Pathogenesis of Fungal Infections

PATH THOG OGEN ENES ESIS IS OF FUNGAL INFECTIONS

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

















Virulence is a complex interrelationship between the infecting organism and the host.  Pathogenesis involves interaction (and sometimes modification) of factors on both sides.  This is particularly true of fungal pathogenesis. There is no single factor that causes or permits these organisms to be agents of diseases that range from 























Fungal pathogens can be divided into two general classes, primary pathogens and opportunistic pathogens. Fungi in the former class usually have an environmental reservoir and infect individuals who have either been exposed to a large dose or who are immunologically naive to the fungus. Opportunistic pathogens take advantage of debilitated or immunocompromised hosts to cause infection. They may have an environmental reservoir (e.g.Cryptococcus neoformans, neoforman s, Aspergillus fumigatus ) or exist as





















Human body is a hostile environment and offers great resistance to fungal invasion. Most fungi are saprophytic and their t heir enzymatic pathways function more efficiently at the redox potential of non-living substrates than at the relatively more reduced state of living metabolizing tissue.

















The complex interplay between fungal virulence factors and host defence factors will determine if a fungal infection will cause a disease.  Infection depends on inoculum size and the general immunity of the host 

















Primary Pathogens primary pathogens pathogens are those fungi that cause disease in non-compromised patients.  This distinction is necessarily a gray one, because C. neoformans, a model opportunist, sometimes causes disease in healthy individuals, and the primary pathogens, such as C. immitis, are much more virulent in virulent in immunocompromised patients.  Furthermore, infection by a primary pathogen often leads to subclinical disease. However, the distinction is worth making in the effort to understand general 



















Opportunistic Pathogens 

Opportunistic pathogens incite disease in hosts whose local or systemic immune

















POTENTIAL VIRULENCE FACTORS 

Because of the complex nature of the host-fungus interaction, there are few

















Fungal Pathogenicity (virulence factors): 

Ability to adhere to host cells by way of cell wall glycoproteins



















Ability to acquire iron from red blood cells as in Candida albicans

















 

Having a unique enzymatic capacity Exhibiting thermal dimorphism



















Growth at Elevated





































Adherence























































































































































































































































CRYPTOCOCCUS

















MULTIPLE PARASITIC CELL FORMS  Dimorphic fungi regulate their cellular morphology in response to environmental conditions. conditions. For example, ellipsoidal single cells of C. ) predominate predominate in albicans ( blastospores blastospores ) rich media, media, whereas filaments composed

















Candida albicans

















Candida albicans

















A variety of environmental changes, including a shift from an aerobic to a fermentative metabolism or growth on particular compounds such as N-acetyl glucosamine,, cause C. albicans to switch from yeast to glucosamine filamentous growth.  This change is accompanied by changes in carbohydrate metabolism and an interruption of electron transfer within the cell . Both temperature (a shift to 37oC) and pH can regulate C. albicans 





















Many molds form conidia, or vegetative spores; scattered by wind or water, these small, resistant cells serve as a mode of dissemination. In the case

































PHENOTYPIC SWITCHING  The capacity of fungi to undergo an epigenetic change (regulation (regulation of expression of gene





















A particular strain, WO-1, that has two major colony phenotypes, “white” and “opaque”. White colonies almost exclusively contain the





















































Adaptations of Specific









































































































































































































































































Hypersensitivity: As a result of dermatophyte infection some fungusfree skin lesions of variable morphology occur elsewhere on the body, which are thought to result from hypersensitivity to the fungus. fungus. These reactions are called "id reaction".  These reactions are also seen n Candida Candid a infections.  An inflamed boggy lesion of the scalp called the kerion may result from a strong immune reaction 

















Id’s reaction

















Kerion























Granulomas due to intracellular fungi represent delayed hypersensivities. hypersensivities . Many fungi are significant allergens to humans, the allergens being spores, conidia, hyphae and other fungal products. On inhalation they may produce allergic pulmonary diseases such as allergic bronchopulmonary aspergillosis, farmer's lung, maple bark stripper's lung, bronchial asthma etc, which may

















Infection Routes ENDOGENOUS  C. albicans is part of the normal human body flora, and it can become pathogenic if it moves to a compartment that reacts to its presence.  Other Candida species may become the major endogenous gut yeast when





















A breakdown of gut mucosa, from oncologic chemotherapy, radiation, trauma, concurrent viral ulcers, etc.,

















EXOGENOUS  Fungi that are environmental saprobes can cause invasive disease in humans if



















Examples C. immitis among immunocompetent or the opportunistic A. fumigatus or Pneumocystis carinii

















Pathogenesis of Fungal Infections

Recommend Documents