INFECTION, DISEASE, & IMMUNITY

1. INFECTION, DISEASE, &IMMUNITY

2. Infection: The invasion of one organism (the host) by another. There are 4 possible outcomes of an infection: • 1. The host overcomes and destroys the invader. • 2. A symbiotic, mutualistic relationship develops. • 3. A symbiotic, commensalistic relationship develops. • 4. A symbiotic, parasitic relationship develops.

3. SYMBIOTIC, MUTUALISTIC RELATIONSHIP (+, +) Both the host and the invading organism benefit. This is a rare occurrence. One example is Lactobacillus in the female reproductive tract. The bacteria maintain a protective acidic environment that prevents Candidiasis.

4. SYMBIOTIC, COMMENSALISTIC RELATIONSHIP (+, 0) The host is unaffected but the invading organism benefits. This is a rare occurrence. One example is E. coli in the gastrointestinal tract. The bacteria obtain housing and nutrients, but the host is unaffected.

5. SYMBIOTIC, PARASITIC RELATIONSHIP (+, -) The host is negatively affected, the invading organism benefits. This is a common occurrence. One example is a super-infection of Candidaalbicans leading to candidiasis.

6. The Bodies Normal Flora • Many microbes colonize the human body, they are part of our normal ecology. Some examples include: • Staphylococcus epidermidison the skin • Streptococcus mutans in the oral cavity • Pneumococci and mycoplasmas in the respiratory system • E. coli and Candida albicansin the digestive tract

7. The Term “Disease” • This is a very general term that refers to an overall decrease in an individual’s state of well-being. The word literally means “without ease”. • Infection may lead to disease, but not in every case. Your dog can be infected with fleas, but not diseased. • Not all disease involves microbes. Clinical depression and alcoholism are both diseases.

8. Development of Disease • A Pathogen is an organism capable of causing disease. • “Pathos” literally means suffering. • The degree of pathogenicity is described by the term “virulence” ( meaning “full of Poison”)

9. Degrees of Virulence • Microbes display different degrees of virulence. • Some are highly virulent, for example Salmonella typhi(Typhoid) • Others are moderately virulent such as Candida albicans (Yeast Infection). • Many are avirulent and do not cause disease or infection.

10. Opportunistic Microbes • Many microbes are opportunistic and will cause infection and disease in a weakened or immuno-compromised individual. • Microbes also have the ability to mutate and become virulent. 0157:H7 is a very virulent mutant strain of Escherichia coli.

11. Development of Disease • There are 5 stages in the development of disease. • The first stage is the incubation stage. • During this stage the population size is small, but the growth potential is great. • The generation time of the pathogen will determine the incubation time. • Incubation time is highly variable: Cholera = 1 – 3 days, Chicken Pox = 14 days, Leprosy = 3 – 6 years. • Incubation time is influenced by the # of microbes introduced into the host, the host’s resistance, the mode and location of entry, and other factors.

12. Development of Disease • The second stage in the development of disease is the Prodromal Symptoms stage. • During this stage the population size is growing rapidly, the growth potential is great, and the microbe is beginning the affect the host. • During this stage the host experiences flu-like symptoms such as nausea, fever, headache, and malaise.

13. Development of Disease • The third stage in the development of disease is the Acme stage. “Acme” means the highest point. • During this stage the population size is large, and the microbe is greatly affecting the host. • During this stage the host experiences the symptoms that characterize the disease. • For examples, the appearance of pox in small pox infections, jaundice associated with hepatitis, the red rash associated with scarlet fever. These are often accompanied by chills, dry skin, and high fever. • Some diseases are clinical and display distinct symptoms, some are subclinical and display few visible symptoms.

14. Development of Disease • The fourth stage in the development of disease is the decline or defervescence stage. This literally means to stop (defer) the boiling (efervescence). • During this stage the population size of the microbe is declining due to the immune response, medication, etc. • This stage is characterized by sweating, abatement of the fever, the return of normal color, appetite, and behavior.

15. Development of Disease • The fifth stage in the development of disease is the convalescence stage. • During this stage the population size of the microbe is rapidly declining and is heading for extinction. • This stage is characterized by complete recovery of the individual.

16. Population Growth Curve • The stages in the development of disease are well illustrated by a population growth curve. • Growth curves illustrate the population dynamics of microbial growth.

17. Disease Transmission • There are 2 basic types of disease transmission: • Direct Transmission and Indirect Transmission. • Direct Transmission involves close contact with an infected host. • Indirect Transmission does not involves direct contact with the host, but rather contact with vectors, fomites, contaminated food, or contaminated water.

