Pathology of blackleg in cattle in California, 1991-2015

Abstract

Blackleg is an infectious disease of cattle and rarely other ruminants, produced by Clostridium chauvoei and characterized by necrotizing myositis. In most cases of blackleg, the large muscles of the pectoral and pelvic girdles are affected, with other skeletal muscles and the heart involved less frequently. We studied 29 blackleg cases selected from the archives of the California Animal Health and Food Safety Laboratory, 1991-2015. Immunohistochemistry was also evaluated to detect C. chauvoei in formalin-fixed, paraffin-embedded (FFPE) tissues of cattle. Nineteen animals had gross and/or microscopic lesions in both skeletal muscle and heart, 9 had lesions in the skeletal musculature alone, and 1 in the heart alone. Gross lesions in the skeletal musculature involved the following muscle groups: hindquarters ( n = 8), forequarters ( n = 5), neck ( n = 5), lumbar area ( n = 3), brisket ( n = 2), diaphragm ( n = 2), abdominal wall ( n = 1), thoracic wall ( n = 1), and tongue ( n = 1). Of the 20 animals that had lesions in the heart, 11 had pericarditis and myocarditis; 7 had pericarditis, myocarditis, and endocarditis; and 1 each had pericarditis and myocarditis. Immunohistochemistry was 100% sensitive to detect C. chauvoei in FFPE skeletal muscle and/or heart of cattle with blackleg. Simultaneous lesions in skeletal musculature and heart were relatively common in blackleg cases in California; the most affected skeletal muscles were those of the hindlimbs.

Keywords: Blackleg; Clostridium chauvoei; cattle; myocarditis; myositis.

Figures 1–3.

Lesions in cattle with blackleg. Figure 1. Distribution of gross lesions according to the type of muscle (n = 29). Figure 2. Distribution of gross lesions in skeletal muscle anatomical regions (n = 28). Figure 3. Distribution of lesions in the heart (n = 20).

Figures 4–11.

Lesions in cattle with blackleg. Figure 4. Affected muscles in the hindlimb are dry, friable, red-to-black, and emphysematous. Figure 5. The pericardial sac is covered by fibrinosuppurative exudate, which creates multiple adhesions to the epicardium. Figure 6. Focally extensive myocardial hemorrhage and necrosis affecting the right ventricle of the heart. Figure 7. Severe, diffuse myonecrosis with contraction bands, hypereosinophilia, and loss of cross-striations in skeletal muscle. H&E. Figure 8. Fiber vacuolation and fragmentation; some of the fragmented myofibers are infiltrated by neutrophils in skeletal muscle. H&E. Figure 9. Neutrophilic arteritis in myocardium, characterized by fibrinoid necrosis and infiltration with neutrophils. * = thrombus; a = arterial wall. H&E. Figure 10. Skeletal muscle with positively stained Clostridium chauvoei (arrow) associated with neutrophilic infiltration and edema. Insert: higher magnification showing the positively stained rods (arrow). Immunohistochemistry for C. chauvoei. Figure 11. Fluorescent antibody test for Clostridium chauvoei on a skeletal muscle smear showing many fluorescent rods.