1. Copyright Pearson Prentice Hall
Biology
Copyright Pearson Prentice Hall

2. 19–3 Diseases Caused by Bacteria and Viruses (p485-490)
Photo Credit: ©National Institute for Biological Standards and Control, England/Photo Researchers, Inc.
Copyright Pearson Prentice Hall

3. 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.
Copyright Pearson Prentice Hall

4. Bacterial Disease in Humans
19–3 Diseases Caused by
Bacteria and Viruses
Bacterial Disease in Humans
Bacterial Disease in Humans
Growth of pathogenic bacteria disrupts the body’s equilibrium by interfering with its normal activities and producing disease.
Copyright Pearson Prentice Hall

5. 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.
Other bacteria release toxins (poisons) that travel throughout the body interfering with the normal activity of the host.
19–3 Diseases Caused by
Bacteria and Viruses
Bacterial Disease in Humans
Copyright Pearson Prentice Hall

6. Bacterial Disease in Humans
1. Breaking down the cells for food
Tuberculosis
The bacterium Mycobacterium tuberculosis, which causes tuberculosis, is inhaled into the lungs, where it destroys the lung tissue. The bacterium also may enter a blood vessel and travel to new sites in the body where it destroys more tissue.

7. Bacterial Disease in Humans
2. Releasing toxins
Streptococcus Infections
Release enzymes that destroy connective and muscle tissues.
Strept throat, pneumonia, impetigo
Complication of a strep infection can be scarlet fever - this is when the bacterium releases a toxin that gets into the blood stream. A severe immune response to streptococci can lead to rheumatic fever.
Copyright Pearson Prentice Hall

8. Streptococcus Infection
Large-scale cell death and tissue destruction is “flesh eating” disease.

9. Bacterial Disease in Humans
Food Poisoning
Salmonella
Staphylococcus
Clostridium botulinum

10. Bacterial Disease in Humans
Bacterial Diseases
Bacteria cause disease in the body. Some of the diseases caused by pathogenic bacteria are listed in the table.
Copyright Pearson Prentice Hall

11. Bacterial Disease in Humans
Many bacterial diseases can be prevented by vaccines.
A vaccine is a preparation of weakened or killed pathogens.
When injected into the body, a virus may prompt the body’s immunity to the disease.
Immunity is the body's ability to destroy new pathogens.
Copyright Pearson Prentice Hall

12. Bacterial Disease in Humans
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. ex.: penicillin and tetracycline
A reason for increased human life expectancy is an increased understanding of how to prevent and cure bacterial infections.
However, bacteria can develop antibiotic resistance by
spontaneous or induced genetic mutations
acquisition of resistance genes from other bacteria (ex. by conjugation)
Limiting antibiotic uses limit development of bacteria resistance
Copyright Pearson Prentice Hall

13. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Controlling Bacteria
There are various methods used to control bacterial growth, including:
sterilization
disinfectants
food processing
Copyright Pearson Prentice Hall

14. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Controlling Bacteria
Sterilization by Heat 
Sterilization destroys bacteria by subjecting them to great heat.
Most bacteria are killed by prolonged high temperatures.
Copyright Pearson Prentice Hall

15. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Controlling Bacteria
Disinfectants 
Disinfectants are chemical solutions that kill pathogenic bacteria.
They are used to clean rooms where bacteria may flourish.
Copyright Pearson Prentice Hall

16. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Controlling Bacteria
Food Storage and Processing
Bacteria can cause food to spoil.
Refrigerated food stays fresh longer because the bacteria will take longer to multiply.
Boiling, frying, or steaming can sterilize certain foods.
Copyright Pearson Prentice Hall

17. Viral Disease in Humans
19–3 Diseases Caused by
Bacteria and Viruses
Viral Disease in Humans
Like bacteria, viruses produce disease by disrupting the body's normal equilibrium.
Viral Disease in Humans
Copyright Pearson Prentice Hall

18. Viral Disease in Humans
Viruses can attack and destroy certain cells in the body, causing symptoms of the disease.
Other viruses cause infected cells to change patterns of growth and development.
Copyright Pearson Prentice Hall

