectious bursal disease virus in the remaining chickens.

Measurement of antibodies to infectious avian encephalomyelitis virus by ELISA.

An enzyme-linked immunosorbent assay (ELISA) for the measurement of antibody to avian encephalomyelitis virus (AEV) is described. The wells of microtitre trays were coated with antibody to AEV, to which was bound a partially purified AEV preparation as an immunosorbent. The assay described is specific, in that antibody activity was not detectable in specific-pathogen-free (SPF) chickens except following inoculation with AEV. Inoculation of SPF chickens with a number of other viruses did not induce a detectable response. Furthermore, there was agreement between the ELISA and virus neutralisation test in terms of the rank order of a number of test sera and in the positive/ negative classification of sera. Both ELISA and virus neutralisation were capable of detecting an antibody response within 9 days of primary vaccination indicating that the ELISA was of comparable sensitivity to virus neutralisation. The amount of antibody in a sample was estimated relative to a reference serum preparation, and the results recorded as units of antibody activity. Using this method of data expression it has been possible to demonstrate that these assays are reproducible with little within-assay (co-efficient of variation = 5.6%) or between-assay (co-efficient of variation = 9.8%) variation for the mid-range sample.

Serological identification of avian adenoviruses isolated from cases of inclusion body hepatitis in Victoria, Australia.

Sixteen avian adenoviruses isolated from 12 cases of inclusion body hepatitis (IBH), 3 cases of respiratory disease, and a case of ruptured tendons were compared using antisera raised against 9 fowl adenovirus prototype strains. Eleven isolates from livers of birds with IBH were classified into 4 different serological groups: 1) YR36 (type 7)-related; 2) HVI (type 8)-related; 3) Variants--type 6-,7-, and S-related; and 4) Type 50--not closely related to any of the prototype antisera tested. These results indicate that, as in other countries, IBH in Victoria is associated with several serologically distinct adenoviruses. The other five adenovirus isolates were found to be related to CELO (type 1).