VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

PATHOGENESIS

• Dermatophilus congolensis causes very severe clinical disease and its infection is most common in tropical and subtropical regions.

Diseases caused by Dermatophilus species

• Dermatophilus congolensis mainly affects Cattle, horses, sheep and goats, but many animal species and man can be infected.
• The disease has many names
  • Cattle : Rain scald, Streptothricosis, Dermatophilosis
  • Sheep: Mycotic dermatitis (general infection), lumpy wool (wool- covered skin) and strawberry foot rot (skin of lower leg and coronet)
• The bacterium produces disease in many animal species. It is also a zoonosis.
• The common name for the disease is dermatophilosis or streptothricosis.
• As far as is known the bacterium is considered an obligate parasite, living only on animals.
• Infection is spread by contact, biting insects, fomites and by other unknown means.
• Moist conditions and high relative humidity are known to promote the prevalence of the disease.
• D. congolensis causes skin infections most commonly seen in cattle, sheep, goats, horses and polar bears in zoological collections.
• The infec­tion is characterised by the formation of thick crusts which come away easily with a tuft of hair, leaving a moist, depressed area with bleeding points from capil­laries.
• Infections can be localised but have a tendency to spread over large areas of the body and the morbid­ity and mortality can be high, especially in tropical regions.

• The position of the lesions varies with the predisposing conditions.
• In periods of high rainfall the lesions tend to occur along the backs of animals.
• Where there is a heavy infestation with Amblyomma ticks the lesions are present in the predilection sites of the ticks: dewlap, axillae, udder and scrotum.
• In the dry season, in tropical regions, when feed is scarce the lesions are on the muzzle, head and lower limbs due to the animals foraging in thorn-covered scrub.
• Though the disease does not lead to death in the adult cattle, deaths in young goats and cattle have been reported.
• In sheep, the disease is called mycotic dermatitis and is seen in three forms
  • Dermatitis of the wool-covered areas of the body or lumpy wool
  • Dermatitis of the face and scrotum; and
  • Dermatitis of the lower leg and foot, which may result in severe ulcerative dermatitis referred to as "strawberry foot rot".
• Infections have been reported in dogs and cats. In dogs, spontaneous dermatophilosis has been confined to the intugementary structures, whereas deeper tissue lesions in the form of abscesses have been reported in the felines.
• Lymph node enlargements with draining fistulas of the subcutaneous and submucosal tissues have also been reported in cats.