Infectious Laryngotracheitis
It's a respiratory viral disease that affects unvaccinated flocks of chickens starting from the sixth week of age.
This disease is caused by one group of Herpes viruses.
It spreads in the cold winter months, and it decreases in the hot summer months.
These viruses are very weak outside the bird's body, as direct sun rays kill it in a few minutes, and any disinfectant such as phenic or Iodine kills it in a few minutes also.