Understanding Infectious Diseases: From Microorganisms to Global Impacts

1. PowerLecture:Chapter 18 Life at Risk: Infectious Disease

2. Learning Objectives • Differentiate between the microorganisms that normally live on and in you and those which cause infection and disease. • List the general characteristics of viruses, bacteria, and other parasites. • Describe the different patterns of infectious disease and how you can protect yourself.

3. Impacts/Issues Virus, Virus Everywhere

4. Virus, Virus Everywhere • West Nile virus is a virus with historical and present-day importance. • In 324 B.C. it quite possibly killed Alexander the Great. • In 1999 West Nile virus was discovered in the U.S., the first time it had ever been seen in the Western Hemisphere. Figure 18.15

5. Virus, Virus Everywhere • Avian (bird) flu, caused by the H5N1 virus, is rapidly spreading around the globe, evidence that no place is safe when it comes to infectious disease.

6. Video: West Nile Virus • This video clip is available in CNN Today Videos for Anatomy and Physiology, 2003, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

7. Useful References for Impacts/Issues The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • CDC: West Nile Virus • CDC: Avian Influenza • InfoTrac: Avian Flu, West Nile Virus, and Lyme Disease. Robert Charles Moellering Jr. et al. Patient Care for the Nurse Practitioner, April 2006.

8. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu. • Killing mosquitoes is the best defense against West Nile virus. Some people object to spraying, fearing harmful effects on health or wildlife. Would you support a spraying program in your area? • a. Yes, spraying pesticides to kill mosquitoes is an effective way to limit the spread of this disease. • b. No, the pesticides used to control the virus do more harm than good.

9. Useful References for How Would You Vote? The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Suit over West Nile Spraying Goes Forward against City. New York Law Journal, June 13, 2005. • InfoTrac: Study Claims Risks of West Nile Spraying Exaggerated. Pesticide & Toxic Chemical News, May 3, 2004. • InfoTrac: A Global Market Isn’t as Easy as It Looks. Business Week, Sept. 3, 2001. • Maine Environmental Policy Institute: Overkill

10. Section 1 Some General Principles of Infectious Disease

11. Some General Principles of Infectious Disease • The body is home to a great many “friendly” microorganisms. • Many species of microorganisms colonize the epithelial tissues of the skin, mouth, nasal cavity, conjunctiva, GI tract, urethra, and vagina. • All possess some sort of adhesion proteins on their surfaces that allow them to “stick” to our tissues; pathogens, on the other hand, often do not have this ability to “stick.”

12. Fig. 18.1, p.340 conjunctivae of eyes nasal cavity and nasopharynx mouth skin intestinal tract urethra vagina (females)

13. Some General Principles of Infectious Disease • Different types of pathogens cause disease in different ways. • An infection occurs when a pathogen enters cells or tissues and multiplies; if this growth interferes with normal body function, then it is termed a disease. • Infectious diseases are those diseases that can be passed from one person to another.

14. Some General Principles of Infectious Disease • Pathogens produce disease in different ways. • Some bacteria produce toxins, chemicals that are poisonous to human tissues; the disease botulism is caused by a bacterial toxin produced by Clostridium botulinum. • Septic shock is another condition resulting from bacterial toxins. • Viruses cause disease by invading and destroying body cells; others become latent in the cell, only manifesting some time after infection. • Some pathogenic fungi release enzymes to digest human tissues; parasitic worms and protozoa may damage tissues directly or trigger harmful immune responses.

15. Some General Principles of Infectious Disease • To cause an infection, pathogens must meet several requirements. • Pathogens must have a host, an organism that a pathogen can infect; a reservoir is a place where the organism can survive and remain infectious, including other organisms (carriers), soil, and water.

16. Some General Principles of Infectious Disease • The pathogen must have a way to leave the reservoir and enter a host, attach to the host’s body, and enter the tissues. • Pathogens must have some way to avoid the host’s defenses so that it can reproduce inside the host. • The pathogen finally must be able to return to a reservoir or move to a new host. • Infectious diseases are sometimes grouped according to reservoirs; a zoonosis is an infectious disease carried by animals that can also infect humans.

17. Some General Principles of Infectious Disease • Emerging diseases present new challenges. • Emerging diseases are those that only recently have begun to infect humans or which were present only in limited areas previously. • Factors influencing the emergence of new diseases include increased human population density, ease of travel, and such medical concerns as antibiotic resistance.

