Coxiella burnetii - Q Fever

Coxiella burnetii - Q Fever

 

Q-fever, a worldwide zoonoses, is caused by Coxiella burnetii.

Epidemiology

  • Incidence – <50/year in U.S.
  • Transmission
    • Important reservoirs of C. burnetii include cattle, sheep and goats as well as rodents and cats that feed on them
    • Infection in these animals is enzootic and usually asymptomatic
    • Bacteria infects humans via:
      • Inhalation of contaminated dust particles and aerosols
      • Handling/ingesting infected raw meat or milk

Organism

  • Gram-negative coccobacillus
  • Obligate intracellular parasite (family Rickettsia) with worldwide distribution

Risk Factors

  • Occupational – farmers, veterinarians, abattoir workers, military personnel
  • Ingestion of unpasteurized dairy products

Pathophysiology

  • Coxiella burnetii exists in two antigenic phases -- phase I and phase II
  • Acute disease
    • Antibody level to phase II is usually higher than that to phase I, often by several orders of magnitude,
    • Antibody level is generally detected during the second week of illness
  • Chronic disease
    • Antibodies to phase I antigens generally require longer to appear and indicate continued exposure to the bacteria

Clinical Presentation

  • Incubation period about 2-6 weeks
  • Symptoms
    • Most cases are self-limiting febrile illnesses
      • Fever peaks in 2-4 days near 40°C, then gradually declines over period of 1-2 weeks
    • Constitutional – malaise, anorexia, myalgias, weakness, intense headache
    • Pneumonitis or bronchitis – tachypnea, rales, rhonchi, cough, wheezing
    • Hepatitis – nausea, vomiting, diarrhea,  anorexia, elevated transaminases, rarely jaundice
  • Chronic disease rare (<1%)
    • The presence of endocarditis is pathognomonic for chronic disease
      • Occurs in patients with pre-existing heart valve damage, immunosuppression or chronic renal disease
      • May result in culture negative endocarditis
      • Symptoms – low-grade fever, cardiac failure, hepatosplenomegaly, clubbing of digits
    • Other organs may be involved – hepatitis, vascular infection, osteomyelitis, lymphadenitis

Diagnosis

  • Indications for testing
    • Febrile illness with appropriate risk factors
  • Laboratory testing
    • Antibody titers by IFA, ELISA
      • Acute disease –Phase I and II IgM increased, Phase II IgG increased
        • May take 3-4 weeks after onset of illness to rise
      • Chronic disease – Phase I IgG and IgA increased  
    • DNA testing
    • Immunohistochemical staining
    • Culture tests are not recommended; available only in research laboratories

Disease Monitoring

  • IgG Phase I – use to monitor treatment efficacy except a decrease in successful therapy

Treatment

  • Treatment is curative; monitor titers to assess treatment success

See Also