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Host-pathogen interaction Host-pathogen interaction is a dynamic process, wherein most pathogens have evolved many strategies to co-exist with host cells by reducing their visibility or virulence, while the components of host immune system attempt to suppress or eliminate them without damage in host tissues (Casadevall and Pirofski, 2000). During this eliminatory process, however, many host cells become injured or dead. Perhaps the most obvious outcome in host-pathogen interactions is cell death at host or pathogen level. In most of the infectious diseases, both pathogen and host immune system involve in disease pathogenesis and causing tissue injuries. Tissue damage in the host that mounts weak immune response is primarily pathogen-mediated, whereas the damage in the host that mounts strong immune response is host-mediated. However, in many interactions between the host and pathogens, there is a continuum between pathogen-mediated and host-mediated damages that impair normal functions of host tissue and result in a state of disease. Microbial and Molecular Pathogenesis A number of factors in respect to host (eg. genetic make-up, physiological and nutritional status, and environmental factors influences the life style) and pathogens (eg. virulence, dose and number of infection, and species-specificity) determine the outcome of a disease. Hence it is not as easier to understand the pathogenesis and pathology of a disease as it is thought. Understanding the mechanism by which microbial pathogens interact with host cells and thereby infliction of disease is highly perplexing for scientists who work in the field of microbial pathogenesis. In earlier days, microbes were thought to be the primary aggressors responsible for development of diseases in susceptible host. However, the advancement in microbiology and immunology about the attributes of pathogens and their host has changed our understanding that microbes may not always result in a state of disease. In the milieu of host-pathogen interactions, both host factors and pathogens are responsible for causing a disease (Casadevall and Pirofski, 2000). Pathogens can cause damage through its virulence factors (secretary products and its cell wall toxic components), while host-mediated damage is driven by host immune cells, inflammatory mediators, cytokines and host cell derived toxic products etc (Fink and Cookson, 2005). The complex interactions between these components at different stages of infection determine the severity and final outcome of a disease
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