tailieunhanh - Chapter 114. Molecular Mechanisms of Microbial Pathogenesis (Part 11)

Transmission to New Hosts As part of the pathogenic process, most microbes are shed from the host, often in a form infectious for susceptible individuals. However, the rate of transmissibility may not necessarily be high, even if the disease is severe in the infected individual, as transmissibility and virulence are not linked traits. Most pathogens exit via the same route by which they entered: respiratory pathogens by aerosols from sneezing or coughing or through salivary spread, gastrointestinal pathogens by fecal-oral spread, sexually transmitted diseases by venereal spread, and vector-borne organisms by either direct contact with the vector through a blood. | Chapter 114. Molecular Mechanisms of Microbial Pathogenesis Part 11 Transmission to New Hosts As part of the pathogenic process most microbes are shed from the host often in a form infectious for susceptible individuals. However the rate of transmissibility may not necessarily be high even if the disease is severe in the infected individual as transmissibility and virulence are not linked traits. Most pathogens exit via the same route by which they entered respiratory pathogens by aerosols from sneezing or coughing or through salivary spread gastrointestinal pathogens by fecal-oral spread sexually transmitted diseases by venereal spread and vector-borne organisms by either direct contact with the vector through a blood meal or indirect contact with organisms shed into environmental sources such as water. Microbial factors that specifically promote transmission are not well characterized. Respiratory shedding is facilitated by overproduction of mucous secretions with consequently enhanced sneezing and coughing. Diarrheal toxins such as cholera toxin E. coli heat-labile toxins and Shigella toxins probably facilitate fecal-oral spread of microbial cells in the high volumes of diarrheal fluid produced during infection. The ability to produce phenotypic variants that resist hostile environmental factors . the highly resistant cysts of E. histolytica shed in feces represents another mechanism of pathogenesis relevant to transmission. Blood parasites such as Plasmodium spp. change phenotype after ingestion by a mosquito a prerequisite for the continued transmission of this pathogen. Venereally transmitted pathogens may undergo phenotypic variation due to the production of specific factors to facilitate transmission but shedding of these pathogens into the environment does not result in the formation of infectious foci. In summary the molecular mechanisms used by pathogens to colonize invade infect and disrupt the host are numerous and diverse. Each phase of the .