Susceptibility of Turkeys to Infectious Laryngotracheitis

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Abstract
An isolate of infectious laryngotracheitis (ILT) was propagated in turkey embryos and transferred through 96 generations. It was still virulent for chickens after these passages. Turkey poults were susceptible to infection at the 22nd passage. Subsequent trials demonstrated that the original isolate, propagated in chicken embryos, was capable of infecting turkeys by the respiratory tract route. In further trials, other ILT isolates infected turkeys and induced respiratory signs and lesions. The pathological changes were primarily in the upper respiratory tract and involved the infraorbital sinus, turbinates, and palatine cleft. Laryngeal lesions were observed, occasionally. The trachea and lower respiratory tract were not affected as frequently, or as severely, as in ILT infection of chickens. Gross and microscopic changes were described. There was a marked difference among 5 ILT isolates in their apparent invasiveness and virulence for turkeys. Two virus isolates, from vaccines virulent for chickens and to be applied as vaccines by the vent route, incited moderate to severe respiratory signs. A 3rd ELT vaccine virus for vent application induced only mild signs and lesions in day-old poults. Two other vaccine isolates, to be given by eye drop and considered mild in chickens, were essentially innocuous for turkeys. An age resistance factor was apparent and related to the particular ILT isolate employed. Other factors affecting host resistance were discussed, and the need was emphasized for a more intensive search to determine possible reservoirs of virus infection outside the usual host. The recent isolation of ILT virus from peafowl was mentioned.

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