The bacterium Rickettsia rickettsii is the etiological agent of an acute, severe disease called Rocky Mountain spotted fever (RMSF) in the United States or Brazilian spotted fever (BSF) in Brazil. In addition to these two countries, the disease has also been reported to affect humans in Mexico, Costa Rica, Panama, Colombia and Argentina (Paddock et al. 2008). Common clinical signs and symptoms are fever, nausea, vomiting, rash, myalgia, anorexia and headache. The case-fatality rate is 5-10% in the United States and 10-40% in Brazil , Angerami et al. 2006, Chapman et al. 2006.Like humans, dogs are also susceptible to R. rickettsii infection. However, despite the wide distribution of R. rickettsii in the Western Hemisphere, reports of R. rickettsii-induced illness in dogs have been restricted to the United States, where the following clinical abnormalities have been observed: fever, lethargy, anorexia, depression, cutaneous petechiae and echymoses, epistaxis, conjunctivitis, ocular discharge, lymph node enlargement, diarrhea, weight loss, dehydration and central nervous system involvement (mostly paraparesis or tetraparesis, ataxia and vestibular syndrome). Hematological abnormalities include anemia, thrombocytopenia and mild leucopenia at the onset of fever followed by leukocytosis (Keenan et al. 1977a, b, Breitschwerdt et al. 1988, Comer 1991. Case-fatality rates in dogs have been reported to be 3% (Greene 1987), 7% (Greene et al. 1985) and 0% in a more recent study (Gasser et al. 2001).Several serological studies among healthy Brazilian dogs indicate that these animals were infected by R. rickettsii, as shown by high antibody titers to R. rickettsii, at least four-fold higher than titers to other Rickettsia species known to occur in Brazil , Pinter et al. 2008. However, nothing is known about the pathogenicity of South American strains of R. rickettsii for dogs. Since ecological differences and genetic polymorphisms between strains of R. rickettsii from the United States and South America have been reported (Eremeeva et al. 2003, Karpathy et al. 2007, it is not known how pathogenic South American strains of R. rickettsii are for dogs. For this purpose, the present study evaluated experimental infection of dogs with a Brazilian strain of R. rickettsii.
MATERIALS AND METHODSEight six-month-old female dogs were used in the study, consisting of five mongrels and three beagles. Dogs were provided by a laboratory animal room, where they were reared with no contact with ticks and under strict sanitary control, being regularly treated with antiInfection of dogs with Rickettsia rickettsii • Eliane M Piranda et al.
697worm medication (Pirantel, Febantel, Praziquantel; Vermivet Plus ® , Biovet, Brazil) and immunized with commercial vaccines for enteroviruses, hepatitis, influenza and leptospirosis (Octa-Cino-Vacin ® , Biovet, Brazil). During the two weeks before starting the experiment, the dogs were clinically healthy and their paired serum samples (14 days interval) were shown to contain no reactive antibodies to eithe...
