Chapter 38

1. Chapter 38 Human Diseases Caused by Bacteria

2. Bacterial Pathogens • of the bacterial species, only a few are pathogenic to humans • some pathogens have been known since antiquity • others have been recently recognized as disease producers

3. Table 38.1

4. Airborne Diseases • most involve the respiratory system • some are skin diseases

5. Diphtheria • caused by Corynebacterium diphtheriae • gram-positive • lysogenized strains produce an exotoxin that inhibits protein synthesis and is responsible for pathogenesis • resistant to drying • airborne transmission by nasopharyngeal secretions • crowding increases likelihood of transmission

6. Diphtheria… • usually observed in individuals >30 years old with weakened immunity to diphtheria toxin and living in tropical areas • cutaneous diphtheria • infection at a wound or skin lesion • slow-healing ulceration

7. Diphtheria… • diagnosis • observation of pseudomembrane in throat • bacterial culture • treatment, prevention, and control • antitoxin given to neutralized unabsorbed exotoxin in patient’s tissues • antibiotic therapy • active immunization with DPT (diphtheria-pertussis-tetanus) vaccine

8. Figure 38.1

9. Tuberculosis (TB) • caused by Mycobacterium tuberculosis • ~ 1/3 of world’s population infected • transmission • person to person • also transmitted from infected animals and their products

10. TB - Course of Disease • lung macrophages that have phagocytosed M. tuberculosis often die in the attempt to kill the bacteria • tubercles form • composed of bacteria, macrophages, T cells and human proteins • subsequent changes in tubercle may occur

11. Figure 38.3 (a)

12. Figure 38.3 (b)

13. Persons Infected With TB • develop cell-mediated immunity (sensitized T cells) • basis for tuberculin skin test • incubation period • 4-12 weeks • symptoms • fever, fatigue, weight loss • cough • characteristic of pulmonary involvement • may result in expectoration of bloody sputum

14. TB • diagnosis • observation of acid-fast bacteria, chest X-ray, DNA-based tests, Mantoux or tuberculin skin test • antimicrobial therapy • multi-drug-resistant strains of tuberculosis (MDR-TB) have developed • prevention and control • rapid, specific therapy to interrupt spread, retreatment of patients with MDR-TB, immunization, improved sanitation and housing, and reduction in homelessness and drug abuse

15. Pertussis • whooping cough • highly contagious disease that primarily affects children • caused by Bordetella pertussis • produces adhesins and several toxins • transmission by droplet inhalation

16. Pertussis… • clinical manifestations • 7 to 14 day incubation • initially coldlike symptoms and inflamed mucous membranes • followed by prolonged coughing sieges with inspiratory whoop • permanent or long-lasting immunity develops • treatment, prevention, and control • bacterial culture, fluorescent antibody staining, and serological tests • antibiotic therapy • immunization with DPT vaccine

17. Invasive Streptococcus A Infections • caused by certain strains of S. pyogenes • carry genes for exotoxins • Superantigens (Select Agent) • tissue-destroying protease

18. Invasive infections… • clinical manifestations • necrotizing fasciitis • destruction of sheath covering skeletal muscle • myositis • inflammation and destruction of skeletal muscle and fat tissue • toxic shock-like syndrome (TSLS) • precipitous drop of blood pressure, failure of multiple organs, and high fever

19. Figure 38.6

20. Streptococcal Pharyngitis • commonly called strep throat • spread by droplets of saliva or nasal secretions • infection in throat (pharyngitis) or on tonsils (tonsillitis) • signs and symptoms of disease not diagnostic because many viral infections have similar presentation • physical manifestations • redness, edema, and lymph node enlargement in throat

21. Streptococcal Pharyngitis • diagnosis • rapid kits • treatment and control • antibiotics important for children to lessen chance of complications such as rheumatic fever and glomerulonephritis • control by preventing contact with contaminated materials or discharges from infected individuals

22. Arthropod-Borne Diseases • generally rare • some are of historical interest • some newly emerged

23. Ehrlichiosis • caused by Ehrlichia chaffeensis • two forms • human monocytic ehrlichiosis (HME) • human granulocytic ehrlichiosis (HGE)

24. HME and HGE • transmitted from dogs and white tail deer, the primary reservoirs, to humans by ticks • HME caused by Ehrlichia chaffeensis • infects circulating monocytes • clinical manifestations • nonspecific febrile illness resembling Rocky Mountain spotted fever • diagnosis • serological tests and DNA probes • treatment, prevention, and control • antibiotic therapy • tick control measures

