Avian infectious laryngotracheitis

Abstract

Infectious laryngotracheitis (ILT), caused by Iltovirus or gallid herpesvirus I (GaHV- 1) of Alphaherpesvirinae, is an acute highly contagious viral respiratory disease of chickens. The disease is characterized by sneezing, expectoration of blood-mixed mucus, severe haemorrhagic tracheitis and conjunctivitis amidst mortality of up to 70% in its acute form, and a milder form shows varying degrees of catarrhal tracheitis, sinusitis and conjunctivitis with relatively low morbidity and occasional mortality. ILT has been associated with colossal economic loss to the poultry industry due to high mortality, reduced egg production, poor growth and expenses spent on vaccination, biosecurity management and treatment to counteract secondary infections. Vaccination and strict biosecurity measures are the principal components in controlling disease. Live attenuated and recombinant viral vector vaccines are commercially available. The live attenuated tissue culture or chicken embryo origin vaccines significantly reduce the mortality; however, these vaccines retain or regain their virulence after birdto- bird passage leading to outbreaks simulating classical disease in unprotected flocks. The recombinant viral vector vaccines are reported to be a safer alternative, but still they are not completely safe as they often fail to reduce shedding of the challenge virus posing threat of outbreaks. Now, several new strategies to improve the live attenuated as well as recombinant vector vaccines are being evaluated in order to have a better ILT vaccine that would have least residual virulence and mass application potentials.