obligate intracelluar parasites

• Ehrlichia (anaplasma) phagocytophilum


  • The causative agent of granulocytic anaplasmosis in dogs (E. ewingii as well), horses and other animals
  • Infection may be subclinical to acute (fever, lethargy and anorexia)
  • The disease occurs in Northern and Central Europe and in North America
• Ehrlichiosis/anaplasmosis diagnosis in dogs

  • Microscopic examination (often inconclusive)
  • Serologic tests (e.g. IF, more reliable, especially for paired samples of sera)
  • Molecular methods (PCR)
• Rickettsiaceae


  • Contains obligate intracellular parasites that reside in host-cell cytoplasm or nucleus and are not bound by vacuoles
  • Rickettsiae are coccobacilli or short rods, 0.8 – 2 μm long
  • Cannot be stained by Gram method
  • Parasitize in humans and animals
  • Transmission by arthropods
• Rickettsia rickettsii


  The causative agent of Rocky Mountain spotted fever in humans and occasionally in dogs; the disease can be fatal; the mortality rate is 3-5%
• R. prowazekii


  The etiologic agent of epidemic typhus, a louse-borne disease of humans worldwide; mortality may reach 60% in untreated patients over 50 years of age
• Coxiella burnetii


  • The causative agent of Q fever (query fever)
  • Shares some rickettsial properties: obligate intracellular growth, failure to stain with the Gram method, transmission (in some cases) by ticks
  • Small, pleomorphic rod-shaped bacterium 0.2 – 0.4 μm wide and 0.4 – 1μm long
  • Life cycle includes small- and large-cell variants (SCV and LCV)
  • Small, spore-like forms are resistant to elevated temperatures, UV light, desiccation and some disinfectants
• Q fever transmission


  • Direct or indirect contact (inhalation of contaminated dust and dried excretions, ingestion of unpasteurized milk, arthropod bites etc.)
• Q fever in domestic animals

  Usually a subclinical form; the organism can localize in the mammary gland, uterus and placenta leading to abortions (mainly in sheep and goats)
• Q fever in humans

  • Flu like: sudden onset of fever, malaise, headache, myalgia (muscle pain), joint pain, upper respiratory problems, dry cough, pleuritic pain, chills, gastrointestinal symptoms and splenomegaly
  • Veterinarians, abattoir workers, farm workers, shearers, laboratory workers etc. are at higher risk
  • The case fatality rate is usually low (up to 5%)
  • The chronic form of Q fever (in 5% of infections) may involve endocarditis; the mortality rate is higher (65% in untreated cases)
• Q fever outbreak in the netherlands: 2007-2010, more than 40,000 cases (62% of patients developed pneumonia) and about 20 deaths including 11 deaths in 2010, linked to dairy goat farms near densely populated areas, probably caused by transmission of contaminated dust particles
• Chlamydiaceae


  • Gram-negative obligate intracellular pathogens
  • Parasites of mammals, birds and reptiles (often asymptomatic infections)
  • Cell wall contains cytoplasmic and outer membranes, but no peptidoglycan layer
  • Outer membrane contains a genus-specific LPS and a serotype-specific MOMP
  • Chlamydia are probably "energy parasites"
• Chlamydial development cycle


  1. Elementary body (EB, 0.2 – 0.4 μm, infectious form)

  2. Reticulate body (RB, 0.8 – 1.0 μm, noninfectious, metabolically active)

  3. Four phases: (1) dormant phase; (2) induction of metabolic activity within EB; (3) transformation of EB into RB; (4) reversion of RB back into EB
• Chlamydial habitat and mode of infection

  • Infect the mucosal membranes of the respiratory and GI tracts
  • Elementary bodies are shed in secretions and feces of asymptomatic or clinically infected animals
  • Can survive for long periods in soil and feces
  • Animals and humans are infected mainly by inhalation of infectious dust and droplets
• Chlamydiaceae diagnosis


  • Cytology (cytologic examination, dark purple inclusions within cells)
  • Serologic tests (enzyme immunoassays, CF, latex agglutination, paired serum samples most useful)
  • Cannot be cultivated on artificial media, embryonated eggs and cell cultures used
  • Direct fluorescent antibody test and EIAs to detect antigens
  • Molecular methods (PCR, nucleic acid probes)
• Chlamydia trachomatis


  A human pathogen, causes a STD and preventable blindness (trachoma, granular conjunctivitis) worldwide
• Chlamydia suis


  Causes infections of the GI tract (mostly asymptomatic) in swine
• Chlamydia psittaci


  • Primarily a pathogen of birds (in more than 150 species), virulence varies by serovar, clinical signs (in case of virulent strains): anorexia, fever, conjunctivitis, yellowish-green gelatinous droppings, decrease in egg production
  • Important human pathogen (zoonosis!), flu like illness, person-to-person transmission does not occur
• Chlamydia pneumoniae


  Causes bronchitis and pneumonia
• Chlamydia abortus


  Comprises previous strains of Ch. psittaci associated with abortions in sheep (EAE), goats, cattle and swine
• Chlamydia felis


  A well-recognized cause of conjunctivitis, rhinitis and sometimes pneumonia in cats