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TOPIC 7.docx

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HLTH 101
Glenn Ward

TOPIC 7: CHANGES IN HEALTH THROUGH EMERGING AND RE-EMERGING INFECTIOUS DISEASES 3: CURRENT AND EMERGING INFECTIOUS DISEASES THAT THREATEN HUMAN HEALTH 1. CURRENT/EMERGING PLAGUES i. AIDS  globally, approximately 33 million people are HIV positive (some sources believe that the number is actually much higher)  in 2007, 2 million deaths occurred due to AIDS, and 2.7 million new infections occurred  globally, the number of deaths and of new cases has been declining since 2005, but some regions are still reporting increases  most new infections and deaths occur in sub-Saharan Africa  the greatest rates of increase are being reported in Eastern Europe and Central Asia  important characteristics of AIDS:* a) no vectors or animal reservoirs (only transmits from human to human) b) low infectiousness o generally requires exchange of bodily fluids c) long latency o takes from 10-15 years from initial HIV infection to “full blown” AIDS  provides extended opportunity to transmit the infection d) “hedonistic” modes of transmission (not in all cases) o sexual activity, intravenous drug use  makes it difficult to eliminate risky behavior  act is done because it is pleasurable e) invades and destroys specific helper T-cells o necessary part of our immune system o seeks and destroys the cellʼs CD4+ receptors o allows the virus to enter and destroy CD4+ T-cells  leads to immune suppression, increased susceptibility to infections  lead to potential for more severe effects in developing regions where other infections are common  also has implications for treatment, since most potential anti-virals to HIV would likely lead to the destruction of the host cells, and these host cells are essential to the health of the person ii. Influenza  “yearly” disease (annual fluctuations)*  mortality ranging from the thousands in some years to the millions in others  influenza viruses are RNA viruses  3 main types influenza based on the level of severity o based on the nature of the internal antigens  influenza C: the mildest form  influenza B: occurs in humans only, and has moderate severity  influenza A: potentially severe, often leads to pandemics, and the virus is identified in both animals and humans o important characteristics of influenza A: a) is transmitted mainly through aerosol transmission*  generally through respiratory droplets b) the incubation period is from 18-72 hours c) symptoms include cold symptoms, muscle pain, congestion, and fever  these symptoms last from 5-10 days d) the virus replicates in respiratory epithelial cells  eventually leads to death of these cells e) these viruses have the capacity for antigenic change*  antigens are those things on a surface on a molecule that tell your immune system that it doesn’t belong to your body so your immune system mount an attack on these bodies, viruses fight back by changing their antigens, one of the main features of influenza viruses  the viral coat contains two major glycoprotein antigens: 1) hemagglutinin which has at least 15 subtypes (H1-H15)  hemagglutinin aids in the binding of the virus to the surface of the hostʼs cells 2) neuraminidase which has at least 9 subtypes (N1-N9)  neuraminidase aids in the release of the virus from the hostʼs cell  viral antigenicity changes through either or both of two general processes:* 1) antigenic drift  RNA mutation within the virus leads to expression of new type of glycoprotein antigen 2) antigenic shift  genetic recombination can occur between RNA fragments from more than one strain from more than one host species o i.e., pig exposed to human and bird virus  the same cell will then contain RNA fragments from more than one strain  this can lead to the formation of a new viral strain which can then be transmitted to a new host, including humans  when influenza viruses undergo antigenic shift or genetic drift, the new viruses formed will be ones from whom humans may have little or no antibody protection  major human infl. A pandemics:* 1918: H1N1 1956: H2N2 1968: H3N2 1977: H1N1 2009: H1N1  the H and N subtypes are not necessarily correlated with virulence or infectiousness o for example, the pandemics of 1918, 1977, and 2009 all involved H1N1  however, the virus exhibited decreased virulence each time  recent and emerging epidemics/pandemics:* 1. H5N1: avian influenza o so far has been seen only in Southeast Asia o associated with a high human case fatality rate (over 60% of the 400 or so humans who have been infected so far have died) o not easily transmitted (evidence so far indicates that it can only be transmitted to humans from birds) 2. H1N1: Swine flu (2009) o easily transmitted from humans to humans o fortunately, it is associated with a low case fatality rate (evidence suggests that it was less than 10%?) iii. Malaria  has been called "humanity's worst health problem"*  in 2008, the global prevalence was about 250 million, making malaria the most prevalent serious infectious disease by far (far more prevalent that AIDS)  about 40% of the human population is at risk for malaria o up to 1 million people die each year from malaria (most are under age 5) o in Africa, a child dies every 45 seconds from malaria, on average (again, far more than die from AIDS)  the word “malaria” is derived from the French term for “bad air” to indicate that people historically thought of malaria to be caused by some harmful substance in the air  we now know that it is caused by the Plasmodium parasite o 4 main types o Plasmodium falciparum is the most serious o it is characterized by a complicated life cycle:*  the lifecycle is divided between the mosquito (primarily Anopheles) and human blood cells  female Anopheles are a major reservoir  the parasite is transmitted from the saliva of the mosquito into the bloodstream of the human  it then travels to the liver where it reproduces and then travels to the red blood cells (RBCs)  in the RBC, they reproduce further  plasmodium reproduction leads to the destruction of the RBC, so the resulting offspring must seek out new RBCs in which to reproduce further  the death of the RBCs leads to hemolytic anemia  patterns of chills, fever  recovery or coma, and, in many cases, death iv. Drug Resistant Bacterial Infections  the creation of drug resistant bacteria is at least partly due to the evolutionary concepts described in Topic 5  these concepts apply to all living organisms o therefore, even though we deal in this section with bacteria, the phenomena we discuss could also apply to viruses  bacterial phenotypes have general and specific features:* a) general features, common to all living organisms, are that chromosomal DNA determine some part of the phenotype (short generation/fast reproduction = new genotypes causing new phenotypes) b) specific features include plasmid DNA and transposons: 1. plasmid DNA  subcellular organelles that can transfer mutations and “adaptive” alleles to other bacterial cells 2. Transposons
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