B107 - DERMATOPHILOSIS

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B107 - DERMATOPHILOSIS

Nature of the disease
Dermatophilosis, (also known as streptothrichosis and sometimes improperly called mycotic dermatitis) is due to a actynomyces bacterium, Dermatophilus congolensisis. It causes an exudative, pustular dermatitis that affects a wide range of animals and is particularly severe in Ruminants when associated with infestation by the tick Amblyomma variegatum
Classification
OIE List B disease
Susceptible species
  • Cattle, sheep, goats, horses
  • Less frequently pigs, dogs, cats and humans (minor zoonosis)
  • Wild species: mammals and reptiles.
Distribution
Dermatophilosis is an ubiquitous disease and is found in all continents.
Clinical signs 
Dermatophilosis occurs in a chronic or an acute form.

The chronic form is the most common. It involves non-pruriginous lesions on the upper part of the body (neck, withers, back and hindquarters), towards the ends of the legs, but also in the anal and scrotal region, on the teats and on the fetlocks. In small ruminants, the lesions are concentrated on the head.

The acute form is less common, occurring in predisposed individuals in the humid tropics (susceptible imported breeds), in the presence of ticks (Amblyomma variegatum). Lesions are found all over the skin of affected animals. Their condition deteriorates and they die within a few weeks of the advent of scabby lesions.

At the initial stage of the disease there is papulae that raise the fur and a coagulated serous exudate. The number of lesions and their volume increase until they coalesce. Later there is a hyperkeratosis stage, with the formation of yellowish, thick and more or less flaky scabs.

Post-mortem findings 
Animals that die from Dermatophilosis exhibit extended and generalised dermatitis and sometimes pneumonia and signs of intercurrent diseases.
Differential diagnosis 
  • Nodular dermatitis 
  • Contagious ecthyma of small ruminants, 
  • Mange (demodectic and chorioptic), 
  • Staphylococcia, 
  • Ringworm, chorioptic mange, 
  • Besnoitosis,
  • Photosensitivity.
Specimens required for diagnosis 
Laboratory diagnostic is usually done by identification of the bacterium. from  scabs or smears of the exudate beneath the scabs. Techniques include direct detection by microscopic examination of stained bacterium and immunofluorescence.

Serological diagnosis by ELISA is also available.

Transmission   
Dermatophilosis is transmitted by direct contact between animals but also through indirect contact such as housing or biting arthropods. There are a number of risks factors such as:
  • Humidity,
  • Warm temperature,
  • Abundance of biting arthropods (Amblyomma variegatum, Boophilus microplus, Hyalomma), Sarcoptes mites, Demodex mites, mosquitoes and stinging and bloodsucking flies,
  • Genotype of animals.

Risk of introduction   
The risk of introducing dermatophilosis is through importation of live animals. Chronic and unapparent carriers represent the biggest risk.
Control / vaccines  
Animals can be treated with antibiotics that diffuse well in the tegument such as erythromycin, penicillin, spiramycin, tetracyclines.

The control of Dermatophilosis should take into account control of arthropods vectors and the elimination of chronic carriers.

There is no vaccine available.

References
  • Dermatophilosis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 613-615
  • Mycotic Dermatitis, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 857-861
  • Office International des Epizooties, 2003