RFLP analysis of recent Northern Ireland isolates of infectious laryngotracheitis virus: Comparison with vaccine virus and field isolates from England, Scotland and the Republic of Ireland

Restriction fragment length polymorphism (RFLP) analysis was used to assist epidemiological investigations following the recent introduction of infectious laryngotracheitis virus (ILTV) to commercial poultry flocks in Northern Ireland (NI). A 4.9 kbp PCR product of the ILTV ICP4 gene was generated from each of 16 field isolates of ILTV originating from England, Scotland, NI and the Republic of Ireland (RoI) and of the single vaccine strain currently licenced for use within the United Kingdom. With the exception of isolate PV6/94 from RoI, all field isolates generated RFLP patterns, following digestion with HaeIII, similar to that obtained using the vaccinal strain. Following MspI digestion, NI isolates were indistinguishable from the vaccinal strain and recent English isolates. However, one English and one Scottish isolate, both made prior to the introduction of vaccination, and two isolates from RoI generated a second pattern following digestion with MspI.