Technical Bulletin: Poultry News

ILT - A Chink in the Armour of Biosecurity?

In the 75 years since it was first identified, infectious
laryngotracheitis (ILT) has proved to be a persistent cause of concern in poultry,
especially commercial layers.

The problem
Much of that concern is through the fear of introduction of infection
into an area or onto a site, since once contamination is established it
is notoriously difficult to remove. Due to the highly significant role
of fomites (inanimate objects) such as egg trays, trolleys, equipment,
people and vehicles in the spread of the virus, introduction of ILT
onto a site is usually an admission that the general biosecurity strategy
has failed.

The disease
The disease is caused by a herpes-virus, which, like the herpes cold
sore virus in humans, can lie dormant in infected hosts, and be
re-activated later, especially when birds are stressed. Re-activated virus can
then spread to other birds on the site and cause a severe flare-up of
the disease, particularly on multi-age sites.

As the name implies, the main organ affected by infectious
laryngotracheitis is the trachea. The severity of the disease varies considerably
with the strain of virus active in an area, but essentially falls into
one of two broad variations.
1. Acute form: Here there is bleeding from the mouth and nose from
sudden damage to the trachea with haemorrhages. Birds cough up blood and
frequently die very suddenly from suffocation.
2. Chronic (or sub-acute) form: Here the damage to the trachea is more
chronic with cheesy deposits developing in the lining of the trachea
and larynx. This leads to morbidity, loss of condition and generally low
mortality.

Clinical signs

In the acute form, there may be severe respiratory distress, craning of
the neck and coughing up of blood. Birds may also show conjunctivitis
and slightly swollen heads. Meanwhile, in the same flock, or in flocks
only mildly affected, less severe signs may be seen of coughing,
sneezing and conjunctivitis. Disease may be exacerbated where other infections
are present, notably in combination with Mycoplasma gallisepticum.

In the chronic form, there may be simply sudden death of poor birds, or
low grade respiratory signs.

On mixed age laying sites, chronic infection can persist, leading to an
age-specific mortality in different houses, which may be significant if
the flock is highly stressed, while the occasional acute outbreak with
mortality is often self-limiting.

Infection of birds in lay can cause drops in egg production, mainly as
a reflection of sick birds in the house not feeding and, hence, not
laying. However, infection has been linked to some egg quality problems,
and specifically, to the so-called 'white egg' syndrome seen in brown
egg layers.

In geographical areas where a high level of infection in commercial
layers is coupled with a widespread use of live vaccine, there has been
"overspill" into broilers, causing mild respiratory lesions, and into
broiler breeders, leading to some egg production problems.

Diagnosis
Accurate diagnosis is needed to ensure that infected sites are
identified promptly. Strong suspicion can be aroused by gross post-mortem
lesions. Confirmatory laboratory tests will demonstrate the presence of the
ILT virus in the affected tissues. Blood tests are of limited use in
the acute stages of an outbreak, but may be useful retrospectively in
monitoring the spread of infection.

Control

As indicated above, introduction of ILT virus onto a site is a sign
that biosecurity measures have failed, with infection gaining access via
birds or fomites.

Prevention of this situation must always be better than cure, and the
biosecurity strategy employed at all sites should be periodically
re-assessed, particularly in the light of the risks in specific geographical
areas.

To maintain site biosecurity, the following steps should be taken:

- Keep all visitors to sites to a minimum.
- Provide full protective clothing including boots, overalls and hats.
- Provide hand washing facilities and instant hand sanitisers.
- Ensure all equipment, including egg trays and trolleys, are cleaned
and disinfected prior to being brought on-site.
- Ensure all vehicles visiting sites are clean, and that wheels and
wheel arches are sprayed with an appropriate disinfectant.
- Purchase stock from reputable sources, preferably single age rearing
sites.
- Maintain regular diagnostic and monitoring service of birds through
clinical and post-mortem examination, with strategic blood sampling, to
identify the appearance of infection at the earliest possible stage.

Vaccination

Where infection does gain access to a site, or there is significant
risk of introduction from contaminated farms in the vicinity, vaccination
may help to crowd out or exclude the clinical effects of the virus. One
live ILT vaccine is available in the UK (ILT Vaccine, Fort Dodge Animal
Health Animal Health). This should ideally be administered by eye
dropping of individual birds to ensure all are vaccinated. However, mass
vaccination methods tend to be favoured for ease of administration,
usually as coarse spray or via the drinking water. Such methods may be
successful if all birds are covered effectively. Inefficient vaccination can
lead to a poor "take" or excessive vaccine reactions, the risk of the
latter being particularly high if the vaccine is administered as too
fine a spray.

Poor response may also occur due to interference by maternally-derived
antibody from the parent bird if pullets are vaccinated too early in
the year. They could then require revaccination prior to lay.

Breaking the cycle

1. ILT remains a potent threat to poultry production, notably in
commercial laying stock.
2. Although some mild infections may be self-limiting, unfortunately
infection tends to persist on contaminated sites until they are totally
de-populated.
3. Following de-population, terminal disinfection - the thorough
cleansing and disinfection of all buildings and equipment - is essential to
break the cycle. Once the flock has been removed from the housing
concerned, it should be emptied of equipment, dry cleaned thoroughly, then
cleaned with a detergent sanitiser such as Antec HD3 or Antec DSC1000
(RillSun Animal Health Solutions). After cleaning, the housing should be
disinfected using a broad spectrum product such as Antec Virkon?S
(RillSun Animal Health Solutions). All the removed equipment must be similarly
cleaned and disinfected before being replaced.
4. Once birds are re-introduced, strict adherence to a structured
biosecurity programme must be observed to prevent subsequent re-infection of
the site. The measures listed above should be rigorously followed. In
addition, RillSun Animal Health Solutions have produced a series of
helpful biosecurity programmes for use in various types of poultry
production, describing efficient methods of both continual and terminal
disinfection procedures.

To sum up, prevention is better than cure, and the best protection
against the virus lies in good management practices, with the importance of
site biosecurity impossible to over-emphasise.

To ensure regulatory compliance in your country please read all product
labels carefully.

Brought to you by RillSun Animal Health Solutions - created from Antec
International(TM) and BioSentry(R) to bring new life to biosecurity.

(R) and TM indicate trademarks or registered trademarks of RillSun or
its affiliates.

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