Chapter 19-3: Diseases Caused by Bacteria and Viruses

• Bacteria and viruses are everywhere in nature, but only a few cause disease.

• Disease-causing agents are called pathogens.

Bacterial Disease in Humans• Many bacteria live

on and within our bodies.

• Growth of pathogenic bacteria disrupts the body’s equilibrium by interfering with its normal activities and producing disease.

How do bacteria cause disease?

1. They damage the cells and tissues of the infected organism directly by breaking down the cells for food.

2. Or they release toxins (poisons) that travel throughout the body interfering with the normal activity of the host.

Preventing Bacterial Disease

• Many bacterial diseases can be prevented by vaccines (a preparation of weakened or killed pathogens).

• When injected into the body, a vaccine may prompt the body’s immunity to the disease.

Treating Bacterial Disease• If infection occurs, drugs can

be used to destroy bacteria. • These drugs include

antibiotics, which are compounds that block the growth and reproduction of bacteria.

• A reason for increased human life expectancy is an increased understanding of how to prevent and cure bacterial infections.

Viral Disease in Humans• Viruses produce disease by disrupting the

body's normal equilibrium.• How do viruses cause disease?

1. Lytic: viruses can attack and destroy certain cells in the body, causing symptoms of the disease.

2. Lysogenic: other viruses cause infected cells to change patterns of growth and development.

Viral Disease Prevention/Treatment

• Vaccines are the best protection against viral diseases, but only work if used before an infection begins.

• Viral diseases cannot be treated with antibiotics.

• Symptoms may be treated with over-the-counter medicines.

Bacterial Diseases Viral Diseases

• Lyme disease

• Tetanus

• Tuberculosis

• Bacterial meningitis

• Strep throat

• Common cold

• Influenza

• AIDS

• Chicken pox

• Hepatitis B

• West Nile

40-1: Infectious Disease

• Disease: any change, other than an injury, that disrupts the normal function of the bodyo Can be inherited, caused

by materials in the environment, or produced by pathogens (disease causing agents).

The Germ Theory of Disease• Idea that infectious

diseases are caused by microorganisms, or germs

• Observed by French chemist Louis Pasteur and German bacteriologist Robert Koch

Koch’s Postulates• Series of guidelines used

to identify the microorganism that causes a specific disease

• These rules are important because identifying pathogens that cause disease is the first step toward prevention or cures.

The Postulates (or rules)1. The pathogen should always be found in a

sick organism, not a healthy one.2. It must be isolated and grown in the lab.3. When injected in a new host, it should cause

the same original disease.4. The injected pathogen should be isolated

from the new host and identical to the original pathogen.

Agents of Disease• For many pathogens, the human body

provides just the right conditions for growth.

Agent Example

Viruses Common cold, flu, warts

Bacteria Botulism, Anthrax

Protists Malaria, African Sleeping Sickness

Worms Schistosoma

Fungi Athletes foot, ringworm

Fungi: athlete's foot

Worms:

SchistosomaProtists:

Trypanosoma

How Diseases Are Spread

• Coughing, sneezing, or physical contact

• Contaminated food or water

• Vectors: infected animals that carry pathogens from person to person

Fighting Infectious Diseases• Antibiotics: compound that blocks the growth

and reproduction of bacteria (no effect on viruses)

• Over-the-Counter Drugs: treat only the symptoms, but do not actually treat the cause of the infection