Rickettsia rickettsii

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Rocky Mountain spotted fever

  • Caused by Rickettsia rickettsii
  • Affects humans and dogs
  • Various tick vectors, which acquire the organism from small mammals
  • Transovarial and trans-stadial transmission within the tick population
  • Organisms replicate in endothelial cells of infected dogs, cause vasculitis, increased vascular permeability and haemorrhage
  • Clinical signs
    • Incubation period 2-10 days; course less than 2 weeks
  • Fever, depression, conjunctivitis, retinal haemorrhage, muscle and joint pain, coughing, dyspnoea, oedema of extremities
  • Neurological signs in dogs include stupor, ataxia, neck rigidity, seizures and coma
  • Death from cardiovascular, neurological or renal damage in severely-affected animals
  • Gross pathology includes haemorrhage, splenomegaly and lymphadenopathy
  • Diagnosis
    • Rising antibody titre during an indirect fluorescent antibody test or ELISA
    • Thrombocytopenia and leukopenia during early phase
  • Treatment and control
    • Tetracycline therapy for two weeks
    • Tick removal from dogs