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Infectious Laryngotracheitis (ILT)

Avian Laryngotracheitis, Avian Diphtheria, Trach, Trake, Laryngo

Infectious Laryngotracheitis (ILT) Overview

Infectious Laryngotracheitis (ILT) is an acute respiratory tract infection of chickens, caused by the Laryngotracheitis Virus (LTV). LTV is also called the Gallid herpesvirus 1 and is a type of herpesvirus, classified as a member of the Iltovirus genus within the Herpesviridae family and Alphaherpesvirinae subfamily. The virus was first discovered in 1925 and it is the first avian viral disease in which an effective vaccine was developed. ILT usually manifests in chickens as signs relating to conjunctivitis, sinusitis, and tracheitis.
Infectious laryngotracheitis
LTV strains vary in virulence from highly virulent strains that is highly infectious and usually fatal to low virulent strains that cause mild to inapparent infections. The two historically most common presentations of ILT are classified as two forms--mild epizootic and severe epizootic. Today, most infections that occur in chickens involve the mild enzootic form of LT.

ILT Forms Comparison Table

Mild Epizootic FormSevere Epizootic Form
Associated Clinical SignsWatery eyes - appears as tiny bubbles in the corner of eye.

Swelling of infraorbital sinuses - appears as facial or eyelid swelling.

Nasal discharge - often persistent.



Difficulty breathing - gasping

Moist respiratory sounds - rales, gurgling, cawing or whistling noises when breathing.

Generalized sickness - unthriftness, ruffled feathers.

If adult laying hens - decreased egg production.
Severe coughing - often involving blood-stained mucus that dries on nostrils, lower beak, possibly feathers. Sometimes it is found throughout the coop environment.

Severe difficulty breathing - stretching necks upward, gulping for air, open-mouth breathing

Head shaking

Disease CourseMost chickens recover in 10-14 days, but can take up to 30 days.May take up to 45 days for chickens to fully recover. Survivors tend to have a lingering cough.
Typical AgeYoungAdults
MortalityUp to 2%10 to 20%
Affected organsLimited to the epithelium of the conjunctiva and infraorbital sinuses and sometimes congestion and edema.Lesions may extend throughout the upper and lower respiratory tract and the ocular conjunctiva. The trachea and larynx are the most consistently affected areas, ranging from mild accumulation of mucus to varying amounts of inflammation, diptheritic mucoid or hemorrhagic casts, and necrosis. When really severe, hemorrhages may be present in the trachea, oral cavity, and nasal passages.

Example Disease Course for Mild ILT
Example disease course for mild form of ILT
ILT is spread to flocks through:
  • Indirect transmission through contaminated people or fomites (equipment, clothes, hands, bedding litter, etc.)
  • Exposing unvaccinated flock members to chickens that either received the ILT vaccine or who were previously infected with ILT but had recovered. These chickens serve as carriers of the ILT virus, often shedding the virus in their feces when they are stressed.
  • Improperly burying dead chicken's carcasses, making them accessible to wild animals or domestic cats and dogs.
Infected chickens are able to quickly spread the virus to remaining flock members through their respiratory secretions and airborne particles released during sneezing and coughing, as well as by contaminating the environment through shedding the virus in their feces. Some infected birds can become latent and start up again when stressed, sometimes without showing any clinical signs of infection.

Incubation Period
Clinical signs tend to appear in chickens 6 to 12 days after exposure to the ILT virus.

Contamination of the environment
ILT virus can live for 8 to 10 days in droppings and up to 70 days in carcasses at ambient temperatures of 13-23ºC. The virus lasts longer in the winter due to the cool temperature. The virus may survive for up to 80 days in tracheal exudate (throat exudate) on non-conductive material such as wood if not disturbed. Sunlight, heat and desiccation (drying) are the three natural enemies of the ILT virus. Birds that become infected with ILT carry the disease for life, and may manifest signs of infection when under stress.

Clinical Signs

Nasal discharge
Moist rales
Eye discharge
Bubbles near eye
Head shaking
Labored, open-mouthed breathing
Facial swelling
Respiratory sounds (gurgling, choking, rattles)
Extending neck
Decreased egg production
Blood-stained mucus
Unthrifty appearance


  • Virus isolation
  • Detection of LTV antigens in tracheal tissues or respiratory mucus through the use of fluorescent antibody, immunoperoxidase, electron microscopy, DNA hybridization, antigen capture enzyme-linked immunosorbent assay (ELISA) and by Polymerase Chain Reaction (PCR) tests.
  • Detection of LT virus-specific DNA
  • Serolo


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Therapy for conjunctivitisSigns can often be relieved by applying a warm, damp facecloth to the eyes to help crustiness from forming.
Colloidal silverSpray into chickens mouth, place a few drops in the chicken's mouth to swallow, or put a few drops on the chicken's nostrils for them to inhaleG Damerow
Apple cider vinegarMay help clear mucus from mouth and throat. Add 1 tablespoon of apple cider vinegar to each gallon of water (double dose if using hard water)G Damerow


  • Implementing biosecurity procedures
  • Vaccination : Vaccinate all flock members, first with a mild vaccine strain then about 4-6 weeks later with a more virulent vaccine strain. This produces an immunity that lasts at least one year. Molted flocks should be vaccinated again at the end of the molt period.
  • Mixing of birds should only be done when a complete history of the birds is available, and it is absolutely certain that a potential ILT "carrier" is not present.


Mortality may vary from 5 to 70% depending on the severity of the disease. Most chickens recover in 2 weeks.

Scientific References

Good Overviews

Age Range

All ages of poultry are susceptible, although chicken 14 weeks and older are more frequently infected.

Risk Factors

  • Combining chickens that were previously vaccinated for ILT with chickens that are unvaccinated
  • Introducing a new chicken into the flock
  • Housing chickens that have previously recovered from a respiratory infection with other birds.
  • Improper burial of dead birds on the premises