Gangrenous dermatitis (GD) is a bacterial disease of
chickens and turkeys which primarily affects the skin and tissues below the
skin in the abdomen of the bird. Gangrenous dermatitis is bilieved to be caused
by species of clostridia, usually Clostridium
perfringens or Cl. Septicum, but
many other bacteria have been isolated from Gangrenous dermatitis lesions.
Dr Donald Ritter, director of health services,
Mountaire Farms, Inc, speaking at Delmarva Poultry Industry National Meeting,
said that the number of flock affected by Gangrenous dermatitis in commercial
poultry has been on the rise in the USA in recent years.
Gangrenous dermatitis occurs in poultry flocks raised
on built-up litter. Dr Ritter said that historically, this condition has been
linked to flocks whose immune systems were impaired by prior infection with
infectious bursal disease virus or with chicken anaemia virus, but that many
flocks with Gangrenous dermatitis today appear to have protection against these
viruses.
Broiler flocks with Gangrenous dermatitis experience a
sudden increase in mortality at 5-7 week of age – up to 1% daily for up to 2
weeks. Turkey flocks experience a similar mortality pattern but from 12-20
weeks of age. It is rare to find birds with Gangrenous dermatitis lesions alive.
Clostridia are spore-forming and so they can persist
in the environment for long periods of time and are resistant to most
disinfection procedures. Once affected by Gangrenous dermatitis, many houses
envolve into endemic Gangrenous dermatitis sites where the disease recurs in
most flocks. There is also a seasonal pattern observed in the incidence of
Gangrenous dermatitis cases in chicken: the greatest number of cases occurs
during spring and summer. Penicilin is the treatment of choice.
Gangrenous dermatitis skin lesions consist of dark
purple areas with excessive red thickened serous exudate (‘jelly’) with
associated emphysema (‘gas’) in subcutaneous tissue around the hips, abdomen
and occasionally the wings in chickens. Typical skin lesions are located in the
tail head area of turkeys. Some lesions are close to skin scratches in
de-feathered hip areas.
Because Gangrenous dermatitis lesions are often found
close to damaged areas of skin caused by toe-nail scratches, the presumed route
of infection has been through the damage skin. The localised skin infection
then produces bacterial toxins that quickly kill the bird. However, many birds
with Gangrenous dermatitis lesions have intact skin in affected areas, or may
have lesions on the wings or crop areas of the bird also unaffected by skin
damage.
Clostridia form part of the normal anaerobic
intestinal flora of poultry, so the itestine provides another possible direct
route of infection. The bacteria may enter the bloodstream via mucosal
disruption in the gut. Damage to the gut caused by coccidia has been proposed
as a source of Gangrenous dermatitis infection.
Dr Ritter
conclude, “I believe that Gangrenous dermatitis will be proven to be primary
‘gut disease’ when all field and research data have been collected and
carefully scrutinised. (Watt publishing)
