Pathology in Practice

Justin M. Stilwell 1Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Alexandra St. Pierre 2Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Kira L. Epstein 2Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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Nicole L. Gottdenker 1Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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History

A 5-month-old approximately 15-kg (33-lb) Anglo-Nubian doe was evaluated because of respiratory distress. Three months earlier, the goat had been transported 800 miles to new owners. The new owners first noted signs of intermittent fever and periodic respiratory distress (tachypnea, episodes of open-mouthed breathing, and prolonged periods of recumbency) 6 weeks earlier. Clinical signs persisted throughout the 6-week period with variable severity, and antimicrobial treatments resulted in temporary resolution of the doe's fever and respiratory signs. The doe was brought to the hospital following an approximately 12-hour period of unrelenting open-mouthed breathing, recumbency, and inappetence.

Clinical and Gross Findings

At the hospital, the doe was immediately provided with 100% oxygen via a mask because of its obvious respiratory distress. The doe was thin (body condition score, 2/5), tachycardic (176 beats/min), tachypneic (80 breaths/min), and normothermic (rectal temperature, 38.7°C [101.7°F]). The doe had no nasal discharge, and airflow was present at both nares; no coughing or sneezing was observed throughout the physical examination. Analysis of a venous blood sample revealed high PCV (48%; reference interval, 22% to 38%) and total solids concentration (7.2 g/dL; reference interval, 6.4 to 7.0 g/dL), consistent with moderate dehydration. Heparinized whole blood lactate concentration was high (13.5 mmol/L; reference interval, 1.00 to 1.33 mmoL/L). The leukogram was unremarkable, and plasma fibrinogen concentration was considered normal (300 mg/dL; reference interval, 100 to 400 mg/dL). Cardiothoracic auscultation revealed no murmur, arrhythmia, or adventitious lung sounds. Thoracic ultrasonographic findings were unremarkable, but echocardiography was not performed. Thoracic radiography revealed a mild, bilateral, cranioventral alveolar pattern with possible right-sided enlargement of the cardiac silhouette. The doe subsequently developed respiratory arrest; cardiac arrest ensued with death confirmed by cardiac auscultation and loss of corneal reflex.

During necropsy, mild postmortem autolysis was evident. There was a large, approximately 2.5-cm-circumference and 1.2-cm-long intravascular mass in the pulmonary artery that had effaced and was strongly adhered to the pulmonic valve, causing nearly complete valve and pulmonary artery occlusion (Figure 1). The mass was off-white to yellow and friable to firm, with some fibrinous strands within it. The right ventricular lumen was moderately dilated with a diffusely congested endocardial surface. No jet lesions were apparent along the endothelial surface of the ventricle or pulmonary artery. The remaining cardiac and pulmonary structures were grossly unremarkable. The only other notable gross finding was a 1.5 × 1.0-cm, off-white to yellow, slight depression in the cortex of the right kidney (chronic infarction). Tissue specimens were collected and placed in neutral-buffered 10% formalin for histologic examination.

Figure 1—
Figure 1—

Photographs of a mass in the heart at the level of the pulmonic valve (A) and a cross section through the formalin-fixed mass and heart wall (B) of a 5-month-old Anglo-Nubian doe with a 6-week history of intermittent fever and respiratory distress. In panel A, the mass has circumferentially effaced the valve and severely narrowed the vascular lumen. In panel B, the mass (asterisk) has effaced the pulmonic valve and extends into the pulmonary artery (arrow).

Citation: Journal of the American Veterinary Medical Association 257, 6; 10.2460/javma.257.6.603

Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page

Histopathologic and Microbiological Findings

The fixed tissue specimens were processed routinely and stained with H&E stain. Microscopically, the pulmonic valve was completely replaced by a homogeneous, finely granular, acellular, eosinophilic mass that was consistent with a thrombus (Figure 2). The thrombus filled the valvular lumen, extending into the pulmonary artery, and was adhered to the endothelium. Dense aggregates of deeply basophilic, granular material (mineral) surrounded the thrombus. A few cloud-like colonies of basophilic, gram-positive cocci were scattered throughout the mass (Figure 3). The tunica intima and multiple regions of the tunica media of the pulmonary artery were markedly expanded by infiltrates of macrophages, fibroblasts, and fewer lymphocytes, plasma cells, and neutrophils. A focally extensive region of the tunica adventitia was markedly expanded by edema, hemorrhage, and numerous neutrophils and macrophages. A sample of the thrombus underwent aerobic bacterial culture, which yielded light growth of an α-hemolytic Streptococcus sp.

Figure 2—
Figure 2—

Photomicrograph of a section of the heart valve mass of the goat in Figure 1. The mass consists of amorphous, eosinophilic fibrillar and basophilic mineralized debris (asterisk), which is attached to the pulmonic valve (arrows) and has incited extensive inflammation within the valve and artery wall (arrowheads). H&E stain; bar = 1 mm. Inset—Multifocal colonies of basophilic cocci are disseminated throughout the mass. H&E stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 257, 6; 10.2460/javma.257.6.603

Figure 3—
Figure 3—

High-magnification photomicrograph of a section of the heart valve mass. Notice that gram-positive cocci (darkly stained) have formed cloud-like colonies within the mass. Gram stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 257, 6; 10.2460/javma.257.6.603

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: marked, chronic, circumferential, vegetative pulmonic valvular endocarditis, endarteritis, and thrombosis with intralesional cocci.

Case summary: pulmonary artery occlusion secondary to vegetative valvular endocarditis of the pulmonic valve in a goat.

