Coxiella burnetii

Coxiella burnetii is an intra-cellular bacteria that causes Q fever

Coxiella burnetii

A dry fracture of a Vero cell showing Coxiella burnetii

Immunohistochemical detection of Coxiella burnetii

Coxiella burnetii is a Gram-negative, obligate intracellular bacterium that causes the zoonotic disease Q fever. It primarily affects ruminants such as cattle, sheep, and goats, which serve as the main reservoirs. The organism is highly infectious, extremely resistant to environmental stress, and transmissible through aerosolized particles.

Overview

Coxiella burnetii is notable for its environmental resilience, including resistance to heat, desiccation, and many disinfectants. It is capable of surviving in the environment for extended periods and can be transmitted through contaminated dust particles. Infections in humans often occur through inhalation of these particles, especially in agricultural settings.

Transmission

• Primary transmission is via inhalation of contaminated aerosols from amniotic fluid, urine, feces, or placenta of infected animals.
• Secondary routes include ingestion of unpasteurized milk, tick bites, and rarely person-to-person transmission or blood transfusion.
• Occupational exposure affects veterinarians, livestock farmers, abattoir workers, and researchers.

Epidemiology

• First described in Australia in 1935 and in the United States in the 1940s.
• Q stands for "query" fever, referencing the initially unknown cause.
• C. burnetii is found worldwide except in New Zealand.
• In the U.S., Q fever became nationally notifiable in 1999.

Q Fever Trends in the U.S.

• Case reports increased from 19 in 2000 to 173 in 2007.
• In 2017, 153 acute cases and 40 chronic cases were reported to the CDC.

Pathogenesis

C. burnetii infects cells of the mononuclear phagocyte system and survives in the acidic environment of the phagolysosome.

Signs and Symptoms

Acute Q fever symptoms:

• Fever up to 40.5°C (105°F)
• Fatigue, headache, myalgia
• Cough, chest pain
• Nausea, vomiting, diarrhea
• Hepatitis, pneumonia, and myocarditis in severe cases

Chronic Q fever:

• Can develop months or years post-infection
• Most commonly manifests as endocarditis
• Risk factors: valvular heart disease, vascular grafts, pregnancy, and immunosuppression

Diagnosis

PCR, serology using indirect immunofluorescence assay (IFA), and immunohistochemistry are commonly used.

Laboratory Criteria

• Paired sera showing ≥ fourfold rise in IgG titer
• Phase II IgG dominance = acute Q fever
• Phase I IgG dominance = chronic Q fever

Treatment

Doxycycline is the first-line therapy.

Acute Q fever

• Doxycycline 100 mg twice daily for 14 days
• Trimethoprim/sulfamethoxazole is used in pregnancy

Chronic Q fever

• Doxycycline plus hydroxychloroquine for 18–24 months
• Duration is guided by clinical response and serologic monitoring

Prevention

• No licensed vaccine available in the United States
• Preventive measures include:
  • Avoiding contact with birthing animals
  • Proper disposal of placental tissues
  • Consumption of pasteurized milk only

Public Health Impact

• Potential use as a biological weapon
• Notable outbreak in the Netherlands between 2007–2010
• Underdiagnosed due to nonspecific symptoms and limited awareness

See Also

• Q fever
• Gram-negative bacteria
• Zoonosis
• Obligate intracellular parasite
• Veterinary public health
• Bioterrorism