Actinobacillosis in animals

Actinobacillosis is an uncommon but impactful disease that causes chronic swelling and inflammation of soft tissues in animals, especially ruminants like cattle, goats, sheep, and buffalo. Best known for causing a condition called “wooden tongue,” it leads to firm, painful swelling of the tongue and other tissues(Lymph nodes, skin, and may organs). The disease can also rarely appear in horses or humans, often resulting from bites or direct contact with infected animals.

Etiology of Actinobacillosis:

• The primary causative organism is Actinobacillus lignieresii, a gram-negative bacterium.

• It normally resides harmlessly in the upper digestive tract of ruminants (e.g., cattle, sheep, goats).

• It becomes pathogenic when it invades deeper soft tissues through cuts or abrasions in the skin or mucosa.

• Once inside the tissue, it triggers a chronic pyogranulomatous reaction, especially in the tongue and surrounding areas.

• Lesions often yield pure cultures of A. lignieresii, though secondary bacterial infections are common.

• New research reveals that strains isolated from horses, although phenotypically similar, are genetically distinct from ruminant strains.

• These equine isolates have been classified separately as Actinobacillus genomospecies 1 due to their unique genotypic traits.

Epidemiology of Actinobacillosis:

Occurrence:
Actinobacillosis affects cattle and sheep globally. It’s usually sporadic but can cause outbreaks, especially in sheep flocks and cattle herds exposed to rough forage.

Transmission:
Actinobacillus lignieresii lives naturally in the mouths of ruminants. It enters soft tissues through injuries to the tongue, lips, or skin, often caused by coarse feed or sharp objects.

Risk Factors:
Risk increases with abrasive pastures (e.g., burnt peat, prickly pear), sharp-edged straw, copper deficiency, and trauma from equipment. Subclinical infections are common.

Zoonotic Risk:
Rarely infects humans, typically via animal bite wounds, but is not considered a major zoonotic threat.

Pathogenesis of Actinobacillosis:

• Infection begins locally when A. lignieresii enters through minor wounds or abrasions in soft tissues.

• It initiates an acute inflammatory response, which progresses into granulomatous lesions containing necrotic tissue and pus.

• Suppuration (pus formation) is common, and abscesses may rupture and discharge externally.

• The infection often spreads to nearby lymph nodes, leading to regional lymphadenitis.

• In cattle, involvement of the tongue leads to early-stage painful enlargement, which disrupts normal eating by impairing the animal’s ability to grasp and move feed within the mouth.

• As the disease advances, the tongue becomes fibrotic and deformed, severely affecting feeding behavior.

• In rare cases, the infection may become visceral, affecting internal organs in a pattern similar to actinomycosis.

Clinical signs:

Cattle

• Anorexia

• Hypersalivation

• Tongue-chewing

• Tongue swelling

• Tongue hardness

• Pain on palpation

• Nodules

• Ulcers

• Fibrosis

• Tongue immobility

• Prehension difficulty

• Lymphadenitis

• Node rupture

• Odorless pus

• Slow healing

• Recurrence

• Snoring respiration

• Dysphagia

• Cutaneous granulomas

• Red nodules

• Painful swellings

• Bleeding lesions

• Caseation

Sheep

• Jaw lesions

• Facial nodules

• Nasal involvement

• Yellow-green pus

• Granular discharge

• Lymph node swelling

• Fibrous thickening

• Lip scabbing

• Nasal discharge

• Starvation

• Mastitis

Camels

• Lip abscesses

• Mandibular swelling

Buffaloes

• Skin lesions

• No tongue signs

Horses

• Rare cases

• Tongue infection

• Muzzle lesions

• Intermandibular swelling

• Other soft tissue sites

Differential diagnosis by:

1.  Rabies
2. Esophageal obstruction
3. Tuberculosis
4.  Cutaneous lymphosarcoma
5. Foreign bodies in the mouth

Necropsy Findings:

In cattle, necropsy is rarely carried out for diagnosing actinobacillosis. However, in sheep, notable findings may include lymphatic vessel inflammation (lymphangitis) and abscesses filled with thick, sticky yellow-green pus near the site of infection. When tissue samples from these lesions are stained, characteristic “club-shaped” bacterial colonies can be observed under a microscope. Laboratory culture of these tissues typically confirms the presence of Actinobacillus lignieresii.

Treatment of Actinobacillosis:

Primary Treatment – Iodides

• Potassium iodide

  • Oral route

  • 6–10 g/day

  • Duration: 7–10 days

  • Discontinue on iodism signs (e.g., tearing, anorexia, dandruff, coughing)

• Sodium iodide

  • IV injection

  • 70 mg/kg as a 10–20% solution

  • Rapid improvement (within 24–48 hrs for soft-tissue lesions)

  • Repeat in 10–14 days for bony lesions

Adverse Effects

• Iodism: lacrimation, anorexia, dandruff, coughing

• Injection reactions: restlessness, rapid breathing, staggering

• Pregnancy risk: possible abortion in late-term cows (rare)

• Subcutaneous irritation: swelling and pain (sheep use standard route)

Sheep Dosing (SC)

• Sodium iodide

• 20 mL of 10% solution

• Weekly for 4–5 weeks

Antibiotic Therapy

• Streptomycin (IM)

• Penicillin

• Sulfonamides

• Broad-spectrum antibiotics

• Often used in combination with iodides

Adjunct Therapy

• Isoniazid

  • 10 mg/kg/day

  • Oral or IM

  • Duration: 3–4 weeks

  • Effective for actinomycosis and an adjunct in actinobacillosis

Cutaneous Cases

• May require extended therapy

• Streptomycin and/or dihydrostreptomycin

• Duration: 2–4 weeks

Prevention:

• Feed Carefully: Offer soft, clean feed that won’t cause cuts or abrasions inside the mouth.

• Keep Equipment Clean: Regularly disinfect feeding tools and water troughs to lower bacterial exposure.

• Monitor Animals Closely: Look for early signs like swelling around the mouth or difficulty eating, and act quickly.

• Separate Infected Animals: If you suspect a case, isolate the animal to prevent spreading contamination through shared spaces.

• Support General Health: A balanced diet and a stress-free environment improve animals’ natural resistance to infections.

• Staff Awareness: Ensure farm workers know the symptoms and importance of early intervention.

Conclusion:

Actinobacillosis, especially known for causing “wooden tongue” in cattle, is a localized bacterial infection that can significantly impact animal health if left untreated. Although not contagious in the usual sense, it spreads within the animal’s body after injury, making early detection vital. With timely treatment—usually involving iodide therapy and supportive care—most animals recover well. Awareness, prompt intervention, and good management practices are key to reducing its occurrence and ensuring herd health.

Frequently Asked Questions (FAQs)

Q1: What triggers actinobacillosis in animals?
A: It usually occurs when the bacterium Actinobacillus lignieresii enters soft tissues through minor injuries, especially in the mouth or tongue.

Q2: Which species are typically affected?
A: Cattle are most commonly affected, but the condition can also occur in sheep and other ruminants.

Q3: What signs should I look for?
A: Look for a swollen, firm tongue, drooling, difficulty eating, or hard lumps under the skin, often around the jaw or head.

Q4: How is this condition treated?
A: Sodium iodide given orally or intravenously is the main treatment. In some cases, antibiotics like oxytetracycline may be added to support recovery.

Q5: Is actinobacillosis contagious between animals?
A: No, it doesn’t typically spread from one animal to another. It starts from internal infection due to trauma.

Q6: Can it spread to humans?
A: Very rarely. It’s considered a low-risk zoonosis, and standard hygiene when handling animals helps prevent exposure.