Infectious laryngotracheitis (ILT)
Infectious laryngotracheities, caused by fowl Gallid Herpesvirus 1 belonging to the family Herpesviridae, is a quickly spreading acute respiratory disease of chicken, mostly 5 to 10 months old and seldom less than 10- week-old. The virus can be cultivated on the chorioallantoic membrane of the chick embryo and in tissue culture.
Epidemiology: All breeds of fowls appear to contract the disease readily and birds of all ages are susceptible although the incidence is greater in older than in younger stock. Turkeys, ducks, pigeons and geese are not susceptible. Recovered birds may be carriers throughout their life and may spread the disease.
Clinical signs: The symptoms of the disease are watery eyes and a tendency for the affected bird to remain quiet, fits of coughing and sneezing and the presence of a grayish-white material adherent to the mucous membrane in mouth and throat. Some birds may have blood stained beaks resulting from the coughing up of blood-stained exudates. In a laying flock, drop in egg production is a variable factor. In severe cases, neck is raised and head extended during inspiration - 'pump-handle respiration'. Head shaking and coughing is characteristic. Among adults, there is always certain mortality from suffocation and it may reach 50% or more. The course of the disease usually ranges from 7 to 15 days, although symptoms may be manifested for as long as 1 month.
Diagnosis: It is diagnosed by isolation of the virus in chick embryos and inoculation of the suspected virus into immunized and susceptible birds. The agar-gel diffusion and fluorescent antibody tests are used for the demonstration of the viral antigen in affected tissues. Neutralizing antibodies may be detected by pock or plaque reduction assays.
Treatment, prevention and control: Vaccination with a live egg-adapted attenuated virus is carried out in birds above 6 weeks of age. The vaccine is applied by brushing on to the mucous membrane of the cloaca. A modified live virus vaccine developed in cell-culture is also available. Mass immunization through aerosol or in drinking water has also been tried with success. Practical measures for the prevention and control of laryngotracheitis consist of strict application of the principles of hygiene and sanitation. All the affected birds and their contacts should be disposed off and the poultry houses should be thoroughly cleaned and disinfected. After emptying, incubators and brooders should be cleaned and disinfected. Healthy birds should be isolated at some distance from the condemned birds.