1. 13: Infectious Diseases
Your Health Today, 6th edition

2. The Process of Infection
Infection: disease or condition caused by a microorganism
Microorganisms are the tiniest living organisms on earth that eat, reproduce, and die
Infection is considered an illness or disease if it interferes with your usual lifestyle or shortens your life
Process of infection often follows a typical course

3. Figure 13.1 Stages of infection.
Exposure: organism enters body
Incubation period (no symptoms)
Prodromal period (vague sense of not being well)
Invasive phase (full-blown illness)
Acme (peak of disease): either the immune system gains control, medical treatment occurs, or death ensues
Decline phase (symptoms brought under control)
Convalescent phase (body is repairing damage)
Sequelae (remaining symptoms the body can’t repair)

4. The Chain of Infection
Chain of infection: the process by which an infectious agent, or pathogen, passes from one organism to another
Pathogen: infectious agent capable of causing disease
Pathogens often live in large communities, called reservoirs
Some cannot survive in the environment and require a living host
To cause infection, they must have a portal of exit from the reservoir or host, and a portal of entry into a new host

5. The Chain of Infection (2)
Vector: animal or insect that transmits a pathogen from a reservoir or an infected host to a new host
Breaking the chain of infection at any point can either increase or decrease the risk of infection
Virulence: speed and intensity with which a pathogen is likely to cause an infection
Epidemic: widespread outbreak of a disease that affects many people

6. Figure 13.2 The Chain of infection.
Breaking the chain at any point decreases the risk of infection.
Susceptible host has factors that influence risk of infection, such as burns
Infectious agent or pathogen, such as a bacterium or virus
Reservoir, where the organism survives, such in a human
Portal of exit, how the organism leaves, such as via blood
Mode of transmission, how it spreads, such as by direct contact
Portal of entry, how it enters a new host, such as through broken skin

7. Pathogens
Viruses: tiny pathogens consisting of a genome (DNA or RNA) and protein covering
Examples: HIV; common cold (over 200 viruses); influenza; human papillomavirus (warts, cervical cancer); hepatitis A, B, C; polio; rabies
Bacteria: single-celled organisms that are spherical, rodlike, or spiral in shape
Staphylococcus aureus and MRSA; Neisseria meningitides (meningitis); chlamydia; gonorrhea; tuberculosis

8. Pathogens (2)
Prions: organisms believed to consist entirely of protein
Bovine spongiform encephalopathy (mad cow disease); Creutzfeldt-Jakob disease (CJD); Kuru
Fungi: single-celled or multicelled organisms
Candidiasis (yeast infection); tinea (athlete’s foot, ringworm); histoplasmosis
Helminths: parasitic worms that live on or in host
Hookworm; pinworm; tapeworm; liver flukes

9. Pathogens (3)
Protozoa: single-celled organisms that generally live independently of host
Giardia; toxoplasmosis; amebiasis; malaria; trichomoniasis
Ectoparasites: complex organisms that usually live on the host’s skin
Fleas; ticks; lice; scabies; bed bugs

10. External Barriers Skin is the body’s first line of defense
Nasal passages and ear canals are protected by hair
Lungs are protected by the cough reflex and cilia
Saliva contains proteins that break down bacteria
Stomach acids make it difficult for most organisms to survive
Small intestines contain bile and enzymes that break down pathogens
Vagina is slightly acidic, discouraging the growth of abnormal bacteria

11. The Immune System
Immune system: complex set of cells, chemicals, and processes that protects the body against pathogens when they succeed in entering the body
Innate immune system: part of the immune system designed to rapidly dispose of pathogens in a nonspecific manner
Acquired immune system: highly specialized response that recognizes specific targets

12. Innate Immune System
Acute inflammatory response: the body’s initial reaction to tissue damage, bringing blood to the site of injury or infection
Cells of the innate immune system:
Neutrophils and macrophages: white blood cells that travel to areas of infection or tissue damage and digest damaged cells, foreign particles, and bacteria
Natural killer cells: white blood cells that recognize and destroy virus-infected cells or those that have become cancerous

