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The Control of Gapeworm Infection:
Introduction:
Gapeworms
are the most significant of the worm infestations to affect gamebirds. Infection is caused
by a roundworm called Syngamus trachea and the clinical signs of 'gapes' results from
physical blockage of the windpipe by the worms. Clinical signs may however vary in birds
from the typical outstretched neck and open beak as a bird attempts to breathe, to a cough
and shaking of the head, 'a snick' as the bird attempts to remove the windpipe
obstruction. In some cases these typical signs are not present and affected birds
loose condition and may die with few respiratory signs being seen.
Life-cycle of the parasite:
Adult
worms, present in the windpipe of infected birds, produce eggs that are coughed up by the
bird and are then swallowed to be passed out in the faeces. Worm larvae develop in the
eggs. When another bird picks these eggs up as it feeds that bird will then become
infected. An alternative route for infection is that earthworms eat the eggs containing
larvae and the larvae migrate to the muscles of the earthworm where they remain until the
worm is eaten by another bird. As earthworms can live up to eight years, infection can be
present on land from which birds have been excluded for several years. Once a bird has
swallowed larvae, the larvae make their way to the windpipe via the lungs - this usually
takes about 4-5 days. Therefore, even if birds have been successfully wormed it could be
as little as one week before clinical signs are again seen in the birds. The frequency
between worming needs therefore to be adjusted depending on the level of infection in the
pens.
Control of gapeworm disease:
Clinical
disease is seen in both breeding birds and in rearing stock, particularly those in the
release pens. Birds appear to develop some form of immunity as they get older but this
seems to decline as the breeding season approaches.
If
birds are overwintered on the farm they should be routinely wormed before being moved to
their winter quarters. All breeding stock should be wormed when they are moved to the
breeding pens and if the breeding pens have been used in the previous year the birds
should be wormed again two weeks after the initial treatment. As worm burdens can
adversely affect egg production birds should always be treated if clinical disease is
confirmed.
In
rearing birds disease can be seen from two weeks of age but more usually it is seen in the
release pens. This may be because rearing fields are often changed yearly and although
infection can remain in the earthworm population, levels of infection will have declined
if the area has not been used to rear birds for several years. In contrast release pens
are often in the same place for many years and so infection is able to remain at
significant levels even when birds are not present. In addition, members of the crow
family may also be infected with gapeworms and these may have access to release pens but
should not have access to rearing pens. All birds entering the release pens should be
wormed routinely after being in the pens for 7-10 days. This will allow them to pick up
some worms prior to treatment and hopefully allows some immunity to develop. Some keepers
prefer to wait until clinical signs are present before treating the birds and if the
management of the birds is good this can be very effective.
The
most highly contaminated areas in the release pens are usually around the feeders and
drinkers. Significant control of infection can be obtained by placing the feeders and
drinkers off the ground on a weld-mesh grid to prevent birds picking up food off the floor
from these areas. Regularly moving feeders and drinkers to clean ground will also help
reduce contamination and these measures will also be helpful in controlling
Trichomoniasis. Providing additional feeders and drinkers will further reduce the level of
contamination as will the use of suitable disinfectants on contaminated areas.
It
can be seen from the lifecycle of the gapeworm that complete control of infection is
virtually impossible for game birds. Control of gapes depends both on the sensible use of
medication and good management, particularly of feeding and drinking areas in release
pens. Other respiratory diseases can give similar clinical signs to gapes so it is
important that if clinical disease is seen a correct diagnosis is obtained from your
veterinary surgeon so that appropriate medication can be given.
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