ACTINOBACILLOSIS Wooden Tongue

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