Experimental infection with Rickettsia rickettsii in an Amblyomma dubitatum tick colony, naturally infected by Rickettsia bellii.

Amblyomma dubitatum engorged females, naturally infected by Rickettsia bellii, were used to establish a laboratory colony. Larvae, nymphs, and adults were exposed to two strains of Rickettsia rickettsii by feeding on needle-inoculated guinea pigs, and thereafter reared on uninfected guinea pigs. After acquisition feeding, engorged larvae and nymphs molted to nymphs and adults, respectively, which were shown to be infected (confirming transstadial perpetuation), and were able to transmit both strains of R. rickettsii to uninfected animals, as demonstrated by clinical, serological, and molecular analyses. However, the larval, nymphal, and adult stages of A. dubitatum showed to be only partially susceptible to R. rickettsii infection, since in all cases, only part of the ticks became infected by this agent, after being exposed to rickettsemic animals. While transovarial transmission of R. rickettsii was inefficient in the A. dubitatum engorged females of the present study, 100% of these females passed R. bellii transovarially. Because it has been reported that a primary infection by a Rickettsia species would preclude transovarial transmission of a second Rickettsia species, it is likely that the ineffectiveness of A. dubitatum to perpetuate R. rickettsii by transovarial transmission was related to its primary infection by R. bellii; however, it could also be related to unknown factors inherent to A. dubitatum. The relevance of A. dubitatum as a natural vector of R. rickettsii to humans or animals is discussed.

[Ehrlichia canis in dogs attended in a veterinary hospital from Botucatu, São Paulo State, Brazil]. / Ehrlichia canis em cães atendidos em hospital veterinário de Botucatu, Estado de São Paulo, Brasil.

This study investigated the etiology of canine ehrlichiosis and possible clinical and epidemiological data associated with the infection in 70 dogs suspect of ehrlichiosis attended at the Veterinary Hospital of the São Paulo State University in Botucatu city during 2001 and 2002. Dogs were evaluated by clinical-epidemiological and hematological data and molecular analysis by partial amplification and DNA sequencing of the ehrlichial dsb gene. E. canis DNA was amplified and sequenced in 28 (40.0%) dogs. Dogs younger than 12 months old showed significantly higher infection rates (65.0%; P < 0.05). Diarrhea, apathy, and anorexia were the major clinical signs observed in 55.2% (P = 0.05), 47.0% (P > 0.05), and 42.4% (P > 0.05) of the PCR-positive dogs, respectively. Twenty-five anemic (<5.5 x 10(6) RBC x microL (-1)), and 8 leukopenic (<5.5 x 103 WBC x microL (-1)) dogs were PCR-positive (P > 0.05). All 28 PCR-positive dogs showed thrombocytopenia (< 175 x 103 platelets x microL (-1)) and revealed statistical significance (P < 0.05). E. canis was the only Ehrlichia species found in dogs in the studied region, with higher infection rates in younger dogs, and statistically associated with thrombocytopenia.

Ehrlichia canis em cães atendidos em hospital veterinário de Botucatu, Estado de São Paulo, Brasil / Ehrlichia canis in dogs attended in a veterinary hospital from Botucatu, São Paulo State, Brazil

O presente estudo investigou a etiologia da erliquiose monocítica canina em 70 cães atendidos no Hospital Veterinário da Universidade Estadual Paulista, na cidade de Botucatu, durante 2001 e 2002. Os cães foram avaliados segundo achados clínicos, epidemiológicos e laboratoriais e pela amplificação parcial e sequenciamento do gene dsb de Ehrlichia. DNA de Ehrlichia canis foi amplificado e sequenciado em 28 (40,0 por cento) cães. Observou-se maior frequência deanimais positivos com idade até 12 meses (P < 0,05). Diarreia, apatia e anorexia foram os sinais clínicos mais frequentes observados em 55,2 por cento (P = 0,05), 47,0 por cento (P > 0,05) e 42,2 por cento (P > 0,05) dos cães PCR positivos, respectivamente. Vinte e cinco cães com anemia (<5,5 × 10(6) eritrócitos.µL-1) e 8 com leucopenia (<5,5 × 10³ leucócitos.µL-1) foram positivos na PCR, porém não apresentaram associação estatística (P > 0,05) frente à infecção por E. canis. Todos os 28 cães positivos na PCR apresentaram trombocitopenia (<175 × 10³ plaquetas.µL-1; P < 0,05). E. canis foi a única espécie de Ehrlichia detectada em cães da região estudada, com alta taxa de infecção em cães jovens e, estatisticamente, associadaa cães trombocitopênicos.

This study investigated the etiology of canine ehrlichiosis and possible clinical and epidemiological data associated with the infection in 70 dogs suspect of ehrlichiosis attended at the Veterinary Hospital of the São Paulo State University in Botucatu city during 2001 and 2002. Dogs were evaluated by clinical-epidemiological and hematological data and molecular analysis by partial amplification and DNA sequencing of the ehrlichial dsb gene. E. canis DNA was amplified and sequenced in 28 (40.0 percent) dogs. Dogs younger than 12 months old showed significantly higher infection rates (65.0 percent; P < 0.05). Diarrhea, apathy, and anorexia were the major clinical signs observed in 55.2 percent (P = 0.05), 47.0 percent (P > 0.05), and 42.4 percent (P > 0.05) of the PCR-positive dogs, respectively. Twenty-five anemic (<5.5 × 10(6) RBC.µL-1), and 8 leukopenic (<5.5 × 10³ WBC.µL-1) dogs were PCR-positive (P > 0.05). All 28 PCR-positive dogs showed thrombocytopenia (<175 × 10³ platelets.µL-1) and revealed statistical significance (P < 0.05). E. canis was the only Ehrlichia species found in dogs in the studied region, with higher infection rates in younger dogs, and statisticallyassociated with thrombocytopenia.