Bacterial Endocarditis (Vegetative Endocarditis) in Cattle

Bacterial endocarditis, also known as vegetative endocarditis, is a serious, often fatal infectious disease of cattle characterized by inflammation and infection of the endocardial surface of the heart, most commonly affecting the heart valves. The disease is typically a sequel to a primary bacteremia originating from a distant focus of infection, such as mastitis, metritis, foot abscesses, or traumatic reticuloperitonitis. In cattle, the most frequently affected valves are the tricuspid and mitral valves, with the aortic and pulmonary valves less commonly involved. The infection leads to the formation of large, friable vegetative lesions on the valve leaflets, which can cause valvular insufficiency, congestive heart failure, and systemic embolization. The disease is most commonly seen in adult dairy cattle, particularly in early lactation, and is associated with significant economic losses due to decreased milk production, poor reproductive performance, and high mortality. The condition is often chronic and insidious, with clinical signs developing over weeks to months. Early diagnosis is challenging, and the prognosis is generally poor, especially when congestive heart failure has developed. The disease is of major clinical importance in both dairy and beef cattle, and a thorough understanding of its pathogenesis, clinical presentation, and management is essential for bovine practitioners.

The primary causative agents of bacterial endocarditis in cattle are Gram-positive bacteria, with Trueperella pyogenes (formerly Arcanobacterium pyogenes) being the most frequently isolated organism, accounting for up to 80% of cases. Other common pathogens include Streptococcus spp., particularly Streptococcus bovis and Streptococcus uberis, and occasionally Staphylococcus aureus, Escherichia coli, and Pasteurella multocida. In some cases, mixed infections are present. The bacteria gain access to the bloodstream from a primary site of infection, such as the udder (mastitis), uterus (metritis), foot (foot abscess, digital dermatitis), or the gastrointestinal tract (traumatic reticuloperitonitis). The presence of a pre-existing valvular lesion, such as from previous inflammation or congenital abnormalities, may predispose to bacterial colonization. The virulence factors of Trueperella pyogenes include pyolysin, a hemolysin that is cytotoxic to neutrophils and macrophages, and fimbriae that facilitate adhesion to host tissues. The bacteria adhere to the valvular endothelium, leading to platelet aggregation and fibrin deposition, forming a vegetative lesion. The vegetation provides a protected environment for bacterial growth, making treatment difficult. The disease is not contagious, but the underlying primary infections may be herd problems, such as contagious mastitis or foot rot.

Bacterial endocarditis is a sporadic disease in cattle, with a low morbidity but high mortality. It is most commonly diagnosed in adult dairy cattle, particularly in the first few weeks of lactation, but can also occur in beef cattle and occasionally in calves. The disease is more prevalent in housed cattle, especially those with poor hygiene and high stocking density, which predispose to foot and udder infections. The incidence is higher in herds with endemic mastitis, metritis, or lameness. There is no breed predilection, but high-producing dairy cows may be at increased risk due to metabolic stress and immunosuppression in early lactation. The disease is more common in older cattle, with a mean age of 5-6 years. The morbidity rate is typically less than 1% in affected herds, but the case fatality rate is high, often exceeding 80% if untreated. Economic losses arise from premature culling, decreased milk production, treatment costs, and reduced reproductive performance. The disease is more frequently diagnosed in the winter months, possibly due to increased confinement and associated infections.

The pathogenesis of bacterial endocarditis begins with a transient or persistent bacteremia, which may arise from a primary infection site. The bacteria must adhere to the endocardial surface, which is normally resistant to bacterial colonization. Pre-existing valvular damage, turbulent blood flow, or immune-mediated inflammation may predispose to adherence. Once adhered, the bacteria stimulate platelet aggregation and fibrin deposition, forming a vegetation. The vegetation is composed of fibrin, platelets, red blood cells, and bacteria, and it can grow to several centimeters in diameter. The infection causes valvular insufficiency, leading to volume overload of the affected heart chamber. For example, tricuspid valve insufficiency leads to right-sided heart failure, with jugular venous distension, hepatic congestion, and peripheral edema. Mitral valve insufficiency leads to left-sided heart failure, with pulmonary edema and respiratory distress. The vegetation may also embolize to distant organs, causing infarcts in the lungs, kidneys, brain, or other tissues. The chronic infection leads to systemic signs of inflammation, including fever, weight loss, and anemia. The disease is often progressive, and the development of congestive heart failure is a poor prognostic indicator.

