Page 1040 - Clinical Small Animal Internal Medicine

978 Section 9 Infectious Disease

disease, oral trauma, and bite wounds. Lesions most com- sequencing, are now the diagnostic techniques of choice
VetBooks.ir monly develop around the jaw and neck. for identifying the infecting species as they provide accu-
rate and rapid results. It is important to note that culture
Cutaneous and subcutaneous actinomycosis manifests
as flocculent to firm masses often with draining sinus
tracts typically on the thoracic wall, flanks or limbs. and polymerase chain reaction (PCR) can be negative in
some cases. Furthermore, culture or detecting organisms
These lesions in dogs are often secondary to migrating using PCR without compatible clinical signs may not be
grass awns. In cats, they are associated with bite wounds. clinically significant since Actinomyces are commensals.
Thoracic actinomycosis can present as pneumonia, lym-
phadenopathy, intra‐ or extrapulmonary masses or pyo- Therapy
thorax. Thoracic actinomycosis in cats occurs secondary The combination of surgery and antimicrobial treatment
to aspiration of oral flora whereas canine infections are is generally superior to antimicrobial treatment alone in
secondary to inhalation and migration of grass awns. resolving Actinomyces infections in which a foreign body
Clinical signs may be nonspecific, such as lethargy and is suspected. Thoracotomy and debridement are recom-
weight loss, or can include tachypnea, dyspnea, and cough- mended in dogs with pyothorax, while cats generally
ing. Foreign bodies in dogs can migrate further into the require only tube thoracostomy in addition to medical
retroperitoneum, resulting in abscessation in this area. therapy. This likely reflects the difference in etiologies in
Abdominal, visceral, and central nervous system infec-
tions can develop from extension of subcutaneous infec- which canine infections generally result from foreign body
migration and feline infections are caused by aspiration of
tions, foreign body migration or hematogenous spread. oral flora. Prolonged antimicrobial therapy for several
Osseous infections can result from extension from other months is often required to resolve infection. Actinomyces
locations or contamination of orthopedic implants.
spp. are susceptible to high doses of penicillins as well as
other antibiotics (Table 108.1). As actinomycosis often
Diagnosis occurs as a component of a mixed bacterial infection,
identification, susceptibility testing, and treatment of the
A provisional diagnosis of actinomycosis is based on the co‐infectious agents are also imperative for resolution.
identification of Gram‐positive, nonacid‐fast filamentous
organisms on cytologic examination of fluid or tissues Prognosis
from suspicious lesions using a modified Ziehl–Neelson
(Kinyuon) method. A definitive diagnosis requires either The prognosis for dogs and cats with subcutaneous and
isolation and phenotypic identification of the causative soft tissue actinomycosis and for cats with pyothorax is
agent using biochemical methods, chemotaxonomy, and generally good when treated for sufficient time. However,
serology or identification using molecular methods. reported survival rates in dogs with thoracic disease are
Molecular methods, most commonly 16S rRNA gene variable and CNS actinomycosis is invariably fatal.

Table 108.1 Antimicrobials used to treat Actinomyces and Nocardia infections

Canine Feline

Actinomyces spp. Penicillins Penicillins
● Ampicillin (10–20 mg/kg IV/IM/SC q6–8h) ● Ampicillin (10–20 mg/kg IV/IM/SC q6–8h)
● Amoxicillin (10–30 mg/kg IM/SC/PO q12h) ● Amoxicillin (10–30 mg/kg IM/SC/PO q12h)
Macrolides/Lincosamides Macrolides/Lincosamides
● Clindamycin (5 mg/kg IV/IM/SC/PO q12h) ● Clindamycin (5 mg/kg IV/IM/SC/PO q12h)
● Erythromycin (10 mg/kg PO q8h) ● Erythromycin (10 mg/kg PO q8h)
Chloramphenicol* (50 mg/kg IV/IM/SC/PO q8h) Chloramphenicol* (50 mg IV/IM/SC/PO/cat q12h)
Nocardia spp. Sulfonamides Sulfonamides
● Trimethoprim‐sulfonamide* (30 mg/kg PO q12h) ● Trimethoprim‐sulfonamide* (30 mg/kg PO q12h)
Amikacin (10–30 mg/kg IV/IM/SC q24h)* Amikacin (10–15 mg/kg IV/IM/SC q24h)
Imipenem‐cilastatin (3-10 mg/kg slow IV q8h) Imipenem‐cilastatin (3-10 mg/kg slow IV q8h)
Cefotaxime (25–50 mg/kg IV/IM/SC q6h) Cefotaxime (22 mg/kg IV/IM/SC q6–8h)
* Potential severe adverse drug effects.
For all medications please consult comprehensive formularies for potential adverse drug effects, interactions, and contraindications.
Please see text for further information regarding treatment protocols.
IM, intramuscular; IV, intravenous; PO, by mouth (per os); SC, subcutaneous.