Diagnosis of Infectious Laryngotracheitis Outbreaks on Layer Hen and Broiler Breeder Farms in Vojvodina, Serbia

SIMPLE SUMMARY: Infectious laryngotracheitis is a very important respiratory disease of poultry. It causes inflammation of the upper respiratory tract and mucous membranes of the eye. A large number of birds in the flock can be infected and mortality is variable. It is a viral disease, transmitted horizontally in a flock and causes great economic losses. In this study, we presented data on the occurrence of the disease after 20 years in unvaccinated flocks in the Vojvodina region and proposed a strategy for the prevention and control of this disease. Infected flocks had a severe clinical symptoms with a decrease in egg production and increased mortality. Clinical symptoms lasted from two to four weeks. We prevented the spread of the virus in one flock applying emergency vaccination with live vaccine. It can be concluded that the disease can easily spread between unvaccinated flocks. The most important thing is to improve biosecurity measures on the farm and implement vaccination in endemic areas. ABSTRACT: Infectious laryngotracheitis (ILT) is a respiratory disease of poultry characterized by high morbidity and variable mortality. ILT is caused by Gallid alpha herpesvirus-1 (GaHV-1), which is transmitted horizontally and most susceptible are chickens older than 4 weeks. After almost two decades since last appearance of this disease in Vojvodina, an outbreak occurred from April 2020 to August 2021 on five laying hen farms and one broiler breeder flock farm. Clinical signs were mild to severe respiratory symptoms, unilateral or bilateral head swelling, serous nasal discharge, conjunctivitis and increased tearing. There was a decrease in feed consumption (2.1–40.0%) and egg production (2.7–42.0%), weight loss and mortality increased (0.8–31.5%). Pathomorphological changes were localized in the upper respiratory tract. Total of 200 carcasses were examined; 40 pooled samples were analyzed by PCR, and 40 by bacteriological analysis. ILT virus was confirmed in tracheal tissue samples. Infected flocks were not vaccinated against this disease. Five flocks had coinfection with Avibacterium paragallinarum. Three-to-four weeks after the first reported case in the flock, clinical symptoms had ceased. Future control and prevention strategies will involve the procurement of flocks vaccinated by recombinant vaccine or the registration of live attenuated vaccines and their use during the rearing period.