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PowerLecture: Chapter 18 Life at Risk: Infectious Disease 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. Impacts/Issues Virus, Virus Everywhere 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 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. 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. Video: Bird Flu CLICK TO PLAY From ABC News, Environmental Science in the Headlines, 2005 DVD. 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. 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. 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 Section 1 Some General Principles of Infectious Disease 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.” conjunctivae of eyes nasal cavity and nasopharynx mouth skin intestinal tract urethra vagina (females) Fig. 18.1, p.340 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. 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. 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. 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. 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. 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 Video: Germs in Pakistan CLICK TO PLAY From ABC News, Human Biology in the Headlines, 2006 DVD. Video: Mask of Technology CLICK TO PLAY From ABC News, Human Biology in the Headlines, 2006 DVD. 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. Section 2 Viruses and Infectious Proteins 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. viral RNA protein subunits of coat a rodlike virus Fig. 18.3a, p.342 spike proteins b polyhedral virus Fig. 18.3b, p.342 DNA protein coat sheath tail fiber c complex virus Fig. 18.3c, p.342 viral coat (proteins) viral enzyme spike proteins viral RNA d envelope enveloped polyhedral virus Fig. 18.3d, p.342 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. 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. f Many new virus particles assembled. e Genetic information translated into viral proteins c Host metabolic machinery transcribes the viral genes. viral DNA some proteins for viral coat other proteins for viral envelope g Viral envelope proteins become inserted into host’s plasma membrane. h Particles leave nucleus, move to plasma membrane. nuclear envelope j The finished particle is equipped to infect a new potential host cell. i Virus particles bud from plasma membrane. Their viral coat becomes wrapped in protein-spiked membrane, which becomes the viral envelope. Fig. 18.4, p.342 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. 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 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. 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 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. 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. Section 3 Bacteria— The Unseen Multitudes 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. DNA capsule bacterial flagellum pilus plasma membrane cell wall ribosomes in cytoplasm cytoplasm Fig. 18.6, p.344 Bacteria—The Unseen Multitudes • Bacterial flagella allow for motility; pili help bacteria attach to objects or each other. Figures 18.7 and 18.14b Animation: Prokaryotic Body Plan CLICK TO PLAY 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. Animation: Prokaryotic Fission CLICK TO PLAY 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. 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 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 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 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. 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. Section 4 Infectious Fungi, Protozoa, and Worms 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 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 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 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. Animation: Life Cycle of a Beef Tapeworm CLICK TO PLAY 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. Section 5 Malaria: Efforts to Conquer a Killer Useful References for Section 5 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: Malaria WHO: Malaria InfoTrac: Fatal Inaction: There Is a Silver Bullet for Africa’s Malaria Epidemic. Joshua Kurlantzick. Washington Monthly, July–Aug. 2006. InfoTrac: Push for New Tactics as War on Malaria Falters. Celia W. Dugger. The New York Times, June 28, 2006. Malaria: Efforts to Conquer a Killer Malaria kills nearly 3 million people annually, mostly children in Africa; 110 million new cases arise each year. The cause of the disease is a protozoan called Plasmodium, which is transmitted by the female Anopheles mosquito. Animation: Life Cycle of Plasmodium CLICK TO PLAY a Plasmodium zygotes sporozoite develop in the gut of female mosquitoes. They become sporozoites, which migrate to the insect’s salivary glands. b Mosquito bites human, bloodstream carries the sporozoites to liver. e Some of the merozoites enter liver, cause more malaria episodes. g Female mosquito bites, sucks