Ebook Infectious diseases in critical care: Part 2
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Ebook Infectious diseases in critical care: Part 2
Chapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2nited States and worldwide. Approximately 5- 15% of the world's population develops the disease annually. In the United States, 114,000 hospitalizations and 36,000 deaths are thought to occur annually [1], with an estimated annual economic impact of 3-5 billion dollars |2]. Complications of influenz Ebook Infectious diseases in critical care: Part 2a include primary and secondary pneumonias, respiratory failure and rarely myositis and neurologic failures. These complications often lead to ICƯ admEbook Infectious diseases in critical care: Part 2
ission, especially in the elderly or immunocompromised population.Superimposed on these annual epidemics are periodic pandemics, the most famous beingChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2rvative attack and mortality rates, it is estimated that in the United States alone the next influenza pandemic may result in 314,000-734,000 hospitalizations, and claim between 89,000 and 207,000 lives, with an economic impact of 70- 170 billion dollars [4|. In the new pandemic, it is projected tha Ebook Infectious diseases in critical care: Part 2t the ICƯ capacity in the United States will be overwhelmed, requiring the painful decision to withhold care from patients unlikely to survive, focusiEbook Infectious diseases in critical care: Part 2
ng on patients most likely to respond to ventilatory and other therapy.27.2HistoryThe influenza virus has likely been causing annual epidemics and perChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2a classic review of historical pathology by Hirsch, 299 outbreaks of influenza occurring at an average interval of 2.4 years were calculated between 1173 and 1875 [6|. Industrialization and the increased pace of transportation resulted in increasingly rapid spread of severe pandemic influenza. This Ebook Infectious diseases in critical care: Part 2culminated in the 1918-1919 “Spanish Influenza.” This famous pandemic was notable for its surprisingly heavy toll on young adults, with mortality rateEbook Infectious diseases in critical care: Part 2
s in some areas reaching 5- 10%. In the United States, draconian infection control measures included closing public schools, creating quarantines, andChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2influenza virus is a member of the Orthomyxoviri-dae family, a family which includes influenza A, B, c, Thogoto virus, and the infectious salmon anemia virus. This family is characterized by a host derived envelope, a negative sense Single stranded, segmented RNA genome, and envelope glycoproteins i Ebook Infectious diseases in critical care: Part 2mportant in viral entry and exit from cells. The morphology of the three1917H1N11957-►1977H1N11957 H2N2 1968------ ►1968 H3N2Fig. 27.1. Influenza A anEbook Infectious diseases in critical care: Part 2
tigenic shiftssubtypes of influenza is similar, with an 80-120 nm vi-ron size, 9-12 structural proteins, and 7-8 gene segments. On the surface of the Chapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2viral replication. The hemagglutinin facilitates entry of the virus into host cells by attachment to sialic-acid receptors. A major function of the neuraminidase is to catalyze the cleavage of glyco-sidic linkages to sialic acid, which allows the completed virion to be released from infected cells [ Ebook Infectious diseases in critical care: Part 27). There are at least 16 antigenetically diverse hemagglutinins and 9 distinct neuraminidases in influenza A, the majority of which exist in non-humaEbook Infectious diseases in critical care: Part 2
n hosts (8|. Influenza A viruses are typically designated HxNy where the X and y represent which hemagglutinin and neuraminidase, respectively, the viChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2nsic meaning; the numbers only represent a way to distinguish between types of the molecules. In contrast, influenza B has only one known hemagglutinin and only one neuraminidase. Other viral proteins include the Matrix (M) protein, which controls nuclear transport, the NucleoproteinEbook Infectious diseases in critical care: Part 2
es in viral proteins. Influenza c is somewhat morphologically distinct, and is classified in a different genus from influenza A and B. It infects bothChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2 Influenza B infects only humans, typically causing severe disease in the elderly or high risk patients. It rarely causes epidemics, and does not cause pandemics. Influenza A infects many hosts, including humans, birds, swine, horses, and marine mammals. It is a common cause of both annual epidemics Ebook Infectious diseases in critical care: Part 2 and periodic pandemics.27.3.1Antigenic VariationWhile infection with influenza results in the development of both humoral and cell mediated protectivEbook Infectious diseases in critical care: Part 2
e immunity, individuals may be re-infected periodically. This is secondary to changes in influenza antigens resulting in virus subtypes to which humanChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2 changes occur via changes in the surface glycoproteins of the virus, neuraminidase and hemagglutinin. Two types of antigenic change are described, known as antigenic drift and antigenic shift.27.3 Virology 28527.3.1.1Antigenic DriftAntigenic drift refers to the minor antigenic changes which occur i Ebook Infectious diseases in critical care: Part 2n the hemagglutinin and neuraminidase proteins. The mechanism of antigenic drift is the gradual accumulation of amino acid substitutions due to pointEbook Infectious diseases in critical care: Part 2
mutations in the hemagglutinin and neuraminidase genes (10, 11]. As mutations accumulate, antibodies generated by exposure to previous strains do not Chapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2 of the new strains acts as a type of natural selection; new strains with less immune recognition become the predominant strain in annual epidemics. Antigenic drift is present in both the influenza A and B subtypes.27.3.1.2Antigenic ShiftAntigenic shift occurs only in influenza A. Compared with prev Ebook Infectious diseases in critical care: Part 2ious strains, the predominant circulating virus possesses a different hemagglutinin, neuraminidase, or both. There is little or no antibody recognitioEbook Infectious diseases in critical care: Part 2
n of these new stains, thereby creating strains that may become a source of epidemic and pandemic influenza. There is a strong association between antChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2 of both the hemagglutinin and neuraminidase 112,13]. The less extensive pandemic of 1968 was associated with only a shift to a new hemagglutinin (shift to H3N2) (14). Interestingly, the “pseudo-pandemic” of 1977, which involved an influenza A virus which had shifted back to HIN1, affected primarily Ebook Infectious diseases in critical care: Part 2 younger individuals, born after the H1N1 virus had last circulated (15).Antigenic shift can occur through a variety of mechanisms. Non-human influenzEbook Infectious diseases in critical care: Part 2
a is selective in its tropism, and cannot easily replicate in humans [16]. However, avian influenza viruses may replicate in non-avi-an, non-human resChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the Un Ebook Infectious diseases in critical care: Part 2 novel virus capable of replication in and transmission between humans [17]. This reassortment process may happen frequently, but may result in viruses with decreased pathogenicity or limited tropism in humans, and therefore severe pandemics do not begin.Alternatively, mutations may occur directly i Ebook Infectious diseases in critical care: Part 2n a non-human virus, such as an avian virus, that allow the virus to readily spread from person to person 118]. This process may occur partially, so tEbook Infectious diseases in critical care: Part 2
hat spread from animals to humans is possible, but human-to-human spread does not occur. An example is H5N1 avian influ-28627 InfluenzaChapter 2727 InfluenzaP.R. Brookmeyer, K.F. Woeltje27.1IntroductionInfluenza infections account for significant morbidity and mortality both in the UnGọi ngay
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