* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 17
Survey
Document related concepts
Tuberculosis wikipedia , lookup
Bovine spongiform encephalopathy wikipedia , lookup
Brucellosis wikipedia , lookup
Rocky Mountain spotted fever wikipedia , lookup
Schistosoma mansoni wikipedia , lookup
Neglected tropical diseases wikipedia , lookup
Meningococcal disease wikipedia , lookup
Oesophagostomum wikipedia , lookup
Schistosomiasis wikipedia , lookup
Onchocerciasis wikipedia , lookup
Chagas disease wikipedia , lookup
Leptospirosis wikipedia , lookup
Visceral leishmaniasis wikipedia , lookup
African trypanosomiasis wikipedia , lookup
Sexually transmitted infection wikipedia , lookup
Transcript
PART 3: Microorganisms, Humans, and Disease • Epidemiology and transmission of disease Epidemiology • Epidemiology is the study of disease in populations, and includes the transmission, incidence, frequency, and distribution of disease. • The Centers for Disease Control in Atlanta is the main source of information in the United States: their publication “Morbidity and Mortality Weekly” tells us how many people are sick and how many have died from various diseases (light reading with coffee in the morning). • They are also responsible for tracking and identifying emerging diseases, and report their findings to the World Health Organization. Disease occurrence • Incidence of a disease refers to the percentage of the population that gets the disease during a given time period; • Prevalence refers to the percentage of a population which has the disease during a given time period. Virulence of a pathogen • Virulence refers to the DEGREE of pathogenicity for a given pathogen. • Virulence can be measured as the LD50 (lethal dose for 50% of inoculated hosts) or the ID50 (infectious dose for 50% of inoculated hosts) • The ID50 can range from literally 1 cell to 1 billion cells! – (some pathogens are more able to cause disease, that is they are more virulent, than others) More terms • A disease is said to be communicable if it can be transmitted from one host to another. – A contagious disease is very easily communicable. Contrast AIDS w/ the flu. • A disease is said to be non-communicable if it cannot be transmitted from one host to another, usually because it is acquired from the environment (e.g. botulism) Frequency of occurrence • Sporadic - occurs only occasionally in a population (e.g. typhoid fever) • Endemic - constantly present in a population (e.g. the common cold) • Epidemic - acquired by many people in a given area over a short time (often the flu); AIDS? • Pandemic - epidemic worldwide - AIDS? The Spread of Infection • A reservoir is a continual source of infective pathogens. Reservoirs may be – Human - people infected with the pathogen; – Animal - zoonoses are diseases that can be transmitted from animals to humans (rabies); also, vectors like mosquitoes are considered animal reservoirs; – Non-living - soil or water; the pathogen can exist stably outside a host (B. anthracis because it forms endospores; Vibrio cholerae [causes cholera] often persists in water contaminated from feces) Disease Transmission (careful, parts of this are a little tricky!) • Contact transmission: – Direct contact: transmission of a pathogen by physical contact between living reservoir and host; no intermediate object is involved. Ex. Touching (the common cold), kissing (infectious mononucleosis), sexual intercourse (HIV) – Indirect contact: transmission of a pathogen from a living reservoir to a host via an intermediate object, called a FOMITE. Example: HIV transmission via sharing hypodermic needles. – Droplet transmission: transmission of a pathogen from a living reservoir to a host via droplets of mucus which travel less than 1 meter via sneezing, coughing, etc. (the flu) Disease Transmission • Vehicle transmission: transmission of a pathogen by physical contact between NON-LIVING reservoir and host. • Non-living reservoirs are often food, water, or air. – Foodborne transmission - foods that are incompletely cooked or unsanitary (Salmonella poisoning, trichinosis) – Waterborne transmission - water is often contaminated by poorly treated sewage (cholera) – Airborne transmission: transmission is considered airborne if the pathogen can travel more than 1 meter from the host (tuberculosis) PLEASE: Recognize the difference between vehicle transmission and indirect contact! Arthropod vectors: Biological transmission • A special form of direct contact in which an arthropod harbors a pathogen and transmits it from host to host. We discussed malaria as an example, also Lyme disease. Etiology - the cause of disease • Koch's postulates: Robert Koch was the first microbiologist to come up with a set of rules to determine which microorganism caused which disease. • Koch showed that Bacillus anthracis causes anthrax and that Mycobacterium tuberculosis causes tuberculosis, among others. • What did he say? Koch's Postulates • The same pathogen must be present in every case of the disease; • The pathogen must be isolated from diseased host in pure culture; • The cultured pathogen must be capable of causing the disease in healthy lab animals; • The pathogen must be re-isolated from the inoculated lab animal. Potential Exceptions to Koch's Postulates • Viruses and certain bacteria cannot be cultured normally; • Some diseases (pneumonia) may be caused by a variety of different pathogens; • Some pathogens may be able to cause several different diseases (S. pyogenes); • Certain pathogens cause diseases in humans only, so would not infect lab animals (no, you can't experiment with humans yet!). HIV is an example.