![]() ![]() At least four pandemics of influenza occurred in the 19th century, three in the 20th century, and one thus far in the 21 st century. The name “influenza” originated in 15th century Italy, from an epidemic attributed to “influence of the stars.” The first documented pandemic, or worldwide epidemic, that clearly fits the description of influenza was in 1580. Influenza is an infectious viral illness. Inactivated vaccines first developed and used in the late 1930s and 1940s.Influenza A and B viruses isolated in the 1930s.Estimated 21 million deaths worldwide in pandemic of 1918-1919.Some bacteria can cause shock through the release of toxins (virulence factors that can cause tissue damage) and lead to low blood pressure. Patients with septicemia are described as septic, which can lead to shock, a life-threatening decrease in blood pressure (systolic pressure <90 mm Hg) that prevents cells and organs from receiving enough oxygen and nutrients. If bacteria are both present and multiplying in the blood, this condition is called septicemia. The term toxemia describes the condition when toxins are found in the blood. When viruses are found in the blood, it is called viremia. Bacteremia involving pyogens (pus-forming bacteria) is called pyemia. The presence of bacteria in blood is called bacteremia. Various terms ending in –emia are used to describe the presence of pathogens in the bloodstream. The downside of this mechanism of dispersal is that the blood also includes numerous elements of the immune system. ![]() Many pathogens achieve invasion by entering the bloodstream, an effective means of dissemination because blood vessels pass close to every cell in the body. Concerned that the infection is spreading, the physician decides to conduct additional tests to determine what is causing these new symptoms.īacterial Exoenzymes and Toxins as Virulence FactorsĪfter exposure and adhesion, the next step in pathogenesis is invasion, which can involve enzymes and toxins. He is now experiencing a stiff neck and hemiparesis (weakness of one side of the body). This enables the bacterium to produce actin tails, move around the cell’s cytoplasm, and spread from cell to cell without exiting into the extracellular compartment. ActA is expressed on the surface of Listeria and polymerizes host actin. ![]() A second gene regulated by PrfA is actA, which encodes for a surface protein known as actin assembly-inducing protein (ActA). One of the genes regulated by PrfA is hyl, which encodes a toxin known as listeriolysin O (LLO), which allows the bacterium to escape vacuoles upon entry into a host cell. These genes are regulated by a transcriptional factor known as peptide chain release factor 1 (PrfA). A cluster of virulence genes encoded on a pathogenicity island is responsible for the pathogenicity of L. Listeriosis is fatal in about one in five normal healthy people, and mortality rates are slightly higher in patients with pre-existing conditions that weaken the immune response. Once ingested, these bacteria invade intestinal epithelial cells and translocate to the liver, where they grow inside hepatic cells. Listeria monocytogenes, the facultative intracellular pathogen that causes listeriosis, is a common contaminant in ready-to-eat foods such as lunch meats and dairy products. Based on Michael’s symptoms, the results of his blood test, and the fact that Michael was the only one in the family to partake of the hot dogs, the physician suspects that Michael is suffering from a case of listeriosis. Instead, it appears the portal of entry was the gastrointestinal route. There is no indication that the bacteria entered the blood through an injury. The presence of bacteria in Michael’s blood is a sign of infection, since blood is normally sterile. \): Some Bacterial Adhesins and Their Host Attachment Sites Pathogen ![]()
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