Makindo Medical Notes

🐄 Coxiella burnetii (Q fever) can cause culture-negative endocarditis, often missed due to intermittent fever, absence of vegetations on echo, and negative blood cultures. 👉 Always maintain a low threshold for serology or PCR in patients with unexplained fever, valvular disease, or animal contact.

📖 About

• Q = Query fever, first described in Queensland in the 1950s.
• Worldwide zoonosis, affecting both animals and humans.
• Endocarditis is the key chronic complication; can be subtle and delayed in diagnosis.
• Presents in both acute (self-limiting febrile illness) and chronic (endocarditis, hepatitis) forms.

🦠 Characteristics

• Coxiella burnetii is a Gram-negative obligate intracellular coccobacillus.
• Extremely resilient – survives drying, persists in dust, and is highly infectious.
• Closely related to the Rickettsiae, but more environmentally stable.

🐑 Source

• Reservoir: Livestock – cattle, sheep, goats, camels.
• Transmission: Inhalation of aerosols from birth products (placenta, amniotic fluid), faeces, urine.
• Unpasteurised milk & cheese can transmit infection.
• Ticks are vectors in animals but not a major source in humans.
• Human-to-human spread is very rare.

⚠️ Pathogenicity & Clinical Features

• Acute Q fever:
  • PUO, pneumonia, hepatitis, erythema nodosum.
  • Miscarriage or stillbirth if infection occurs in pregnancy.
• Chronic Q fever:
  • Endocarditis (culture-negative, insidious).
  • Myocarditis, chronic hepatitis ± fibrosis.
  • Rarely neurological: encephalitis, neuropathy, Guillain–Barré syndrome.
• Key exam clue: farmer/vet with fever, negative cultures, and valvular disease.

🧪 Investigations

• Blood cultures: usually negative.
• Serology (mainstay):
  • Acute infection → ↑ Phase II IgG (>200).
  • Chronic infection → ↑ Phase I IgG (>800).
• PCR for Coxiella DNA can confirm diagnosis.
• Bloods: ↑ ESR, ↑ LFTs, thrombocytopenia.
• Echo: may miss vegetations; consider TEE if suspicion high.

💊 Management

• Acute Q fever: Doxycycline for 2 weeks (or tetracycline 500 mg TDS × 10 days).
• Chronic Q fever (endocarditis, vascular infection): Long-term doxycycline + hydroxychloroquine for 18–24 months.
• Valve surgery may be required if medical therapy fails.
• ⚠️ Avoid tetracyclines in pregnancy – alternatives include co-trimoxazole.

🛡️ Prevention

• No widely available vaccine (though one exists in Australia for at-risk workers).
• Prevent by avoiding unpasteurised dairy, especially in pregnancy.
• Protective equipment (masks, gloves) when handling livestock or animal products.
• Public health measures: control of infection in herds, safe disposal of animal birth products.