25. Lyme Disease • LD or Lyme borreliosis • caused by Borrelia burgdorferi, B. garinii, and B. afzelii Figure 38.8 (a)

26. Lyme disease… • transmitted from animal reservoirs by ticks • deer, field mice and woodrats • clinical manifestations vary with stage of disease

27. Stages of Lyme disease • localized stage • develops 1 week to 10 days after infection • expanding, ring-shaped, skin lesion • flu-like symptoms • disseminated stage • occurs weeks or months after infection • neurological abnormalities, heart inflammation, and arthritis • late stage • occurs years later • demyelination of neurons, behavioral changes, and symptoms resembling Alzheimer’s disease and multiple sclerosis

28. Figure 38.8 (b) and (c)

29. Lyme disease… • diagnosis • isolation of bacterium, PCR, and serological tests • treatment, prevention, and control • antibiotic therapy most effective in early stages • tick control and avoiding ticks

30. Plague (A Select Agent) • caused by Yersinia pestis, a gram-negative organism • initial spread by contact with flea-infested animals followed by spread among people by airborne transmission • in body multiply in blood and lymph • survive and proliferate in phagocytic cells

31. Plague Yersinia pestis – proliferates inside phagocytic cells Figure 38.9 (a)

32. Plague… • clinical manifestations • subcutaneous hemorrhages, fever, and buboes (hence name bubonic plague) • high mortality if untreated • pneumonic plague arises from: • primary exposure to infectious respiratory droplets of infected persons or cats • secondary to hematogenous spread in a patient with bubonic plague

33. Plague Yersinia pestis causative agent Figure 38.9 (b) and (c)

34. Plague… • diagnosis made in reference labs which use direct microscopic examination, culture and serological tests, and PCR • treatment, prevention, and control • antibiotic therapy • ectoparasite and rodent control, isolation of human patients, prophylaxis of exposed persons, immunization of persons at high risk

35. Direct Contact Diseases • most involve skin or underlying tissues • some can become disseminated

36. Gas Gangrene or Clostridial Myonecrosis • most commonly caused by Clostridium perfringens • gram-positive, spore-forming rod • produce gas gangrene, a necrotizing infection of skeletal muscle or clostridial myonecrosis • secretes toxin and tissue damaging enzymes • transmitted by contamination of injured tissue by spores from soil or bowel microbiota

37. Gas gangrene… • clinical manifestations • severe pain, edema, drainage, and muscle necrosis • diagnosis • recovery of appropriate clostridial species and characteristic disease symptoms • treatment, prevention, and control • surgical debridement, administration of antitoxin, antibiotic therapy, and hyperbaric oxygen therapy • prompt treatment of all wound infections and amputation of limbs

38. Figure 38.11

39. Leprosy • Hansen’s disease • caused by Mycobacterium leprae • invades peripheral nerve and skin cells, becoming obligate intracellular parasite • humans are only significant reservoir • transmitted after prolonged exposure to infected individuals • probably spread in nasal secretions

40. Leprosy… • clinical manifestations • incubation usually 3 to 5 years • initial symptom is slightly pigmented skin eruption • development of disease thought to be related to strength of cell-mediated immune response to bacterium

41. Forms of leprosy • tuberculoid (neural) leprosy • mild, nonprogressive form • associated with delayed-type hypersensitivity • damaged nerves and regions of skin that have lost sensation and are surrounded by a border of nodules • lepromatous (progressive) leprosy • individuals do not develop hypersensitivity • skin tissue killed, leading to progressive loss of facial features, fingers, toes, and other structures • disfiguring nodules form all over body

42. Figure 38.13

43. Leprosy… • diagnosis • direct fluorescent antibody staining of biopsy specimens, serodiagnostic tests, DNA amplification and ELISA • treatment, prevention, and control • antibiotic and drug therapy, and immunotherapy with vaccine • identification and treatment of patients and prophylactic therapy for uninfected household members

44. Peptic Ulcer Disease and Gastritis • caused by Helicobacter pylori • colonizes gastric mucus-secreting cells • produces urease, which acts to increase pH • releases toxins that damage epithelial mucosal cells Figure 38.14

45. H. pylori disease… • transmission probably from person to person • common source has not been ruled out • diagnosis • culture of gastric biopsy specimens, examination of stained biopsies, serological testing, urea breath test, tests for ammonia in urine, and detection of urease activity in biopsies • treatment, prevention, and control • a combination of drugs to decrease stomach acid and antibiotics to kill the bacteria