ACTINOBACILLOSIS (Wooden Tongue)

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ACTINOBACILLOSIS (Wooden Tongue)

Nature of the disease
Actinobacillosis is a specific infectious disease caused by a gram-negative coccibacilli belonging to the genus Actinobacillus. Infection with A. lignieresii is responsible for the wooden tongue disease characterised by the presence of granulomas with pus containing small, hard yellow to white granules. Many other Actinobacillus spp. (e.g. A. actinoides, A. suis, A. pleuropneumoniae and A. equuli) are also pathogens affecting soft tissue.
Classification
SPC List D disease
Susceptible species
Actinobacillus lignieresii affects mostly cattle and sheep but the disease is also known to occur in horses, pigs, dogs and chickens.
Distribution
The disease occurs worldwide. It usually occurs sporadically, preferentially in areas with copper deficiency or pasture with abrasive weeds. High prevalence is recorded in some areas in New Zealand.
Clinical signs 
In cattle, actinobacillosis mainly affects the tongue (‘wooden tongue’), the lymph nodes of the head and neck. The characteristic lesion is a granuloma of the tongue, with discharge of pus to the exterior. Infection usually begins as an acute inflammation with sudden onset of:
  • inability to eat or drink for several days
  • drooling saliva
  • rapid loss of condition
  • painful and swollen tongue
  • nodules and ulcers on the tongue
Animals may occasionally die from starvation and thirst in the acute stages of the disease. As the infection becomes chronic, fibrous tissue is deposited and the tongue becomes shrunken and immobile and eating is difficult.

Local lymph nodes may be enlarged and abscesses may form and discharge creamy pus, which may contain granules.

Less commonly the jaw, lungs, oesophageal groove, or udder may be affected. Rarely granulomas may occur anywhere on the skin or internal organs.

In sheep, the tongue is not commonly affected. Multiple purulent granules occur in the skin if the face, lips, nose, jaw and neck with regional lymph nodes usually being involved. Lesions develop into abscesses that rupture and discharge yellow-green pus containing granules. Affected sheep have difficulty in eating and many die of starvation.
Post-mortem findings 
At post-mortem, animals will often be in poor condition. Granulomatous lesions containing pus may be seen in and around the mouth. There are often ulcers up to 1 cm in diameter. Encapsulated abscesses may be found in local lymph nodes. In chronic cases there is fibrous connective tissue proliferation and hardening and distortion of the tongue (‘wooden tongue’) is common.
Differential diagnosis 
Similar granulomatous lesions may be seen with infections caused by:
  • Actinomyces bovis
  • Staphylococci spp
  • Streptococci spp
  • Corynebacterium pyogenes
Specimens required for diagnosis 
The disease can be strongly suspected on clinical grounds. Diagnosis can be confirmed by microscopic examination of smears made from pus, or by culturing the organism.

The pus contains small brownish-white granules, which upon microscopic examination are seen to consist of colonies of Gram- negative, rod-shaped bacteria surrounded by club-shaped structures.
Transmission   
The organism enters tissues of the mouth through epithelial damage associated with rough fodder e.g. containing sharp stems or thorns, where it multiplies locally. A. lignieresii is considered to be a normal rumen inhabitant of sheep and cattle. It survives 4 to 5 days in forage or hay and consequently actinobacillosis is not considered to be a highly contagious disease.
Risk of introduction   
The risk of actinobacillosis can be reduced by not grazing animals on poor quality, coarse fodder, but this is often not feasible.
Control / vaccines  
Actinobacillosis is readily treated. Treatment can involve surgical debridement and flushing with iodine. Administration of potassium iodide orally (6 to 10 g a day for 10 days) or intravenous injection of sodium iodide at 10 % (8 g for 100kg) are effective to stop the acute signs of the disease within two days. 
Antibiotics can be used; streptomycin is considered the treatment of choice, tetracylcines and tilmicosin are also effective.

No vaccines are available. 

Control of actinobacillosis is best achieved by early recognition and prompt treatment of cases; isolation or disposal of animals with disease is recommended.
References
  • Actinobacillosis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 429; 1016
  • Actinobacillosis, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 852-854