Submitted to: Avian Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2002
Publication Date: 2/4/2003
Citation: Kommers, G.D., King, D.J., Seal, B.S., Brown, C.C. 2003. Virulence of heterogeneous-origin newcastle disease virus isolates before and after sequential passages in domestic chickens. Avian Pathology. Interpretive Summary: Newcastle disease virus (NDV) isolates vary in virulence from those that cause severe disease, which is reportable and a cause of trade sanctions, to those that produce only a mild non-reportable disease similar to the common cold of man. Most if not all birds species can be infected with NDV. However, because of species differences in susceptibility to different NDV strains new isolates must be tested by inoculation of susceptible chickens to determine their inherent virulence for chickens. To simulate the consequences of virus entry and bird to bird spread of these isolates in a chicken flock, six selected NDV isolates were passaged serially in chickens and the virulence of the isolates before and after passage in chickens was evaluated. A dramatic change in virulence was noted in only one of the isolates after chicken passage. The passaged isolate from a dove produced high mortality with severe hemorrhagic lesions, a change from inducing no clinical disease in chickens before passage. One isolate from a pheasant retained its high virulence and four isolates one of moderate virulence from an anhinga and three low virulence isolates from a smuggled yellow nape parrot and from chickens were unchanged by passage. Isolates like the one from the dove pose a great risk to poultry. No markers were identified to predict the virulence change of that isolate therefore limiting poultry exposure by effective biosecurity remains the primary protection available against such isolates.
Technical Abstract: Four serial passages of six Newcastle disease virus (NDV) isolates were performed in 2-week-old White Leghorns. The viruses were recovered from chickens (Ckn-Live Bird Market and Ckn-Australia isolates), exotic (Yellow Nape [YN] Parrot, Pheasant, and Dove isolates) and wild birds (Anhinga isolate). Infected chickens were monitored clinically and euthanatized with tissues sampled for histopathology and immunohistochemistry. Pathotyping tests and sequence analysis of the fusion protein cleavage site were performed before and after passages. The moderately virulent Dove isolate became highly virulent with serial passage. The originally highly virulent Pheasant isolate had an increase in the intracerebral pathogenicity index (ICPI) and the intravenous pathogenicity index (IVPI) with passages in chickens. Virulence increase was not observed with Ckn-LBM, YN Parrot, Ckn-Australia, or Anhinga isolates after four chicken passages. The results demonstrate the high risk for domestic chickens represented by some NDV-infected non-poultry species such as doves.