History

In a herd of 200 predominantly Angus cattle, 6 animals were found dead overnight with 2 additional animals found down. The animals that were down had an increased respiratory rate and rectal temperatures of 38 °C (normal range, 36.7 °C to 39.1 °C); these animals died on farm shortly after physical exam. Treatment was attempted with vitamin K (unknown dosage) and pumping approximately 0.23 kg of activated charcoal into the rumen. A 7-month-old female Angus heifer weighing 264 kg was euthanized by gunshot and submitted for necropsy at the Wisconsin Veterinary Diagnostic Laboratory (WVDL) the same day. Additional tissues, including heart, lung, liver, kidney, mesenteric lymph node, forestomachs, abomasum, intestine, tracheobronchial lymph node, and blood, from a 7-month-old male Holstein (weight unknown) who died overnight were submitted for testing as well.

Clinical and Gross Findings

At necropsy, the heifer was in good body condition with mild postmortem autolysis. Skeletal muscles in the right forelimb were congested and hemorrhagic with moderate edema. There was serosanguinous fluid free in the thorax, abdomen, and pericardium. Multifocal to coalescing hemorrhage and edema expanded the myocardium, epicardium, and pericardium (Figure 1). There were multiple fibrinous adhesions between the pleura, pericardium, and epicardium. The lungs were diffusely congested and edematous with multifocal hemorrhages and numerous pleural fibrin tags. Thymic lobules were multifocally disrupted by hemorrhage and edema. The liver was mildly swollen and congested. There was segmental congestion of the small intestine. No other clinically important findings were identified.

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Necropsy images of the isolated trachea, lungs, and heart (A) and the heart on cut section (B) of a euthanized 264-kg 7-month-old Angus heifer that was 1 of 2 calves found down, tachypneic, and febrile along with 6 other herdmates that were found dead in a herd of 200 feeder calves. The heart has multifocal to coalescing foci of dark hemorrhage and edema (asterisks) on the epicardial surface (A) that extend into the myocardium (B). The lungs are diffusely congested and edematous with multifocal hemorrhages and numerous pleural fibrin tags.

Citation: Journal of the American Veterinary Medical Association 262, 7; 10.2460/javma.24.02.0129

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Histopathologic and Microbiological Findings

Sections of heart, pericardium, lung, sternal and tracheobronchial lymph nodes, skeletal muscle (right shoulder), thymus, liver, kidney, forestomachs (rumen, reticulum, omasum), abomasum, small and large intestine, and mesenteric lymph nodes, were evaluated microscopically. In sections of the grossly affected heart, there was marked coagulative necrosis and hemorrhage (Figure 2). Myofibers were degenerate and fragmented with marked infiltrates of neutrophils. There was marked interstitial hemorrhage, edema, and fibrin expanding the myocardium. The epicardium was extensively effaced by similar infiltrates. Vessels were frequently dilated with luminal fibrin thrombi.

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Photomicrograph of the heart of the heifer in Figure 1. There is marked coagulative necrosis and hemorrhage (asterisk). Myofibers are degenerate and fragmented with marked infiltrates of neutrophils (arrow). H&E stain; bar = 200 µm. Inset—There is extensive interstitial hemorrhage, edema, and fibrin with marked neutrophils. H&E stain; bar = 20 µm.

Citation: Journal of the American Veterinary Medical Association 262, 7; 10.2460/javma.24.02.0129

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Other clinically important histologic findings included a similar necrohemorrhagic pleuritis, pericarditis, pneumonia, lymphadenitis, and myositis. There was widespread vascular congestion in all tissues examined.

Anaerobic culture swabs from the affected forelimb skeletal muscle and heart isolated numerous bacteria identified as Clostridium chauvoei and confirmed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF; Bruker Daltonics Microflex LT/SH Biotyper) using MBT Compass 4.1 Software (Bruker Daltronics) for analysis.

Similar histopathologic findings were identified in the tissues received from the 7-month-old male Holstein. Similar tissue cultures isolated mixed flora that was considered clinically irrelevant.

Morphologic Diagnosis and Case Summary

Morphologic Diagnosis: Necrohemorrhagic myocarditis, acute, multifocal to coalescing, severe.