Several factors predispose cattle to bacterial endocarditis. Intrinsic factors include high milk production, which is associated with metabolic stress and immunosuppression in early lactation. Older cattle, particularly those in their third or greater lactation, are at higher risk. Genetic factors may play a role, but specific genes have not been identified. Extrinsic factors include poor hygiene in the environment, which increases the risk of mastitis, metritis, and foot infections. Overcrowding and poor ventilation in barns contribute to the spread of infectious agents. Inadequate hoof care and wet, dirty bedding predispose to foot abscesses and digital dermatitis. Poor calving hygiene and retained fetal membranes increase the risk of metritis. In addition, any condition that causes a prolonged bacteremia, such as chronic mastitis or severe lameness, increases the risk of endocarditis. Iatrogenic factors, such as intravenous catheterization, can also introduce bacteria into the bloodstream. Nutritional factors, such as vitamin E and selenium deficiency, may impair immune function and increase susceptibility to infection.

The clinical signs of bacterial endocarditis in cattle are often vague and progressive, developing over weeks to months. Early signs include decreased milk production, reduced appetite, weight loss, and a fluctuating fever. As the disease progresses, signs of heart failure may become apparent. With right-sided heart failure, there is jugular venous distension, subcutaneous edema of the brisket and ventral abdomen, and diarrhea due to intestinal congestion. With left-sided heart failure, there is tachypnea, dyspnea, and crackles on lung auscultation. On cardiac auscultation, a heart murmur is often detected, typically a holosystolic murmur best heard over the tricuspid or mitral valve area. The murmur may be accompanied by a thrill. The heart rate is often elevated, and arrhythmias may be present. In some cases, embolic events may cause acute lameness, neurological signs, or sudden death. The cow may be lethargic and reluctant to move. In advanced cases, the cow may become recumbent. The disease is often misdiagnosed as pneumonia, traumatic reticuloperitonitis, or other chronic debilitating conditions.

Differential diagnoses for bacterial endocarditis in cattle include: 1) Traumatic reticuloperitonitis (hardware disease): presents with acute onset of anorexia, fever, and abdominal pain, but no heart murmur or signs of heart failure. Rumen motility is decreased, and there may be a ping on percussion over the reticulum. 2) Pericarditis: often secondary to traumatic reticuloperitonitis, presents with muffled heart sounds, jugular distension, and edema, but no murmur. Ultrasonography shows pericardial effusion. 3) Congestive heart failure from other causes, such as dilated cardiomyopathy or congenital defects: may have similar signs of heart failure, but no murmur or vegetation on echocardiography. 4) Pneumonia: presents with fever, tachypnea, and crackles, but no heart murmur or jugular distension. 5) Liver abscessation: presents with weight loss, fever, and decreased production, but no heart murmur. 6) Chronic mastitis or metritis: may cause fever and weight loss, but no cardiac signs. 7) Endocarditis due to other bacteria, such as Streptococcus spp., may have similar signs, but culture and sensitivity are needed for differentiation. 8) Neoplasia, such as lymphosarcoma, may cause weight loss and heart failure, but is more common in older cattle and may have lymphadenopathy.

The diagnostic approach to bacterial endocarditis in cattle should be systematic. 1) Obtain a thorough history, including signalment, production stage, and any recent infections (mastitis, metritis, foot problems). 2) Perform a complete physical examination, with special attention to the cardiovascular system. Auscultate the heart on both sides, noting any murmurs, arrhythmias, or muffled sounds. Check for jugular venous distension, peripheral edema, and mucous membrane color. 3) If a murmur is detected, consider further cardiac evaluation. 4) Perform a complete blood count and serum biochemistry profile. Look for leukocytosis with a left shift, anemia, hyperglobulinemia, and elevated fibrinogen. 5) Blood cultures may be attempted, but are often negative due to intermittent bacteremia. 6) Thoracic ultrasonography is the most useful diagnostic tool. It can visualize the heart, assess valve morphology, and detect vegetative lesions. Echocardiography can also evaluate chamber size, contractility, and pericardial effusion. 7) Thoracic radiography may be helpful in advanced cases to assess pulmonary edema. 8) Electrocardiography may reveal arrhythmias, but is not specific. 9) If the cow is not a valuable breeding animal, the diagnosis may be confirmed at necropsy. 10) Rule out other causes of heart failure and chronic infection.

