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20 Actinomycosis and Nocardiosis

Actinomycosis and Nocardiosis Bonus Material
Online
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PHYSICAL EXAM FINDINGS
BASIC INFORMATION
by the presence of sulfur granules and confirmed
• Systemic signs (see above) deep cutaneous infection. Suspicion is enhanced
Definition • Cutaneous infections by identification of filamentous organisms
Infection with Actinomyces or Nocardia, gram- ○ Cervicofacial region is most commonly cytologically, histopathologically, or on culture.
positive, branching, filamentous bacteria affected (up to 50% of cases in dogs).
○ Inflammation, marked exudate produc- Differential Diagnosis
Epidemiology tion, draining tracts, local extension • Uncomplicated abscesses and other deep
SPECIES, AGE, SEX ○ Skin lesions may develop into SQ abscess pyodermas
• Cats and dogs of any age and either sex and may be masslike and painful. • Neoplasia
• Middle-aged or older, male cats and large- • Pyothorax, pneumonia: systemic and respira- • (Pyo-)granulomatous diseases (e.g., fungal,
breed, male dogs may be predisposed. tory signs Pythium or Lagenidium, mycobacterial)
• Disseminated infection • Sterile nodular panniculitis
RISK FACTORS ○ Skin lesions often present (see above)
• Outdoor cats that fight with other cats ○ Neurologic deficits possible (by direct Initial Database
• Dogs kept outdoors or used for hunting CNS infection or extension of vertebral • Evaluate exudate grossly for the presence of
• Important risk factors include osteomyelitis) sulfur granules, recalling that these granules
○ Immunosuppressive drug therapy ○ Ophthalmic changes if ocular infection may or may not be present.
○ Infection with feline retroviruses • Cytologic evaluation (Diff-Quik, Wright-
○ Animal fight injuries Etiology and Pathophysiology Giemsa, and/or Gram stains) of lesions or
○ Concurrent chronic illness • Nocardia spp. are aerobes commonly present exudate may reliably demonstrate filamentous
• Disseminated nocardiosis, including central in soil, detritus, and organic debris. Actino- organisms.
nervous system (CNS) infection, reported myces spp. are anaerobic or microaerophilic • Aerobic culture is typically successful in
in dogs treated with cyclosporine organisms present in the normal oropharyn- isolating Nocardia spp.
geal flora of cats, dogs, and people. • Actinomyces spp. are more fastidious, and
CONTAGION AND ZOONOSIS • Nocardia and Actinomyces infections may be overgrowth of co-infecting organisms may
• Not highly contagious during casual contact transmitted by physical trauma and penetrat- obscure the diagnosis.
but may be transmitted through bites, ing injuries (bites, scratches, and migrating
scratches, or contact of exudate with broken foreign material). Advanced or Confirmatory Testing
skin • Pyothorax results from direct inoculation of • Positive acid-fast staining of filamentous
• Caution while handling infected animals or organisms into the pleural space from bite organisms (cytology or biopsy) supports a
exudate is warranted. Standard barrier wounds or other penetrating trauma. Pneumo- Nocardia diagnosis, but negative staining
precautions are recommended. nia develops from inhalation of organisms and/ cannot be used to differentiate actinomycosis
• Immunosuppressed people are at increased or contaminated foreign material. Putatively, from nocardiosis.
risk. multinodular pulmonary infections may result • Histopathologic evaluation of tissue is used
from hematogenous spread. to rule out other disorders. In actinomy-
ASSOCIATED DISORDERS • Abdominal abscesses, peritonitis, and internal cosis/nocardiosis, histology may confirm
• Actinomyces and Nocardia spp. have been organ infections are associated with dis- pyogranulomatous inflammation, with or
isolated from pyothorax exudate in dogs and seminated disease or direct inoculation of without a fibrous capsule and/or filamentous
cats. the peritoneal cavity. organisms.
• Actinomyces and Nocardia spp. may be • Copious exudate inhibits phagocytosis and
components of polymicrobial infections, impairs antibiotic distribution and activity. TREATMENT
particularly those caused by bite wounds, • Sulfur granules are grossly visible yellow, tan,
migrating foreign material, or other penetrat- or pale, 1-2 mm concretions of bacteria and Treatment Overview
ing injuries. exudate that are highly characteristic of but • Reduction of exudate by surgical intervention
not pathognomonic for actinomycosis or is advocated when practical.
Clinical Presentation nocardiosis. • Clinical improvement is often detectable
DISEASE FORMS/SUBTYPES • Actinomyces infections are often present as within 2 weeks. Duration of therapy depends
• Deep cutaneous and subcutaneous infections: a co-infection with other bacteria (e.g., oral on clinical response (a common treatment
most common in dogs flora). period is 6-12 weeks, but up to 12 months
• Pyothorax, pneumonia • Nocardia spp. are facultative, intracellular may be required).
• Disseminated/systemic infections (often pathogens that may flourish in animals with • Prolonged antibiotic therapy should be
involving the skin but bone, CNS, and other impaired cell-mediated immunity. based on results of culture and susceptibility
anatomic sites may be affected) • The risk of dissemination of infection testing.
increases with chronicity, compromised • Some species of Nocardia (e.g., N. farcinica)
HISTORY, CHIEF COMPLAINT immune status, and when adequate therapy are highly resistant to antibiotic treatment
• Nonspecific clinical signs: fever, lethargy, is delayed. and justify a more intensive or combination
inappetance, weight loss drug treatment.
• Cutaneous infections: history of a chronic DIAGNOSIS
non-healing wound with exudate or an Acute and Chronic Treatment
indolent spreading infection is typical. Diagnostic Overview • Actinomyces spp. are usually susceptible to
• Signs related to the site of infection (e.g., Actinomycosis or nocardiosis should be con- penicillin V (40 mg/kg PO q 8h) and its
coughing, tachypnea, and dyspnea with sidered when a highly exudative infection is derivatives or clindamycin (11-30 mg/kg PO
thoracic infections) present, particularly in cases of pyothorax or q 12h).

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