2009, Islam, Afm Fakhrul, Walkden-Brown, Steve W, Groves, Peter John, Wells, Ben

An experiment was conducted to develop and optimize a chicken bioassay to detect the presence of infective viral pathogens in poultry litter from a variety of sources. The experiment also aimed to determine the effect of type of chickens and age of exposure to litter on the level of viral infectivity. The bioassay detected chicken anaemia virus, infectious bursal disease virus and fowl adenovirus from chicken litters. SPF chickens showed higher sensitivity than commercial broiler chickens without any effect of age of exposure, however, the assay was more sensitive in broiler chickens when exposed at day 8. We conclude that the bioassay based on exposure of day-old SPF chickens is a viable assay of viral infectivity of poultry litter.

2008, Islam, Afm Fakhrul, Walkden-Brown, Steve William, Groves, Peter John, Underwood, G J

Two experiment in commercial broiler chickens vaccinated with herpesvirus of turkeys (HVT) and challenged with Marek's disease virus (MDV) investigated the effects of the vaccination-to-challenge interval (VCI) on vaccinal protection against Marek's disease, and the kinetics of MDV and HVT load in the spleen and feather dander determined using real-time quantitative polymerase chain reaction. Experiment 1 in isolators tested VCI of 2, 4 and 7 days, while Experiment 2 in floor pens tested VCI of 0, 2, 4, 7 and 10 days. MDV challenge induced gross Marek's disease lesions in 14% to 74% of chickens by 56 days post-challenge. Vaccinal protection increased from ~40% too ~80% with increasing VCI between days 2 and 7 in both experiments, but not thereafter. MDV was detected in both the spleen and dander at 7 days post-challenge and increased rapidly to approximately 21 days post-challenge, after which levels plateaued, rose or fell gradually depending on treatment. HVT was also shed in significant amounts, 1 to 2 logs lower than for MDV, with a clear peak around 14 to 21 days post-vaccination. Vaccination significantly reduced the log₁₀MDF load in the spleen (vaccination, 2.99±0.20/10⁶ spleen cells; unvaccinated, 4.60±0.23/10⁶ spleen cells) and dander (vaccinated, 5.28±0.13/mg; unvaccinated, 6.00±0.18/mg) from infected chickens. The MDV load had a significant negative association with the VCI and the level of vaccinal protection. Measurement of dander production in Experiment 1 and the dust content of air in Experiment 2, combined with determination of the MDV load in these, enabled estimation of total daily shedding rates of MDV per chicken and of the MDV load in air for the first time.

2003, Islam, Afm Fakhrul, Groves, Peter John, Walkden-Brown, Steve William, Arzey, K E, Burgess, Susan

Automated 'in ovo' vaccination (IOJ) against Marek's disease in broiler chickens is now a routine practice in the poultry industry. This method deposits vaccine mostly into the extra-embryonic (EE) spaces around the embryo, principally the amnion. In earlier experiments of ours, manual EE (MEE) vaccine deposition has not produced good protection in contrast to the apparent efficacy of the automated 'in ovo' method. Two experiments are reported, one confirming this difference in protection and the other demonstrating that there are significant differences in the precise site of vaccine deposition between the two methods, with a higher incidence of allantoic deposition in the case of MEE (25.5%) compared to OIJ (5.7%). However, this finding alone cannot explain the difference in protection between the two methods. We suggest that different methods of vaccinal virus uptake from the amnion may be involved.

2007, Islam, Afm Fakhrul, Walkden-Brown, Steve William, Groves, Peter John, Underwood, G J

Objectives: To examine the effects of varying the doses of turkey herpesvirus (HVT) vaccine and Marek's disease virus (MDV) challenge at two intervals after vaccination on the protection of chickens against challenge with MDV. Design and procedure: Experiment 1, a dose response study, consisted of 11 doses of HVT vaccine administered at hatch followed by challenge with 100 plaque forming units (pfu) of MDV 5 days post vaccination. Experiment 2, a 2 x 6 x 2 factorial design, included two HVT vaccine types, six different doses of HVT vaccine and 50 pfu and 200 pfu of MDV challenge 2 days post vaccination. All chickens were reared up to day 56 post challenge when all survivors were killed humanely. Dead and killed chickens were examined for gross MD tumours. Results: Experiment 1 showed a significant positive linear relationship between dose of HVT vaccine and protective index in chickens challenged 5 days post vaccination. However the range of protective index observed was limited. In Experiment 2 neither HVT vaccine provided significant protection at any dose. There was no significant effect of vaccine type or MDV challenge dose on overall protection against challenge. Chickens challenged with 200 pfu of MDV had significantly higher mortality and MD incidence than those with 50 pfu. Conclusions: HVT vaccine dose had a significant impact on protective index, but vaccination to challenge interval appeared to have greater impact on the protective efficacy of vaccination. A fourfold increase in challenge dose increased mortality rate and incidence of MD.

2012, Walkden-Brown, Steve W, Groves, Peter John

Since 2004 a major Australian poultry company in has used routine monitoring for MDV serotype 1 (MDV1) in poultry dust using serotype-specific real-time quantitative PCR (qPCR) as part of their MD management strategy, particularly in one production region. Dust samples are collected from one house for each farm batch at approximately 6 weeks of age. Combined with standard PCR monitoring of in ovo HVT vaccination in spleen samples, the monitoring program allows assessment of broiler vaccination value, assessment of the seasonal pattern of MDV1 presence and evaluation of MDV1 challenge levels over time. In the one region monitored consistently over the period MDV levels in dust have fallen to very low levels in the last two years. Monitoring has also allowed a rapid comparison of MDV1 status in new sections of the operation. Between 2005 and 2011 1487 shed dust samples were analysed for MDV1 by qPCR with 22.5% being positive for MDV overall. The positive rate ranged from a low of 6% in 2007 to 40% in 2010. Mean (±SD) MDV copy number per mg of dust in positive samples was 4.51±3.2 x 105 on the untransformed scale or 3.96±1.14 on the log10 transformed scale. The range in annual averages on the two scales was 0.091 to 13.2 x 105 with peak levels in 2009 reflecting samples from a new region with very high counts. The experience has been that routine monitoring of MDV by qPCR is a useful tool in managing cost effective control of MD in broiler operations.