When you have a common communicable infectious disease like a cold or the flu, do you do anything to protect others, such as members of your family, from catching your illness? If so, what? Would you do anything differently after reading this chapter? If so, what? Would you use CAM to help “cure” your cold? Why or why not?
Chapter 14
Infection,
Immunity, and
Noninfectious
Disease
Diseases
• Infectious diseases are caused by pathogens, such as
bacteria, rickettsias, viruses, fungi, and parasitic worms.
• Noninfectious diseases are caused by genetic
abnormalities, interactions between heredity and
environmental factors, or environment alone.
Noninfectious Diseases:
Genetic Diseases
• Two types
– Inherited diseases
– Diseases cause by errors when egg or sperm
(gametes) form
• Inherited diseases are transmitted only by gene transfer
from parents to offspring.
– Caused by disorders of genes; defects arise through
mutations
– Cystic fibrosis, Duchenne/Becker muscular
dystrophy, sickle cell disease, Down syndrome
Noninfectious Diseases:
Genetic Diseases
• Diseases caused by errors in sex cell division
– Down syndrome
• Affects approximately 1 in 1,000 newborns
• A child with Down syndrome has three instead of
the normal two chromosome #21s.
• Risk of having a baby with Down syndrome
increases dramatically in women who are over 30
years of age.
Noninfectious Disease: Genetic
Diseases
• Diseases caused by errors in sex cell division
– Down syndrome
• Mental retardation
• Developmental delays
• Physical defects
– Stocky build
– Short hands
– Flattened facial features
Noninfectious Disease
• Conditions caused by interaction of genes and
environment include:
– Asthma
– Ulcers
– Diabetes mellitus
– Migraine headaches
– Cardiovascular disease
– Cancer
Noninfectious Disease
• Certain conditions, such as temporomandibular
disorder and carpal tunnel syndrome are caused by the
ways in which people use their bodies.
Trends in Infectious Disease
• Primary causes of death in the United States are
noninfectious diseases.
• In 2010, influenza and pneumonia were the only
infectious diseases among the top 15 killers of
Americans.
• Worldwide, however, infectious diseases are the
leading causes of death.
• Misuse of antibiotics has created resistant bacteria.
The Chain of Infection
• Infection results from interaction between a pathogen
(the agent of infection) and a host (the organism that
supports the growth of the pathogen).
• The link between the pathogen and the host is
transmission, the route by which the pathogen gets to
the host.
The Chain of Infection
The Chain of Infection
• Pathogen
– Severity of an infectious disease depends on:
• Type of pathogen
• Virulence of pathogen
• Pathogen’s ability to multiply and spread within
body
• Pathogen’s ability to combat the body’s defenses
• The body’s reaction to the pathogen
The Chain of Infection
• Pathogen
– Common pathogens
• Bacteria (e.g., rickettsias)
• Viruses (e.g., HIV)
• Fungi (e.g., athlete’s foot)
• Protozoans (e.g., malaria)
• Parasites (e.g., roundworms)
• Arthropods (e.g., mosquitoes)
The Chain of Infection
• Reservoir
– Environment in which the pathogen lives
• Portal of exit
– Means by which the pathogen leaves the
infected host
• Transmission
– Communicable diseases are infectious diseases
that spread from person to person.
– Noncommunicable diseases are not spread from
person to person.
The Chain of Infection
• Transmission
– Noncommunicable diseases
• Infections can be caused by
– Growth of bacteria that normally inhabit the
body
– Ingestion of toxins or poisons produced by some
bacteria
The Chain of Infection
• Transmission
– Noncommunicable diseases
• Infection with pathogens from environmental or
animal sources
– Lyme disease, an example of an infection
contracted from an animal source, is
transmitted by ticks harboring the bacterial
pathogen from infected animals, such as mice
and deer.
The Chain of Infection
• Transmission
– Communicable diseases
• Transmitted from person to person:
– By direct or indirect contact
– By a common vehicle (food, water, a common
drinking glass)
– Through the air
– By vectors (organisms other than humans,
such as mosquitoes)
The Chain of Infection
• Portal of entry
– Means by which a pathogen enters an
uninfected host
• Establishment
– Establishment of a new infection in a
previously uninfected host
The Chain of Infection
• The host
– Stress and lack of sleep can reduce resistance to
infection.
– High-intensity or exhaustive exercise can suppress
the immune system.
– Race and age affect resistance or susceptibility to
disease.
– Presence of other diseases can weaken the body’s
defense mechanisms.
Immunity
• Immunity is protection from disease.