18. Direct Transmission • Direct Disease Transmission includes such things as hand shaking, kissing, sexual contact, and contact with feces. • Contact with aerosol droplets from sneezing and coughing is also considered direct transmission.

19. Indirect Transmission • Indirect Disease Transmission includes contact with fomites which are inanimate objects such as clothing, bedding, or syringes. • It also includes contact with vectors such as fleas, ticks, or mosquitoes. • Contaminated water and food is a common form of indirect transmission.

20. Reservoirs and Carriers • A Reservoir is an organism that harbors and transmits a disease but has never displayed the symptoms of the disease. For example, the monkey on the movie “Outbreak”. • A Carrier is an organism that has had the disease, recovered from it, and now sheds the pathogen. Typhoid Mary is a classic example of a carrier.

22. Types of Diseases • Diseases can be classified based on their ease of transmission, geographical distribution, or level of severity.

23. Ease of Transmission • Many diseases are classified based on their ease of transmission: • Communicable Diseases can be transferred between hosts. Those that are easily transferred are known as Contagious. For example, influenza is highly contagious. • Non-communicable Diseases are acquired directly from the environment. For example, tetanus.

24. Geographical Distribution • Some diseases are classified based on their geographical distribution: • Endemic diseases result in isolated, low level outbreaks. For example, tetanus or food poisoning. • Epidemic diseases result in outbreaks that spread rapidly and affect a large area. For example a cold virus. • Pandemic disease have worldwide distribution. For example, HIV.

26. Level of Severity • Some diseases are classified based on their level of severity: • Acute Diseases develop rapidly and have severe symptoms . They exhibit the classic stages of disease. An example is chicken pox. • Chronic Diseases develop slowly, linger, may never reach climax, and involve a long convalescence. An example is Hepatitis A.

27. Establishment of Disease • The establishment of disease in influenced by the Portal of Entry, Dose, Tissue Penetration, Enzyme Compliment, and the presence or absence of Toxins.

28. Establishment of Disease • Portal of Entry: Varies with pathogen. Common portals are airborne, foodborne, and through vectors. • Dose: The dose must be adequate to cause disease, this varies with pathogen. • Tissue Penetration: Also knows as invasiveness. This is critical to some, but not all. For example, influenza remains on the surface of the tissue, but tetanus bacteria must penetrate into the tissue.

29. Establishment of Disease • Enzymes are commonly used by pathogens to fight the host’s defenses. Examples include: • Coagulase – Produces blood clots and protects microbe against phagocytosis (ex. Boils formed by staphylococci). (Staphylococci). • Hyaluronidase – Dissolves polysaccharide that binds cells together, this enhances penetration. (Streptococci, Staphylococci, Pneumococci). • Streptokinase – Dissolves fibrin clots to enhance invasiveness. (Streptococci). • Leukocidin – Destroys phagocytes, inhibits phagocytosis. (Staphylococci & Streptococci). • Hemolysins – Dissolves red blood cells, limits oxygen delivery. (Staphylococci).

30. Toxins • Many microbes produce toxins that cause ill effects. • Exotoxins are located in the cytoplasm of the pathogen, elicit an antibody response, can be converted to toxoids, are secreted by the live pathogen, and have specific effects such as paralysis. Botulinum toxin is an exotoxin. • Endotoxins are located in the cell wall of the pathogen, do not elicit an antibody response, can not be converted to toxoids, are released when the pathogen is destroyed, and have very general effects such as fever, vomiting, diarrhea, and inflammation. Salmonella produces endotoxins.

31. Resistance to Disease • Resistance to disease occurs along 2 main fronts, Non-specific barriers to disease and specific barriers to disease. • Non-specific barriers to disease provide generic protection. • Specific barriers to disease target specific pathogens through an immune response.

32. Non-Specific Barriers to Disease • Non-specific barriers to disease include: Physical and Chemical Barriers, The Lymphatic System, The Inflammatory Response, and Fever.

33. Non-Specific Barriers to Disease(Mechanical and Chemical Barriers) Physical and Chemical Barriers include: • The Integumentary System • Mucous membranes • Acidity • Bile • Enzymes • Interferons

34. Non-Specific Barriers to Disease(Physical and Chemical Barriers) • The integumentary system is our primary line of defense against microbes. However, openings in the integumentary system can act as entry portals for microbes and must have some form of protection. • All true openings in the integumentary system are protected by mucous membranes. Mucous helps trap and remove invading microbes. • The acidity of the stomach and female reproductive system also help inhibit microbial growth.