13. Acquired Immune System
Develops as you are exposed to potential infections and vaccinations
Lymphocytes: white blood cells that circulate in the bloodstream and lymphatic system
If lymphocytes encounter an antigen—a marker on the surface of a foreign substance—they rapidly duplicate and “turn on” their specific function
To main types of lymphocytes: T cells and B cells

14. Acquired Immune System (2)
T cells monitor events inside cells
Helper T cells “read” cells’ infection messages and trigger production of killer T cells and B cells
Killer T cells attack and kill foreign cells and infected body cells
Suppressor T cells slow down and halt the immune response when the threat has been handled
B cells monitor the blood and tissue fluids
When they encounter a specific antigen, they mature and produce antibodies: proteins that bind to specific antigens and trigger their destruction

15. Immunity
After surviving infection by a pathogen, you often acquire immunity to any future infections by the same pathogen
B and T cells become memory cells when exposed to an infectious agent, allowing recognition and quick action to destroy the invader
Vaccine: preparation of weakened or killed microorganisms administered to confer immunity
Protects you by stimulating an immune response
Protects society by shrinking the reservoir of infectious agents

16. Recommended Adult Immunizations (Figure 13.5)
Recommended for all persons who meet the age requirement and lack documentation of vaccination or past infection (all covered by the Vaccine Injury Compensation Program):
Influenza: all adults, 1 dose annually; covered by the Vaccine Injury Compensation Program
Tetanus, diphtheria, pertussis (Td/Tdap): all adults, substitute Tdap for Td once, then Td booster every 10 years
Varicella: lifetime, 2 doses
Human papillomavirus (HPV), Female: aged 19–26, 3 doses
Human papillomavirus (HPV), Male: aged 19–21, 3 doses
Zoster: aged 60 and over, 1 dose
Measles, mumps, rubella (MMR): aged 19-47, 1 or 2 doses depending on indication; and aged 60 and over, 1 dose
Pneumococcal 13-valent conjugate (PCV13): aged 65 and older, 1 dose
Pneumococcal polysaccharide (PPSV23): aged 65 and older, 1 dose
Source: “Recommended Adult Immunization Schedule for Adults Aged 19 Years and Older, by Vaccine and Age Group, United States, 2016,” Centers for Disease Control and Prevention, February 1, 2016, “Recommended Adult Immunization Schedule—United States, 2015,” Centers for Disease Control and Prevention, 2015, Mortality and Morbidity Weekly Report, 64 (4).

17. Recommended Adult Immunizations (Figure 13.5) (Continued)
Recommended for persons with a risk factor (some covered by the Vaccine Injury Compensation Program):
Human papillomavirus (HPV), Male: aged 22–26 years, 3 doses
Pneumococcal 13-valent conjugate (PCV13): aged 19–65 years
Pneumococcal polysaccharide (PPSV23): aged 19–65 years, 1 or 2 doses depending on indication
Hepatitis A: any age, 2 or 3 doses depending on indication
Hepatitis B: any age, 3 doses
Meningococcal 4-valent conjugate (MenACWY) or polysaccharide (MPSV4): any age, 1 or more doses depending on indication
Meningococcal B (MenB): any age, 2 or 3 doses depending on vaccine
Haemophilus influenza type b (Hib): any age, 1 or 3 doses depending on indication
Source: “Recommended Adult Immunization Schedule for Adults Aged 19 Years and Older, by Vaccine and Age Group, United States, 2016,” Centers for Disease Control and Prevention, February 1, 2016, “Recommended Adult Immunization Schedule—United States, 2015,” Centers for Disease Control and Prevention, 2015, Mortality and Morbidity Weekly Report, 64 (4).

