Infectious laryngotracheitis is caused by gallid alpha herpesvirus type 1, commonly known as infectious laryngotracheitis virus (ILTV). It is an economically important respiratory disease of poultry that affects the industry worldwide. ILTV infection can result in severe production losses due to death and/or decreased egg production. Transmission is via direct contact with infected birds and fomites (including contaminated litter, farm equipment, and handlers' clothing), as well as airborne spread between nearby farms. Deficits in biosecurity and transportation of infected birds facilitate transmission of the virus. Respiratory signs are similar to those of other infectious diseases in poultry (eg, tracheitis, conjunctivitis). Diagnosis is based on real-time PCR assay and histological evaluation. Histological analysis of infected tissue reveals syncytia and intranuclear inclusion bodies in the trachea, larynx, and conjunctival mucosa. Infection is controlled by vaccination and improved biosecurity.
Infectious laryngotracheitis (ILT) is caused bygallid alpha herpesvirus type 1 (GaHV-1), commonly known as infectious laryngotracheitis virus (ILTV). ILTV infects poultry farms worldwide, with disease reported in areas of many countries where poultry are intensively reared. Samples tested from ILT outbreaks in the US demonstrate increased virulence of the virus, enabling it to replicate and spread more rapidly and making it harder to control.
Clinical Findings of Infectious Laryngotracheitis in Poultry
ILT is an acute, highly contagious herpesvirus infection of chickens, pheasants, peafowl, and, less commonly, turkeys that is characterized by severe dyspnea, coughing, rales, gasping, and expectoration of bloody mucus (see infectious laryngotracheitis video and blood mucus image). It can also be a subacute disease with nasal and ocular discharge, tracheitis, conjunctivitis (see conjunctivitis images), and mild rales. Wild birds, including pigeons and waterfowl, can carry the virus without showing clinical signs.
Courtesy of Dr. Maricarmen García.
The wall in this photograph is splattered with bloody exudate produced by broiler chickens coughing and gasping for air, a characteristic clinical sign of severe forms of infectious laryngotracheitis.
Courtesy of Dr. Maricarmen García.
Mild (A) and severe (B) conjunctivitis due to infectious laryngotracheitis in broiler chickens.
Courtesy of Dr. Maricarmen García.
Mild (A) and severe (B) hemorrhagic trachel exudate due to infectious laryngotracheitis in broiler chickens.
Courtesy of Dr. Maricarmen García.
Courtesy of Dr. Maricarmen García.
The wall in this photograph is splattered with bloody exudate produced by broiler chickens coughing and gasping for air, a characteristic clinical sign of severe forms of infectious laryngotracheitis.
Courtesy of Dr. Maricarmen García.
Mild (A) and severe (B) conjunctivitis due to infectious laryngotracheitis in broiler chickens.
Courtesy of Dr. Maricarmen García.
Mild (A) and severe (B) hemorrhagic trachel exudate due to infectious laryngotracheitis in broiler chickens.
Courtesy of Dr. Maricarmen García.
ILT lesions vary depending on the virulence of the virus.
In mild forms of the disease, viral infection of the tracheal mucosa induces production of serous or mucoid exudates, mucosal edema, and congestion.
In severe forms of the disease, the tracheal mucosa is congested, hemorrhagic, and roughened with mucoid, mucohemorrhagic, or fibrinonecrotic exudates that can result in tracheal occlusion and death from asphyxia (see hemorrhagic tracheal exudate images).
After recovery from ILT, birds become carriers for life and are a source of infection for susceptible birds. The latent virus can be reactivated if an infected bird is under stressful conditions, and viral particles are shed in respiratory tract secretions and in feces.
ILTV is transmitted horizontally via respiratory tract secretions after a single bird in a flock is infected. Several epidemics have been traced to the transport of infected birds or contaminated equipment and litter. There is no evidence of vertical transmission (from parent to offspring during pregnancy or the birth process).
Diagnosis of Infectious Laryngotracheitis in Poultry
PCR assay
Histological evaluation
Rapid and accurate diagnosis of ILT is central for the establishment of swift control measures. Diagnosis can be based on detection of microscopic lesions, such as syncytia and intranuclear inclusion bodies in the trachea, larynx, and conjunctival mucosa (see tracheal tissue images), which are pathognomonic of infection.
Courtesy of Dr. Maricarmen García.
Diagnosis of ILT can be rapidly confirmed by the detection of viral DNA using virus-specific PCR assays. Field isolates and vaccine strains of are routinely differentiated by PCR amplification of single or multiple ILTV genome areas, followed by sequencing of the PCR products and analysis of the sequences obtained.
Field isolates and vaccine strains also have been differentiated by deep sequencing of partial or full genome sequences. Genotyping reveals whether the ILTV strain originated either from previously used live, attenuated vaccines or from previous outbreak strains, or whether it is a new field strain.
Control of Infectious Laryngotracheitis in Poultry
Biosecurity
Vaccination
ILT is controlled by biosecurity and vaccination. ILTV vaccines are either live, attenuated or viral vector recombinant vaccines. Live vaccines originate from virulent viral strains that were attenuated by consecutive passages in embryos or tissue culture. They are administered to individual birds via eye drops or, if there is an outbreak, through mass vaccination in drinking water or by spray in the field.
The fowlpox virus (FPV) and herpesvirus of turkeys (HVT) are the two main vectors for expressing ILTV immunogenic proteins. FPV-ILT and HVT-ILTV vaccines are administered at the hatchery in ovo or subcutaneously to chicks at one day of age. The FPV-ILTV vaccine can also be administered by wing web vaccination in the field. Studies have shown that dual ILT vaccination, in which recombinant ILT vaccine is administered at the hatchery and live, attenuated vaccines (derived from either embryos or tissue culture)are administered in the field, provides the best protection against ILT infection.
Zoonotic Risk of Infectious Laryngotracheitis in Poultry
There is no zoonotic risk of infectious laryngotracheitis.
Key Points
Infectious laryngotracheitis is an acute respiratory disease of poultry.
The disease is caused by gallid alpha herpesvirus type 1 (GaHV-1), or infectious laryngotracheitis virus (ILTV).
Severe and mild presentations of the disease have been identified.
Rapid diagnosis is achieved by histological examination of the trachea and conjunctiva and by PCR analysis.
Intervention strategies for control are biosecurity and vaccination.
For More Information
Garcia MC, Spatz S. Infectious laryngotracheitis. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, assoc eds. Diseases of Poultry. 14th ed. Wiley; 2019:189-209. doi:10.1002/9781119371199.ch5
Davison S. Infectious laryngotracheitis. In: Brugère-Picoux J, Vaillancourt J-P, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. ASAF; 2015:172-175.
