Genomic stability for PCR detection of infectious laryngotracheitis virus and infectious bronchitis virus in poultry dust samples stored under different conditions

Summary Dust collected from the poultry house has been increasingly used as a population level sample to monitor presence of pathogens or to evaluate the administration of live vaccines. However, there are no guidelines for the storage of this sample type. This study investigated the stability of infectious laryngotracheitis virus (ILTV), a DNA virus, and infectious bronchitis virus (IBV), an RNA virus, in poultry dust kept under temperature and moist conditions that mimic on-farm and laboratory storage. Dust samples were collected from chicks spray vaccinated with a live IBV vaccine and inoculated with a field ILTV strain via eye drop. Samples were stored under different moisture conditions (dry 2% moisture, moist 22-71% moisture) and temperatures (-20oC, 4oC, 25oC, 37oC) for different durations (0, 7, and 14 days, and 1, 2, 3 and 4 months) in a factorial arrangement followed by quantitative PCR for detection of virus genome copies (GC). The length of storage, moisture level, and storage temperature affected the viral genome load for ILTV and IBV but did not affect the number of positive samples for each virus. All treatment combinations were ILTV positive for at least 4 months. In dry dust, storage temperature or duration had quantification of ILTV or IBV GC. Moisture addition had a detrimental effect on viral genome load causing an overall reduction of 0.3-log10 for ILTV GC (7.29 and 6.97 log10, P=0.0001), and 1.3-log10 for IBV GC (5.95 and 4.66 log10, P=0.0001), which are unlikely to have biological significance. In conclusion, dry dust can be stored at any temperature up to 37˚C for at least 4 months without loss in qPCR detection of ILTV or IBV GC. Collection or storage of moist dust should be avoided or air drying prior to storage is recommended if only moist dust is available.