Effects of reticuloendotheliosis virus on the response of chickens to infectious laryngotracheitis virus

Abstract

SUMMARYEffects of reticuloendotheliosis virus (REV) on the response to infectious laryngotracheitis virus (ILTV) were investigated in young chickens with and without maternally derived antibody (MAb) to REV. In the first experiment a group of 1-day-old chickens without REV MAb were inoculated at 1 day of age with REV whilst another group of similar chickens were left uninoculated. All chickens were vaccinated with ILTV at 7 days of age. There was a significantly higher proportion of infectious laryngotracheitis (ILT) post-vaccinal ophthalmia (p.v.o.) in the group inoculated with REV.In the second experiment chickens with and without MAb to REV were inoculated at 1 day old with REV. These chickens, together with others not inoculated with REV, were vaccinated with ILTV isolate SA-2 8 days later. A virulent ILTV isolate, G, was used to challenge all the chickens 20 days after vaccination. Again the chickens without MAb to REV inoculated with REV showed a higher proportion of ILT p.v.o. and a significantly higher mortality rate due to ILT following vaccination. In the chickens inoculated with REV at 1 day of age and not vaccinated but challenged with ILTV there was a significantly higher mortality and rate of clinical signs due to ILT in those birds without than in those with REV MAb. In both experiments chickens from REV negative parents were found to be free of REV neutralising MAb. However, only 30% of chickens originating from a flock known to be infected with REV had a titre of 1/40 or higher. In spite of this, this group was significantly more resistant than the group without REV MAb to the immunosuppressive effect of inoculation at 1 day old with REV. This was demonstrated by their lower susceptibility (i.e. less p.v.o. and mortality) to the vaccination and challenge with ILTV. Chickens without REV MAb developed neutralising antibodies within 2 weeks of inoculation with REV. Irrespective of the REV MAb status 1-dayold chickens inoculated with REV were viraemic within a week.

Field isolates of fowlpox virus contaminated with reticuloendotheliosis virus

“…However, the age of infection is important, as birds that are infected transovarially or in their first week of life are immunodepressed, while those that are infected at 3 weeks of age or older have little evidence of clinical immunodepression (Le et al, 1983). Motha (1982) also reported cases of infectious laryngotracheitis (ILT), when day-old chickens without maternal antibodies against REV were vaccinated with ILT vaccine after being exposed to REV. Explanations of the current fowlpox situation in Australia, with respect to REV contamination, include the possibility that contaminated field isolates may be derivatives of a contaminated vaccine used in some regions of NSW, where the poultry industry is centred.…”

Distribution of virus and tumour formation in ducks experimentally infected with reticuloendotheliosis virus

“…Buffy coat cells, 0.2 ml of serum, 1.0 ml of thin albumen or cell-free tissue homogenates were used for virus isolation. The preparation and handling of buffy coat cells have been described previously (Motha, 1982). The thin albumen samples were handled in a similar manner to the buffy coat cells.…”

“…REV viraemia was determined by the duck embryo fibroblast (DEF) plaque test (Motha, 1982) and indirect immunofluorescent antibody (IFA) test (Bagust and Dennett, 1977). When viraemic samples were detected in the DEF plaque test, a virus neutralisation test was carried out to determine the specificity of the cytopathic effect (CPE).…”

“…Ltd., Ingleburn, New South Wales, Australia. The preparation of cell cultures and virus stock and storage of the virus have been described previously (Motha, 1982).…”

“…The detection of neutralising antibodies was carried out as described previously (Motha and Egerton, 1983). For end-point titration the serum or plasma samples were further diluted in serial two-fold steps and the titre was expressed as 50% end-point (Reed and Muench, 1938).…”