Experimental Ehrlichia chaffeensis infection in beagles

Abstract

A canine model for human monocytic ehrlichiosis was used to assess persistent infection and antigenic variation of Ehrlichia chaffeensis. Two beagle dogs were infected subcutaneously with E. chaffeensis Arkansas strain. The dogs were observed for 6 months after inoculation for clinical signs, blood chemistry changes, antibodies to E. chaffeensis and presence of E. chaffeensis in the blood. Both dogs developed thrombocytopenia, but exhibited normal body temperatures during the entire course of infection. In one dog, E. chaffeensis was cultivated for up to 74 days post-inoculation and E. chaffeensis DNA was detected in the dog's blood for up to 81 days. In the other dog, E. chaffeensis was cultured for up to 102 days and E. chaffeensis DNA was detected in the blood for up to 117 days. PCR amplification and DNA sequence analysis indicated that there was no genetic variation in the 120 kDa outer-membrane glycoprotein gene of E. chaffeensis during infection of the dogs. The dogs developed antibodies to the immunodominant proteins of E. chaffeensis, including the 175, 140, 120, 80, 50 and 28 kDa proteins, starting in the fifth week post-inoculation. The dogs maintained high antibody titres throughout the 6-month study period. These results indicate that dogs become carriers of E. chaffeensis for 2-4 months after infection without exhibiting signs of clinical disease, suggesting that dogs may serve as a natural host for E. chaffeensis.

Expression of Members of the 28-Kilodalton Major Outer Membrane Protein Family of Ehrlichia chaffeensis during Persistent Infection

“…The sera from two male beagle dogs (dog ACC and dog ADJ) experimentally infected with E. chaffeensis at 6 months of age were used in this study, and infection of the dogs was reported elsewhere previously (38). Briefly, the dogs were infected by subcutaneous inoculation of 10 6 E. chaffeensis (Arkansas strain)-infected DH82 cells (7).…”

“…Recombinant P28 fusion proteins were purified with ProBond resin (Invitrogen), a nickel-charged Sepharose resin that binds to the His tag. The genes p28-15 and p28-19 were cloned into the PCR T7/CT TOPO vector as previously described (38). The genes for GP120 and P110, outer membrane proteins of E. chaffeensis, were cloned previously in the pGEX expression vector and expressed as GST fusion proteins in E. coli (32,33).…”

“…Twelve p28 genes were cloned into the pET102/D-TOPO expression vector as part of this study, and p28-15 and p28-19 were cloned into pCRT7/CT TOPO previously (38). Dog sera collected from day 0 to day 462 post-E. chaffeensis infection were used in Western blotting with 10 recombinant P28 OMPs (P28-8 to P28-19).…”

“…Thus, mammalian hosts are essential for the persistence of E. chaffeensis. Anaplasma and Ehrlichia species can cause persistent infection in their natural mammalian hosts (1,3,6,11,14,28,29,38). Persistent or prolonged ehrlichial infection in humans has been reported for both E. chaffeensis (10,25) and A. phagocytophilum (8,15).…”

Direct Identification of Ehrlichia Canis by a Novel Polymerase Chain Reaction Method and Molecular Analysis of the Citrate Synthase (gltA) Gene from Various Italian Strains

“…However, experimental study has documented the dog's susceptibility to E. chaffeensis infection and its role as a natural host for E. chaffeensis. 10 Because of the possibility that dogs under natural conditions can be infected by both E. canis and E. chaffeensis, there is need for laboratory tests to differentiate between the 2 bacteria. Sequencing of the genes encoding the p30 surface protein and 16S ribosomal RNA (16S rRNA) has revealed a close genotypical relation between E. canis and E. chaffeensis.…”