Infectious Laryngiotracheitis

Infectious Laryngiotracheitis also known as Haemorrhagic tracheitis in animals.

Infectious Laryngiotracheitis is a viral respiratory tract infection of chicken that may result in severe production losses due to mortality or decreased egg production.

The diseases occur as epizootic and mild enzootic form. The epizootic form of infection is characterized by severe dyspnoea, gasping and expectoration of bloody mucus and high mortality.

The mild enzootic form of infection is characterized by nasal and ocular discharge, mucoid tracheitis, sinusitis, conjunctitvitis, general unthriftness and low mortality.

Etiology

• Gallid herpesvirus 1 is belonging to the sub family Alphaherpesvirinae, family Herpesviridae.
• It is a double stranded DNA virus.
• Latency is a common characteristic feature of this virus.
• The virus is sensitive to detergents and lipid solvents.

Epidemiology

• Chicken is the primary natural host for this virus.
•  Birds of all age groups are affected but this disease is mostly common in adult birds.
•  Mortality may reach 50%.

Transmission

• Natural portals of entry for infectious laryngiotracheitis virus (ILTV) are through the upper respiratory and ocular routes.
• Ingestion is also a mode of infection.
• Transmission occurs more readily from acutely infected birds than through contact with clinically recovered carrier birds shed the virus intermittently.

Clinical manifestation

• Incubation period is 6-12 days.
• Nasal discharge, moist rales followed by gasping and coughing, rattling noise and extension of neck during inspiration are seen.
• Anorexia, depression, reduced egg production.
• Mouth and beak may be blood stained from the tracheal exudates.
• Bird infected with low virulent strain causes mild respiratory signs and reduced egg production, unthirftiness,  watery eyes, conjunctivitis, swelling of infra orbital sinuses and persistent nasal discharge.
• Recovered bird act as carrier and become source of infection for susceptible birds.

Necropsy Finding

• Blood, mucus and yellow caseous exudates in trachea.
• Microscopically desquamative, necrotizing tracheitis.

Diagnosis

• Based on clinical signs and lesions.
• Isolation of virus in chicken embryo by chorioallantoic route of inoculation.
• Cell cultures of choice are Chicken embryo liver cells (CEL), and Chicken kidney cells. A maximum of two passages in CEL and CK cell cultures required.
• Histopathology-Intra nuclear inclusion bodies in tracheal epithelium.
• Detection of viral antigens by PCR.

Differential diagnosis

• Diphtheritic form of fowl pox
• New castle disease
• Infectious bronchitis
• Fowl adenovirus
• Aspergillosis

Prevention and control

• Rearing of birds under dust free environment.
• Mild expectorant can be used.
• Vaccination should be practiced in endemic area.
• Vaccination of adult birds with modified live attenuated vaccine shorten the course of disease during an outbreak.
• Layer flocks generally vaccinated twice before the onset of egg production. The modified live  attenuated vaccine is typically administered by eye drop at 7 weeks of age  and again at 15 weeks of age by eye drops, spray, drinking water.
• Recombinant  fowl pox and herpes virus of turkey viral-vectored vaccines expressing genes of ILT virus are commercially available  for in ovo, subcutaneous and wing web inoculation at least 8 weeks of age or 4 weeks prior to onset of egg production.