• Clinical science

Collection of zoonotic diseases


Zoonotic diseases are infections that are transmitted from animals to humans. While animals may transmit infection directly, they usually serve as hosts for a pathogen that is then transmitted to humans by a vector (e.g., ticks, fleas). Zoonoses are usually endemic to certain geographical regions, and peaks in incidence often correlate with the life cycle of the transmitting vector. Common diseases include Q fever, Rocky mountain spotted fever, endemic typhus, ehrlichiosis, and babesiosis. Although these conditions differ in their exact presentation, symptomatic cases typically present with fever, flulike symptoms, and possibly skin rashes. In some cases of fulminant disease, there may be complications such as disseminated intravascular coagulation, shock, and organ failure. Most zoonoses are treated with antibiotics and respond well to treatment.

Q fever

  • Definition: notifiable zoonotic disease with cattle, sheep, and goats as the primary reservoir
  • Pathogen: Coxiella burnetii (gram-negative, intracellular)
  • Epidemiology
    • Worldwide occurrence
    • 160–170 cases of acute Q fever per year in the US
    • 70% of cases occur in men
    • Peak incidence from April to June
  • Route of transmission
    • Inhalation of aerosols from the secretions of infected livestock or animals about to give birth
    • Ingestion of raw milk produced by infected animals
  • Risk groups: slaughterhouse workers, farmers, shepherds, veterinarians
  • Pathophysiology: development of antigens
    • Phase I antigens: seen when C. burnetii is highly infectious
    • Phase II antigens: seen when C. burnetii is less infectious
Type of Q fever Acute Q fever Chronic Q fever
Incubation period
  • 2–6 weeks
  • Months to years
Clinical features
Diagnostics Serology via IFA (best initial test)
  • Anti-phase II antibody IgG titers ≥ 200 and IgM titers ≥ 50
  • In cases of negative IFA but high clinical suspicion, perform PCR on serum or tissue samples before administering antibiotics.
  • Anti-phase I antibody IgG titers > 800 or persistently high levels of anti-phase I antibody 6 months after completing therapy
Additional findings
  • Avoid consuming unpasteurized milk products


Rocky Mountain spotted fever (RMSF)



Endemic typhus (also known as murine typhus)