18. Risk Factors for Infection
Controllable risk factors:
Eating a balanced diet
Exercising
Getting enough sleep
Managing stress properly
Receiving vaccinations, when available
Good hygiene
Protecting skin from damage
Avoiding tobacco and environmental tobacco smoke

19. Risk Factors for Infection (2)
Uncontrollable risk factors:
Age
There is higher risk at both ends of the lifespan
Infants have passive immunity—temporary immunity from antibodies in pregnancy and breastfeeding
Genetics
Uncontrollable sociocultural factors
Overcrowded living environments
Poverty

20. Disruption of Immunity
The immune system can malfunction
Autoimmune diseases: the immune system mistakenly identifies a part of the body as “nonself” and creates an immune response, causing damage to body cells and tissues
Allergies: the body identifies a harmless foreign substance as an antigen and creates an immune response
Anaphylactic shock: life-threatening systemic allergic response requiring immediate medical attention
Stress: long-term stress, especially, can suppress the immune system, leading to illness

21. Food-Related Pathogen Transmission
More than 250 organisms are associated with food-related illnesses
Complexity of the U.S. food system means most foods travel a thousand miles or more before reaching the table
Risk of contaminated food is increased
Number of people that can be infected is increased
Difficulty of tracking infection back to the source also increases

22. Behavior-Related Pathogen Transmission
Travel
SARS outbreak (2003)
Climate change
Changing patterns of infectious disease, especially water-borne and vector-borne diseases
Sexual behavior
Three key factors in exposure to an STI: partner variables, personal susceptibility variables, and sex act variables
Illicit drug use
Use of contaminated needles and syringes
Hepatitis C

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Figure 13.6 Death rate from infectious diseases, United States, 20th century.
Sources: Adapted from “Achievements in Public Health, 1990–1999: Control of Infectious Disease” (MMWR serial online), 1999, Morbidity and Mortality Weekly Report, 48 (29), p. 621, “Trends in Infectious Disease Mortality in the United States During the 20th Century,” by G.L. Armstrong, L.A. Conn, and R.W. Pinner, 1999, Journal of the American Medical Association, 281, pp. 61–66; “Water Chlorination Principles and Practices: AWWA Manual M20,” American Water Works Association, 1973, Denver, CO: AWWA.
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24. Antibiotic Resistance
Antibiotic: drug that works by killing or preventing the growth of bacteria
Antibiotic resistance: lessened sensitivity to the effects of an antibiotic
Two factors are believed to account for antibiotic resistance:
Frequency with which resistant genes arise naturally among bacteria through mutation
Inappropriate use of antibiotics in health care, home care, and food production

25. Vaccination Controversies
As vaccine-prevented diseases become less common, people begin to question the necessity and safety of the vaccines
Serious reactions to currently recommended vaccinations are very rare
If rates of vaccination drop, the likelihood of a disease recurrence increases

26. Global Infectious Diseases
Four leading causes of global infectious disease mortality:
Pneumonia: infection of the lungs or lower respiratory tract; can be viral or bacterial
Leading cause of death in children after the first month; leading cause of death in low-income countries; and third most common cause of death for all ages worldwide
Diarrhea: kills an estimated 700,000 children per year
Tuberculosis: world’s most common infectious disease
Latent infection: not currently active but could reactivate
Malaria: mosquito-borne disease that caused 584,000 deaths in 2013

27. Infectious Diseases on Campus
Pertussis (whooping cough): infection of the respiratory tract that is highly contagious
Staphylococcus aureus skin infections: from a common bacterium carried on the skin or in the noses of healthy people
Urinary tract infections (UTIs): most common bacterial infection in women

28. Sexually Transmitted Infections
Sexually transmitted infections (STI) are spread predominantly through sexual contact
Preferred terminology over sexually transmitted disease (STD) because often there are no symptoms
Primary pathogens: viruses and bacteria

29. HIV/AIDS
Cause: Human immunodeficiency virus (HIV) attacks cells of the immune system, especially macrophages and CD4 cells (a subcategory of helper T cells)
Uses the cell’s DNA to replicate itself
Methods of transmission:
Sexual conduct
Injection drug use
Contact with infected blood or body fluids
Universal precautions taken in health care settings
Mother-to-child transmission

30. HIV/AIDS (2) Early symptoms are easily mistaken other infections
Eventually the immune system can no longer function fully, signaling the onset of acquired immune deficiency syndrome (AIDS)
Opportunistic infections produce symptoms
Rapid weight loss
Cough
Night sweats
Diarrhea
Rashes or skin blemishes
Memory loss

