Culture-negative endocarditis in dogs: Bartonella
6-year-old male German Shepherd living in the countryside with frequent ticks and fleas, with intermittent fever, lethargy and shifting lameness. It has a new diastolic murmur at the left base and a bounding femoral pulse. Echocardiography shows a hyperechoic, oscillating lesion on the aortic valve with aortic regurgitation. Three blood cultures from different veins were taken before antibiotics and, after 7 days' incubation, all three are negative.
What is most appropriate now?
chevron_right Show answer and explanation
A. Rule out infective endocarditis, because the blood cultures are negative
A substantial proportion of canine endocarditis cases are culture-negative. An oscillating vegetation with new valvular regurgitation is by itself a major criterion.
B. Start immunosuppressive corticosteroids for the polyarthritis
The polyarthritis is probably reactive (immune complexes) or septic, secondary to the endocarditis. Immunosuppressing a dog with an endovascular infection can be catastrophic.
C. Suspect Bartonella and request serology and PCR, while continuing to treat as endocarditis
Correct. Bartonella grows poorly in conventional blood cultures, mainly affects the aortic valve and is a leading cause of culture-negative endocarditis. Serology and PCR on blood (or valve tissue, if obtained) support the diagnosis and guide antibiotic choice.
D. Consider Staphylococcus aureus, the typical organism in culture-negative cases
Staphylococci and streptococci are common causes of endocarditis, but they grow well in blood culture: they usually give positive cultures.
lightbulb Key takeaway
The modified Duke criteria combine major criteria (echocardiography showing an oscillating vegetation or new valvular regurgitation; repeatedly positive blood cultures) and minor criteria (fever, medium-to-large breed, subaortic stenosis, emboli, polyarthritis, positive Bartonella serology). Bartonella is zoonotic and vector-borne: reinforce flea and tick control.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.