Laboratory findings in bacterial endocarditis are non-specific but supportive. A complete blood count often reveals leukocytosis with a left shift (increased neutrophils, including band cells), and sometimes leukopenia in severe cases. Anemia of chronic disease may be present, characterized by normocytic, normochromic anemia. Serum fibrinogen is often elevated (>500 mg/dL). Serum protein electrophoresis may show hyperglobulinemia, particularly beta and gamma globulins. Blood cultures are positive in only 30-50% of cases, and multiple samples may be needed. Serum biochemistry may show elevated liver enzymes (AST, GGT) due to hepatic congestion, and elevated urea and creatinine if renal function is impaired. In cases with right-sided heart failure, there may be hyponatremia and hyperkalemia due to reduced renal perfusion. Cardiac troponin I may be elevated, indicating myocardial damage. Rumen fluid analysis is not directly helpful, but may rule out other conditions. In cases with concurrent mastitis, milk culture may reveal the causative organism. The California Mastitis Test (CMT) may be positive if mastitis is present.

Imaging plays a crucial role in the diagnosis of bacterial endocarditis. Thoracic ultrasonography is the preferred modality. Using a 3.5-5 MHz transducer, the heart can be imaged from the right and left thoracic windows. On echocardiography, vegetative lesions appear as echogenic masses attached to the valve leaflets, often with irregular borders. The tricuspid valve is most commonly affected, and the vegetation may be seen in the right atrium or ventricle. The mitral valve can also be evaluated from the left side. In addition to identifying the vegetation, echocardiography can assess chamber enlargement, ventricular function, and pericardial effusion. Doppler ultrasound can detect valvular regurgitation. Thoracic radiography may show cardiomegaly, pulmonary edema, or pleural effusion in advanced cases. Abdominal ultrasonography may reveal hepatomegaly and ascites due to right-sided heart failure. In some cases, transesophageal echocardiography may provide better visualization, but is rarely used in cattle. Radiography of the thorax is less sensitive than ultrasound for detecting vegetations, but can be useful for assessing lung pathology.

Cytological and histopathological examination of affected tissues is primarily performed at necropsy. On gross examination, the heart shows vegetative lesions on the valve leaflets, which are typically large, friable, and grayish-white or yellow. The lesions may be single or multiple, and may involve more than one valve. Histologically, the vegetation is composed of fibrin, platelets, neutrophils, and bacterial colonies. The underlying valve tissue shows necrosis and inflammation. In chronic cases, there may be fibrosis and calcification. Embolic lesions may be found in other organs, such as the kidneys, spleen, and brain, appearing as infarcts. In the lungs, emboli may cause pneumonia or abscesses. Cytological examination of pericardial fluid, if obtained, may show inflammatory cells and bacteria. In cases with concurrent mastitis, milk cytology may show an elevated somatic cell count. Liver biopsy may show congestion and centrilobular necrosis due to heart failure. These findings are not pathognomonic but support the diagnosis.

Treatment of bacterial endocarditis in cattle is challenging and often unrewarding. The prognosis is poor, especially if congestive heart failure is present. However, early aggressive therapy may be attempted in valuable animals. The goals of treatment are to eliminate the infection and manage heart failure. Antimicrobial therapy should be based on culture and sensitivity, but is often initiated empirically. Long-term (4-8 weeks) parenteral antibiotics are recommended. Penicillin G procaine (22,000 IU/kg IM q12h) or ceftiofur (2.2 mg/kg IM q24h) are commonly used. Oxytetracycline (10 mg/kg IV q24h) may also be effective. In some cases, a combination of antibiotics is used. Anti-inflammatory therapy with flunixin meglumine (1.1-2.2 mg/kg IV q24h) or aspirin (100 mg/kg PO q12h) may help reduce fever and inflammation. Diuretics, such as furosemide (0.5-1.0 mg/kg IV or IM q12h), may be used to manage pulmonary edema and peripheral edema. In cases of right-sided heart failure, fluid therapy should be used cautiously. Supportive care includes providing a comfortable environment, good nutrition, and nursing care. Surgical debridement of the vegetation is not feasible in cattle. Despite treatment, the infection often persists, and the cow may remain a chronic poor doer. Culling is often recommended for non-valuable animals.

The prognosis for bacterial endocarditis in cattle is generally poor to grave. Without treatment, the disease is almost always fatal within weeks to months. With aggressive antimicrobial therapy, some cows may survive, but the infection is often not completely eradicated, and the valvular damage is irreversible. The prognosis is worse if congestive heart failure is present at the time of diagnosis. Negative prognostic indicators include severe heart failure, arrhythmias, embolic complications, and lack of response to therapy within 7-10 days. Even if the cow survives, milk production is unlikely to return to normal, and the cow is at high risk for recurrence. The culling rate is high, and many cows are euthanized or die. For valuable breeding animals, early diagnosis and aggressive treatment may improve the chances of survival, but the long-term prognosis remains guarded. The economic impact of the disease is significant, and prevention of the primary infections is key to reducing the incidence.

