Mycobacterium spp

From Dog
Atypical mycobacterial infection in a dog which responded to antimicrobial therapy[1]
Disseminated Mycobacterium spp in a dog with weight loss, diarrhea and ascites
Opportunistic leproid granuloma on the hip of a dog[2]
Pulmonary granuloma from a dog infected with M. tuberculosis, showing numerous acid-fast bacilli (stained bright red), demonstrated by using Ziehl Neelsen staining[3]
Gross pathological changes of the lung and heart observed in a dog which died from M. bovis infection[4]

Mycobacterium spp are a broad group of zoonotic[5] Gram-positive aerobic bacteria which cause dermal, pulmonary and systemic diseases in dogs.

Mycobacteria are widespread saprophytes, but approximately one-third of identified species are also opportunistic pathogens in humans and dogs, associated with skin, soft tissue, bone, and pulmonary infections as well as disseminated disease. Clinical and experimental evidence indicates a major role for the cell-mediated immune response in the pathogenesis of infection[6].

Dog to human and human to dog infections have been reported commonly[7][8], and many affected dogs live a greater proportion outdoors in rural environments. Immunosuppression appears to play a pivotal role in etiopathogenesis in household pets[9].

Species which are pathogenic to dogs include:

  • Mycobacterium tuberculosis complex (zoonotic)
- Mycobacterium tuberculosis[10][11]
- Mycobacterium bovis[12]
- Mycobacterium microti
  • Mycolactone-producing mycobacteria
- Mycobacterium ulcerans
  • Mycobacterium fortuitum clade
- Mycobacterium fortuitum[13]
  • Mycobacterium avium complex
- Mycobacterium avium sub paratuberculosis (paratuberculosis)[14]
- Mycobacterium avium sub hominissuis[15]
- Mycobacterium avium sub intracellulare
  • Mycobacterium chelonae clade
- Mycobacterium chelonae (zoonotic via bite-wounds)[16]
  • Mycobacterium smegmatis clade
- Mycobacterium goodii
- Mycobacterium smegmatis
  • Ungrouped
- Mycobacterium flavescens
- Mycobacterium kansasii[17]
- Mycobacterium vaccae (saprophytic; use as adjuvant in atopy)[18]

Atypical mycobacterial dermatitis

Atypical mycobacteria, caused by M. avium intracellulare-complex which can create a number of different clinical symptoms including scale, draining nodules and hair loss.

The primary routes of exposure in dogs and cats to 'atypical' mycobacteria are direct contact or ingestion of organisms from soil, water, or animal carcasses or feces; aerosolized transmission is considered less common. All species of non-tuberculous mycobacteria are considered of low virulence, typically causing severe disease only in immunosuppressed individuals.

Leproid granuloma syndrome

Canine leproid granuloma syndrome was coined to describe a nodular pyogranulomatous disease affecting the skin and subcutis of dogs[19] and affects principally short-coated breeds[20].

With M. ulcerans, M. fortuitum, M. goodii and M. smegmatis infections, lesions are usually confined to the skin, with leprosy-like dermal ulcers and panniculitis[21][22].

Infections often involve single or multiple nodules, usually on the head and especially on the dorsal fold of the ears, but the cervicothoracic region, dorsum or flank are also affected. Patients are often systemically well, although fever, local pain and lameness may be noted.

The pathology of canine leproid granuloma syndrome is highly uniform and is suggestive of saprophytic mycobacterial involvement[23]. Histopathological findings include nodular to diffuse pyogranulomatous, lymphoplasmocytic inflammatory infiltrates, with or without necrosis, localized in the dermis or subcutaneous tissue.

Diagnosis of leproid granuloma is based on microbial culture[24] or PCR assays, which is usually required, particularly for those mycobacteria which are nonculturable or difficult to culture[25][26][27].

Disseminated tuberculosis

While uncommon in both dogs and cats, historical data suggests that dogs are more likely to be infected with M. tuberculosis following exposure to infected humans, while cats were more likely to be infected with M. bovis with exposure assumed to be related to the consumption of contaminated animal products[28].

Clinical findings in dogs infected with M. tuberculosis include anorexia, weight loss, vomiting[29] and leukocytosis[30]. Radiography usually reveals pleural and pericardial effusion, ascites, and hepatomegaly[31].

Disseminated pulmonary infections involve mediastinal lymphadenopathy[32] and calcospherite-like bodies and caseous necrosis of the trachea[33] and pulmonary parenchyma, with formation of tubercle-like granulomas in lungs and, rarely, the liver[34] and brain[35]. Generalized peritonitis has also been reported with M. microti[36].

Chronic cases may be associated with hypertrophic osteoarthropathy[37].

As with Escherichia coli, nitric oxide-resistant Mycobacterium spp have been associated with poor outcomes[38].


Treatment of localized lepromatous-like infections involves a combination of surgical debridement and medical therapy with drugs such as doxycycline and ciprofloxacin[39].

Prolonged antibacterial therapy is required for disseminated infections with drugs such as clarithromycin[40], moxifloxacin[41], ciprofloxacin[42], pradofloxacin[43], clofazimine, rifampicin and dapsone[44].


  1. Animal dermatology
  2. Medical dictionary
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