Clinical Manifestations of Canine Nocardiosis

1 Canine Nocardiosis

Epidemiology

The disease occurs sporadically only in some regions, mainly in police and hunting dogs trained in the field, especially where thorny plants are common; the bacteria enter through skin wounded by thorns. Household dogs are less affected. Dogs of any age, breed or sex can be infected, but it does not transmit directly between pets or from pets to people.

Clinical symptoms

The disease is divided into cutaneous, thoracic and systemic forms.

(1) Cutaneous form

Mostly chronic; lesions are mainly under the skin of the limbs and neck. The wound site develops cellulitis, abscesses, pyogranulomas, nodular ulcers and multiple fistulas, involving local lymph nodes.

(2) Thoracic form

Labored breathing, fever, obvious pain on chest compression.

(3) Systemic form

Fever, anorexia, emaciation, cough, labored breathing, twitching of the head, neck and limbs.

Pathological changes

Superficial lymph node enlargement, liver and spleen enlargement, peritonitis, ascites, nodular lesions in lung tissue, enlarged hilar lymph nodes and pleural effusion.

Differential diagnosis

(1) Canine nocardiosis vs. canine distemper

Both show fever, anorexia, cough and, with neurological signs, twitching of head, neck and limbs.

Difference: distemper infects via digestive/respiratory tract, not skin, with biphasic fever. Smears show light-blue nuclei, rose cytoplasm, red inclusions. Nocardiosis smears show beaded bacteria, Gram-positive, some branched and filamentous; in acid-fast stains some bacteria are red.

(2) Canine nocardiosis vs. canine actinomycosis

Both occur in subcutaneous tissue and mucosa, causing local abscesses, pyogranulomas, cellulitis and necrosis, with fistulas discharging pus.

Difference: Nocardia is Gram-positive, non-motile, with hyphae (beaded, some branched and filamentous), acid-fast, aerobic, sensitive to sulfonamides, partly red in acid-fast stain. Actinomyces is a pleomorphic bacillus or branched hyphae, non-acid-fast, anaerobic.

(3) Canine nocardiosis vs. canine pythiosis

Both infect through wounds, invading skin and causing subcutaneous nodular granulomas, abscesses, even fistulas discharging pus.

Difference: treat the lesion pus/exudate with potassium hydroxide, then direct microscopy or stain with Parker ink plus equal-volume 40% KOH; the phycomycete hyphae stain rapidly, showing broad, non-septate, coenocytic hyphae, confirming the diagnosis.

Notes

A preliminary diagnosis is based on epidemiology and clinical signs; confirmation needs lab staining of secretions/biopsy smears or culture.

Prevention and treatment

(1) Prevention

For dogs working in the field, disinfect any wound immediately. Treat sick dogs promptly; if concurrent with distemper, the prognosis is poor.

(2) Treatment

Treatment: surgical curettage, thoracic drainage, and long-term antibiotics and sulfonamides.

1. Co-trimoxazole: 30 mg/kg orally twice daily for 6 months.

2. Penicillin: initial dose 100,000-200,000 IU/kg IM once daily for 6 months.

3. Ampicillin: 20-30 mg/kg orally 2-3 times daily for 6 months.