Infectious Laryngotracheitis (ILT)

Synonym: Avian diphtheria, ILT

• It is an acute, viral respiratory disease of chickens characterized by respiratory distress, fits of coughing causing expulsion of blood- and blood-stained mucus.

Etiology:

• Gallid herpesvirus 1; also known as ILTV of Herpesviridae family
• DNA virus, measuring 80-100µm in diameter
• Virus is sensitive to heat, disinfectants and lipolytic agents.
• Virus is destroyed in 10-15 minutes at 55°C
• In dead birds, at 37°C, virus remains viable for about 48 hours

Epidemiology:

• Disease was first recognized in USA and also recorded in UK in 1925.
• Virus is present in Asia, Europe, Australia, New Zealand and Asia
• Chickens of all ages are susceptible; usually between 3-9 months of age.
• Males are more susceptible than female birds.

Transmission:

• Through air from exudates of nares, oropharynx, trachea and conjunctiva of infected birds.
• Ingestion of infected material
• Through contaminated litter, equipment, clothing, eggs or chicken handling appliances.
• Rats, crows, vulture acts as mechanical carriers
• Birds recovered from outbreaks acts as carriers.
• Vertical transmission donot occur.

Pathogenesis:

• Virus gains entry through aerosol in URT
• Virus replicates within cells of conjunctiva, sinus, larynx, and trachea.
• Damage of epithelial cells and these cells are replaced by inflammatory cells and debris.
• Virus gain entry into nerve and becomes latent after reaching trigeminal nerve.
• Stress factors such as handling of birds, laying eggs triggers the virus and virus is reactivated.
• Following reactivation, virus then reaches respiratory tract, conjunctiva and produce clinical signs.

Clinical Findings:

Disease appears in several form:

i. Per-acute form

ii. Acute form

iii. Mild form

iv. Asymptomatic form

i. Per-acute form:

• Sudden death of birds without any signs and symptoms
• Acute dyspnea, coughing, expectoration of blood clots or blood-stained mucus containing exudate from nares.
• Birds usually dies within 1-3 days.

ii. Acute form:

• Difficulty in breathing
• Gasping with its head and neck upward and beak wide open
• Breathing is accompanied by loud harsh cry
• Abnormal respiratory rales are heard.
• Nasal discharge and conjunctivitis in some birds
• In severe distress, cyanosis of face and wattles.
• Death usually occurs in 3-4 days.

iii. Mild form:

• Respiratory sounds, slight coughing and head shaking
• Nasal discharge
• Conjunctivitis
• Affected birds shows depression and may lie down on their back in severe case.
• Egg production is stopped for a certain time and returns to normal in uncomplicated cases.

iv. Asymptomatic form:

• Signs often go unnoticed.
• No symptoms are seen.

PM Findings:

• It varies with severity of cases.
• Hemorrhagic tracheitis along entire length in per-acute cases
• Trachea are filled with blood stained mucus along its entire length.
• In acute form, caseous exudate, mucus and some hemorrhage may occur in trachea and usually produce obstructive plugs.
• Trachea is congested and becomes cyanotic.
• Nostrils may show caseous exudate.
• Congestion of lungs and thickening of air sacs.

Diagnosis:

• Based on history and clinical findings
• Based on PM findings
• Mild cases are often difficult to diagnose through clinical and PM findings; so, ELISA is performed to demonstrate antibodies.
• Histopathological examination of tissue reveals intranuclear inclusion bodies.
• Isolation and propagation of virus in CAM of chicken embryo
• Serum neutralization test in chick embryo and cell culture
• Gel diffusion test, PCR

Differential Diagnosis:

1. Ranikhet Disease (ND):

• Respiratory sings are less severe than ILT
• Neurological signs are present along with respiratory signs
• Rapid spread with higher mortality

2. Infectious bronchitis (IB):

• Eggs are abnormal in shape and of poor quality
• Rapid spread with higher mortality
• Reproductive tract are also affected along with respiratory tract

3. Chronic Respiratory Disease (CRD):

• Disease spread slowly with low mortality
• Air sac are mainly affected.
• Air sacculitis with caseous exudate.

4. Avian Influenza (AI):

• Cyanosis of comb/wattle is prominent in case of AI
• Edema of head
• Multifocal hemorrhage in visceral organ.

5. Diptheritic form of fowl pox:

• Yellowish plaques in mouth, larynx, and trachea
• Cutaneous scabs on comb/wattle are often present.

Treatment:

• There is no specific treatment.
• Broad spectrum antibiotics may be used to check secondary bacterial infection.

Control Measures:

• Segregation of affected birds are necessary to prevent further spread of disease.
• Birds may be vaccinated at 1-3 days of age in endemic areas and in other areas, it is done at 3-18 weeks of age.
• Care should be given to avoid mixing of vaccinated and recovered ones with susceptible ones.
• Strict biosecurity measures in poultry house should be followed.
• Disinfection and fumigation of poultry houses and equipment after spread of disease is essential to prevent further spread.
• Extensive movement of people and vehicles within farm should be reduced.
• Separate equipment should be used for each facility to prevent cross-contamination.
• Movement of wild birds and rodents should be controlled within farm.