Comments

Valvular bacterial endocarditis in small ruminants, particularly goats, is not well described. To our knowledge, only 3 limited case reports of vegetative valvular endocarditis in goats have been published.1–3 In a previous report,1 infections with Trueperella pyogenes (formerly Corynebacterium pyogenes) and Streptococcus faecalis were associated with lesions in 4 sheep and 1 goat, but it is not clear which heart valves were affected or which bacteria were present in the sheep, the goat, or both. Goats experimentally infected with Mycoplasma caprae develop vegetative valvular endocarditis and necrotic mural myocarditis.2 In 2 reports,2,3 the tricuspid and aortic valves were affected by lesions induced by the infection. At our institution, the only other case of vegetative valvular endocarditis in a goat was caused by infection with Streptococcus spp and the aortic valve was affected (unpublished data). In sheep, valvular endocarditis with involvement of the mitral and aortic valves has been associated with experimental infection with Listeria monocytogenes, and in 2 cases, the tricuspid valve was affected but no attempt at bacterial isolation was made.4–6 Pulmonic valve involvement, as in the case described in the present report, is generally considered the least common site for valvular endocarditis in animals.7 Alpha-hemolytic streptococci and T pyogenes are common isolates obtained from ruminants with bacterial endocarditis, and these organisms are susceptible to penicillin procaine and cephalosporin treatment, respectively.7,8

In goats and sheep, infection with Streptococcus dysgalactiae has been implicated as a cause of systemic disease with secondary endocarditis.9–11 In 1 report11 of lambs, a definitive source of infection was not identified, but possible routes of infection included the umbilicus with bacteremia and seeding of the pulmonic valve or ingestion of streptococci from environmental or milk contamination with subsequent infiltration of the intestinal tract. Although other lesions (eg, polyarthritis or omphalitis) were not evident in the goat of the present report, it is possible the such signs resolved with treatment prior to presentation with subclinical, progressive enlargement of the thrombus; however, this is speculative because the medical history of the animal before acquisition was unknown. Inappropriate dosing, dosing interval, or duration of treatment prior to presentation could have resulted in this goat's initially protracted course of disease and eventual development of a thrombotic vegetative lesion.

Microthrombi form as a result of endothelial damage, particularly in regions of turbulent, high-velocity blood flow as seen in cases of valvular insufficiency. In the presence of underlying infectious disease, such as with polyarthritis, omphalophlebitis, pneumonia, or mastitis, persistent bacteremia may allow these microthrombi to be colonized, triggering an inflammatory cascade and the development of valvular endocarditis with or without enlargement of the inciting thrombus. Experimentally, valvular vegetative endocarditis has been induced in goats by IV administration of bacteria without previous damage to a valve.2 Owing to the chronicity and extent of the valvular mass and relative lack of other systemic lesions, a definitive cause for thrombus formation and bacterial seeding in the goat of the present report was not determined.

Although considered less likely, sudden death of the goat of the present report could be explained by pulmonary thromboembolism originating from the valvular thrombus. Pulmonary thromboembolism could have contributed to the pulmonary pattern identified on radiographs; however, there was no evidence of thromboembolism grossly or histologically within the lung or pulmonary vessels. Chronic renal infarction detected grossly could have been indicative of previous thromboembolism, although it was more likely attributable to a previous systemic, hypercoagulable state, such as that which develops with sepsis, and not directly related to the right-sided valvular endocarditis. Inadequate cardiac function, poor pulmonary perfusion, and potentially poor systemic oxygenation as result of near-complete obstruction of the vascular lumen were considered the primary contributors to the goat's respiratory distress and death.

Animals in respiratory distress require immediate triage, stabilization with supplemental oxygen, and prompt identification of the underlying problem while minimizing handling stress. Along with primary pulmonary disease, differential diagnoses for nonpulmonary causes of respiratory distress in small ruminants include hyperthermia, pain, bloat, acidosis or other metabolic disturbance, and shock. Congenital cardiac anomalies and acquired cardiac failure (including valvular endocarditis) are less commonly recognized causes of tachypnea and respiratory difficulty.8 Clinical signs vary depending on the severity and chronicity of valvular disease, but there is often a lack of an audible murmur associated with classic valvular insufficiencies when valves are severely affected, as found in the case described in the present report and in cows and sheep.5,8 Cardiothoracic ultrasonography is a noninvasive but underutilized diagnostic procedure that can assist in the diagnosis of respiratory disease in small ruminants. In an acutely distressed animal, the degree of respiratory compromise may preclude the use of echocardiography in an emergency setting. Species-specific reference intervals for echocardiographic variables in small ruminants are available, and echocardiography is performed when the animal is either standing or in lateral recumbency, as described for horses.8,12 For the goat of the present report, thoracic ultrasonography was performed to assess for primary pulmonary disease, given that primary respiratory disease rather than cardiovascular disease is more commonly associated with respiratory distress in goats. Ultrasonography of the lungs can be accomplished rapidly, whereas echocardiography, even when performed by an experienced operator, may be time-consuming. Medical management of bacterial valvular endocarditis requires long-term administration (duration of treatment from weeks to months) of broad-spectrum antimicrobials. Ultimately, bacterial valvular endocarditis has a guarded to grave prognosis.

Descriptions of bacterial endocarditis in goats are scarce in the veterinary medical literature and limited in scope. For the goat of the present report, vegetative valvular endocarditis involving the pulmonic valve resulted in near-complete obstruction of the pulmonary artery, respiratory distress, and sudden death. Although respiratory distress in small ruminants is more commonly associated with primary pulmonary disease, clinicians should consider nonpulmonary differential diagnoses for affected animals, particularly those that are young or potentially not immunocompetent.

References

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