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)