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Infectious Laryngotracheitis

Other Names: Avian Laryngotracheitis, Avian Diphtheria, Laryngo

Infectious laryngotracheitis (ILT) is a highly contagious upper respiratory tract disease of chickens and occasionally, pheasants and peafowl. It is caused by the infectious laryngotracheitis virus (ILTV), also known as Gallid herpesvirus 1 (GaHV-1). The virus replicates in the conjunctiva and tracheal mucosa, during the first week of infection. The epithelial cells lining the larynx and trachea are always affected, while the respiratory sinuses, air sacs, and lung tissues may or may not be affected.

There are two main forms of infectious laryngotracheitis which occur in chickens, a severe acute or epizootic form and a mild form.
  • Severe or epizootic form: Causes significant respiratory distress, haemorrhagic tracheitis, blood-mixed mucus expelled by head shaking, sneezing, and conjunctivitis. Mortality ranges from 5 to 70%.
  • Mild Form: Causes mild to moderate catarrhal tracheitis, sinusitis, and conjunctivitis. It is associated with low morbidity and occasional mortality ranging from 0.1 to 2%.
Infectious laryngotracheitis
The ILTV has the ability to establish latency in the chicken's trigeminal ganglin during the lytic phase of infection. It gets reactivated when carriers are stressed.

How is the virus transmitted to chickens?

ILT is spread to flocks through:
  • Introducing new chickens to the flock who have received the vaccine, actively infected, or recovered carriers. Vaccinated and recovered chickens will only shed the virus in their feces when subjected to stressful conditions. Actively infected chickens will transmit the virus mainly through respiratory secretions and airborne particles from coughing or sneezing.
  • Indirect transmission through contaminated people or fomites (equipment, clothes, hands, bedding litter, etc.)
  • Improperly burying dead carcasses, making them accessible to wild animals or domestic cats and dogs.

What is the incubation period?

The incubation period of infectious laryngotracheitis virus is 3-14 days. Chickens who receive the ILT vaccine are capable of infecting non vaccinated birds with the milder field strain of ILT contained within the vaccine. Vaccinated birds will shed the virus in their feces for up to 14 days following inoculation.

How long does the virus survive in the environment?

ILT virus can live for 8-10 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.

How is ILT diagnosed?

Infectious laryngotracheitis can be diagnosed by ELISA, virus isolation, indirect fluorescent antibody testing, or by histopathology where intranuclear inclusion bodies are found.

Clinical Signs

Eye discharge
Nasal discharge
Gurgling sounds
Head shaking
Expelling blood-mixed mucous
Difficulty breathing


  • History
  • Clinical signs
  • Physical exam
  • 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.

Reported Cases

  • Case 1: Infectious laryngotracheitis in a Laying hens backyard flock A 12-month-old black and white female laying chicken from a small backyard flock was received for necropsy.  The owner had elected euthanasia of this bird following a clinical exam revealing acute abnormal respiration including open mouth breathing.  Another bird in the flock had similar clinical symptoms and had died.  Following euthanasia and refrigeration, the bird was submitted by the referring veterinarian to the Texas A&M Veterinary Medical Diagnostic Laboratory in Gonzales, Texas for necropsy. Necropsy revealed changes only within the trachea. Blood and fibrinous exudate were present in the upper one-third of the trachea. The underlying mucosa had a roughened appearance. Microscopically sections of trachea had extensive exudation of red blood cells, fibrin, heterophils, and macrophages into the tracheal lumen. Many degenerating epithelial cells contained eosinophilic intranuclear inclusions characteristic of avian herpesvirus. The lamina propria contained large numbers of lymphocytes and plasma cells. Polymerase chain reaction (PCR) evaluation of tracheal swabs was positive for infectious laryngotracheitis virus. Ref

  • Case 2: Infectious laryngotracheitis in a Chicks Infectious laryngotracheitis (ILT) caused by herpesvirus was diagnosed in 18-day-old brown broiler chicks with a history of respiratory signs including open mouth breathing and tearing eyes. Gross lesions were limited to increased mucus in the trachea, and microscopic lesions included mild to severe laryngitis, tracheitis, sinusitis, rhinitis and conjunctivitis associated with syncytia and intranuclear inclusion bodies consistent with ILT. This disease was confirmed by PCR and immunohistochemistry. The birds were also positive for Infectious bronchitis virus by PCR. Ref

  • Case 3: Infectious laryngotracheitis in a Chickens Infectious laryngotracheitis (ILT) cases were seen with increased incidence in broiler chickens between 22 and 61-days-old. Typically, the chickens exhibited severe respiratory distress with open mouth breathing, lacrimation and increased mortality. Gross and histological lesions consist of severe laryngitis, tracheitis, bronchitis, sinusitis and conjunctivitis associated with syncytia containing intranuclear viral inclusion bodies. ILT was confirmed in most cases by fluorescent antibody test and PCR. Ref

  • Case 4: Infectious laryngotracheitis in a Laying pullets Infectious laryngotracheitis (ILT) associated with vaccination in a flock of 8-week-old layer pullets caused increased mortality and “wet” eyes. The flock had been vaccinated for ILT in the drinking water at 6 weeks of age. At necropsy the birds had “almond” shaped eyes with a clear secretion, and reddened conjunctiva, larynx and trachea. Histopathology revealed inflammation, hemorrhage and syncytial cells containing intranuclear inclusion bodies in the conjunctiva, larynx and trachea, which are diagnostic lesions of ILT. PCR was also positive for ILT. Ref


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 inhale.



  • Reduce stress
  • 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.
  • Minimize stress.

Scientific References

Good Overviews

Age Range

The disease is usually seen in adult chickens and pheasants, over 14 weeks of age.

Risk Factors

  • Stress
  • Mixing chickens who received the ILT vaccine with unvaccinated birds and putting them under stressful conditions.