MMG301 1nd EditionExam # 4 Study Guide Lectures: 33 - 41Lecture 33-Prevalence: number of cases (new + existing) in a population at a given time-A “snapshot” of the total number of cases within a population-Often reported as a percentage of population having the disease-Incidence: number of new cases in a population over a given time period-Outbreak: sudden increase in cases above normal low levels-endemic: disease occurs at normal levels, no coherent pattern-epidemic: larger incidence of disease, larger populations and regions are infected-pandemic: covers many continents on the earth are involved-Basic Reproductive Number R0: number of infections that one infected individual causes; example a person sneezes, how many people catch their cold?-generation time: the time that it takes to get from the initial infected individual to the next infected individual-Common source epidemics: all the individuals who get sick get the pathogen from the same source; example from food or water-Host-to-host epidemics: the pathogen spreads from individual to another individual, takes time for the pathogen to incubate in each individual-Index case: the first case of an epidemic; aka “patient zero”-Example of Seasonal Cycles: Disease prevalence increases seasonally when insect vectors emerge-vector: live agent that transmits disease-Incidence of California encephalitis follows the prevalence of the mosquito vector with peaks in summer months-Infection: initial exposure and entry-Incubation: time between infection and onset of symptoms; can be days or years-Acute stage: fever and other symptoms at their worst-Decline: symptoms subside, reduced fever-human à human … epidemic-animal à animal … epizootic-Reasons why emerging diseases are becoming more common:-Ecological changes/economic development – agriculture, dams, deforestation-Human demographics – population growth, migration; wars; I.V. drug use-Increased international travel-Technology and industry – centralized processing of food supplies, overuse of antibiotics-Microbial adaptation – ability to undergo genetic changes and acquire genes-Shortcomings of public health measures – cutbacks in mosquito abatement and pollution controlLecture 34-Responsible for about ½ of all severe sore throat cases-Untreated cases can lead to sequelae, or a follow-up diseases-Scarlet fever: can result from certain strains of Streptococcus pyogenes that carry a lysogenic bacteriophage (prophage produces an erythrogenic (red, to produce) exotoxin (causes pink-red rash)-Rheumatic fever: a bacterial cell surface antigen resembles normal human surface antigen-Patient’s immune system begins attacking normal tissues such as heart, kidneys, joints (an autoimmune disease)-Invasive infections: Some virulent strains can invade deep tissues:-Exotoxins and “M-protein” of bacterial surface act as a superantigen (elicits a hyper-immune response leading to tissue destruction; 30% fatality rate-Necrotizing fasciitis: “Flesh-eating bacteria”; bacteria do not eat flesh, bacteria produce toxins that cause tissue damage; necrosis means tissue death-Group A strep: most common group; many asymptomatic carriers; strep throat, necrotizing fasciitis, impetigo; typically Streptococcus pyogenes -Group B strep: newborn babies (most commonly sepsis and meningitis), pregnant women, the elderly, and adults with other illnesses -Name: Streptococcus agalactiae -Most common cause of life-threatening infections in infants-About 25% of women are asymptomatic carriers of Group B strep in vagina-Streptococcus pneumoniae: causes several diseases-Normally lives in the back of the nose and throat, or the upper respiratory tract of healthy individuals-Pneumonia: invasive lung infections-impaired lung function due to infection (bacterial, viral, or fungal)-Vaccine available that prevents about 60 of the 90 known strains-Death occurs in 14% of hospitalized adults with invasive disease-More commonly seen in the elderly-Bacterial meningitis: infection of the fluid that surrounds the spinal cord and thebrain-More severe than the viral meningitis -Symptoms develop in several hours to 1-2 days (nausea, headache, vomiting, discomfort looking into bright lights)Lecture 35-Leprosy – also known as Hansen’s Disease-Pathogen is Mycobacterium leprae-Unknown mode of transmission, but recent studies point to the respiratory route, but direct contact also possible-Not considered highly contagious; easily treated with antibiotics-Bacteria invade macrophages associated with peripheral nerves and respiratory tract-Bacteria eventually produce lesions on the skin-Damage to tissues and secondary infections lead to disfigurement-Diagnosis usually by microscopy of tissues stained using Ziehl-Neelsen method; acid-faststain-Over 230,000 new cases in 2012 – mostly in developing countries-Bacterial meningitis – most commonly Neisseria meningitidis (causes meningiococcal disease); but also Haemophilus influenzae, Streptococcus pneumoniae, and a few other bacteria-As much as 30% are carriers of N. meningitidis – found in nasopharynx-Airborne microbe attaches to upper respiratory tract and eventually invades bloodstream (= bacteremia)-Symptoms include headache, vomiting, neck pain, leading to coma and death in a matter of hours-About 4,100 cases per year in U.S.; 500 deaths-There are also viral pathogens causing viral meningitis (but disease is less severe), as well as fungal meningitis (extremely rare)-Legionnaires’ disease (Legionellosis) - Legionella pneumophila-First outbreak at an American Legion convention in Philadelphia, 1976-An aerobic, Gram-negative rod-A water borne organism, but is inhaled in droplets-Lives as part of a microbial community in water storage tanks, air conditioning systems, soil and aquatic habitats-Inhaled Legionella settles in the lungsLecture 36-Staphylococcus: -S. aureus: normal flora of humans and certain animals skin and upper respiratory tract, but some types are pathogenic; produce a variety of virulence factors-Can cause these diseases:-acne, boils (skin abscess)-foodborne illness (gastrointestinal tract; food poisoning)-impetigo (outer skin infection)-blood (bacteremia, septicemia)-meningitis-wound infections-otidis media (inner ear)-endocarditis (heart), others-some types are pyogenic (cause formation of pus)-some form an abscess (enclosed formation of pus, usually from infection or an object that gets embedded in the skin)-Gonorrhea: Neisseria
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