Restriction endonuclease analysis of Delmarva field isolates of infectious laryngotracheitis virus

Restriction endonuclease (RE) digestion patterns of six Delmarva field isolates of infectious laryngotracheitis virus (ILTV) were compared with three standard reference strains. With one exception, all of the field isolates generated RE digestion patterns identical to an embryo-propagated vaccine strain of ILTV when the six-base-recognizing REs EcoRI, HindIII, PstI, and BamHI were used. In order to increase the sensitivity of the RE analysis technique, a more sensitive DNA fingerprinting approach using four-base-recognizing enzymes was developed. One field isolate could be differentiated from the embryo-propagated vaccine strain using all three enzymes, Sau3AI, MspI, and HinfI. A second isolate could be differentiated only by comparing HinfI digestion patterns. This work provides additional evidence that differentiable strains of ILTV exist in the United States. Furthermore, currently used RE analysis methods may not be sensitive enough to discriminate between field isolates and vaccine strains of ILTV, thus challenging the theory that vaccine strains of ILTV are responsible for field outbreaks of infectious laryngotracheitis.