[Safety and potency of different vaccines against avian infectious laryngotracheitis].

The safety spreading properties and potency of three commercial vaccines used for the prevention of avian infectious laryngotracheitis have been studied. Results showed that the different strains are not safe when administrated by the intratracheal route; when administrated by the ocular route, the vaccinal reaction was limited to a transitory conjunctivitis. Under certain conditions of proximity the vaccine viruses spread from vaccinated to contact chickens. Good protection was afforded by vaccination by ocular route, but not when the vaccines were administrated in the drinking water. There was concordance between the level of protection following vaccination and the neutralising antibodies titres. The protection was relatively short-lived: 10 to 15 weeks after vaccination, half of challenged birds showed clinical signs of the disease, and 20 weeks after vaccination all of them were sick.