35. Non-Specific Barriers to Disease(Physical and Chemical Barriers) • Bile is an emulsifier produced by the liver and stored in the gallbladder. Its primary function is to aid in the digestion of fats, but it also inhibits microbial growth. • Some enzymes also have anticrobial properties, for example lysozyme. Lysozyme is found in tears and saliva and digests the peptidoglycan of gram-positive bacteria. • Interferonsare antiviral proteins that are produced by body cells that have been exposed to viruses. These proteins lead to the production of a secondary protein that binds to the viral mRNA and inhibits viral replication.

36. Non-Specific Barriers to Disease(Physical and Chemical Barriers)Lymphatic System • Three main functions • Fluid balance • Fat absorption • Defense

37. Lymphatic System • Lymphatic vessels • Form a one-way system • Begins with lymphatic capillaries • Tiny, closed-ended vessels • Take up excess tissue fluid (lymph) • Vessels merge and then enter one of two ducts: • Thoracic duct • Right lymphatic duct • Vessels have valves and movement of lymph depends on skeletal muscle contraction • Edema is localized swelling caused by the accumulation of lymph

38. Fig 13.1

40. Organs, Tissues, and Cells of the Immune System • Primary Lymphatic Organs • Lymphocytes originate and/or mature in these organs • Red Bone Marrow • Site of stem cells that produce blood cells • In an adult, red bone marrow is found in: • Sternum • Vertebrae • Ribs • Skull • Part of the pelvic girdle • Proximal heads of the humerus and femur • Lymphocytes differentiate into B and T lymphocytes • B lymphocytes mature in the red bone marrow • T lymphocytes mature in the thymus

41. Organs, Tissues, and Cells of the Immune System • Thymus Gland • In the thoracic cavity • Largest in children and shrinks as a person ages • Lobules are filled with lymphocytes • Produces thymic hormones • Aids in maturation of T lymphocytes • May have other functions in immunity • Critical to immunity

42. Fig 13.2

43. Fig 13.3

44. Organs, Tissues, and Cells of the Immune System • Secondary Lymphatic Organs • Places where lymphocytes encounter and bind with antigens • Spleen • Largest lymphatic organ • Consists of two types of tissue: • White pulp – has a concentration of lymphocytes • Red pulp – surrounds venous sinuses and is involved in filtering blood • Blood entering the spleen is filtered through venous sinuses • Lymphocytes and macrophages react to pathogens • Macrophages engulf debris and remove old red blood cells

45. Organs, Tissues, and Cells of the Immune System • Lymph nodes • Small structures occurring along lymphatic vessels • Connective tissue • Forms a capsule • Divides node into compartments • Contains nodules packed with B lymphocytes • Sinus that contains T lymphocytes • Lymph passing through the sinus is filtered by macrophages • T lymphocytes fight infection and attack cancer cells

46. Organs, Tissues, and Cells of the Immune System • Lymphatic nodules • Concentrations of lymphatic tissue not surrounded by a capsule • Tonsils • Peyer patches (intestinal wall) • Appendix

47. Nonspecific Defenses • Fever • Fever is a nonspecific defense in which the body elevates the internal temperature. • Fever impedes bacterial growth and stimulates the immune response. • Fever develops when the sweating reflex shuts down, peripheral circulation is reduced, and the core temperature is elevated. Shivering may also occur.

48. Nonspecific Defenses • Inflammatory reaction • Four signs: • Redness (Rubor) • Heat (Calor) • Swelling (Tumor) • Pain (Dolor) • Chemical mediators cause capillaries to dilate and become more permeable • Excess blood causes redness and increased temperature • Fluids and proteins escape the capillaries due to increased permeability and cause swelling and clot formation • Migration of phagocytes to site of injury

49. Fig 13.4

50. Nonspecific Defenses • Natural killer cells • Kill virus-infected cells and tumor cells • Large, granular lymphocytes • No specificity and no memory • Protective proteins • Complement Proteins • Composed of blood plasma proteins • Activated when pathogens enter the body • Amplify the inflammatory response • Bind to the surface of pathogens, ensuring that they will be phagocytized • Form a membrane attack complex that punches holes in the walls and membranes of bacteria • Interferons • Produced by virus-infected cells • Produce substances that interfere with viral replication