Diseases and Epidemiology

1. Diseases and Epidemiology

2. Epidemiologists—what do they do? • They identify a problem, collect data, formulate and test hypothesis • Epidemiology is as old as medicine • Who gets sick, why and when • John Snow (Broadway pump) can be considered as the father of Epidemiology • Determine the problem (outbreak) and implement control measurements to prevent additional disease • Often described as “disease detective”

3. Definitions Disease: occurs when an infection results in an abnormal state of health Pathology: concerned with the cause of disease Infection: is the invasion or colonization of the body by pathogenic microorganism

4. Normal Microbiota • Animals, including humans, are generally free of microbes in utero • At birth, a normal/characteristic microbial population will begin to establish itself • The newborn’s first contact with MO is usually lactobacilli, which multiply rapidly prior birth • More MO are introduced as the newborn breathes and feeding begins

5. Normal Microbiota • Many usually harmless MO establish themselves inside other parts of the adult body & on its surface • Typical human body contains 1x1013 body cells, yet harbors 1x1014 bacteria • Normal flora does not produce disease • Transient microbiota are present for days/weeks/or months and then disappear

6. Normal Microbiota • Microbial antagonists: once established the normal biota can benefit the host by preventing the overgrowth of harmful MO • It involves competition among MO

7. Relationship btw the normal microbiota and the host • Presence of normal microbiota in the adult human vagina maintains a local pH of 3.5-4.5 & prevents overgrowth of the yeast Candida albicans • If the bacterial population is eliminated by antibiotics, excessive douching or deodorants, the pH of the vagina reverts to neutral and C. albicans flourishes

8. Definitions Symbiosis: living together---relationship btw host & normal microbiota Commensalism: one of the organism is benefiting –the other one is unaffected Mutualism: is a type of symbiosis that benefits both organisms I.e. the large intestine has E.coli, that synthesizes vitamin K and some B vitamins These vitamins are absorbed into the bloodstream

9. Opportunists • Opportunistic pathogens: they do not cause disease in their normal habitat in a healthy person, but will in a different environment • MO that gain access through broken skin or mucous membranes can cause opportunistic infections • Or if the host is already weakened or compromised by infection (AIDS)

10. The Etiology of Infectious Diseases • Some disease—polio/Lyme disease or TB have a well known etiology • The etiology of Alzheimer’s disease is unknown • Hemophilia is an inherited disease • Osteroarthritis are degenerative diseases

11. Koch’s postulates • In 1877 he published some early papers on anthrax, a disease of cattle that can occur in humans • He demonstrated that Bacillus anthracis, were always present in the blood of animals that had the disease and were not present in healthy animals • Koch showed that a specific infectious disease (anthrax) is caused by a specific MO that can be isolated and cultured on artificial media

12. Koch’s 4 postulates • Same pathogen must be present in every case of the disease • Pathogen must be isolated from the diseased host & grown in pure culture • Pathogen from pure culture must cause disease when it is inoculated in a healthy animal • Pathogen must be isolated from inoculated animal & must be shown to be the original MO

13. Classifying Infectious Diseases • Symptoms: changes in body function (pain/malaise) • Signs: are objective changes the physician can observe & measure • Syndrome: specific group of symptoms or signs • Communicable disease: disease that spreads from one host to another, either directly or indirectly (chickenpox, measles, gentical herpes)

14. Patterns of Disease Sporadic Disease : typhoid fever in the US—disease occurs occasionally Endemic: a disease constantly common in a poplulationcommon cold Epidemic : influenza Pandemic : an epidemic disease that occurs worldwide (influenza)

15. Development of Disease Reservoir: for a disease to perpetuate itself there must be a continuous source either living or an inanimate object that provides the pathogen with adequate conditions for survival & multiplication

16. Classifying Infectious Diseases Communicable disease: disease spreads from host to host (TB, typhoid fever, gential herpes) Noncommunicable diseases: Clostridium tetani produces disease only when introduced into the body via abrasions or wounds

17. Acute disease: develops rapidly but lasts only a short time (influenza) Chronic disease: develops more slowly, and the body’s rx’s may be less severe (Mono, TB and Hepatitis B) Primary infection: is an acute infection that causes initial illness Secondary infection: is one caused by an opportunistic pathogen after primary infection has weakened the body’s defenses (Pneumocystic pneumonia –AIDS)

18. 3 types of transmission categories Direct contact: person-to-person (touching, kissing) (common cold/influenza, measles, scarlet fever) Indirect contact (fomites):contaminated syringes, toys, thermometers (Hep B and tetanus) Droplet transmission: mucus droplets that travel short distances (1m)—sneeze contains 20,000 droplets (influenza, pertussis (whooping cough)

19. 5 types of vehicle transmission Waterborne: pathogens are spread by contaminated H2O or poorly treated sewage Food-borne: foods that are incompletely cooked, poorly refrigerated or prepared under unsanitary conditions

22. Foodborne: Mother was changing the diapers of her infant and returned to canning products for the church picnic and the individual purchasing the last batch of the canned items became sick;

24. Foodborne infections: Didn't anyone know?

26. Airborne transmission: spread of agent by droplet nuclei in dust that travels >1m Mechanical transmission: passive transport of the pathogen on the insect’s feet or other body parts (houseflies can transfer typhoid fever and bacillary dysentery (shigellosis) from the feces Biological transmission: active process/ is more complex---arthropod (insect) bites an infected person or animal & ingests some of the infected blood—(Plague/Lyme disease)

27. Nosocomial infections: infection acquired while staying in the hospital or nursing homes • Prevention: aseptic techniques such as Lister and Semmelweis & use of disposable materials • 2 Mio people per year contract nosocomial infections & nearly 90,000 die as a result • MO in the hsp environment • Compromised status of host • Chain of transmission Combo of all 3 poses significant risk

28. Four different stages in the development of disease • Compromised host (cancer, surgery, HIV+) • Microorganisms in the hospital (antibiotic resistant ones & higher prevalence due to environment) • Nosocomial infections (urinary tract, surgical site, lower respiratory, bacteremia & skin infections) • Chain of transmission (direct/indirect contact w/ medical personel, fomites & ventilation system)