Ticks can harbor and transmit multiple human and animal microbial pathogens. Viruses and bacteria can trigger and potentially suppress vertebrate host and arthropod vector antimicrobial immune response, but little is known about the effect of coinfection on pathogen replication or infectivity at the cellular level. In this study, tick cell lines Ixodes scapularis and I ricinus were infected sequentially with the arthropod-borne pathogens Borrelia burgdorferi, Ehrlichia ruminantium, or Semliki Forest virus (SFV).
Six different scenarios were evaluated. There were 3 cases of enhanced replication: 1) B burgdorferi enhanced replication of E ruminantium; 2) B burgdorferi enhanced replication of SFV, and; 3) E ruminantium enhanced replication of SFV. If true synergistic interaction between these pathogens exists and can be correlated to in vivo activity, this may lead to novel approaches for controlling ticks and tick-borne diseases. Further study is necessary to determine if these results come from direct pathogen-pathogen interactions or from effects on host cell defense mechanisms.