Download Infectious Laryngotracheitis (ILT)

Haemorrhagic lesions in trachea
Infectious Laryngotracheitis (ILT)
Cause
ILT is caused by a virus belonging to the
herpes group. Only one serotype is known.
Transmission
Field infection occurs from bird to bird by the
respiratory route. Most outbreaks of ILT on
farms are traced back to transmission by
contaminated people or equipment (visitors,
shoes, clothing, egg boxes, used feeders,
waterers, cages, crates etc.). The incubation
period varies from 4 to 12 days.
Species affected
Chickens and pheasants are natural hosts for
ILT.
Clinical signs
Respiratory distress is usually quite
pronounced due to build up of blood,
sloughed tracheal lining and even caseous
exudate in larynx and trachea. When a
caseous plug occludes the larynx or trachea,
the affected chickens will have extreme
difficulty breathing ("pump handle"
breathing) and will frequently die from
suffocation. Mortality is approximately 1 %
per day in a typical ILT outbreak. Milder
forms of ILT outbreaks occur where less
virulent strains of ILT virus are involved.
Conjunctivitis and respiratory sounds
(wheezing) can be observed, with little or no
mortality in such cases.
The disease spreads through a chicken
house more slowly than either IB or ND. Egg
production in laying flocks will usually
decrease 10 to 50 %, but will return to
normal after 3 to 4 weeks.
Diagnosis
In a chicken flock, spreading of respiratory
distress, with possible coughing up of blood
and mortality is indicative of ILT. Bloody
mucus and cheesy exudate can be found in
larynx and trachea. In the laboratory a
definite diagnosis can be made by
histological examination of tracheal tissues
or virus isolation from tracheal mucus in
embryonated chicken eggs.
Treatment and control
Prevention of ILT by vaccination with mild
eye-drop vaccine is by far the best control
method. Sometimes such vaccines are
applied by drinking water or spray methods
with variable success. Even when an
outbreak of ILT has been detected in a
chicken flock, immediate vaccination is
advisable to stop the spread of infection.