Experimental infection of dogs with a Brazilian strain of Rickettsia rickettsii: clinical and laboratory findings

• Published in: Memórias do Instituto Oswaldo Cruz Vol. 103; no. 7; pp. 696 - 701
• Main Authors: Piranda, Eliane M, Faccini, João Luis H, Pinter, Adriano, Saito, Tais B, Pacheco, Richard C, Hagiwara, Mitika K, Labruna, Marcelo B
• Format: Journal Article
• Language: English
• Published: Brazil Instituto Oswaldo Cruz, Ministério da Saúde 01.11.2008; Fundação Oswaldo Cruz (FIOCRUZ)
• Subjects: Animals; Brazil; Disease Models, Animal; DNA, Bacterial - blood; dog; Dog Diseases - microbiology; Dog Diseases - transmission; Dogs; Female; Ixodidae; PARASITOLOGY; Rickettsia rickettsii; Rickettsia rickettsii - pathogenicity; Rocky Mountain Spotted Fever - microbiology; Rocky Mountain Spotted Fever - transmission; Rocky Mountain Spotted Fever - veterinary; spotted fever; tick; Ticks - microbiology; TROPICAL MEDICINE; spotted fever; Brazil; Rickettsia rickettsii; tick; dog
• ISSN: 0074-0276; 1678-8060; 1678-8060; 0074-0276
• DOI: 10.1590/S0074-02762008000700012

The bacterium Rickettsia rickettsii is the etiological agent of an acute, severe disease called Rocky Mountain spotted fever 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. 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 has been restricted to the United States. The present study evaluated the pathogenicity for dogs of a South American strain of R. rickettsii. Three groups of dogs were evaluated: group 1 (G1) was inoculated ip with R. rickettsii; group 2 (G2) was infested by R. rickettsii-infected ticks; and the control group (G3) was infested by uninfected ticks. During the study, no clinical abnormalities, Rickettsia DNA or R. rickettsii-reactive antibodies were detected in G3. In contrast, all G1 and G2 dogs developed signs of rickettsial infection, i.e., fever, lethargy, anorexia, ocular lesions, thrombocytopenia, anemia and detectable levels of Rickettsia DNA and R. rickettsii-reactive antibodies in their blood. Rickettsemia started 3-8 days after inoculation or tick infestation and lasted for 3-13 days. Our results indicate that a Brazilian strain of R. rickettsii is pathogenic for dogs, suggesting that canine clinical illness due to R. rickettsii has been unreported in Brazil and possibly in the other South American countries where BSF has been reported among humans.