This is supported by the fact that several viruses have been detected in GCF [30, 31], that periodontal pockets have been described as a compatible environment for viral infection and survival, and that gingival and periodontal ligament fibroblasts in rat and human tissues could express ACE2, which is considered as the main receptor for the virus entry into target cells [32]. The gene discussed is ACE2; the disease is viral infectious disease.