Case summary: Clostridium chauvoei myocardial infection (“blackleg”) in a heifer.

Comments

Clostridium chauvoei is an anaerobic, gram-positive bacteria that is commonly found as highly resistant spores in soil and is the causative agent of blackleg.¹ There are many other clostridial diseases, including gas gangrene in cattle caused by Clostridium septicum, which can have similar pathological presentations.² Blackleg is common in younger pastured cattle that are well fed and in otherwise good health. Clinical signs may not always be observed before death, but can include limb weakness, difficulty standing, fever, loss of appetite, muscle swelling, and dehydration.^3,4 Death often occurs soon after the onset of clinical presentation (typically within 24 hours).

Typically, spores are ingested during pasture grazing.⁴ Spores then travel through the digestive system and likely get absorbed into the bloodstream through the intestines.³ The spores travel through the bloodstream and can reach multiple tissues where they can remain dormant for years. Injury of the tissues can create an anaerobic or low oxygen tension environment allowing for the spores to germinate.⁵ As bacteria replicate, associated exotoxins are produced, leading to localized tissue damage and a systemic toxemia.¹ Information on the exact toxins produced is scarce; however, it is postulated that C chauvoei toxin A (CctA) is the main toxin responsible for typical pathological findings, but other possibly associated toxins include cytolysin and neuraminidase.^3,4

Typical blackleg lesions are found in the heart and/or skeletal musculature and lesions commonly can be found in multiple different regions. Skeletal musculature lesions can most frequently be found in the rear quarters, but also the forequarters, neck, lumbar area, brisket, diaphragm, abdominal wall, thoracic wall, and tongue.³ Externally, the tissues appear swollen and dark, while internally muscles are red to black, dry, friable, and contain multiple cavities containing gas.³ Animals with heart lesions frequently have grossly and histologically evident myocardial lesions and commonly have associated pericarditis/endocarditis.³ Less common lesions are only observed microscopically.⁴ Previously, it was believed that heart lesions were not very common for blackleg; however, several retrospective population reviews that examined archived cases show that heart lesions are relatively common in affected cattle. In cases of suspected blackleg, gross and histologic examination of both skeletal and heart musculature is recommended.⁴

Clostridium chauvoei spores can remain dormant in soil for many years and begin to germinate once in favorable anaerobic conditions. Soil containing C chauvoei spores can enter the topsoil of grazing pastures in multiple ways, such as being carried by wind or during periods of heavy rainfall.³ Infection can also result from exposure to a C chauvoei-infected animal’s feces or carcasses.³ In the herd in this report, the route of exposure was unknown, but suspected to be environmental introduction of infected feed.

There are a few ways to confirm the presence of C chauvoei bacteria and/or toxins in animals with suspected blackleg. Anaerobic bacterial culture of affected tissues is often the most available diagnostic method; however, C chauvoei is fastidious and can be difficult to culture.³ Fluorescent antibody test (FAT) or immunohistochemistry can also be used to identify C chauvoei on impression smears or histologic sections of affected muscle tissue, respectively.^1,3 Molecular testing, such as PCR, can also be performed to confirm the presence of C chauvoei genetic material.¹ Tests available may vary with the regional diagnostic laboratory. In this case, bacterial culture was used to isolate and identify C chauvoei from both skeletal and heart musculature of the animal submitted for full body necropsy. Despite a similar clinical and pathologic presentation, C chauvoei was not isolated from the tissues submitted from the second animal submitted, showing the unreliability of culture in these cases. Primary differentials associated with the described lesions include other types of clostridia, including C septicum, C perfringens, C sordellii, and C novyi.

Vaccination for common clostridial diseases (such as blackleg and gas gangrene) is available for cattle. In the United States, between 87.5% and 92.5% of cattle are vaccinated for clostridial diseases.⁵ In limited studies, it has been shown that depending on the inoculating dose the vaccine is 50% to 100% efficacious experimentally.⁵ While experimental evidence would suggest that clostridial disease vaccination is variably poor at protecting against blackleg, anecdotal evidence supports that this vaccine is efficacious in protecting animals from severe clinical disease.⁵ One year after the death of the animal in this case report, the farm has instituted a vaccination protocol and has had no similar outbreaks

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.