Figure 6. Animal model for Lyme disease and human granulocytic ehrlichiosis (HGE) co-infection.

These diseases share a tick vector, Ixodes scapularis, and to analyse whether Ehrlichia sp. and Borrelia burgorferi (the causative agents of HGE and Lyme disease, respectively) co-infection leads to increased severity of spirochaete-induced Lyme arthritis a mouse model has been developed. Mice are infected intradermally with either spirochaetes (B. burgdorferi cultured in vitro) or HGE (blood culture from a SCID mouse, see inset panel)¹⁷⁸. Arthritis and presence of the two pathogens can then be determined through histopathology, PCR to detect bacterial DNA and by assessing immune responses. Ticks were allowed to feed on all groups of mice to assess transmission of the pathogens. After feeding, PCR (HGE) and immunofluorescence (B. burgdorferi) were used for pathogen detection.