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Figure 13.7 Adults and children estimated to be living with HIV in 2014.
Source: “Core Epidemiology Slides,” by Joint United Nations Programme on HIV and AIDS (UNAIDS), media_asset/ _epi_core_en.ppt.
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32. HIV Testing Many kinds of tests can now be done
CDC recommends testing at least once for anyone between the ages of 13 and 64
In addition, HIV testing is recommended if you:
Are pregnant or planning to get pregnant
Have had sex with someone who is HIV positive or you did not know the person’s status
Have used IV drugs and shared drug equipment
Have exchanged sex for drugs or money
Have been diagnosed with another STI
Have been sexually assaulted

33. Management of HIV/AIDS
Antiretroviral agents do not cure the infection, but slow the rate of replication and destruction, prolonging life and improving quality of life
Drug cocktails: complicated drug combinations that combat the development of resistant viral strains
Complexity, cost, and risk of side effects increase
New prevention strategies continue to be developed
Pre-exposure prophylaxis (PrEP)
Adult male circumcision
Vaccine trials are under way
Empowering women

34. Bacterial STIs
Chlamydia: most common bacterial STI; young women at greatest risk
Gonorrhea: highest rates in young women; rates in Blacks 15 times higher than Whites
Pelvic inflammatory disease (PID): infection of uterus, fallopian tubes, and/or ovaries
Syphilis: if untreated, can lead to serious complications
Bacterial vaginosis (BV): alteration of the normal vaginal flora

35. Viral STIs
Human papillomavirus (HPV): most common STI in the U.S; more than 40 types
Genital herpes: no cure; prevention particularly important
Hepatitis: inflammation of the liver

36. Other STIs
Trichomoniasis: caused by a protozoan; transmitted from person to person by sexual activity
Candidiasis: vaginal yeast infection
Pubic lice and scabies: in adults, most often sexually transmitted

37. Prevention of Infectious Diseases
Support your immune system by adopting healthy lifestyle practices
Cover your cough
Avoid touching your face or mouth
Get an annual flu shot and booster vaccines as recommended
Minimize your use of antibiotics
If exposed, minimize chances of passing it on
For travel, learn about potential infections at your destination

38. Prevention of Infectious Diseases (2)
Practice the ABCDs of STI prevention:
A for abstain: Abstain from sex until you are ready for a long-term relationship, and abstain between relationships
B for be faithful: Be faithful and maintain a monogamous relationship
C for condoms: Use condoms
D for detection: Promote detection by being tested and following recommended screening guidelines
Take steps to prevent new diseases from taking hold in your community

39. In Review
What causes infection, and how does the body protect itself from infectious diseases?
How are infectious diseases changing?
What are the most common infectious diseases?
What are the most serious and most common sexually transmitted diseases?
How can infectious diseases be prevented?

40. Long image descriptions
Appendix A

41. figure 13.6 Death Rate, Infectious Diseases Appendix
In 1900, there were as many as 800 deaths from infectious diseases per 100,000 population in the United States
Forty states established health departments
Around 1910, the first continuous municipal use of chlorine in water took place
A sudden peak in infectious disease deaths, at over 900 per 100,000, occurred as a result of the influenza pandemic of 1918; but by 1920 the rate had fallen to below 400 per 100,000
The last human-to-human transmission of plague took place in the 1920s; the first use of penicillin took place in the early 1940s; the Salk vaccine was introduced in the 1950s; and the Vaccination Assistance Act was passed in the 1960s
From the early 1950s to the year 2000, the rate of deaths from infectious disease in the U.S. remained below 100 per 100,000 population
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42. figure 13.7 Adults and Children with HIV Appendix
In North America and Western and Central Europe, an estimated 2.4 million people were living with HIV in 2014
In the Caribbean, 280,000
In Latin America, 1.7 million
In Eastern Europe and Central Asia, 1.5 million
In Asia and the Pacific, 5 million
In the Middle East and North Africa, 24,000
In Sub-Saharan Africa, 25.8 million
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