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Infectious Laryngotracheitis (ILT)


By Dr Rob Marshall


Infectious laryngotracheitis (ILT) is a viral respiratory disease caused by a herpes virus. Infections with ILT virus occur in both young and adult chickens.


Typically, birds in one area of yard show clinical signs and die, and the disease spreads relatively slowly through the other birds in other pens.


Daily mortality progressively increases and can affect many birds each day. Severity of clinical signs and mortality rates vary widely among outbreaks depending on the immune status of the flock, initial exposure dose, age of the birds, virulence of the viral strain, co-infections with other respiratory pathogens, and environmental factors that adversely affect the respiratory system. Outbreaks are generally more severe in older rather than younger broiler flocks.




  • Eye symptoms


  • Gaping

  • Cough and gurgling sounds

  • Head shaking


Infected birds are lethargic and have swollen eyelids, reddened conjunctivae, and watery eyes as seen in this photo. In severe cases, eyelids may be adhered with dry, crusty, ocular discharge sticking to the eyelids and skin around the eye.


Severely infected birds exhibit mouth breathing, coughing, and gargling respiratory noises. Some birds stretch out their neck while trying to breath as seen in this photo.

ILT must be assumed when there is evidence of coughing up blood as seen in this photo. This finding is a characteristic clinical sign that occurs in birds with badly damaged tracheas.


Bloody mucus may be found on and around the beak, and in the oral cavity. Spots of dried bloody exudate may be found in the bird’s environment on sidewalls and equipment when flocks are severely affected

Difficulties with ILT

  • Looks like other respiratory diseases.


  • Develops carrier state.

  • Spread through air & contaminated clothing etc.

  • Vaccination not always successful.


ILT is an acute virus infection of the upper respiratory tract of chickens with symptoms common to other respiratory type diseases such as Infectious bronchitis, Infectious Coryza and Aspergillosis.


Birds that recover should be considered carriers for life. ILT may be harbored in specialty poultry such as exhibition birds and game fowl such as pheasants. Purchasing of infected adult fowls can introduce the disease into a clean flock if a carrier bird is among the new birds.


ILT is spread through the air and may spread from flock to flock by contaminated clothing, shoes, car tyres, etc.


Vaccination for ILT is not as successful as for other disease, but is an excellent preventive measure for use in outbreaks and in epidemic areas.


The Disease


  • Mostly affects chickens older than 14 weeks.


  • Outbreaks mostly occur in mature hens.

  • Symptoms mimic other respiratory disease.

  • Chickens and pheasants are affected by LT. Chickens 14 weeks and older are more susceptible than young chickens. Most LT outbreaks occur in mature hens The clinical sign usually first noticed is watery eyes. Affected birds remain quiet because breathing is difficult. Coughing, sneezing, and shaking of the head to dislodge exudate plugs in the windpipe follow. Birds extend their head and neck to facilitate breathing and gape. Inhalation produces a wheezing and gurgling sound. Blood-tinged exudates and serum clots are expelled from the trachea of affected birds. Many birds die from asphyxiation due to a blockage of the trachea when the tracheal plug is freed.

  • Eye discharge, nasal discharge, face swelling, conjunctivitis, sneezing, shaking head, and gurgling sounds are also seen with Infectious Coryza, but Coryza does not cause coughing, gaping or any bloody discharges.

  • Gurgles, gaping, eye discharge, nasal discharge also occur with Infectious bronchitis but IB does not cause coughing, sneezing, head shaking, facial swelling or conjunctivitis.

  • It is difficult to differentiate ILT from Mycoplasma infections as CRD shares most symptoms except bloody discharge and infection is usually not rapidly fatal



  • Vaccination against LT is not as successful as for other diseases, but is an excellent preventive measure for use in outbreaks and in epidemic areas. State approval is required prior to vaccination. Do not vaccinate unless you have a problem on your farm or in your area. If an owner chooses to vaccinate, all chickens on the premises must be vaccinated, including any new birds that are added later.


  • Yearly boosters are advised.

  • Birds should be at least 4 weeks old. Younger birds are less responsive to vaccines.

  • Rapid diagnosis and vaccination can also stop an outbreak from spreading in an infected flock.

  • Eye drop vaccination is recommended for small flocks. For eye drop administration the vaccine is reconstituted with Poulvac® Eyedrop Diluent. The reconstituted vaccine is poured into the diluent bottle that is then fitted with a teat and becomes the dropper bottle. The vaccine is dropped onto the surface of the eye. The chicken should be held in such a way as to make sure the drop does not roll off the surface of the eye as it is applied. If farmers wish to vaccinate through the drinking water, they should read the instruction leaflet with the vaccine.

  • ILT vaccination should not be undertaken simultaneously with infectious bronchitis (IB) vaccination. If ILT is to be used, it is better to vaccinate first against IB and then with ILT at least one week later.


Chinese Silkies are our first choice backyard chicken. They are robust, loveable, quiet, lay good quality eggs and make ideal pets.

Our programmes are a simple and effective way to provide your chicken companions with the best possible care.

Click for information regarding our holistic methods for managing chicken diseases.

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