Nocardiosis is an unusual clinical disease in companion animals. In cats, cutaneous-subcutaneous lesions are the main clinical sign. Usually, cutaneous-subcutaneous signs include abscesses, pustules, fistulas, cellulitis, and mycetoma, generally associated with draining of purulent secretion containing granules . Our cat also presented cellulitis with draining sinuses containing granules, reinforcing the skin lesions as the most common clinical manifestation of feline nocardiosis .
Less frequently feline nocardiosis cause pulmonary and systemic signs . Complications from cutaneous-subcutaneous nocardiosis in companion animals are represented by invasion of adjacent structures, leading to pulmonary, neurologic and/or disseminated (systemic) forms [1, 4]. However, rarely feline nocardiosis have been associated with osteomyelitis . In our cat was diagnosed uncommon mandibular osteomyelitis with intense bone proliferation and osteolysis. The transmission of microorganism in cats is associated with inhalation of soil organisms, consumption of contaminated foods, and inoculation through wounds, such as caused by territorial fights with other felids [1, 14]. Despite no history of previous traumatic lesion in mandibular region or mouth in our cat, the ostemyelitis caused by Nocardia africana probably occurred secondary to periodontitis, due to ingestion of contaminated foods, or traumatic wounds in the gingiva, resembling the transmission route of nocardiosis and actinomycois in livestock .
Clinical laboratory findings in feline nocardiosis are usually nonspecific . In the present report was observed leukocytosis and monocytosis, which are hematologic abnormalities observed in feline nocardiosis [3, 5]. Severe osteolysis observed in radiographic image of mandibula in our cat was indicative of guarded prognosis, although bone infections rarely have been observed in feline nocardiosis [3, 13].
Traditionally, Nocardia species isolated from companion animals have been distinguished by phenotypic characteristics, based on microbiological culture, biochemical characterization, carbohydrate hydrolysis, and antimicrobial susceptibility patterns . In the current report, the microorganism was isolated from samples obtained from a lesion after 72 h of incubation on both sheep blood agar and Sabouraud agar, reinforcing the importance of microbiological culture as a valuable method in the routine diagnosis of Nocardia.
In the present report, the isolate was initially identified as belonging to the N. nova complex . Expanded biochemical test and antibiotic susceptibility patterns were used to differentiate members of Nocardia nova complex. Gram, Panoptico, and modified Ziehl-Neelsen stains revealed the presence of gram-positive, acid-fast, branching filamentous organisms suggestive of Nocardia sp. The histologic findings revealed a suppurative necrosis and abscesses formation usually observed in feline nocardiosis [3, 12]. Our data highlighted the importance of combination of clinical and epidemiological data, hematologic abnormalities, radiographic images, microbiological culture, cytological and histopathological examination to improve the diagnosis of feline nocardiosis.
Sulfonamide-trimethoprim, aminoglicosides and late generation β-lactam drugs are the choices in therapy of feline nocardiosis. Successful treatment of cats with nocardiosis has been observed mainly in skin lesions [3, 12]. In contrast, severe complications and death have been related with disseminated forms (systemic), particularly in cats co-infected with immnunosuppressive diseases [4, 16]. In our cat, despite negative results for feline immunosuppressive diseases, therapy based on antimicrobial susceptibility testing and supportive care, the animal showed progressive worsening of body condition and died.
Recently, polymerase chain reaction, restriction fragment length polymorphisms, DNA- hybridization, and gene sequencing have enabled reclassification of some species of Nocardia. Nocardia cyriacigeorgica, Nocardia brasiliensis, Nocardia otitidiscaviarum, and Nocardia nova complex have been the most common species involved in feline nocardiosis . Nocardia nova complex comprises Nocardia africana, Nocardia nova, Nocardia veterana, and Nocardia kruczakiae species based in recent molecular classification . Nocardia africana infections are considered to be rare in companion animals. Nocardia africana was reported in feline mycetoma in Japan . In addition, 17 cases of feline nocardiosis were described recently in Australia with involvement of Nocardia nova in cutaneous and systemic infections , although these cases have been diagnosed using phenotypic methods.
Currently, human nocardiosis has emerged as an increasingly common opportunistic pathogen among immunosuppressed patients, particularly those infected by AIDS, and other debilitating diseases . Clinically, cutaneous-subcutaneous, pulmonary and/or neurological signs constitute the most common clinical manifestations of human nocardiosis . N. asteroides, N. brasiliensis, N. farcinica and N. nova are species most frequently associated to human disease . The species of Nocardia associated with human nocardiosis are similar to those most frequently found in domestic animals .
The main route of transmission of the genus Nocardia for people appears to be inhalation of the organism in dry warm climate regions, that facilitate the aerosolization and dispersal of pathogen, or caused by traumatic skin inoculation of organism from soil [1, 3, 19]. Microorganisms of the genus Nocardia probably are not transmitted from person-to-person form , and the impact of infected domestic animals in transmission of the disease to humans remains unclear , although cutaneous-subcutaneous infections transmitted to people by bite or scratch wounds from cats have been described elsewhere [20, 21]. Thus, precautions should be taken by humans affected by immune dysfunction, with special attention to avoid contact with soil or organic matter contaminated by domestic animals, and management of animals suspected of nocardiosis, particularly companion animals due to close contact with humans.