One month old, intact male Dorper lamb (Ovis aries).This lamb was smaller than normal at birth and showed poor weight gain while nursing. The owner noticed that it became weak with labored breathing and increased lung sounds. Antibiotic treatment (oxytetracycline) was initiated, but the animal was found dead five days later.
Approximately 70-80% of the lungs contained moderately well-demarcated, often confluent, firm, white-tan nodular areas, with only a small portion of the dorsal-caudal regions unaffected.Â On section, many bronchi were filled with a white-tan material.Â No thymic tissue was identified.Â No other abnormalities were noted.Â
Lung: Filling or effacing up to 75% of alveoli and bronchioles are multifocal to coalescing, variably sized and shaped pyogranulomas characterized by central areas of necrotic cellular debris, high numbers of degenerate and necrotic neutrophils and macrophages, and mineralization surrounded by variable mixtures of neutrophils, large macrophages, fewer lymphocytes and multinucleated giant cells.Â Adjacent, less affected airways and alveoli are often compressed and contain congestion and hemorrhage, fewer numbers of inflammatory cells and multifocal areas of edema and/or basophilic-staining material (mucus).Â On H&E stained sections, faintly-staining, fine filamentous organisms can be seen sporadically at the margins of the necrotic areas.
Special stains revealed numerous, approximately 1 micron thick, beaded to filamentous and occasionally branching, gram-positive (Brown & Brenn) and variably acid-fast (Fite-Faraco) bacteria within areas of inflammation.
Lung: Pyogranulomas, multifocal and coalescing, marked, with necrosis, mineralization and numerous branching, filamentous gram-positive and acid-fast bacteria, lamb (Ovis aries).
Nocardia sp.Â was isolated from the cut surface of affected lung.
Nocardia spp.Â are ubiquitous, saprophytic, aerobic bacteria that are commonly associated with opportunistic infections in animals and people characterized by pyogranulomatous inflammation.Â The organisms are observed as long, thin, beaded filaments with frequent right-angle branching that are said to have a Chinese character pattern.Â They can be easily overlooked on standard H&E stained sections and are better demonstrated with special stains including Gomori methenamine silver (GMS), Gram stains and modified acid-fast stains such as Fite-Faraco.(9)
The primary differential diagnosis for pulmonary nocardiosis includes infections with Actinomyces and some atypical mycobacteria.(9) Actinomycosis is more commonly associated with sulfur granules and Splendore-Hoeppli material, and the organisms are not acid fast.(10) Atypical mycobacteria are much shorter beaded bacilli and do not exhibit true branching.Â
Nocardia are commonly found in the environment, particularly soil enriched with decayed organic matter.Â Routes of infection include inhalation, inoculation, and ingestion.Â In people, Nocardia are generally considered pathogenic bacteria with relatively low virulence.Â With the exception of cutaneous disease, human infection is typically opportunistic, occurring more commonly in the elderly and people with compromised T cell-mediated immunity, as with prolonged steroid treatment or HIV infection.(6) In the present case, it is not clear if the absence of a normal appearing thymus at necropsy was due to a primary condition predisposing the animal to infection (thymic hypoplasia) or a secondary response to the severe infection (thymic atrophy).Â
Nocardiosis is an important cause of pneumonia, pleuritis and empyema in dogs, particularly hunting/sporting dogs in which, following inhalation or ingestion of plant material, migrating grass awns can contaminate the pleural spaces with bacteria resulting in a putrid tomato soup-like hemorrhagic pyothorax.Â In most other species, pulmonary nocardiosis more closely resembles the nodular pyogranulomatous and necrotizing inflammation observed in this lamb.Â Nocardia infections have been infrequently reported in primates, cats, horses, cattle and marine mammals.(1,2,5,8) In cattle, infections have been associated with mastitis, pneumonia, dermatitis, placentitis with abortion, and disseminated disease.(1) Nocardia infections in other ruminants are apparently very uncommon, but have been reported in sheep, goats, llama, bison and reindeer.(3,7,10) Nocardiosis is reportedly a significant and often fatal disease in marine mammals.(8) Pinnipeds, particularly hooded seals, and cetaceans appear to be prone to a systemic form of infection which typically involves the lung and thoracic lymph nodes and, to lesser extent, brain and skin.Â
Lung: Pneumonia, pyogranulomatous, multifocal to coalescing, severe, with numerous filamentous gram-positive, acid-fast bacteria.Â
In addition to discussing nocardiosis in the various species so well described by the contributor, conference participants also discussed the so-called nocardioform placentitis associated with equine abortion.Â Nocardioform placentitis can be caused by several genera of gram positive, branching actinomycetes that share similarities with Nocardia species, including the following: Crossiella equi, Amycolatopsis kentuckyensis, Amycolatopsis lexingtonensis, Amycolatopsis pretoriensis, Streptomyces atriruber, and Streptomyces silaceus.(4) Clinically, nocardioform placentitis presents as late gestation abortion, stillbirth, prematurity or full term but weak foals.Â Grossly, a thick, light brown exudate is often observed in the chorion at the bifurcation of the horns of the affected placenta.Â The organisms do not reach the fetus; thus fetal lesions are those of placental insufficiency.Â Recently, nocardioform placentitis resulted in a record number of equine abortions in the 2011 foal crop in Kentucky.Â The most prominent actinomycetes found in this series of third trimester abortions were Amycolatopsis spp.Â and Crosiella equi; fewer Streptomyces, Microbacterium, Nocardia and Allokutzneria species were identified.(4)
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