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 × 105 Vero cells (1 mL) infected with R. parkeri; G2, inoculated IM with 5.0 × 105 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.