blood from infected human. Gametocytes in blood enter her gut and mature into gametes, which fuse to form zygotes. f Others develop into male, female gametocytes that are released into bloodstream. male gametocyte in red blood cell sporozoites c Sporozoites reproduce in liver cells. merozoite d Offspring (merozoites) enter blood, invade red blood cells and reproduce. They can do so over a prolonged period. Disease symptoms (fever, chills, shaking) become more and more severe. Fig. 18.10, p.347 a Plasmodium zygotes sporozoite develop in the gut of female mosquitoes. They become sporozoites, which migrate to the insect’s salivary glands. b Mosquito bites human, bloodstream carries the sporozoites to liver. e Some of the merozoites enter liver, cause more malaria episodes. g Female mosquito bites, sucks blood from infected human. Gametocytes in blood enter her gut and mature into gametes, which fuse to form zygotes. f Others develop into male, female gametocytes that are released into bloodstream. male gametocyte in red blood cell sporozoites c Sporozoites reproduce in liver cells. merozoite d Offspring (merozoites) enter blood, invade red blood cells and reproduce. They can do so over a prolonged period. Disease symptoms (fever, chills, shaking) become more and more severe. Stepped Art Fig. 18.10, p.347 Malaria: Efforts to Conquer a Killer The symptoms of the disease are periodic bouts of severe chills, high fever, sweats, and shaking leading to debilitation and possibly anemia over time. Individuals who inherit one copy of the gene for sickle-cell anemia are partially protected from the effects of malaria. Many strains of Plasmodium are resistant to drug therapy; drugs are also expensive. Current efforts seek to devise a malaria vaccine. Section 6 Patterns of Infectious Diseases Patterns of Infectious Diseases Infectious pathogens spread in four ways. There are four general ways by which infectious diseases can move between hosts: • • Direct contact with a pathogen by touching the infected person. Indirect contact, as by touching doorknobs or tissues previously in contact with the infected person; this could include food and water. Patterns of Infectious Diseases • Inhaling pathogens that have been released by coughs and sneezes from the infected person; this is the most common mode of transmission. • Contact with a vector, such as mosquitoes, flies, fleas, and ticks, which can transfer the pathogen; these vectors are often called disease vectors. Figure 18.11 Patterns of Infectious Diseases Nosocomial infections are hospital acquired infections affecting 5-10% of all hospitalized patients each year; most are acquired by direct contact. Patterns of Infectious Diseases Diseases occur in four patterns. During an epidemic, disease rates increase above predicted levels; cholera is an example. When epidemics occur in several countries around the world in a given time frame, a pandemic is declared; AIDS is an important example. A sporadic disease breaks out irregularly and affects few people; whooping cough manifests this way. Patterns of Infectious Diseases An endemic disease occurs more or less continuously; the common cold may be the best known example. Virulence is a measure of the damage a pathogen does. Virulence is the relative ability of a pathogen to cause serious disease; how fast the pathogen invades tissues, how severe the damage is, and where the damage is all help define virulence. Antibiotic resistance in certain bacteria has made those microbes highly virulent. Patterns of Infectious Diseases There are many public and personal strategies for preventing disease. Prevention is the best way to combat infectious disease; hand washing is probably the single most important preventative tool. Public health measures include vaccination programs, ensuring standards for safe water, food, and medical supplies, and dissemination of correct and current information. Blood Preventative measures: • Avoid/prevent needle sharing/ IV drug abuse • Maintain pure public blood supplies • Vaccination programs against blood-borne pathogens (e.g., hepatitis B) Respiratory tract Preventative measures: • Hand washing • Cover mouth when coughing or sneezing • Proper disposal of used tissues • Vaccination programs GI tract Preventative measures: • Hand washing • Proper food storage, handling, and cooking • Good public sanitation (sewage, drinking water) Skin Preventative measures: • Hand washing • Limit contact with items used by an infected Fig. 18.13, p.349 Infectious Diseases: Global Health Threats Video: Whooping Cough Immunization This video clip is available in CNN Today Videos for Anatomy and Physiology, 2004, Volume VIII. Instructors, contact your local sales representative to order this volume, while supplies last. Video: Global AIDS 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. Useful References for Section 6 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: The Science of Clean Water. Elettra Ronchi. OECD Observer, Mar. 2003. InfoTrac: Pandemic Dilemma: Who Gets the Shot? Chicago Tribune, June 27, 2006.