The present study evaluated rickettsial infection in

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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...

We report finding Rickettsia parkeri in Brazil in 9.7% of Amblyomma triste ticks examined. An R. parkeri isolate was successfully established in Vero cell culture. Molecular characterization of the agent was performed by DNA sequencing of portions of the rickettsial genes gltA, htrA, ompA, and ompB.

The present study provides a rickettsial serosurvey in 25 dogs and 35 humans in an endemic area for Brazilian spotted fever in the State of São Paulo, where the tick Amblyomma aureolatum is the main vector. Testing canine and human sera by indirect immunofluorescence against four Rickettsia antigens (R. rickettsii, R. parkeri, R. felis and R. bellii) showed that 16 (64%) of canine sera and 1 (2.8%) of human sera reacted to at least one of these rickettsial antigens with titers <FONT FACE=Symbol>³</FONT> 64. Seven canine sera and the single reactive human serum showed titers to R. rickettsii at least four times those of any of the other three antigens. The antibody titers in these 7 animals and 1 human were attributed to stimulation by R. rickettsii infection. No positive canine or human serum was attributed to stimulation by R. parkeri, R. felis, or R. bellii. Our serological results showed that dogs are important sentinels for the presence of R. rickettsii in areas where the tick A. aureolatum is the main vector of Brazilian spotted fever.

Brazil has the third richest bird diversity of the world; however, there are few data concerning ticks (Acari: Ixodidae) parazitizing birds. The aim of the study was to report tick infestations on wild birds from an Atlantic rain forest region of Brazil. During 2 yr, ticks were collected from birds and from the environment in 12 forest sites. A total of 1,725 birds were captured representing 80 species from 24 families. In total, 223 (13%) birds were found infested by immature stages of Amblyomma ticks: 1,800 larvae and 539 nymphs. The prevalence of ticks was higher among birds from the families Thamnophilidae, Conopophagidae, and Momotidae. The most common tick parasitizing birds was Amblyomma nodosum Koch. Other tick species, Amblyomma coelebs Neumann, Amblyomma cajennense (F.), Amblyomma ovale Koch, Amblyomma longirostre (Koch), Amblyomma calcaratum Neumann, and Amblyomma naponense (Packard), were found sporadically. Among free-living ticks collected in the environment, A. cajennense was the most common, followed by A. coelebs, A. naponense, Amblyomma brasilense Aragão, and Hemaphysalis juxtakochi Cooley.

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Plasmids are mobile genetic elements of bacteria that can impart important adaptive traits, such as increased virulence or antibiotic resistance. We report the existence of plasmids in Rickettsia (Rickettsiales; Rickettsiaceae) species, including Rickettsia akari, "Candidatus Rickettsia amblyommii," R. bellii, R. rhipicephali, and REIS, the rickettsial endosymbiont of Ixodes scapularis. All of the rickettsiae were isolated from humans or North and South American ticks. R. parkeri isolates from both continents did not possess plasmids. We have now demonstrated plasmids in nearly all Rickettsia species that we have surveyed from three continents, which represent three of the four major proposed phylogenetic groups associated with blood-feeding arthropods. Gel-based evidence consistent with the existence of multiple plasmids in some species was confirmed by cloning plasmids with very different sequences from each of two "Ca. Rickettsia amblyommii" isolates. Phylogenetic analysis of rickettsial ParA plasmid partitioning proteins indicated multiple parA gene origins and plasmid incompatibility groups, consistent with possible multiple plasmid origins. Phylogenetic analysis of potentially host-adaptive rickettsial small heat shock proteins showed that hsp2 genes were plasmid specific and that hsp1 genes, found only on plasmids of "Ca. Rickettsia amblyommii," R. felis, R. monacensis, and R. peacockii, were probably acquired independently of the hsp2 genes. Plasmid copy numbers in seven Rickettsia species ranged from 2.4 to 9.2 per chromosomal equivalent, as determined by real-time quantitative PCR. Plasmids may be of significance in rickettsial evolution and epidemiology by conferring genetic plasticity and host-adaptive traits via horizontal gene transfer that counteracts the reductive genome evolution typical of obligate intracellular bacteria.