organisms enter through endocytosis, while others simply enter the cell by producing an invasive protein that binds to the host cell. Infection involves multiplication of the organism. Local infections involve a small body area, usually near the portal of entry. Some infections are focal but can spread to a secondary infection elsewhere in the body. Systemic infections involve a widely disseminated organism. Primary infections involve just one pathogen, while a secondary infection involves another pathogen. An example is a bacterial pneumonia after getting influenza. The disease needs to be transmitted in order to pass the disease onto a secondary host. This usually means there must be a portal of exit, which can be the same as the portal of entry or not. It can involve sneezing, direct contact, semen, feces, sweat, or tears—each of which can be a good vehicle to pass on the infection. Vectors can also be part of the transmissibility of the organism.
VIRULENCE FACTORS FOR VIRUSES AND PROKARYOTES There are specific virulence factors that confer a certain level of virulence of a pathogen. These are generally genetic in origin. The absence of certain genes that later diminish virulence is in keeping with the molecular Koch’s postulates. An adhesin is either a protein or glycoprotein that will attach to receptors on a host cell. Bacteria, fungi, viruses, and protozoans will all have adhesins. E. coli that is enterotoxigenic has fimbriae that contain an adhesin which binds to the host cell. Many other bacteria have proteinaceous or glycoprotein-containing adhesins. Invasion of the bacteria often involves toxins or enzymes. The invasion process often involves the bloodstream and elements of the immune system. The presence of organisms can involve bacteremia or bacteria in the blood, viremia or viruses in the blood, toxemia or toxins in the blood, or septicemia, which is the multiplication of the bacteria in the bloodstream. Septic shock refers specifically to hypotension and organ failure that can happen with a patient who has septicemia. Toxins can cause septic shock as well.
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