ABSTRACT
Fowl adenovirus (FAdV) is distributed worldwide and causes economic losses in the poultry industry. The objectives of this study were to determine the hexon and fiber gene changes in an attenuated FAdV isolate from Malaysia in specific pathogen-free chicken embryonated eggs (SPF CEE) and its infectivity in commercial broiler chickens. SPF CEE were inoculated with 0.1 mL FAdV inoculum via the chorioallantoic membrane (CAM) for 20 consecutive passages. The isolate at passage 20 (E20), with a virus titer of 10(8.7)TCID₅₀/mL (TCID₅₀, 50% tissue culture infective dose), was inoculated (0.5 mL) into one-day-old commercial broiler chicks either via oral or intraperitoneal routes. The study demonstrated that 100% embryonic mortality was recorded from E2 to E20 with a delayed pattern at E17 onwards. The lesions were confined to the liver and CAM. Substitutions of amino acids in the L1 loop of hexon at positions 49 and 66, and in the knob of fiber at positions 318 and 322 were recorded in the E20 isolate. The isolate belongs to serotype 8b and is non-pathogenic to broiler chickens, but it is able to induce a FAdV antibody titer. It appears that molecular changes in the L1 loop of hexon and the knob of fiber are markers for FAdV infectivity.
Subject(s)
Adenoviridae , Amino Acids , Chickens , Chorioallantoic Membrane , Eggs , Fowl adenovirus A , Liver , Malaysia , Mortality , Ovum , Poultry , Serogroup , Specific Pathogen-Free Organisms , Viral LoadABSTRACT
The avirulent QU strain of fowl adenovirus, a member of duck adenovirus type 1, could be a potential vector in recombinant vaccine development. To identify a non-essential region for replication of QU virus, a 3.4 kb fragment near the E4 region of QU virus genome was amplified by PCR to construct a plasmid pADGFP, in which ORF1, ORF8 and ORF9 was replaced with a system expressing enhanced green fluorescence protein. Further, a recombinant virus rQUGFP was constructed by homologous recombination after pADGFP and QU virus were co-transfected into chick embryo fibroblast. The one step growth curve of the rQUGFP was found to be identical with that of parent QU virus and the TCID50 titers of different generation recombinants maintained stable. These findings suggest that the region including ORF1, ORF8 and ORF9 of QU virus genome is dispensable for virus replication, and the foreign gene inserted into virus genome can be efficiently and stably expressed. The work lays the foundation for further studies of developing this virus as a vector of recombinant vaccine.
Subject(s)
Animals , Adenovirus E4 Proteins , Genetics , Allergy and Immunology , Fowl adenovirus A , Classification , Genetics , Genes, Viral , Genetics , Genetic Vectors , Genetics , Open Reading Frames , Genetics , Recombination, Genetic , Transfection , Vaccines, Synthetic , Genetics , Allergy and Immunology , Viral Vaccines , Genetics , Allergy and Immunology , Virus ReplicationABSTRACT
In the present study characterisation has been done for six group I fowl adenoviruses (FAV) isolated from outbreaks of infectious hydropericardium (IHP) of chickens that occurred in different states/regions of India during the years 1994-98. These six viruses were identified as FAV serotype 4 by virus neutralisation and restriction endonuclease analyses. Antigenic analyses of the viruses revealed close relationship (R-values 0.93-0.96). Under the experimental conditions, we have been able to induce IHP using FAV serotype 4 isolate AD: 411 and were also able detect FAV antigens in myocardial tissues by immunofluorescence assay (a new observation), an indication that IHP causing FAV serotype 4 strain replicate in myocardial tissue. Restriction endonuclease analysis of the viral genomes (approximately 46 Kb), using Hind III, Sma I, Xba I, Bam HI, Pst I and Dra I produced identical genetic profiles. Pst I and Bam HI profiles for these six vitus isolates were identical to those published earlier for an IHP causing Pakistani FAV serotype 4 isolate KR31. The identical genetic profiles of viruses, chronology of the outbreaks of IHP in Pakistan during 1989 onward and later in Jammu and Kashmir, India (1994), suggest that FAV serotype 4 isolates involved in outbreaks of IHP in India had probably spread from Pakistan. In order to prevent further spread and economic losses due to IHP in India, based on the antigenic relatedness data in this paper, any one of the six studied FAV serotype 4 isolates can be used as a candidate for mass production of CEH culture based killed vaccine.