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Rotavirus Infection:
Rotavirus
infection can be seen in birds of all ages but its effects are most dramatically
seen in young birds between 3 and 14 days old. The infection affects the gut
resulting in wet droppings, the birds are rapidly depressed and vent pecking is
common. Affected birds often eat the litter and may die because of the damage
done to the gut by the virus or by gizzard impaction. A significant number of
the birds that survive the infection become stunted. Although disease and deaths
are most commonly seen in younger birds all ages can be affected. In the older
birds other viruses, in addition to Rotavirus, are often isolated from scouring
birds. Many birds suffer from sub clinical disease so the absence of clinical
disease does not ensure that Rotavirus is not present within a flock. Falls in
egg production due to Rotavirus infection have not been recorded in game birds
but have been seen under experimental conditions in chickens and turkeys.
Birds
start to scour 2 – 5 days after becoming infected. Affected birds will huddle
and deaths may be seen in severe cases within a few hours of the first clinical
signs being observed. Death rates will vary but can be as high as 10% in severe
outbreaks. Whilst showing clinical signs the affected birds pass large numbers
of virus particles in their droppings and they can continue to pass virus for up
to two weeks.
The
virus particles excreted are able to persist on the land for some considerable
time and so the virus can be transmitted between birds both by direct contact
and by the virus being transported about on contaminated boots, equipment etc.
There is no evidence that the virus is spread on or in the egg but the fact that
birds can show disease so early in life does suggest that some birds are exposed
to the virus at a very early age. There is no evidence of birds carrying the
infection for long periods of time in their guts but with older birds often
having sub-clinical infection, the virus can be transmitted about a site from
the older to the younger birds.
Due
to the persistence of the virus on the ground it is practically impossible to
ensure that flocks remain clear of the disease. Transmission of the virus can be
minimised by ensuring that the most vulnerable young stock are visited before
older stock on the farm and that boots and clothing are regularly cleaned and
changed when moving between older and younger stock.
It
is not possible to diagnose Rotavirus infection from a simple post-mortem
examination as the lesions seen can be caused by a variety of conditions.
Further laboratory testing is required to confirm the presence of Rotavirus.
There are some kits designed to rapidly identify the presence of mammalian
Rotaviruses but these are not very useful in detecting Rotaviruses from
gamebirds as they give too may incorrect results. For accurate diagnosis
Electron microscopy or a PAGE (PolyAcrylamide Gel Electrophoresis) test that
detects the presence of the genetic material from the Rotavirus is required.
With both these tests, results will not be immediately available at the time of
the post-mortem examination.
There
is no specific treatment for Rotavirus infection. Affected birds need to be
given re-hydration salts via the water to prevent dehydration and using a water
disinfectant that is effective against viruses E.g. SWC V3 or Virkon-S, will
prevent birds being infected from a contaminated water supply. In some cases
antibiotics may be effective against any secondary bacterial infections but will
have no direct impact on the course of the Rotavirus infection. Vaccines to
control Rotavirus are not at present commercially available but The Game
Conservancy has being doing work with a test vaccine, which appears to have had
some success in their trials. However given the different strains of virus that
occur, the development of an effective commercial vaccine may prove difficult.
Conclusions:
1)
Where
rotavirus infection is suspected, ensure adequate testing is done to confirm the
diagnosis.
2)
In suspect cases and even before diagnosis, chicks should be given
re-hydration salts and the water supply should be treated with a suitable
disinfectant. The sooner treatment commences the less should be the losses.
3) Check
hygiene practices on the site. Are there suitable facilities for staff to clean
boots, equipment and themselves?
4) Check
that as a general rule younger birds are visited first on the site. If sick
birds are found then clean boots, equipment and hands before attending to other
birds on the site. Any birds known to be sick should always be visited last and
if possible isolated from other birds on site.
5) Check
stocking levels and other condition in the houses to ensure other stresses on
the birds are kept to a minimum.
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