Isolating avian paramyxovirus-1 in New Zealand poultry.

Abstract

Avian paramyxoviruses (APMVs) cause a significant economic impact on the poultry industry worldwide. There are nine different serotypes of APMVs, which can infect a wide range of avian species. Newcastle disease (ND) is caused by avian paramyxovirus type 1 (APMV-1) with a ICPI above 0,7. Clinical signs seen in birds infected with APMV-1 vary depending on the pathogenicity of the isolate. As signs of disease caused by APMV-1 in different hosts vary significantly, the diagnosis of ND cannot be made based on clinical signs alone. So far no ND outbreak has occurred in New Zealand and all New Zealand isolates of APMV-1 to date have been apathogenic, so New Zealand is regarded free of the virulent form of NDV. However, seroconversion to APMV-1 is occasionally recognized in commercial poultry flocks during the lay period, and APMV-1 have been isolated from wild waterfowl in New Zealand. A limited number of studies have been undertaken to characterize such NZ isolates of APMV-1. For this reason this research had a look at which APMV-1 isolates are circulating in New Zealand. To do so paired cloacal and tracheal swabs were taken from sero-negative layer birds that were introduced into a commercial poultry flock with known exposure to APMV-1. In total 100 birds were sampled: 50 on the first sampling (2 weeks after introduction to the farm), then 25 on the second sampling (a week later) and 25 on the third sampling (another 2 weeks later). In total 22 blood samples were collected for serology at the second and third time point. From the cloacal and tracheal samples RNA was extracted using Qiagen RNeasy columns and the 45 samples taken at the last time point were tested in a real time RT-PCR using a M-gene assay and a L-TET assay. Also 162 samples from chickens and other domestic birds kept on small backyard farms that were at high risk of getting a APMV-1 infection from wild waterfowl, were tested by this real time RT-PCRs. All samples that were tested with the M-gene assay were negative, only the positive controls were positive. The L-probe tested all the samples negative and there was no positive control sample for this test so no conclusions can be drawn from these results. Since there were no positive samples it was not possible to characterize any isolates. From the results of this research it can be concluded that APMV-1 is not common in New Zealand. More research to characterize the APMV-1 isolates that are circulating in New Zealand should be done, to assure that all circulating APMVs continue to belong to lentogenic and apathogenic types.