Rickettsia rickettsii

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