Microbes are small organisms including bacteria, viruses, fungi, and other single-celled organisms that play important roles in ecosystems and human health. Over billions of years, microbes have evolved and filled virtually every ecological niche on the planet. They can be beneficial or detrimental, and their interaction with humans has led to pandemics and serious diseases from the Antonine Plague to the COVID-19 pandemic, the interactions between microorganisms and humans, as well as the mechanisms of transmission, have played a crucial role in the spread of diseases, understanding their epidemiology and transmission is essential for their control. The epidemiological chain describes the transmission process of an infectious disease and involves elements such as the infectious agent, the susceptible host, the reservoir, the exit door, the door of entry, and the vulnerability of the host. The study of epidemiology and microbiology makes it possible to identify the risk factors associated with the transmission of microorganisms, develop infection control strategies, as well as design and evaluate interventions to prevent the spread of diseases and promote public health. Understanding the biological path of the microbe in the human species is essential for the diagnosis, treatment and prevention of infectious diseases, knowing in depth the infectivity, pathogenicity, virulence, lethality, antigenic power and mutation capacity of infectious agents. This review emphasizes the microbe and its biological pathway through the human species.