EBIO 3400 1st Edition Lecture 23 Outline of Last Lecture I. Alphaproteobacteria II. GammaproteobacteriaIII. BetaproteobacteriaOutline of Current Lecture II. EpidemiologyIII. John Snow IV. Influenza V. Typhoid feverVI. Clostridium tetaniCurrent LectureI. Epidemiology Definition: Epidemiology examines the distribution and determinants of disease frequency in human populationsCombines:MicrobiologyEcologySociologyStatisticsPsychologyMajor goal of epidemiology:When a disease breaks out, epidemiologists try to determine root cause (or etiology), and determine the most effective measures for preventing or controlling the disease. Transmission routes and corresponding safety measures:1. Animal bites - control animal populations or avoid contact2. Personal contact - isolation or treatment of infected persons, immunization3. Ingestion - water quality and food regulations4. Sexual contact - public education regarding "safe sex" and individual treatment Finding patient zero- The first person to have the disease is known as the index case or patient zeroThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Important for containing the spread of a disease- Identify people who had contact with that person Identifying disease trends- Certain diseases are called reportable diseases- Because of their severity and transmissibility- Physicians are required to notify central health organizations (CDC and WHO)II. John Snow Was the first to methodically investigate the source of a disease- John Snow showed by mapping that they were associated with (clustered around) one water pump - First real evidence that cholera was a water-borne disease (via sewage)- Epidemic was stopped by simply removing the pump handleDefinitions: Prevalence = total (cumulative) number of infected individuals in a population new+old cases in a year/pop. at riskMortality = number of deaths per unit time in an infected populationMorbidity = number of cases per unit time in a populationIncidence = No. of new cases in a population per time period new cases in a year/pop. at risk- An Endemic disease is always present at a low frequency in a population. e.g. Lyme disease in sates with a lot of ticks- Epidemic - high frequency over short time e.g. Flu epidemic in China in 2003- Pandemic - an epidemic that occurs over a wide geographic area e.g. AIDSIII. Influenza - Viruses are inhaled or ingested. Spread via sneezing and coughing and touch- Results in fever, chills, headache, aches- Most of the symptoms are caused by lysis (bursting) of cells of the respiratory tract (see Table 25.1)- Leads to secondary infections by bacteria and other viruses - death usually due to secondary infections- > 10,000-40,000 deaths due to flu every year in the USA alone - mostly young, old and immuno-suppressed- Variation in timing of Epidemics• Common-source epidemic - a peak level in a short period of time. Usually results from a single contaminated source• Propagated epidemic – Host-to-host- Slow and prolonged rise in number of cases. Usually from the introduction of an infected individual into a susceptible population- Infected humans are most signature Reservoirs of communicable diseases- Symptomatic - show obvious signs of the disease- Asymptomatic carrier - an infected individual who is a potential source of infection. - Asymptomatic carriers, e.g. 50% of woman infected with Neisseriagonorrhoeae have no symptoms- 60% of the population carry Staphylococcus aureus during some part of their lives. 20% are chronic carriersIV. Typhoid feverSalmonella enterica serovar typhi (Gammaproteobacteria, Enterobacteriaceae)-Colonize small intestine, pass into lymphatic system/bloodstream, in “carriers” the bacteria grow in gallbladder. Symptoms: fever, malaise, abdominal pain, diarrhea-If untreated, mortality rate = 25% bacteria shed in feces-Transmitted via contaminated food/water- 400-500 cases per year in U.S.- 17 million infected per year worldwide, 600,000 deathsPrevention: vaccineTreatment: antibiotics + probioticsV. Clostridium tetani- Anaerobic soil bacteria that secretes a neurotoxin (tetanospasmin)- Lethal dose of tetanospasmin for adult = 175 ng- Causes tetanus (a.k.a “lockjaw”)- 1 million cases worldwide, 300,000-500,000 deaths per year- 100 cases in U.S. per year- 30-60% of tetanus infections lead to deathA. Nosocomial Infections (hospital acquired infections) - Gammaproteobacteria (mostly Enterobacteriaceae) account for the majority of nosocomial infections- P. aeruginosa is a very common cause of nosocomial infections (infections acquired in the hospital). Affects 2/3 of burn patients in hospitals and about 10% of patients with cystic
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