19. Viral Disease in Humans
Viral diseases cannot be treated with antibiotics.
Vaccines are often the best protection against most diseases.
Most vaccines work only if used before an infection begins.
Symptoms may be treated with over-the-counter medicines.
Once a viral disease has been contracted, it may be too late to control the infection. However, sometimes the symptoms of the infection can be treated.
Copyright Pearson Prentice Hall

20. Viral Disease in Humans
Viral Diseases
Viruses cause disease in the body. Some of the diseases caused by viruses are listed in the table.
Copyright Pearson Prentice Hall

21. Viral Disease in Plants and Animals
19–3 Diseases Caused by
Bacteria and Viruses
Viral Disease in Plants and Animals
Viral Disease in Plants and Animals
Viruses produce serious animal diseases. Ex: foot-and-mouth disease.
Some animal viruses can even cause cancer.
Many viruses infect plants. Ex: tobacco mosaic virus
These viruses pose a serious threat to many crops.
Copyright Pearson Prentice Hall

22. Viral Disease in Plants and Animals
19–3 Diseases Caused by
Bacteria and Viruses
Viral Disease in Plants and Animals
Viral Disease in Plant
Unlike animal viruses, most plant viruses have a difficult time entering the cells they infect.
This is partly because plant cells are surrounded by tough cell walls that viruses alone cannot break through. 
Many plant viruses are spread by insects.
The feeding action of an insect pest often provides a perfect opportunity for viral infections to spread. 
ex: Potato yellow dwarf virus is spread by an insect known as the leafhopper. Leafhoppers feed on potato leaves, and they also carry the virus in their tissues.
Copyright Pearson Prentice Hall

23. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Viroids and Prions
Viroids and Prions
Other viruslike particles that can cause disease are viroids and prions.
Viroids cause disease in plants.
Prions cause disease in animals.
Copyright Pearson Prentice Hall

24. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Viroids and Prions
Viroids 
Viroids are single-stranded RNA molecules that have no surrounding capsids.
Viroids enter an infected cell and synthesize new viroids.
They then disrupt the cell’s metabolism and stunt the growth of the entire plant.
Copyright Pearson Prentice Hall

25. Copyright Pearson Prentice Hall
19–3 Diseases Caused by
Bacteria and Viruses
Viroids and Prions
Prions 
Prions contain only protein—no DNA or RNA.
Prions cause disease by forming protein clumps. These clumps induce normal protein molecules to become prions.
Eventually, there are so many prions in the nerve tissue that cells become damaged.
Mad cow disease may be caused by prions.
Copyright Pearson Prentice Hall

26. Copyright Pearson Prentice Hall
Video on Dengue virus infection (2min): Video on dengue vaccine candidate under study (2min):
Copyright Pearson Prentice Hall

27. Copyright Pearson Prentice Hall
19–3
Copyright Pearson Prentice Hall

28. Copyright Pearson Prentice Hall
19–3
Biologists know that bacteria can cause human disease by
entering cells and using the cell to make new bacteria.
producing toxic substances that interfere with normal cell function.
decomposing the remains of dead organisms.
changing atmospheric nitrogen into nitrogen compounds.
Copyright Pearson Prentice Hall

29. Copyright Pearson Prentice Hall
19–3
A process that destroys bacteria by subjecting them to great heat is known as
refrigeration.
sterilization.
pickling.
boiling.
Copyright Pearson Prentice Hall

30. Copyright Pearson Prentice Hall
19–3
Which of the following diseases is transmitted by a mosquito bite?
influenza
measles
West Nile virus
chickenpox
Copyright Pearson Prentice Hall

31. Copyright Pearson Prentice Hall
19–3
Which of the following diseases is thought to be caused by prions?
diphtheria
mad cow disease
tuberculosis
smallpox
Copyright Pearson Prentice Hall

32. Copyright Pearson Prentice Hall
19–3
The best way to combat viral diseases is
to use antibiotics.
to treat individual symptoms.
to use preventive vaccines.
to let the disease “cure itself.”
Copyright Pearson Prentice Hall