18. Some General Principles of Infectious Disease • Many of these diseases are viral; examples include West Nile virus, SARS virus, Ebola virus, and Lyme disease. Figure 18.2

19. Useful References for Section 1 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • Centers for Disease Control and Prevention • CDC: Emerging Infectious Diseases • InfoTrac: Antibiotics Alter the Normal Bacterial Flora in Humans. Biotech Week, April 7, 2004. • InfoTrac: Botulism. Jeremy Sobel. Clinical Infectious Diseases, Oct. 15, 2005.

20. Section 2 Viruses and Infectious Proteins

21. Viruses and Infectious Proteins • A virus is a tiny, noncellular pathogen that can infect the cells of almost every other organism. • A virus consists of a DNA, or RNA, core surrounded by a protein coat (capsid); some viruses additionally have an outer lipid en­velope. • Viruses can replicate only after infecting a cell and taking over that cell’s metabolic machinery.

22. viral RNA protein subunits of coat a rodlike virus Fig. 18.3a, p.342

23. spike proteins b polyhedral virus Fig. 18.3b, p.342

24. DNA protein coat sheath tail fiber c complex virus Fig. 18.3c, p.342

25. viral enzyme viral coat (proteins) spike proteins viral RNA envelope d enveloped polyhedral virus Fig. 18.3d, p.342

26. Viruses and Infectious Proteins • Viruses multiply inside a host cell. • Replication of a virus involves five basic steps: • A virus recognizes, and attaches to, a host cell. • The virus, or its genetic core, enters the cell. • Viral DNA, or RNA, directs the host cell in producing copies of viral nucleic acids and in making viral enzymes and other proteins. • Viral nucleic acids and proteins are assembled into new viral particles. • Newly formed viruses are released from the infected cell.

27. Fig. 18.4, p.342 a An enveloped DNA virus particle contacts the plasma membrane of host cell and fuses with it. coat surrounded by envelope viral DNA DNA virus particle b Once inside the cytoplasm, viral DNA and viral coat separate. plasma membrane of host cell d Host machinery replicates viral DNA. e Genetic information translated into viral proteins c Host metabolic machinery transcribes the viral genes. other proteins for viral envelope f Many new virus particles assembled. some proteins for viral coat viral DNA g Viral envelope proteins become inserted into host’s plasma membrane. h Particles leave nucleus, move to plasma membrane. nuclear envelope i Virus particles bud from plasma membrane. Their viral coat becomes wrapped in protein-spiked membrane, which becomes the viral envelope. j The finished particle is equipped to infect a new potential host cell.

28. Viruses and Infectious Proteins • A cell will serve as a host for the synthesis of new viral particles only if the original virus can recognize and lock onto the cell’s surface. • Some viruses do not kill their host cells outright but enter a period of latency. • One example is the herpes virus, introduced previously as an example of a sexually transmitted disease. • Epstein-Barr virus (EBV) is also a herpes virus; it causes infectious mononucleosis.

29. Viruses and Infectious Proteins • Retroviruses are RNA viruses that use an enzyme called reverse transcriptase to synthesize a DNA molecule for insertion into the host DNA; the integrated form is called a provirus. HIV is a retrovirus. Figure 18.14a

30. Viruses and Infectious Proteins • Prions are infectious proteins. • Prions are small, infectious proteins linked to several rare, fatal degenerative diseases of the nervous system. • Prions are misfolded versions of normal proteins found on brain neurons and other cell types. • Prions can bind to normal proteins and refold them, creating clumps of protein in the brain, destroying brain tissue.

31. Viruses and Infectious Proteins • BSE (bovine spongiform encephalitis) or “mad cow disease” affects cows and can cause variant Creutzfeldt-Jakob disease (vCJD) in humans; prions are also associated with a long known human-only version of CJD. Figure 18.5b

32. Useful References for Section 2 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Cannibals to Cows: The Path of a Deadly Disease. Newsweek, Mar. 12, 2001. • InfoTrac: Cold Sore Virus Can Evade Immune System. UPI NewsTrack, July 17, 2006.

