Investigations into survival and detection of Marek's disease virus and Infectious laryingotracheitis virus in heaped "pasteurized" litter

Abstract

Spent litter used for successive batches of broilers may be "pasteurized" before reuse by heaping for 7-10 days, inducing peak temperatures often exceeding 60°C. We investigated the temperature-time requirements to inactivate MDV and ILTV in infected litter, and the extent to which inactivation could be predicted by enumerating viral genome using qPCR.A preliminary experiment showed that heating infective litter in a sealed rather than porous bag resulted in loss of qPCR detection of ILTV between 5 and 10 days at 60°C but not at 25°C. In two experiments, chicks were exposed to litter derived from ILTV and MDV infected chicks and treated by heating to various temperatures between 25 and 65°C for 5, 10 or 20 days. In both experiments chicks failed to seroconvert to ILTV. qPCR detection of ILTV in experiment 1 revealed temperature- and time-dependent declines in detection but no such decline was observed in experiment 2. A small proportion of chicks seroconverted to MDV in experiment 1 but only in the positive control treatment with no heat treatment. In experiment 2, as for ILTV, there was no seroconversion to MDV. Again as for ILTV, qPCR detection of MDV showed temperature- and time-dependent declines in experiment 1, but not experiment 2. These results demonstrate that qPCR detection of MDV and ILTV in "pasteurized" litter cannot be used to predict the level of infective virus present. We failed to accurately define temperature-time inactivation of these viruses in this material and the possible reasons for this will be discussed.