zoonotic infection

A 48-year-old sheep farmer presents to his GP with a two-week history of persistent fever, severe retro-orbital headache, and profound fatigue. He denies cough, shortness of breath, or rash. On examination, his temperature is 38.5°C, pulse 85 bpm, BP 120/80 mmHg. The remainder of the examination, including chest auscultation, is unremarkable. He has not travelled outside the region recently.

A 55-year-old farmer presents with a week of high fever, severe retro-orbital headache, and profound muscle aches. He denies cough, sore throat, or rash. On examination, temperature is 39.5°C, pulse 90, BP 120/80. Lungs are clear to auscultation. Abdomen is soft, non-tender. Initial bloods show mildly elevated transaminases. What is the most likely diagnosis?

Which zoonotic infection is a leading cause of culture-negative endocarditis?

A 58-year-old man presents to his general practitioner with a 3-week history of intermittent fever, severe headache, and profound fatigue. He describes the headache as diffuse and often retro-orbital, not relieved by simple analgesia. He also reports generalised muscle aches and occasional night sweats. He denies cough, shortness of breath, or gastrointestinal symptoms. His medical history is unremarkable, and he takes no regular medications. He lives on a rural property in Queensland where he raises sheep and cattle. On examination, he is afebrile at the time of consultation (37.2°C), blood pressure is 130/80 mmHg, pulse is 85 bpm, and respiratory rate is 16 breaths per minute. Physical examination is otherwise unremarkable; specifically, there is no rash, lymphadenopathy, or focal neurological signs. Initial laboratory investigations reveal a white cell count of 7.5 x 10^9/L (neutrophils 65%, lymphocytes 25%), haemoglobin 145 g/L, platelets 250 x 10^9/L. Liver function tests show AST 85 U/L (normal <40), ALT 90 U/L (normal <40), alkaline phosphatase 110 U/L (normal <130), total bilirubin 15 µmol/L (normal <20). C-reactive protein is elevated at 45 mg/L (normal <5). A chest X-ray performed a week prior was reported as normal. Given the clinical presentation and epidemiological context, which of the following is the most appropriate initial diagnostic investigation?