Infectious Diseases

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Chapter 21

• Infectious Diseases

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21.1 What are infectious diseases?

• One that is caused by an agent that can pass from
  one organism to another.
• Communicable disease is an infectious disease
  that is passed from one person to another.

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What causes infectious diseases?

• Infectious diseases are caused by pathogens- any
  agent that causes disease.
• In the U.S. the most common pathogens are viruses
  and bacteria.
• Others are fungi, protists, and parasitic worms.
• These must be seem under a microscope

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Bacteria

• Very simple living things
• Each bacterium is a single cell much smaller than
  the ones that make up your body
• Common diseases caused by bacteria are strep
  throat, food poisoning, and urinary-tract
  infections.

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Viruses

• A microscopic disease-causing particle consisting
  of genetic material and a protein coat.
• Cannot reproduce without first invading a living
  cell
• Once inside the cell the viruses genetic material
  acts as a program that directs the cell to make
  more viruses.
• Viruses are specialized to infect only certain
  types of cells. Some diseases that animals can
  get cannot be transmitted to humans.
• Some common diseases caused by viruses are the
  common cold, the flu, cold sores, and measles.

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How are infectious diseases spread?

• In order for the disease to spread to you, a
  pathogen must leave the body one living thing and
  enter your body.
• One way this happens is through the air. This
  happens when one sick person sneezes and
  thousands of tiny drops of mucus and saliva are
  sprayed into the air.
• Someone nearby breaths the droplets and becomes
  infected.

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How spread, cont

• Contact with contaminated objects
• A sick person may leave bacteria or viruses on
  objects like doorknobs, telephones, drinking
  glasses, toothbrushes, towels, and combs.
• Some bacteria or viruses do not live long on
  these objects and others live long enough for
  others to contract the illness.

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How spread, cont

• Person to person
• Shaking hands, kissing, touching the cold sores
  of another person

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cont

• Animals that spread disease
• Humans can get ringworm from handling an infected
  dog or cat
• Possible to get rabies from the bite of an
  infected animal
• A type of encephalitis, inflammation of the
  brain, is spread by mosquitoes
• Lyme disease is a serious bacterial infection
  carried by ticks
• Hantaan virus causes a deadly hemorrhagic fever
  and can be transmitted through contact with feces
  from infected rodents.

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cont

• Food and water
• Usually happens when feces of an infected person
  or animal enters the water system
• People who work with food are required by law to
  wash hands after going to the bathroom
• Also important to wash fruits and vegetables
  thoroughly, because they are grown in fertilized
  soil. Fertilization material may contain feces.
• Large number of bacteria in food may cause food
  poisoning
• To keep your risk of food poisoning low, wash
  hands while cooking, avoid cross contamination,
  refrigerate leftovers right away.
• While camping, do not drink water from lakes and
  streams without purifying it first.

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21.2 Fighting disease

• Infection and disease
• If pathogens do enter your system and begin to
  spread and reproduce, then you are infected
• Being infected is not the same as having the
  disease or being sick
• Your body can put up a good fight against them
  and you may net even get sick
• But you can still get someone else sick

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disease

• If your defenses cannot stop the pathogen quickly
  enough, you may begin to feel sick
• A pathogen can cause disease when it is able to
  multiply in your body and cause damage to your
  cells and tissue
• You then begin to experience symptoms of being
  sick

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Defenses against infection

• Your body has ways of coping with disease causing
  bacteria, viruses, and other pathogens
• Skin- upper layers are make up of dead skin cells
  filled with a tough water-proof protein.
• As you shed dead skin cells you also shed
  bacteria, viruses, and other pathogens on your
  skin

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Defenses, cont

• Chemical warfare on germs
• Many chemical substances in your body act to
  destroy pathogens
• Examples are sweat, oils, saliva, and tears

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Defense, cont

• Stomach acids
• If a pathogen enters the body through the mouth,
  travels to the stomach, than the stomach must
  fight it.
• Stomach acid is 10X stronger than pure lemon
  juice and can also protect your from disease and
  digest your food
• Mucous membranes
• Tissue linings in the openings of your body
• Inside your mouth and nose (cilia)

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Defense, cont

• Inflammation
• When you get a cut and it becomes red and
  infected, that inflammation is the bodies
  reaction to the pathogen
• Helpful microorganisms
• Some microorganisms and helpful and guard you
  against disease
• Harmless bacteria lives on your skin and in your
  mouth

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Defense, cont

• The immune system
• See figure 21-7 on p 448
• All different kinds of cells launch a war on
  the pathogen and an immune response is activated.

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Weapons of the immune response

• Our body has many different kinds of immune cells
  waiting to do battle with pathogens that are
  trying to make us sick.
• There are 2 main types of cells
• T-cells and B-cells

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T-cells

• Mobilize to fight pathogens directly
• These T-cells divide into many cells and attack
  the invaders
• Helper T-cells are the first line of defense
• Then Suppressor T-cells turn off the immune
  response after the pathogen has been defeated

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Antibodies

• B-cells
• Their job is to produce antibodies
• Y shaped molecules that stick to and cover
  foreign molecules in the body.
• The virus or bacteria have little chance at
  attacking body cells if covered with antibodies

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Immunity

• Means when you have had certain diseases, you
  cannot get them again
• Protection against developing a certain disease
  is called immunity
• There are three basic types

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Innate immunity

• Immune to certain diseases just because you are
  who you are

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Active immunity

• Once your body has launched an all out war, your
  body is ready to fight the invader much more
  quickly next time.
• They have memory cells that kick into gear
• Two ways to get active immunity
• To actually get the disease
• To get immunized against the disease
• A way of tricking your body into thinking it
  already had the disease

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Passive immunity

• You have received antibodies from another person
  or animal that have made you resistant to the
  disease
• May get them fro your mother before birth
• May get them from a serum of an animal if you
  have been bitten by an animal with rabies or been
  bitten by a poisonous snake.

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21.3 common infectious diseases

• Viral diseases
• Colds, influenza, cold sores, warts,
  mononucleosis, chickenpox, and AIDS

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Preventing viral diseases

• A number of viral diseases that were common in
  the 40s and 50s are not rare
• Polio, measles, mumps, and rubella
• Today most children are immunized against these
  diseases
• However measles is an exception and it is making
  a comeback and it is recommended to get immunized
  before college
• Most deadly viral disease now is AIDS

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Curing viral diseases

• Antibiotics
• Prevents the cell division and growth of living
  bacterial cells

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Common infectious diseases

• The common cold
• Influenza
• Chicken pox
• Measles
• Mononucleosis
• Hepatitis
• See chart and book for facts and figures,
  symptoms and signs, and treatment of these
  diseases

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Common bacterial diseases

• Strep throat
• Tuberculosis
• Sinus infections
• Malaria
• Hookworm, ringworm, tapeworm, pinworm, roundworm.