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Infectious Laryngotracheitis

Infectious Laryngotracheitis


Infectious Laryngotracheitis (ILT) is a highly contagious upper respiratory infection caused by the infectious laryngotracheitis virus (ILTV). The virus belongs to the Herpesviridae family and is in the subfamily Alphaherpesvirinae. Mild to severe enzootics of the disease have been observed.

Host Range

Infectious Laryngotracheitis is primarily an infection of chickens. Rarely, pheasant and peafowl may be affected. Wild avian species appear to be resistant to the disease. Chickens of all ages are susceptible; however birds older than 4 weeks of age have increased susceptibility to infection. There is no known public health risk to humans associated with ILTV.


ILT is transmitted primarily through direct contact between susceptible birds and clinically recovered carriers. Mechanical transmission can also occur through contaminated equipment and litter. The virus enters the host through the upper respiratory tract and eyes and targets the epithelial cells of the respiratory tract as well as other mucous membranes.

ILT has a worldwide distribution. In countries with intensive poultry production, the disease is mainly controlled through vaccination. In these areas, when the disease does occur, it is usually the milder enzootic form. In developing countries, the virus typically exists as an endemic infection.

Clinical Signs

The incubation of ILT virus is approximately 6-12 days. The clinical presentation varies according to the pathotype of the virus as well as environmental and host factors. In the mild enzootic form, infection is characterized by general unthriftiness, 5-15% drop in egg production, as well as ocular and respiratory signs. The clinical signs may include conjunctivitis (including epihora /watery discharge or hemorrhage), nasal discharge, and swelling of the infraorbital sinuses. The virus primarily affects the cells of the tracheal mucosa and conjuntiva, but occasionally the lungs and air sacs are also affected.

Most chickens recover within 10-14 days, if the infection is not complicated by immunosuppression or a secondary bacterial or mycoplasma infection. The morbidity of the mild forms is typically about 5% and the mortality is very low. However, the economic losses due to reduced egg production are increasingly important in many poultry producing areas in the United States and around the world.

In severe epizootic forms, clinical signs may include coughing, rales, dyspnea, gasping, nasal discharge, and hemorrhagic mucoid expectorations. The morbidity of these forms of ILT is 90-100% and the mortality is typically 10-20%.

Post-mortem Lesions

In mild enzootic forms, gross lesions may be limited to the epithelium of the conjunctiva and infraorbital sinuses. Lesions may include congestion and edema.

In severe epizootic forms, gross lesions may extend throughout the upper and lower respiratory tract and include the ocular conjunctiva. Lesions are most consistently observed in the trachea and larynx. These may range from mild mucus accumulations to varying degrees of inflammation, diptheritic mucoid or hemorrhagic casts, and necrosis. In severe cases, hemorrhage may be found in the trachea, nasal, and oral cavities.

Differential Diagnosis

Respiratory disease associated with ILT must be distinguished from other respiratory pathogens of poultry producing similar clinical signs and gross lesions. These include the diphtheritic form of avian pox virus and infections caused by Newcastle disease virus, avian influenza virus, infectious bronchitis virus, fowl adenovirus, and Aspergillus spp.


In severe acute infections, with high mortality and expectoration of blood, a tentative field diagnosis of ILT can be made. A definitive diagnosis will require laboratory testing. Keep in mind that silent and subclinical forms of ILT have been identified through laboratory testing. In the laboratory, confirmatory testing may include virus isolation, microscopic detection of intranuclear inclusion bodies in respiratory and conjunctival epithelial cells, and the detection of ILT viral antigens in tracheal tissues or respiratory mucus. Demonstration of viral antigen in clinical samples can be performed 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. PCR assays for the detection of viral nucleic acid, has been widely utilized as a confirmatory fast assay. Also, serologic tests like agar gel immunodiffusion test (AGID), serum neutralization, and ELISA could be used in conjunction with other laboratory tests.

Prevention and Control

Attenuated live vaccines available to control ILT are either tissue culture or chicken embryo origin viruses. Despite the fact that most ILT vaccines are often administered by coarse spray and by drinking water, they are labeled for eye drop application. Broilers are only vaccinated in the phase of an outbreak and it is recommended not to vaccinate broilers before 2 weeks of age or after 3 weeks of age. Layer and breeder replacements are vaccinated by eye drop application one or two times during the growing period, using either a tissue culture or embryo-adapted vaccine. Inactivated vaccines are only available at the experimental level because of the high-cost of preparation and delivery.

Selected References

  1. Barhoom, S.A., A. Forgacs, and F. Solyom. 1986. Development of an inactivated vaccine against laryngotracheitis (ILT)-serological and protection studies. Avian Pathol 15:213-221.
  2. Charlton, B. R. (ed). 2006. Avian Disease Manual, 6th ed. American Association of Avian Pathologists (AAAP), 953 College Station Road, Athens, Georgia 30602-4875.
  3. Cove, M.S. 1996. The early history of infectious laryngotracheitis. Avian Diseases 40:494-500.
  4. Guy, J.S. and M. Garcia. 2008. Laryngotracheitis. In Diseases of Poultry, 12th ed. Y.M. Saif. et al. (ed.). Blackwell Publishing, Ames, Iowa.
  5. Roberston, G.M., and J.R. Egerton. 1981. Replication of infectious laryngotracheitis virus in chickens following vaccination. Aust. Vet. J. 57:119-123.
  6. Tripathy, D.N. and M. Garcia. 2008. Infectious laryngotracheitis. In A Laboratory Manual for the Isolation and Identification of Avian Pathogens, 5th edition. L. Dufour-Zavala Louise et al. (ed.) OmniPress, Inc., Madison, Wisconsin.
  7. World Organization for Animal Health (OIE) website. 2008.

Thank you to the following individuals for reviewing these materials:

Maricarmen Garcia
Jaime Ruiz
Jose Bruzual

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