The existing literature on chlamydial persistence is relatively extensive, but focuses mostly on human-infecting chlamydial species [13, 26], whereas, to our knowledge, only 3 in vitro models of persistence have been investigated for C. abortus to date: continuous culture [27], supplementation with IFN-γ [18, 19] and co-infection with porcine epidemic diarrhea virus [20]. This evidence concerns the gene IFNG and coinfection.