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Immunity and Infection
Chapter 17
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The Chain of Infection
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Links in the chain
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Transmitted through a chain (six links)
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Pathogen - disease causing microorganism
Reservoir - natural environment of the pathogen: person, animal,
or environmental space such as soil or water
Portal of exit – saliva, mucous membranes, blood, feces, nose
Means of transmission
 Direct transmission – sneezing, coughing
 Indirect transmission – rats, ticks, mosquitoes
 Vectors – carrier of the pathogen from one host to
another
Portal of entry
 Direct contact with or penetration of the skin
 Inhalation through mouth or nose
 Ingestion
New host
Breaking the chain at any point can prevent disease
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Figure 17.1 The Chain of Infection
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The Body’s Defense System
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Physical and chemical barriers
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Skin, mucous membranes, respiratory tract
The Immune System
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Immunological Defenders
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Neutrophils
Macrophages – “big eaters”
Natural killer cells
Dendritic cells – eat pathogens and activate lymphocytes
Lymphocytes
 T-cells
 Helper, killer, and suppressor
 B-cells
 Memory cells
Antigens and antibodies
“Self” versus “non-self”
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Figure 17.2 The Lymphatic System
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Inflammatory and Immune Responses
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Histamine
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Dilation of blood vessels, heat, redness, swelling
The immune responses: natural and acquired
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Phase 1 – Dendritic cells are drawn to the site
Phase 2 – helper T cells multiply
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Phase 3 – killer T cells strike
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Production of killer T and B cells
Cytokines – chemical messengers
Cell-mediated immune response
Antibody-mediated immune response
Phase 4 – last phase
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Slow down activity
Debris excreted from body
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Figure 17.3 The Immune Response
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Immunity
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An infected person may never get the same
illness again
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Lymphocytes reserved by memory T and B cells =
acquired immunity
Symptoms and contagion
– when viruses are multiplying in the body
or when bacteria are actively multiplying
 Incubation
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Will not feel symptoms until the second or third phase of the
immune response cycle
period – symptoms first appear, but the
infected host may have acquired immunity
 Prodromal
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Epidemics and Pandemics
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Epidemic: a rapidly spreading (greater than
expected) disease or health-related concern
Pandemic: widespread epidemics
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Results only if three criteria are met:
1.
2.
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Little or no pre-existing immunity to the new virus
Efficient human-to-human transmission of the virus
New virus can cause illness
May occur in specific populations or regions
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Immunization
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The process of priming the body to remember
an encounter with a specific antigen
Types of vaccines
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VACCINE- Introduction of a killed or weakened
pathogen to stimulate the body to produce
antibodies
 ACTIVE IMMUNITY - person produces his or her
own antibodies to the microorganism
 PASSIVE IMMUNITY- injection of antibodies
produced by other human beings or animals
 ACQUIRED IMMUNITY- the ability of a memory
lymphocytes to remember a previous infection
(chicken pox)
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Table 17.2 Immunizations Recommended
for Teens and College Students
Immunization Issues
Vaccine shortages in the U.S.
 Vaccine safety
 Are they really worthwhile?
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Allergy: The Body’s Defense
System Gone Haywire
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Allergies: body defends against harmless
substances
 Allergens: substances that provoke allergies
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Pollen, animal dander, dust mites and
cockroaches, molds, food, insects
Allergic response: due to antibody
Immunoglobulin E (IgE)
 Anaphylaxis
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Figure 17.4 The Allergic Response
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Dealing with Allergies
Avoidance
 Medication
 Immunotherapy or “allergy shots”
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Figure 17.5 Pathogens
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Pathogens and Disease
Pathogens: bacteria, viruses, fungi,
protozoa, parasitic worms, prions
 Bacterium – microscopic single-celled organism
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Pneumonia
Meningitis
Strep throat and other streptococcal infections
Toxic shock syndrome and other staphylococcal infections
Tuberculosis
Tickborne infections
Ulcers
Other bacterial infections
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Tetanus, Clostridium difficile, pertussis, urinary tract infections
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Antibiotic Treatment
Actions of antibiotics
 Antibiotic resistance
 Proper antibiotics usage
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 Don’t
take an antibiotic every time you are
sick; effective for bacteria, ineffective for virus
 Use antibiotics as directed; finish full course
 Never take an antibiotic without an
prescription
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Viruses
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Viruses are parasites – they take what they need
Most common contagious disease
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Common cold
Influenza
Measles, mumps, rubella
Chicken pox, cold sores, and other herpesvirus infections
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Varicella-zoster virus
Herpes simplex virus (HSV) types 1 and 2
Epstein-Barr virus (EBV) (causes mononucleosis)
Viral encephalitis
Viral hepatitis (A, B, C)
Poliomyelitis
Rabies
Human papillomavirus (HPV)
Treating viral illnesses
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Figure 17.6 Life Cycle of a Virus
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Types of Pathogens
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Fungi
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Protozoa
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Microscopic single-celled animal: malaria, giardiasis, trichomoniasis,
trypanosomiasis, amoebic dysentery
Parasitic worms
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Primitive plant – yeast infections, athlete’s foot, jock itch, ringworm
Candida albicans
Largest organism that can enter the body to cause infection: tapeworm,
hookworm, pinworm (most common)
Prions
Fatal degenerative disorders of the CNS linked to “proteinaceous
infectious particles” or prions
 Lack DNA and RNA
 Transmissible spongiform encephalopathies (TSEs)
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Spongelike holes in the brain
Creutzfeldt-Jakob disease in humans
Bovine spongiform encephalopathy (BSE) or “mad cow disease” in cattle
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Emerging Infectious Diseases
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Selected infections of concern:
 West
Nile virus
 Severe acute respiratory syndrome (SARS)
 Rotavirus
 Escherichia coli 0157:H7
 Hantavirus
 Ebola
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Factors Contributing to Emerging
Infections
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Drug resistance
Poverty
Breakdown of public health measures
Travel and commerce
Mass food production and distribution
Human behaviors
Bioterrorism
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Other Immune Disorders: Cancer
and Autoimmune Diseases
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If the immune system breaks down
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Getting older
Certain immune disorders (HIV)
Chemotherapy
Autoimmune diseases
 Rheumatoid
arthritis
 Systemic lupus erythematosus
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Support Your Immune System
How to support your immune system
General guidelines
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Balanced diet
Enough sleep
Exercise
Don’t smoke
Moderation of alcohol
Wash your hands
Avoid contact with contagious people
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Plenty of clean water
Avoid contact with vermin
Practice safe sex
Do not use injectable drugs
Vaccinations
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Chapter 17
IMMUNITY AND INFECTION
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