Monitoring Marek's disease virus in broiler flocks using standard and real-time quantitative PCR of spleen and dust samples

Abstract

We report the monitoring of Marek's Disease virus (MDV) on two unvaccinated commercial broiler farms using standard and real-time polymerase chain reaction (PCR). Standard (non-quantitative) PCR for MDV in spleen samples from five birds per shed (three sheds per farm), sampled at approximately weekly intervals, was compared with standard PCR of DNA extracted from shed dust, and quantitative real-time PCR (qPCR) of the same dust samples. The two farms could not be easily differentiated on the basis of standard PCR tests of spleen with the first positive spleens detected at days 27 and 25 on Farms A and B respectively, and 100% positives in a shed reached on days 41 and 32 respectively. Dust became positive to standard PCR at days 34 and 19 (one shed only) respectively for the two farms suggesting a greater MDV load on Farm B. Real-time qPCR of dust samples detected MDV in all dust samples (earliest day 19) and showed an exponential increase in virus content over time. It also revealed clear differences between farms with dust from Farm B containing approximately 10 times more MDV than that of Farm A. This was associated with reduced performance on Farm B as determined by FCR (2.086 v 2.203 for A and B respectively) and late mortality after day 28 (1.96 v 4.03%). These preliminary data suggest that q-PCR of poultry dust will prove useful for the routine monitoring of MD status in broiler flocks.