Disease, Disease Transmission, and Epidemiology

1. Disease, Disease Transmission, and Epidemiology Chapter 14

2. Table 14.1 The Three Types of Symbiotic Relationships

3. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Organisms that colonize the body’s surfaces without normally causing disease Two types

4. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Acquisition of normal microbiota

5. Symbiotic Relationships Between Microbes and Their Hosts How Normal Microbiota Become Opportunistic Pathogens Opportunistic pathogens Normal microbiota that cause disease under certain circumstances Conditions that provide opportunities for pathogens Introduction of normal microbiota into unusual site in body (cuts and abrasions) Immune suppression (radiation therapy) Changes in the normal microbiota (antibiotic use)

6. What is a disease? • Infection • When contaminating organism evades body’s external defenses and multiplies in the host • Most infections are eliminated by the bodies defenses • Disease • Infections may lead to disease • Results when normal body functions are altered

7. Causation of Disease Germ theory of disease Disease caused by infections of pathogenic microorganisms Robert Koch developed a set of postulates to prove a particular pathogen causes a particular disease Exceptions to Koch’s postulates HIV/AIDS Not ethical Syphilis Not culturable in laboratory setting Mycobacterium leprae Never been grown in lab

8. Infectious Disease Symptoms and Signs Symptoms Signs Asymptomatic

9. Classification of Infectious Diseases Terms used to classify infectious disease Acute disease (rapid onset, short period of time ex. Common cold) Chronic disease (develop slowly, continual or recurrent ex. Hepatitis C, TB) Latent disease (pathogen remains inactive for a long period of time before becoming active ex. shingles)

10. The Stages of Infectious Disease Many infectious diseases have five stages following infection ___________________(time between infection and first symptoms and signs of disease) __________________(short time, mild symptoms) ________________(severe stage, signs and symptoms most evident) _______________(gradual decline of signs and symptoms as body returns to normal due to immune response or drug treatment) ___________________ (patient recovers no signs or symptoms)

11. Prodromalperiod(vague,generalsymptoms) Incubationperiod(no signs orsymptoms) Decline(declining signsand symptoms) Convalescence(no signs orsymptoms) Illness(most severe signsand symptoms) Figure 14.10 The stages of infectious diseases Number of microorganisms orintensity of signs or symptoms Time

12. How do we acquire a disease causing organism? Reservoir of infection Reservoir may or may not be harmed by pathogen Most pathogens cannot survive for long outside their host A successful pathogen needs to overcome the innate and adaptive defenses long enough for the pathogen to multiply and exit the host It is a disadvantage for the pathogen to actually kill a host, since the opportunity to be transmitted may be limited and it loses the source of nutrients

13. Reservoirs of infection • Three types of reservoirs

14. Human reservoirs The principle living reservoir- the human body People with signs and symptoms may transmit Infected individuals who are asymptomatic but infective to others (before or after onset of illness) Carriers individuals remain asymptomatic and infective for years (ex. Tuberculosis, syphilis, and AIDS)

15. Animal Reservoirs Zoonoses or Zoonotic diseases (150 diseases) Diseases naturally spread from animal host to humans Acquire zoonoses through various routes Direct contact with animal or its waste (E. coli O157:H7) Animal bites (Rabies) Insect bites (Lyme Disease)

16. Nonliving Reservoirs Soil, water, and food can be reservoirs of infection Presence of microorganisms often due to contamination by feces or urine Can be naturally occurring in environment (Tetanus and botulism) Water (Example: parasitic eggs or E. coli) Meats and vegetables

17. Movement of a pathogen into a host Portals of Entry Sites through which pathogens enter the body Four major pathways Ear Brokenskin Insectbite Conjunctivaof eye Mouth Placenta Censored Vagina Anus Penis Urethra

18. Portals of Entry Skin Outer layer of dead skin cells acts as a barrier to pathogens Some pathogens can enter through openings or cuts Others burrow into or digest outer layers of skin

19. Portals of Entry Mucous membranes Line the body cavities that are open to the environment Respiratory tract is the most common site of entry Entry is through the nose, mouth, or eyes Gastrointestinal tract may be route of entry Must survive the acidic pH of the stomach

20. Portals of Entry Placenta Typically forms effective barrier to pathogens Pathogens may cross the placenta and infect the fetus Can cause spontaneous abortion, birth defects, premature birth Listeria (lunch meats)

21. Portals of Entry Parenteral route Not a true portal of entry A way portals of entry can be bypassed Mechanically depositing pathogens directly into tissues beneath the skin or mucous membranes Hypodermic needles Thorns, nails, etc..

22. The Movement of Pathogens Out of a reservoir: Portal of Exit Pathogens leave host through portals of exit Many portals of exit are the same as portals of entry Pathogens often leave hosts in materials the body secretes or excretes

23. Eyes(tears) Ear (earwax) Nose (secretions) Broken skin(blood) Mouth(saliva, sputum) Figure 14.11 Portals of exit Skin(flakes) In females:Mammary glands(milk, secretions) Censored Vagina(secretions, blood) Censored Anus(feces) Seminal vesicles(semen and lubricating secretions) Urethra(urine)

24. Microbial Mechanisms of Pathogenesis

25. Pathogenicity- the ability of a microorganism to cause disease • Pathogenesis- The mechanism a microorganism uses to cause disease • Virulence- the relative ability of a pathogen to infect a host and cause disease.