• The two types of immunity are
– Nonspecific—comprises a variety of defense
mechanisms that combat any type of damage to the
body, including the invasion of infectious agents
– Specific—function of the immune system; made up
of cells residing in tissues scattered throughout the
body; these cells are able to react to specific
pathogens and foreign molecules
Nonspecific Immunity
• The skin and mucous membranes
– Intact skin: mechanical barrier
– Mucus: keeps membranes moist and traps foreign
particles and organisms
– Cilia: in upper respiratory tract move mucus to the
back of the mouth, to be swallowed
– Tears: chemical defense
– Lysozyme: found in saliva
– Stomach acid: can kill most of the microorganisms
that are in food
Nonspecific Immunity
• White blood cells and phagocytosis
– White blood cells (leukocytes) ingest foreign cells
and debris in process called phagocytosis.
– Neutrophils and macrophages are leukocytes that
protect the body through phagocytosis.
– Lymphocytes are another type of leukocyte.
Nonspecific Immunity
• Lymphatic system
– Comprises vessels and nodes through which tissue
fluid (lymph) flows
• Lymphocytes
• Tonsils
• Spleen
• Thymus
– Removes microorganisms and other foreign
substances from tissue fluid
Nonspecific Immunity
• Inflammation
– Inflammation—a series of responses that occur when
the body is harmed by occurrences such as bacterial
or viral invasion (infection), cuts, chemical damage,
and burns
– The response can be local (affecting the immediate
area that is harmed) or systemic (affecting the entire
body).
Nonspecific Immunity
• Natural killer cells
– Specialized white blood cells that attack cancer cells
and body cells infected with viruses
• Interferons
– Proteins released from cells that are infected with a
virus
– Stimulate uninfected cells to produce a protein that
breaks down hereditary material of virus
– Damaged viruses cannot infect cells and make
copies of themselves.
Specific Immunity
• Antigens: the triggers of specific immunity
– Antigens are usually foreign, or “nonself,” proteins.
– Antigens also can be noninfectious agents such as
pollens or tissue transplants.
– Sometimes, the body perceives its own cells as
foreign and begins attacking and destroying them,
causing autoimmune diseases such as rheumatoid
arthritis.
Specific Immunity
• Antibody-mediated immunity
– Responds to extracellular antigens
• Bacteria and the toxins they produce
– Antibodies interact in lock-and-key fashion with
antigens.
• This binding stimulates the inflammatory
response and phagocytosis.
• Specialized white blood cells, B lymphocytes (B
cells), are involved.
Specific Immunity
• Cell-mediated immunity
– Reacts to intracellular antigens
• Viruses, fungi, few types of bacteria, and
parasites
– Also reacts against foreign tissue transplants and
controls tumor cell growth
Specific Immunity
• Cell-mediated immunity
–Cells involved:
• Cytotoxic T cells—destroy invading intracellular
pathogens by secreting chemicals that break apart
infected host cells
• Helper T cells—secrete chemicals that enhance
the activity of cytotoxic T cells and suppressor T
cells and attract phagocytes to the area
Specific Immunity
• Cell-mediated immunity
– Cells involved:
• Suppressor T cells—shut down the immune
system
• Memory T cells—act like memory B cells,
responding rapidly and forcefully to future
encounters with the same antigens that elicited
the response
Immunity
• Specific and nonspecific mechanisms of the immune
system work together to prevent infection or combat
infection once it occurs.
Protection Against Infectious Diseases
• Inborn immunity—inherited
• Acquired immunity—develops over a lifetime
• Active acquired immunity—an immune system response
developed as a result of contact with a pathogen, which
includes development of memory B cells or T cells; e.g.,
vaccination
• Passive acquired immunity—conferred when a person is
given antibodies; can be acquired naturally when
antibodies from a mother cross the placenta and enter the
bloodstream of a developing fetus
Drugs That Combat Infection
• Antibiotics—kill bacteria or inhibit their growth, but do
nothing to combat viral infections; misuse may result in
producing antibiotic-resistant bacteria
• Antifungal drugs—treat fungal infections; other
medications have been developed to treat parasites and
protozoans
• Antiviral drug—development has been slow because
viruses reside inside cells; an effective drug must kill
the virus without harming its host
Sexually Transmitted Infections
• STIs are spread from person to person by intimate
contact that occurs during sexual activity, primarily
sexual intercourse.
• Pathogens that cause STIs pass from infected sores,
secretions, or tissues of an infected person’s
reproductive tract.
• Most STIs are caused by viruses and bacteria; other
causes include yeast, protozoans, mites, and lice.
Sexually Transmitted Infections
Caused by Viruses
• Cannot be cured
• Three sexually transmitted viruses have been implicated
in the development of certain cancers: HIV, HPV, and
HBV (hepatitis B).
