SUMMARYThe avian herpesviruses infectious laryngotracheitis virus (ILTV) and herpesvirus of turkeys (HVT), as well as the mammalian herpesvirus pseudorabies virus (PRV) were able to provide complete helper activity for the production of infectious avian adenoassociated virus (AAAV) in chicken cells. The presence of AAAV in the infected chicken cell reduced the multiplication of HVT. ILTV or PRV, however, were not affected if used as helper viruses. Infectious AAAV was determined by an indirect immunofluorescence assay and infectious herpesvirus by plaque assays.Avian adeno-associated virus (AAAV) is a defective parvovirus which grows efficiently only in chicken cells co-infected with avian adenovirus (Yates et al., 1973;Pronovost et al., 1979). This report investigates whether or not other avian viruses can provide the helper function required for active multiplication of AAAV in chicken cells. We demonstrate that two avian herpesviruses, infectious laryngotracheitis virus (ILTV) and herpesvirus of turkeys (HVT), as well as pseudorabies virus (PRV), a herpesvirus of mammalian origin, provide complete helper activity for AAAV. A helper activity of human herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) for human AAV has been demonstrated (Buller et al., 1981). We also show that the growth of HVT is reduced in chicken cells co-infected with HVT and AAAV. However, there is no inhibitory effect on the multiplication of the helper virus if PRV or ILTV is used as helper.The AAAV strain ATCC VR-865 was propagated in embryonated chicken eggs (VALO, Cuxhaven, F.R.G.) by co-infection with fowl adenovirus serotype l (CELO virus) and prepurified by 1,1,2-trichlorotrifluoroethane treatment, followed by centrifugation in one discontinuous and two CsC1 equilibrium density gradients. The infectious AAAV particles which band in CsC1 at a density of 1.39 to 1.40 g/ml were collected. The remaining CELO virus in this AAAV preparation was removed by immunoprecipitation using rabbit anti-CELO virus serum and Protein A-Sepharose (Bauer & Monreal, 1985). Serum proteins in the purified AAAV were removed by an additional equilibrium density gradient. The final virus suspension was dialysed against cell culture Medium 199 with Earle's salts.The non-pathogenic ILTV strain ASL (Gelenczei & Marty, 1964) was plaque-purified three times and propagated in primary chicken kidney cells (CKC). The FC 126 strain of HVT (Witter et al., 1970) was obtained as a live vaccine against Marek's disease from E. Vielitz (TAD, Cuxhaven, F.R.G.). The lyophilized virus material was dissolved in SPGA stabilizer, pH 6.5, containing 0.218 M-sucrose, 0'0038 M-monopotassium phosphate, 0.0072 M-dipotassium phosphate, 0.0049 M-monosodium glutamate and 1 ~ bovine serum albumin (Calnek et al., 1970). The DEK strain of PRV (kindly provided by H. Ludwig, Berlin, F.R.G.) was plaquepurified three times and propagated in secondary chicken embryo fibroblasts (CEF).To study the growth cycle of AAAV with ILTV as helper virus and the influence of AAAV on the multiplication ...

The immune response after vaccination with infectious bronchitis virus (IBV) under field conditions was measured by the ELISA, haemagglutination-inhibition (HI) and agar-gel precipitin (AGP), tests. Vaccinations were performed in three flocks and one experimental group via the drinking water with the vaccine strains H 120 and H 52. In each flock 40 random serum samples were taken every 2 weeks and tested individually. In the experimental group blood samples were collected every week from each of the 10 chickens. The primary vaccination with H 120 resulted in a rapid increase of antibody titre as detected by ELISA followed by a slow decrease over the next few weeks. By the HI and AGP tests no antibody responses could be seen after this primary vaccination. Revaccination with the H 52 strain provoked a further increase in ELISA titres. In the experimental group, and in flock W, a similar increase occurred by the HI test and precipitating antibodies appeared. The formation of HI antibodies in flock T (nipple waterers) was somewhat retarded and precipitating antibodies were just detectable. In flock F revaccination did not result in the immediate production of HI and AGP antibodies. However, 6 weeks after revaccination a significant rise in ELISA, HI and AGP antibodies was observed, probably as the result of a field infection. It was demonstrated that, based on the higher sensitivity, the ELISA test is more suitable than HI and AGP to monitor antibody responses to vaccination against infectious bronchitis. Strain specificity in the HI test is discussed as a reason for its failure to detect antibodies after primary vaccination with the highly attenuated vaccine strain H 120.

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