Introduction:
Coronavirus infection in pheasants
tends to cause clinical problems mainly in the breeding stock. It was first reported in
Great Britain causing nephritis and significant mortality in 1994. Since then the disease
has become more common. Blood samples from clinically normal pheasants have shown
antibodies to Coronavirus suggesting birds may be affected without showing signs of
disease. There are many different strains of Coronavirus – those affecting chickens
tend to cause respiratory disease or in laying birds production may be decreased and
eggshell quality affected but kidney involvement is rare. In pheasants, egg quality does
not appear to be affected but egg production and fertility may be depressed. It is
believed that the strains affecting pheasants and causing clinical disease are distinct
from those affecting chickens. There is no medication available to control outbreaks of
disease and the use of antibiotics and / or multivitamins has no discernible beneficial
effect.
Spread of
disease:
The source of infection in
pheasant breeding flocks usually cannot be determined but it is most likely introduced by
a pheasant that is carrying the virus without showing any clinical signs. In flocks were
birds are caught up after the shooting season, and with no previous history of disease,
then the most likely source of infection is a bird that has come in over the boundary. If
birds have been bought in then disease could enter in birds that appear clinically normal.
Chickens and other poultry could possibly carry infection but it is less likely that they
will carry pheasant strains of the virus. In chickens airborne spread over 1000m has been
reported so both birds resident within that radius but not actually on the site of
infection and infected birds being transported along roads within 1000m of stock are
theoretical, but unlikely, sources of infection.
Control of
Corona Virus infections:
Most of the research into
Coronavirus infections has been undertaken in poultry. The virus spreads rapidly amongst
birds in a flock via both the respiratory tract and via faeces. After clinical recovery
the virus can persist in a bird for several months. True egg transmission is not believed
to be significant but transmission by surface contamination of eggs is likely to occur if
eggs are not adequately disinfected. There is no evidence of spread by insects. Good
biosecurity is required to prevent spread between flocks.
In cases of disease in pheasants
it is likely that in addition to caught-up breeding birds being affected the disease may
also be present in the wild population. There is no absolute way of preventing outbreaks
in subsequent years but with good management techniques the disease may cease to appear in
the breeding birds on sites that have previously been affected.
The disease in the wild population
will be lower if every effort has been made to reduce the number of wild birds to a
minimum by shooting out at the end of the season. Known infected birds – and all the
birds in an affected breeding flock should be assumed to be infected – should not be
released back into the wild as this will form a large reserve of infection available to
the next generation of breeding birds.
In an attempted to induce immunity
in the birds, poultry vaccines have been used on the basis that if a few infected birds
enter the breeding pens then the spread of disease may be prevented or reduced. As there
are many distinct strains of Coronavirus it is not possible to ensure control with the
limited number of poultry vaccines that are available. Pheasants may be vaccinated by
eye-drop as they enter the laying pens.
An interesting outbreak of disease
occurred during the 2004 season when disease was diagnosed in 8-week-old birds in a
release pen. The clinical signs of nephritis and visceral gout (urates covering internal
organs) were similar to those seen in breeding birds although the level of mortality
experienced was not as high. The birds had been in the pen for about two weeks and there
was no history of disease in the flock of origin. The Coronavirus isolated in this case
showed no significant relationship to a panel of IB reference sera. It was concluded that
the birds were most likely infected after entering the release pen by wild birds present
in the pen.
What to do next:
As with all disease outbreaks it
is important that a rapid diagnosis is made – in the case of Coronavirus to prevent
spread of disease to other flocks and so that a programme of control for subsequent
seasons can be formulated.
