The human race is under constant threat from infections, including emerging infectious diseases such as outbreaks of new influenza viruses and Ebola hemorrhagic fever, epidemics of AIDS, and re-emergence of tuberculosis. The outbreak of the coronavirus disease 2019（COVID-2019）caused by a novel coronavirus has forced humans to change social lifestyles drastically. Furthermore, measures against infections caused by resident bacteria in the oral cavity, such as aspiration pneumonia, as well as opportunistic/nosocomial infections are urgently required in Japan, where the population is aging. Infectious diseases are caused by bacteria or viruses that enter and proliferate within the body. Some bacteria and viruses are capable of infecting hosts persistently for the rest of their lives and manifesting as symptoms when the hosts’ immunity weakens. In addition to microorganism-host interactions, intricately meshed bacteria-virus interactions are involved. Negative chain reactions between bacteria and viruses have increasingly been shown to play an important role in the onset of periodontal diseases that were previously attributed solely to bacterial infections. It is difficult to understand the whole picture of infectious diseases through conventional studies focusing solely on the oral cavity or a single microorganism.
We believe that elucidation of diverse microorganism-microorganism and microorganism-host crosstalk in pathogenicity, i.e., “bacteria-virus-host interactions,” will open a path to a new understanding of infectious diseases and development of new therapeutic and prophylactic means.
