‘Germ Theory of Diseases’ A Historical and Immunological Perspective

This article revisits the “Germ Theory of Diseases” from historical, philosophical, and immunological perspectives. Al- though the theory, shaped by the pioneering work of Henle, Pasteur, and Koch, became a cornerstone of modern medicine, scientists such as Virchow, Dubos, and Casanova argued that microbes alone cannot fully explain diseases, emphasizing the decisive role of host factors. Today, the concepts of the microbiome and virome reveal that microorganisms are not only harmful but also essential for human health. The gut flora, in particular, plays a critical role in immunity, metabolism, and the nervous system, demonstrating that microbes are indispensable for maintaining bodily balance. The origins of viruses, their modes of transmission, and the immunological functions of bacteriophages remain subjects of debate, while discov- eries such as CRISPR highlight the evolutionary importance of microbial immune mechanisms. Furthermore, prions, trans- posons, and horizontal gene transfer show that genetic diversity and disease mechanisms extend far beyond the germ theo-

ry. In conclusion, I argue that the classical germ theory is insufficient in light of modern knowledge, that viruses must be re- defined, and that microbiology and immunology should adopt a more integrative approach to understanding the role of microbes.