In a recent diagnostic challenge, an 11-year-old spayed female German Wirehaired Pointer presented with alarming symptoms that initially perplexed her veterinary team. Over the course of a week, the dog experienced lethargy, hyporexia, diarrhea, and persistent coughing, culminating in a diagnosis of cardiac tamponade secondary to pericardial effusion.

Upon clinical examination, an echocardiogram revealed no structural abnormalities to account for the effusion, which was characterized cytologically as an exudate with mixed macrophagic and neutrophilic inflammation. Notably, occasional morulae were observed within neutrophils, prompting further investigation.

Advanced molecular diagnostics were employed, utilizing both quantitative PCR (qPCR) and conventional PCR (cPCR) tests conducted at the NC State University's Vector-borne Disease Diagnostic Laboratory. These tests confirmed the presence of Anaplasma phagocytophilum DNA in both pericardial fluid and blood samples.

Initial serological testing using an ELISA (Vetscan Flex4 Rapid Test, Zoetis) returned negative for A. phagocytophilum antibodies, a result possibly influenced by the timing of the test post-infection. However, a subsequent test with the SNAP4DxPlus kit (IDEXX) conducted seven days later confirmed seroconversion, reinforcing the diagnosis of anaplasmosis.

Management of the case included therapeutic pericardiocentesis to relieve cardiac tamponade and a 14-day course of doxycycline administered orally at 5 mg/kg every 12 hours. One month following treatment, a repeat echocardiogram showed no recurrence of effusion, indicating a successful resolution of the acute phase of the disease.

This case highlights several key points for veterinary professionals:

• The importance of considering vector-borne pathogens as differential diagnoses in atypical presentations such as pericardial effusion.

• The utility of combining cytologic evaluation, molecular diagnostics, and serological testing to achieve a definitive diagnosis.

• The effective management of tick-borne diseases with appropriate antimicrobial therapy and supportive care.

Veterinary practitioners should remain vigilant for the signs of tick-borne diseases, even in non-endemic areas, as geographic distributions of vectors and pathogens can expand. This case also underscores the importance of preventive measures such as regular use of acaricides and tick checks to protect canine patients from vector-borne infections. Read full study here: Detection of Anaplasma phagocytophilum in an inflammatory pericardial effusion of a dog