1	Population Biology of Disease Understanding population growth, means of getting to new hosts and evolution is important to controlling the spread of diseases.
2	Reading Assignment For lectures 7 and 8 read Chapter 27 up to section 27.4. Be sure to read and think about the Essay, “Antibiotics and the evolution of drug resistance”, on page 604.
3	Spread of Disease An infectious disease is caused by an organism. Organisms that live on other species must have a way to get from one individual to other individuals (colonization). Bacteria are small and colonize people in many ways.
4	Human Diseases caused by Bacteria Disease name Species How enters body Plague Yersinia pestis flea Cholera Vibrio cholerae water Gonorrhea Neisseria gonorrhoeae sex Anthrax Bacillus anthracis air Tetanus Clostridium tetani cuts Dysentery Shigella dysenteriae water & food
5	Koch’s Postulates to establish a microorganism causes a disease 1) Organism always found in diseased individuals. 2) Organism can be isolated and grown in pure culture. 3) Pure culture of organism can cause disease in healthy host. 4) Organism can be recovered from newly infected host.
6	Koch’s Postulates If all four conditions are fulfilled, Koch accepted the hypothesis that the microorganism was the cause of that specific disease. There are many species of microorganism that can be isolated from a sick individual, so all parts were necessary to accept an organism as the cause of the disease.
7	Disease Terminology An infectious disease is caused by an organism A contagious disease is a disease that can spread directly from person to person Bubonic plague was infectious but not contagious (because it requires a flea vector)
8	Measures of Disease Abundance Prevalence is the proportion of a population that are cases at a point in time. Unsuitable for acute disorders Incidence is the rate at which new cases occur in a population during a specified period.
9	Death vs Recovery A disease is called virulent if it causes death. An increasing death rate is described as increasing virulence. After contracting a potentially fatal disease one either 1) dies or 2) recovers (and normally one is then immune to re-infection).
10	WHY BACTERIAL DISEASES DISAPPEARED Capacity of disease to find suitable host has been reduced by: treatment of water supply and wastewater. Increase of immune individuals by vaccination quarantine (isolate) of diseased individuals. compounds (antibiotics) that kill bacteria without killing human cells have been found.
11	WATER TREATMENT Water supply infrastructure Water filtered, treated with biocides before entering a sealed delivery system. Wastewater Treatment Where are treatment plants of Water Reclamation District (WRD)? What is special about Chicago system?
12	Wastewater & Chicago River Waste accumulated in ditches and the Chicago river which flowed into Lake Michigan contaminating the water supply. http://www.mwrdgc.dst.il.us/history.htm Decision was made to reverse the flow of the Chicago River from into Lake Michigan into the Des Plaines River by digging the Ship and Sanitary Canal.
13	CHICAGO SHIP & SANITARY CANAL Water from Lake Michigan now flows into the Chicago River (most of the flow is pumped as drinking water supply). Wastewater is collected in sewers and transported to one of 3 plants where treatment removes most organic matter through growth of microorganisms. The treated wastewater is released into the canals.
14	Solutions and Problems The diversion of water to the Mississippi drainage resulted in protests by Canada and other states bordering the Great Lakes. The supreme court limited the amount of water that could be diverted. Treated wastewater from Chicago creates some problems for downstream communities.
15	Antibiotics Antibiotics are compounds that are able to inhibit the growth of bacteria. Fungi are the major source of antibiotics for they struggle with bacteria for resources. The discovery of penicillin in 1928 and the ability to produce stable preparations in 1939 revolutionized public health.
16	ANTIBIOTICS Penicillin inhibits the growth of the cell wall of some bacteria. Many antibiotics inhibit bacterial ribosomal function. The bacterial ribosome is smaller than eukaryotic ribosome and sensitive to different compounds. Erythromycin Streptomycin
17	EVOLUTION OF RESISTANCE As an antibiotic comes into widespread use, the advantage enjoyed by a mutant that can tolerate it increases. Some diseases, especially sexually transmitted infections (STI), are now very difficult to treat, because the organism has evolved resistant to multiple antibiotics.
18	Public Health versus Individual Perception There is a conflict between maximizing the benefit for people collectively and the demands of individuals. Antibiotics become known as ‘wonder drugs’ resulting in individuals asking to be treated even in situations where antibiotics do no good . Common use increases the abundance of resistant strains of bacteria.
19	Minimizing the abundance of resistant strains Limiting antibiotic use will minimize the spread of bacteria resistant to it and keep the antibiotic effective longer. Antibiotics are not effective against viral diseases, but they are often prescribed for viral diseases to “do something”. It is a common practice of people to think if some is good, more is better, but this is not true. If people follow directions, we are all better off.
20	Problem A contagious disease can be spread from individual to individual. If the disease can not spread from a dead person, predict whether evolution will tend to favor diseases that grow more rapidly leading to early death versus diseases that grow slowly and prolong the period between infection and death.
21	Vocabulary Infectious disease Contagious disease Antibiotic Water treatment Vector Resistance Wastewater Incidence Prevalence Koch’s postulates Public health Quarantine