DISEASES CAUSED BY BACTERIA AND VIRUSES

Chapter 19 Pgs 485-490

BACTERIAL DISEASE IN HUMANS

Bacteria produce disease in one of two general ways. Some bacteria damage the cells and tissues of the infected organism directly by breaking down the cells for food. Tuberculosis—is inhaled through the lungs, where

it destroys the lung tissue. Other bacteria release toxins (poisons) that

travel throughout the body interfering with the normal activity of the host. Streptococcus (strep throat)—releases toxins into

the bloodstream: can also cause scarlet fever.

PREVENTING BACTERIAL DISEASE

Many bacterial diseases can be prevented by stimulating the body’s immune system with vaccines. Vaccine—preparation of weakened or killed

pathogens Prompts the body to produce immunity to the disease

If a bacterial infection does occur, a number of drugs can be used to attack and destroy the invading bacteria. Antibiotics—compounds that block the growth and

reproduction of bacteria.

CONTROLLING BACTERIA

Various methods1. Sterilization by Heat—most bacteria cannot

survive high temperatures for a long period of time, so most can be killed by exposure to high heat.

2. Disinfectants—chemical solutions that kill pathogenic bacteria. Overuse increases the likelihood that common bacteria will evolve to become resistant to them.

3. Food Storage—Food stored at low temperatures will stay fresh longer because the bacteria will take longer to multiply.

VIRAL DISEASE IN HUMANS

Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium.

In many viral infections, viruses attack and destroy certain cells in the body, causing the symptoms of the disease.

Cannot be treated with antibiotics.

Best protection lies in prevention.

VIRAL DISEASE IN ANIMALS

Viruses produce serious animal diseases as well.

Foot-and-mouth disease that swept through Europe in the late 1990—thousands of cattle were destroyed.

Some animal viruses can cause cancer.

VIRAL DISEASE IN PLANTS

Many viruses infect plants. Serious threat to many

agricultural crops. Many plant viruses are

spread by insects. Feeding action of an insect

pest often provides a perfect opportunity for viral infections to spread.

VIROIDS AND PRIONS

Viruslike particles that can also cause disease

1. Viroids—cause disease in plants1. Single-stranded RNA molecules that have no surrounding

capsids2. Viroids enter an infected cell and direct the synthesis of new

viroids3. Then disrupt the metabolism of the plant cell

and stunt the growth of the entire plant

2. Prions—cause disease in animals1. Cause disease by forming protein clumps2. Contain no DNA or RNA3. Strong evidence that mad cow disease is caused by prions

PICTURE CREDITS

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