Case 209. Ehrlichiosis (adult dog)
         
   
Peripheral blood smear of the dog infected with Ehrlichia canis
   
         
   
Key words : 
Ehrlichia canis, monocytic ehrlichiosis, Q fever, Coxiella burnetti    
         
   
zoonosis
   
     
 
     
The monocyte contains a cluster of fine granules of infected E. canis in the cytoplasm (Giemsa). E. canis is not pathogenic to human. Ehrlichiosis is transmitted by tick bite.   Another view of E. canis-infected canine monocyte (Giemsa). In human, human monocytic ehrlichiosis caused by E. chaffeensis and human granulocytic ehrlichiosis caused by E. phagocytophila are known as emerging infectious diseases.
     
 
     
Coxiella burnetti in a mouse splenic macrophage (Gimenez)
C. burnetti, a causative agent of Q fever, is an obligate intracellular Gram-negative bacterium. Ticks transmit the microbes to animals. Human infection is mainly tranmitted by droplets containing Coxiella of animal origin. Q fever is often presented as atypical pneumonia, accompanying influenza-like signs and symptoms. This zoonotic pathogen of rickettsia group is resistant to heat, dryness and disinfectant, so that it is nominated as a bioterrorist.
  Electron micrograph of Coxiella burnetti in mouse splenic macrophages
Small rods are clustered within the cytoplasm of macrophages to form cytoplasmic inclusions. Chronic Q fever shows features of endocarditis, chronic hepatitis or chronic osteomyelitis. Small epithelioid granuloma (fibrin ring granuloma) is a histologic hallmark of the liver lesion.
     
 
     
Electron micrograph of Coxiella burnetti in a mouse splenic macrophage
Morphology and electron density of C. burnetti in phagosomes of a macrophage are varied. C. burnetti is an exceptional rickettsia, in that it does not necessarily require the anthropod vector for transmission.