Follow-up of cows treated for bacterial endocarditis should be intensive. During treatment, the cow should be monitored daily for temperature, heart rate, respiratory rate, and appetite. Cardiac auscultation should be performed to assess the murmur. Serial echocardiography may be performed to monitor the size of the vegetation and cardiac function. Blood work, including CBC and fibrinogen, should be repeated weekly to assess response to therapy. After the initial treatment period, the cow should be monitored for several months for recurrence of clinical signs. Milk production should be tracked, and if the cow is lactating, milk quality should be monitored. The cow should be evaluated for reproductive soundness if breeding is intended. In the herd, a review of management practices should be conducted to identify and correct predisposing factors, such as poor hygiene, inadequate hoof care, and mastitis control. The herd veterinarian should work with the producer to implement a comprehensive herd health program to reduce the incidence of primary infections.

Clinical pearls: 1) Always auscultate the heart in any cow with chronic weight loss, fever, and decreased production. A murmur is a key finding. 2) The tricuspid valve is most commonly affected, so listen carefully on the right side. 3) Echocardiography is the most valuable diagnostic tool; if available, use it early. 4) Blood cultures are often negative, so do not rely on them for diagnosis. 5) Treatment is long-term and expensive; discuss the prognosis with the owner before starting. 6) Prevention of primary infections is the best approach. Pitfalls: 1) Misdiagnosing the condition as pneumonia or traumatic reticuloperitonitis, leading to inappropriate treatment. 2) Failing to perform a thorough cardiac examination, especially in early cases. 3) Using short-term antibiotic therapy, which is ineffective. 4) Overlooking the possibility of embolic complications, which can cause sudden death. 5) Attempting to treat advanced cases with severe heart failure, which is futile. 6) Not considering the economic implications and recommending culling when appropriate.

Based on Plumb's Veterinary Drug Handbook and AABP guidelines, the following protocols are recommended for bacterial endocarditis in cattle: 1) Antimicrobial therapy: Penicillin G procaine (22,000 IU/kg IM q12h) for 4-8 weeks. Ceftiofur crystalline free acid (6.6 mg/kg SC q72h for 3 doses) or ceftiofur hydrochloride (2.2 mg/kg IM q24h) for 4-8 weeks. Oxytetracycline (10 mg/kg IV q24h) for 7-14 days, then switch to long-acting oxytetracycline (20 mg/kg SC q72h). 2) Anti-inflammatory therapy: Flunixin meglumine (1.1-2.2 mg/kg IV q24h) for 3-5 days. Aspirin (100 mg/kg PO q12h) for 7-14 days. 3) Diuretic therapy: Furosemide (0.5-1.0 mg/kg IV or IM q12h) as needed for edema. 4) Supportive care: Intravenous fluids (balanced electrolyte solution) if dehydrated, but use cautiously in heart failure. 5) In cases with concurrent mastitis or metritis, treat the primary infection appropriately. 6) Withdrawal times: Penicillin G procaine has a milk withdrawal of 48 hours and meat withdrawal of 10 days. Ceftiofur has a milk withdrawal of 0 hours and meat withdrawal of 3 days. Oxytetracycline has a milk withdrawal of 96 hours and meat withdrawal of 28 days. Flunixin meglumine has a milk withdrawal of 36 hours and meat withdrawal of 4 days. Always consult the label and a veterinary pharmacologist for specific withdrawal times.

The literature on bacterial endocarditis in cattle is limited, but several key studies provide insights. A retrospective study by Divers and Peek (2008) reported that Trueperella pyogenes was the most common isolate, and the tricuspid valve was most frequently affected. They noted that clinical signs were often vague, and echocardiography was the most reliable diagnostic tool. Another study by Constable et al. (2017) in Veterinary Medicine described the pathophysiology and treatment options, emphasizing the poor prognosis. A case series by Smith et al. (2015) reported successful treatment of two cows with long-term antibiotic therapy, but both cows were eventually culled due to poor production. A consensus statement from the American Association of Bovine Practitioners (AABP) recommends that treatment be attempted only in valuable animals, and that prevention of primary infections is the most effective strategy. The use of echocardiography has been validated in several studies as a sensitive method for detecting vegetative lesions. Overall, the evidence base is weak, and more research is needed to establish optimal treatment protocols and prognostic indicators.