Search

Restriction enzyme studies have been used to divide the fowl adenoviruses (FAV) into 5 groups - A, B,C,D and E. More detailed restriction enzyme studies of a series of group E FAV field isolates showed that these methods could differentiate between mildly and hypervirulent FAV belonging to this group. We have mapped the genomes of the hypervirulent (CFA 40) and two of the mildly virulent FAV (CFA 44 and CFA 3), using 11 different restriction enzymes: HindIII, BglII, XbaI, NdeI, SpeI, DraI, NotI, StuI, NheI, SfiI, and AvrII. Comparison of the three maps showed that the CFA 3 genome was approximately 3.5 kb smaller than that of CFA 44 and CFA 40. This size difference was discounted as a likely cause of the reduced pathogenicity of CFA 3 as the other mildly virulent virus, CFA 44, was the same size as the hypervirulent CFA 40. Other variations between the three viruses occurred in the region of the hexon and 100 K genes, but further studies are required to determine the significance of these variations in pathogenicity.

Some discussion has centered on whether fowl adenovirus (FAV) serotypes 4 and 10 are distinct serotypes or in fact should be reclassified as a single serotype. We have undertaken a detailed characterisation of representatives of both serotypes in order to determine if types 4 and 10 should be grouped together or retained as distinct serotypes. Examination at the genomic level has revealed considerable similarities and few differences between these 2 serotypes. DNA cross-hybridization failed to distinguish between them and restriction enzyme analysis demonstrated limited sequence differences. In vivo studies demonstrated the cross-protection afforded by a natural route vaccination with serotype 4 FAV when chickens were challenged with serotype 10 FAV. On the basis of these studies it is suggested that these FAV serotypes be combined in future FAV classification. Physical maps for both serotype 4 and 10 have been constructed using the restriction enzymes Hpa I, Dra I, Nde I, Xba I and Not I for both serotypes and in addition Eco RI, Sfi I, Sma I and BglII for serotype 10.

Antisera were raised in chickens to six group E fowl adenoviruses (FAV) which have been divided into a highly virulent (hypervirulent) and a mildly virulent subgroup using restriction endonuclease analysis. Virus neutralisations showed that these two distinct restriction endonuclease groups were distinguishable serologically, and indicated a possible vaccine candidate for use against the hypervirulent FAV. The suitability of this candidate was established in challenge experiments where vaccination with this virus protected against challenge from another hypervirulent virus as well as one of the mildly virulent FAV.