Characterization of infectious laryngotracheitis virus (ILTV) isolates from commercial poultry by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP).

Infectious laryngotracheitis (ILT) is a highly contagious, acute respiratory disease of chickens, of worldwide distribution, that affects growth and egg production and leads to significant economic losses during periodic outbreaks of the disease. Live attenuated vaccines (chicken embryo origin [CEO] and tissue-culture origin [TCO]) have been widely used to control the disease in the United States. It is believed that most of the outbreaks in the United States are caused by vaccine-related isolates that persist in the field and spill over into naïve poultry populations. The objective of this study was to utilize the previously developed polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis to genotype recent ILT virus (ILTV) isolates from commercial poultry. Forty-six samples were collected during January 2006 to April 2007 from five poultry production regions of the United States and were characterized within PCR-RFLP groups III-VI. Sixty-three percent of the samples analyzed were categorized as closely related to the vaccine strains (groups III-V), whereas 33% were categorized as group VI viruses that differed in six and nine PCR-RFLP patterns from the CEO and TCO vaccines; a mixture of group IV and V viruses was detected in two samples (4%). In general, groups V and VI were the most prevalent viruses, found in 52% and 33% of the samples tested respectively. Both types of viruses were detected in vaccinated and nonvaccinated flocks. Although genetically different, both viruses produced severe disease in the field.