Dynamics of Rickettsia parkeri infection in domestic chickens

Abstract

The aim of the present study was to investigate experimental infections by Rickettsia parkeri in domestic chickens (Gallus gallus domesticus) and to determine the dynamics of antibody production during acute and chronic infection. The animals (n = 64) were allocated into eight groups as follows: G1, inoculated intramuscularly (IM) with 2.5 × 10 5 Vero cells (1 mL) infected with R. parkeri; G2, inoculated IM with 5.0 × 10 5 Vero cells (2 mL) infected with R. parkeri; G3, received 1 mL of the inoculum subcutaneously (SC); G4, received 2 mL of inoculum SC; G5, received 1 mL of the inoculum intraperitoneally (IP); G6, injected with 2 mL of the inoculum IP; G7 and G8, received 1 mL and 2 mL of culture medium IM, respectively (negative control groups). All R. parkeri inocula were viable prior to inoculation in the birds. In order to assess the dynamics of antibody production in acute and chronic infection, sera of chickens were collected 3, 7, 14, and 21 d post infection (PI) and assessed using an immunofluorescence antibody test (IFAT). In addition, PCR (gltA gene) was performed using fragments of spleen and lung from euthanized chickens to detect the replication of R. parkeri in tissues during the experimental period. Animals from the G4 and G3 groups exhibited the highest mean antibody titers, with maximum levels observed at 7 and 14 d PI, respectively. Conversely, G2, G4 and G6 exhibited higher mean antibody titers than G1, G3 and G5, respectively. Antibody titers were dose-dependent. Rickettsial DNA was not detected in either spleen or lung tissue. The present study demonstrated that birds seroconvert after being challenged by R. parkeri. However, there was no replication of the agent in the tissues analyzed and rickettsemia was not observed. (1 ml) infectadas por R. parkeri via intramuscular (IM); G2 -5,0 x 105 células Vero (2 ml) infectadas por R. parkeri via IM; G3 -1 ml do inóculo via subcutânea (SC); G4 -2 ml de inóculo via SC; G5 -1 ml do inóculo via intraperitoneal (IP); G6 -2 ml de inóculo via IP, e G7 e G8 -1 e 2 ml de meio de cultivo de células Vero via IM, respectivamente representando os grupos controles negativos. Ressaltase que todos os inóculos de R. parkeri estavam viáveis no momento da inoculação. Os soros das aves foram coletados aos 3, 7, 14 e 21 dias pós-infecção (PI) e testadas por reação de imunofluorescência indireta (RIFI) para avaliar a dinâmica de anticorpos na infecção aguda e crônica. A identificação da multiplicação de R. parkeri nos tecidos, no mesmo período PI, foi realizada por PCR, para um fragmento do gene gltA, em amostras de baço e pulmão provenientes das galinhas eutanasiadas. As aves do G4 e G3 apresentaram as maiores médias de anticorpos obtendo os níveis mais elevados aos sete e 14 dias PI, respectivamente. G2, G4 e G6 apresentaram médias de anticorpos superiores comparados aos G1, G3 e G5 respectivamente, sendo considerada a infecção dose-dependente. Não foi detectado DNA rickettsial nos tecidos avaliados. No presente trabalho foi possível demonstrar que as aves so...