• Human immunodeficiency virus (HIV)
– HIV infection progresses to AIDS.
– In the United States, the AIDS epidemic primarily
affects men who have sex with men.
– Globally, approximately 33.2 million people are living
with HIV.
Sexually Transmitted Infections Caused by
Viruses
• Human immunodeficiency virus (HIV)
– Being infected with HIV does not mean a person has
AIDS; HIV progresses to AIDS.
– Approximately 1 to 3 weeks after infection with
HIV, most people experience flu-like symptoms that
last 1 to 2 weeks.
• Fever, sore throat, headache, rash, and general
weakness and discomfort
– Further symptoms may not develop for 8 to 10 years
(asymptomatic phase).
Sexually Transmitted Infections
Caused by Viruses
• Human immunodeficiency virus (HIV)
– The symptomatic phase of HIV disease usually
begins when the helper T cell numbers have
declined to about 500 cells or fewer per cubic
millimeter of blood (500 cells/mm3). Normal helper
T cell numbers are about 800 to 1200 cells/mm3.
– Symptomatic phase of HIV infection may begin
with fever, night sweats, headache, fatigue, and
diarrhea.
Sexually Transmitted Infections
Caused by Viruses
• Human immunodeficiency virus (HIV)
– A person is usually diagnosed with AIDS when T
cell count drops to 200 cells/mm3, and he or she
develops certain opportunistic infections such as
pneumonia, toxoplasmosis, Kaposi’s sarcoma, and
cytomegalovirus retinitis.
– Wasting syndrome
Sexually Transmitted Infections
Caused by Viruses
• Human immunodeficiency virus (HIV)
– Transmitted through sexual contact with infected
person
– Direct contact with blood, semen, vaginal secretions
– Tears in skin and mucous membranes make it easier
for virus to enter body.
– Any sexual behavior that results in contact with
infected blood, semen, or vaginal secretions is risky.
Sexually Transmitted Infections
Caused by Viruses
• Human immunodeficiency virus (HIV)
– Exposure to infected blood or blood products
• Sharing of contaminated needles and syringes by
injecting drug abusers
• Blood transfusions
– Transfer via placenta during fetal development and
during the labor process
– Breastfeeding
Sexually Transmitted Infections
Caused by Viruses
• Human immunodeficiency virus (HIV)
– HIV is not transmitted through
• Casual contact with infected people
• Sharing things such as telephones, combs, and
eating utensils or using drinking fountains
• Kissing does not appear to transmit HIV.
• Mosquitoes do not transmit HIV.
Sexually Transmitted Infections Caused
by Viruses
• Human immunodeficiency virus (HIV)
– There is no cure for HIV infection and AIDS.
– No effective vaccine has been produced.
– Approved anti-HIV drugs interfere with viral
copying, but the virus mutates quickly and these
drugs soon become ineffective.
• A combination of drugs is used and appears to
work best to retard HIV.
• Highly active antiretroviral therapy (HAART)
seems effective, but has side effects.
• HAART includes new fusion inhibitor drugs.
Sexually Transmitted Infections Caused by
Viruses
• Genital herpes
– HSV-1 causes cold sores around the lips.
– HSV-2 causes sores on genital and anal areas.
• Each viral type can infect both oral and genital
areas.
– After initial infection, incubation period lasts about
1 week.
– Signs and symptoms
• Skin lesions that become filled with fluid that
contains the virus and eventually open
• Headache, fever, weakness, and muscle pain
Sexually Transmitted Infections Caused
by Viruses
• Genital herpes
– Recurrences usually occur 5 to 8 times per year;
stress, lack of sleep are triggers.
– A person without symptoms may shed herpes viral
particles, infecting others.
– Treatment with acyclovir reduces recurrence rate.
– Herpes virus can infect newborns during delivery
and cause serious damage to the infant’s nervous
system or even cause death.
Sexually Transmitted Infections
Caused by Viruses
• Genital warts
– Human papillomavirus (HPV) causes warts.
– Genital warts are not painful, but some types are
associated with cervical cancer.
– Incidence of genital warts is increasing.
– Treatments include medications, freezing,
cauterizing, lasers, and anti-viral injections.
– Vaccine protects against four major types of HPV.
Sexually Transmitted Infections
Caused by Bacteria
• Can be cured
• If not treated, not treated promptly, or not treated
properly, bacterial STIs can damage the reproductive
system, possibly causing infertility.
• Syphilis
• Gonorrhea
• Chlamydial infections
Sexually Transmitted Infections
Caused by Bacteria
• Syphilis
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–
–
–
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Syphilis is caused by a bacterium, T. pallidum.