26. A pathogens goal

27. Virulence factors • Traits a pathogen uses to:

28. Virulence factors • Adhere to host cells • Bacteria and viruses have surface proteins that enable them to bind to complementary host receptors • Adhesins on bacteria • Fimbriae • Attachment proteins on viruses • Host specific interactions • Adhesins and receptors determines the specificity of pathogens for particular hosts • Neisseria gonorrhoeae • Has adhesins on its fimbriae that adhere to cells lining urethra and vagina of humans, can not infect other hosts • Can attach to sperm cells as they swim by!

29. Virulence factors • Traits a pathogen uses to: • Produce extracellular enzymes • Dissolve structural chemicals in the body • To further invade and gain access to nutrients • Produce Toxins • Exotoxins • Secreted by pathogen to destroy host cells • Cytotoxins-Kill host cells or affect their function • Neurotoxins- interfere with nerve function • Enterotoxins- affect cells lining gastrointestinal tract

30. Membrane damaging toxins • Disrupt plasma membranes • Hemolysins • Blood cells

31. Endotoxins • Also called lipid A • Lipid portion of Gram negative LPS • Released when G – cells die naturally, divide, or are digested by phagocytic cells • Cause fever, inflammation, diarrhea, shock

32. Virulence factors • Traits a pathogen uses to: • Antiphagocytic factors • Capsules are composed of chemicals found naturally in the body • Immune cells do not recognize them as foreign antigen • Capsules are slippery which makes it difficult for phagocytes to adhere • Preventing the fusion of lysosomes with phagocytic vesicles. • Pathogen is able to survive inside phagocyte • Secretion of proteases that break down antibodies • IgA in body secretions bind to bacterial adhesins on pili • Rapid turn over of pili • Antigenic variation- genetically alter the type of pili made • Fc Receptors • Gonorrhea produce chemicals which prevents fusion of lysosome with phagosome and secretes a protease which breaks down IgA in mucus.

34. Leave host to “find” new host • Portal of exit

35. Modes of Infectious Disease Transmission Transmission is from a reservoir or a portal of exit to another host’s portal of entry Three groups of transmission

36. Contact Transmission Direct Contact • One person physically touches another • Handshake • Sexual intercourse • Fecal-oral

37. Contact Transmission Indirect Contact • Transfer of pathogens via inanimate objects (called fomites) • Clothing • Doorknobs • Glasses and eating utensils Ex. Scabies: Bedding serves as fomite involved in transmission

38. Contact Transmission: Droplet • Transmission of a pathogen through inhalation of respiratory droplets. • Large microbe saturated droplets fall to the ground no farther than 3 feet from release. • Close proximity necessary • Coughing • Sneezing • Examples of diseases: • Cold, Flu

39. Vehicle Transmission: Airborne • Transmission of a pathogen that is suspended in the air and travels through the air to another host • Very difficult to control! • Remains suspended indefinitely • Coughing • Sneezing • Examples of diseases: • Tuberculosis, Measles

40. Vehicle Transmission: Food • Usually digestive tract diseases • Contamination can occur in a variety of different ways • Animals can harbor pathogens • Salmonella • E. coli O157:H7 • Inadvertently added during food preparation • No handwashing • Staphylococcus aureus • Cross-contamination • Cutting board used on meat and vegetables for your salad • Meat and vegetable processing facilities

41. Vehicle Transmission: Food • Toxin causes illness not the living organisms • Staphylococcus aureusand Clostridium botulinum

42. Vehicle Transmission: Food • Symptoms do not usually appear for at least 1 day • Diarrhea • Thorough cooking before consumption will kill the organisms • E. coli O157:H7 • Salmonella

43. Vehicle Transmission: Water • Can involve large numbers of people • 1993 Cryptosporidium parvum (intestinal parasite) • Watery diarrhea 10-15L a day • Infectious dose: less than 10 organisms • Milwaukee, WI • Infected ~400,000 people from municipal water source

45. Vector Transmission • Biological Vector • Mechanical Vector

46. 1. Biological Vector • Ex: Malaria: Part of life cycle of protozoan, Plasmodium, occurs inside the Anopheles mosquito

47. 2. MechanicalVector • Ex: Trachoma (Blindness): Chlamydia trachomatis carried on feet of fly from infected person's eye to eye of new host

48. Epidemiology • Epidemiologyfocuses on the effect of a pathogen in a population • The study of where and when diseases occur and how they are transmitted in a population. • Why is this field important? • Earth’s population is becoming over populated. • Humans are relying more on mass food production and distribution • Travel to other countries very readily. • Leads to higher incidence, number of new cases of a disease in a population) • Prevalence, the total number of cases, new and already existing in a population

49. Occurrence of an infectious disease can be classified in terms of geographic distribution and frequency. • Sporadic • Endemic • Outbreak • Epidemic • Pandemic

50. Sporadic • A few cases randomly distributed geographically Example: • Plague in U.S.