33. Video: Mad Cow Victim • This video clip is available in CNN Today Videos for Anatomy and Physiology, 2003, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

34. Section 3 Bacteria— The Unseen Multitudes

35. Bacteria—The Unseen Multitudes • Bacteria are prokaryotic cells. • Structural features appear rather simple compared to more complex cells. • There is no nucleus or other membrane-bound organelles. • Most bacteria have a cell wall that makes them strong, semirigid, and gives them shape; coccus, bacillus, and spirillum (spirochete) are common cell shapes.

36. Fig. 18.6, p.344 DNA capsule plasma membrane ribosomes in cytoplasm bacterial flagellum pilus cell wall cytoplasm

37. Bacteria—The Unseen Multitudes • Bacterial flagella allow for motility; pili help bacteria attach to objects or each other. Figures 18.7 and 18.14b

38. Bacteria—The Unseen Multitudes • Bacteria reproduce by prokaryotic fission, a process that can be repeated every 20 minutes. • The chromosome is a single, circular DNA. • Some bacteria possess plasmids, small circles of extra DNA; plasmids may allow for fertility and for the transfer of drug resistance. • Streptococcus is a species of bacteria that causes respiratory tract infections and strep throat; these bacteria possess the ability to transfer genes.

39. Bacteria—The Unseen Multitudes • Bacteria play both positive and negative roles in human society. • Some bacteria are useful, such as those used to make cheese and therapeutic drugs, but most are notorious for the diseases they cause. • Antibiotics are the products of some bacteria and fungi that can be used to kill other bacteria. • Antibiotics do not work against viruses; rather, body defenses such as interferons may block replication of viruses inside cells.

40. Bacteria—The Unseen Multitudes • A biological backlash to antibiotics is under way. • Because antibiotics have been both overused and in some cases inappropriately prescribed, large numbers of bacterial species that were once susceptible to antibiotics are now resistant to their effects. • Staphylococcus aureus may soon be resistant to all available antibiotics. Figure 18.12

41. Bacteria—The Unseen Multitudes • Bacteria cause some important emerging and reemerging diseases. • Lyme disease, caused by the spirochete Borrelia burgdorferi, is an important emerging disease in the United States. Figure 18.8a

42. Bacteria—The Unseen Multitudes • Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a reemerging disease. • Antibiotics had made TB rare by the 1970s in developed nations, but many factors have since allowed the number of TB cases to rise. • In some areas of the world, all new cases of TB are antibiotic resistant. Figure 18.8b

43. Video: Salon Infections • This video clip is available in CNN Today Videos for Biology, 2003, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

44. Useful References for Section 3 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Overdoing Antibiotics. Harvard Health Letter, Nov. 2002. • InfoTrac: Chronic Middle Ear Infections Linked to Resistant Biofilm Bacteria. PR Newswire, July 11, 2006.

45. Section 4 Infectious Fungi, Protozoa, and Worms

46. Infectious Fungi, Protozoa, and Worms • Parasitic fungi and protozoa are small but potentially dangerous. • Common fungal infections include yeast infections, ringworm, and athlete’s foot. • Fungi in athlete’s foot and ringworm release enzymes that degrade keratin in skin; inflammation can also occur. • Yeast infections occur in the vagina and other mucous membranes following changes to the chemistry of the organ system. Figure 18.9a

47. Infectious Fungi, Protozoa, and Worms • Several protozoa are important pathogens. • Entamoeba histolytica causes amoebic dysentery; it enters the body in food and water contaminated with feces. • Giardia intestinalis causes giardiasis; it typically enters the body through water. Figure 18.9b-c

48. Infectious Fungi, Protozoa, and Worms • Trypanosoma brucei is transmitted by the tsetse fly to humans, where it invades the central nervous system and causes African sleeping sickness; untreated, it is fatal. • Cryptosporidium parvum, which causes cryptosporidiosis, is an emerging disease in the U.S.; this organism is highly resistant to common disinfectants. Figure 18.9d

49. Infectious Fungi, Protozoa, and Worms • Worms also can be a serious threat. • Pinworms are small, white roundworms that are easily transferred as eggs from the anal area of one person (usually a child) to the mouth of a new host via contaminated fingers. • Other notorious worms such as tapeworms, hookworms, whipworms, and the large Ascaris intestinal worms can cause damage to body tissues and organs.

50. Useful References for Section 4 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • Structural Genomics of Pathogenic Protozoa: African Trypanosomiasis • InfoTrac: Dark Fungi Emerging as Cause of Lethal Infections. Nancy Walsh. Family Practice News, May 15, 2006.