Incidence of syphilis is increasing.
Incubation period lasts about 3 weeks.
Syphilis has three stages.
Syphilis can damage the brain, heart, and blood
vessels, resulting in paralysis and death.
– Penicillin kills T. pallidum.
Sexually Transmitted Infections
Caused by Bacteria
• Syphilis
– Primary: development of a chancre
– Secondary: After the chancre heals, signs and
symptoms of secondary syphilis occur.
• Usually includes sore throat, weakness, muscle
pain, weight loss, fever, headache, and a rash that
covers the body
– Tertiary stage: tissue-destroying lesions called
gummas develop; gummas not only affect the skin
but can destroy any type of tissue in the body, even
bones.
Sexually Transmitted Infections Caused
by Bacteria
• Gonorrhea
– Gonorrhea is caused by the bacterium Neisseria
gonorrhoeae.
– Most common in those aged 15 to 29 years
– Incubation period is 2 to 8 days.
– Most common cause of pelvic inflammatory disease
(PID) in women
– Gonorrhea is treated with antibiotics.
– It may cause blindness in newborns.
Sexually Transmitted Infections
Caused by Bacteria
• Chlamydial infections
– One of the most prevalent STIs in the United States
– Caused by the bacterium Chlamydia trachomatis
– Mild symptoms in men
• Painful urination and whitish or clear discharge
from urethra
• Bacteria may travel to other parts of the male
reproductive tract and cause inflammation of
epididymides.
Sexually Transmitted Infections
Caused by Bacteria
• Chlamydial infections
– Produces no symptoms in 70% of women
• PID is most serious complication.
• Can infect newborn during birth process and
cause eye and lung damage
– Treated with antibiotics
Other Sexually Transmitted Infections
• Trichomonas vaginalis infections
– Protozoan infection
– Women are 20 times more likely to contract “trich”
infections than men.
– Organism lives in glucose-rich vaginal surface
tissues.
• Normal acid environment of vagina and male
urethra inhibits growth of T. vaginalis.
• If vagina becomes less acid, protozoan can grow
there.
• Infection almost always contracted by having sex
with infected person.
Other Sexually Transmitted Infections
• Trichomonas vaginalis infections
– Signs and symptoms
• In women, abnormal, bad-smelling discharge that
may be thin and foamy
– Itching, burning, swelling, redness, and
tenderness of vulva
• In men, painful urination and urgency to urinate
• Men become infected, but infection usually
subsides without treatment.
Other Sexually Transmitted Infections
• Yeast infections
– Candidiasis
• Acquired through intercourse with infected
person
• Develops in women who are taking antibiotics or
during pregnancy
• Often affects women with poorly controlled
diabetes or other STIs
– Signs and symptoms
• Soreness, burning, irritation, swelling, and a
white vaginal discharge that looks like cottage
cheese
Other Sexually Transmitted Infections
• Pubic lice
– Infestation of lice in pubic area is commonly called
“having crabs.”
• Spread primarily by sexual contact
• Sucks the blood of their host; females lay eggs in
pubic hair.
• Causes itching, swelling, redness, and irritation
• OTC and prescription medications available
Other Sexually Transmitted Infections
• Scabies
– Scabies or “itch mites” burrow into the skin, making
thin, red lines, or bumps in the skin.
• Scabies lay eggs in skin.
• Can be spread through sexual intercourse and also
through bed linens, towels, pillows, or other
household items
• Treatment is with prescription medications.
Protecting Yourself Against STIs
• Anyone who is sexually active can contract an STI.
• The most effective strategies are to abstain from sexual
activity and drug use.
• Limiting the number of sex partners reduces risk.
• Avoid sharing needles and syringes if you are injecting
drugs and avoid sex while under the influence of drugs
or alcohol.
• Always using latex condoms during sexual activity also
reduces risk.
Across the Life Span
• Noninfectious diseases and conditions present at birth
are termed birth defects.
• Some birth defects are caused by environmental
influences.
– Teratogens, substances such as alcohol, can enter the
fetus and cause birth defects.
• Some birth defects are inherited.
– Metabolic diseases (e.g., Tay-Sachs disease)
Across the Life Span
• Most genetic diseases strike early in life.
– Huntington’s chorea does not appear until age 40.
– Alzheimer’s has a strong genetic link.
• Many childhood infections are no longer common due
to routine vaccination of children.
• Sexually active adolescents and young adults are at
highest risk for contracting STIs due to unprotected
sex.
• Infections are a major cause of illness and death among
the elderly.
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