1. Bacterial and viral diseases
Chapter 20 Section 3

2. How do Bacteria Cause Disease?
Bacteria cause disease by destroying living cells or by releasing chemicals that upset homeostasis.
Pathogens: microorganisms (viruses and prokaryotes) that cause disease
As of now, all known prokaryotic pathogens are bacteria. It is a possibility that scientists may discover archaea as being associated with disease in the future.

3. Louis Pasteur
Helped establish what is known as the germ theory of disease.
He did this by showing bacteria to be responsible for a number of human and animal diseases in the s.
Also known for his discoveries of vaccines, microbial fermentation, and pasteurization
(Hence the name, “pasteurization”)

4. Disease Mechanisms There are two general ways of production:
1. Some destroy living cells and tissues of the infected organism directly. Some cause tissue damage when they provoke a response from the immune system.
2. Other bacteria release toxins (poisons) that interfere with the normal activity of the host.

5. Common Human Bacterial Diseases:

6. Damaging Host Tissue
One example that damages host tissue is the bacterium that causes tuberculosis.
The pathogen is inhaled into the lungs, where it triggers an immune response that destroys large areas of tissue
Bacterium may enter a blood vessel and travel to other sites in the body, causing similar damage

7. Releasing Toxins
Includes bacteria that causes diphtheria, and botulism (a deadly form of food poisoning).
Diphtheria has largely been eliminated in developed countries by vaccination, but outbreaks of botulism still claim a lot of lives

8. Controlling Bacteria Various control methods are used:
1. Physical Removal: washing hands, for example, helps dislodge bacteria and viruses (although it doesn’t kill them)
2. Disinfectants: chemical solutions used to clean
3. Food Storage: low temperatures slow the growth of bacteria and keeps food fresher for longer periods of time.
4. Food Processing: boiling, frying, or steaming can sterilize food
5. Sterilization by Heat: higher temperatures will prevent and kill bacteria

9. Preventing Bacterial Disease
Many can be prevented by stimulating the body’s immune system with vaccines
Vaccine: preparation of weakened or killed pathogens or inactivated toxins
Once injected, a vaccine tells the body to produce immunity to the specific disease
Immunity: the body’s ability to destroy pathogens or inactivated toxins

10. Treating Bacterial Diseases
Antibiotics: medicinal drugs that block the growth and reproduction of bacteria.
Ex: penicillin and tetracycline
They disrupt the proteins and cell processes that are specific to bacterial cells without harming the host’s cells.
Antibiotics are not effective against viral infections

11. How do Viruses Cause Disease?
They directly destroy living cells or affect cellular processes in ways that upset homeostasis.
Viruses can produce serious animal and plant diseases.

12. Common Viral Diseases

13. Disease Mechanisms
In many viral infections, viruses will attack and destroy certain cells, which cause the symptoms of the associated disease.
Poliovirus (Polio), for example, destroys cells in the nervous system which will produce paralysis
Other viruses can cause infected cells to change their growth/development pattern, which can sometimes lead to cancer.

14. Preventing Viral Disease
In most cases, the best way to protect against viruses lies in prevention, often by the use of vaccines.
There are vaccines against more than two dozen infectious diseases

15. Innovations in Vaccines
1769: Edward Jenner performs first inoculation against smallpox, using cowpox.
1880s: Louis Pasteur develops vaccines against anthrax and rabies
1923: Albert Calmette and Camille Guerin develop vaccine against TB
1950s: Jonas Salk develops polio vaccine using killed viruses. Albert Sabin develops polio vaccine using weakened viruses.
Children/people struck with polio before the vaccine were placed in machines called iron lungs, which helped them breathe.
Before vaccine development, the Red Cross made the public aware of the threat of tuberculosis using posters such as this one, circa 1919.

16. Innovations in Vaccines
1981: a vaccine against hepatitis B gets government approval
2006: a vaccine against HPV, which can lead to AIDS or certain cancers, is approved

17. Preventing Viral Disease
Effective prevention includes:
Washing your hands frequently
Avoiding contact with sick individuals
Coughing/sneezing into your sleeve or a tissue instead of your hands

18. Treating Viral Diseases
Cannot be treated with antibiotics
Limited progress has been made in developing a handful of antiviral drugs that attack specific viral enzymes that host cells don’t have
Treatments include: antiviral medication that helps speed recovery from the flu virus
Another may, in certain instances, prevent HIV

19. Emerging Diseases
The pathogens that cause emerging diseases are particularly threatening to human health because human populations have little or no resistance to them.
Methods of control have yet to be developed for emerging diseases.

20. Emerging Diseases
If pathogenic viruses and bacteria were not able to change/evolve over time, they would post far less of a threat than they actually do.
Unfortunately, the short time between successive generations of the pathogens allows them to evolve rapidly, especially when humans try to control them.
Emerging disease: an unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control

21. Emerging Diseases
The map shows locations worldwide where specific emerging diseases have broken out in recent years.
Diseases such as severe acute respiratory syndrome (SARS) in Asia have appeared.
At the same time, some diseases thought to be under control have come back.

22. Emerging Diseases
Changes in lifestyle have made emerging disease more of a threat
High-speed travel, for example, allows a person to move halfway around the world in a day.
Large quantities of food and consumer goods are now shipped between regions of that world that previously had little contact with each other.
Human populations that were once isolated by oceans and mountain ranges are now in close contact with parts of the world that are more developed
The possibility of the rapid spread of new diseases is a risk of every trip a person takes and every shipment of food or goods.

23. Emerging Diseases
Because of their sudden appearance and resistance to existing control methods, emerging diseases are of particular concern.
In order to defend against these diseases, we need a deeper understanding of the functions of the molecular structures and genetics of both bacteria and viruses.

24. “Superbugs”
Penicillin (an antibiotic derived from fungi), when it was first introduced in the 1940s, was a miracle drug. Patients were cured almost immediately.
Within a few decades, however, penicillin lost much of its effectiveness, as have other, more current antibiotics.
Evolution can be thanked.

25. “Superbugs”
Because antibiotic use has become so widespread, a process of natural selection that favors the emergence of resistance to powerful drugs has begun.
Physicians must now fight “superbugs” that are resistant to whole groups of antibiotics.
These “superbugs” also transfer drug-resistant genes from one bacterium to another through conjugation.

26. “Superbugs”
An especially dangerous form of multiple drug resistance has recently appeared in a common bacterium. Methicillin-resistant Staphylococcus aureus (MRSA) can cause infections that are especially difficult to control.
MRSA skin infections can be spread by close contact, including the sharing of personal items such as athletic gear, and are especially dangerous in hospitals, where MRSA bacteria can infect surgical wounds and spread from patient to patient.

27. “Superbugs”
Infection by MRSA can be very serious or fatal for people in hospitals and nursing homes who have weakened immune systems.
This table shows the incidence of MRSA infections in U.S. hospitals during a 13- year period.

28. New Viruses
Because viruses replicate so quickly, their genetic makeup can change rapidly. This sometimes allows a virus to jump from one host species to another.
Researchers have evidence that this is how the virus that causes AIDS originated (moving from nonhuman primates into humans)
Public health officials are especially worried about the flu virus
Gene shuffling among different flu viruses that infect wild/domesticated bird populations has led to the emergence of a “bird flu” that is similar to the most deadly human versions of flu.
Only very slight genetic changes may be needed for the bird flu virus to make the jump to humans, where there would be little natural resistance to it.

29. Prions
In 1972, Stanley Prusiner became interested in scrapie (an infectious disease in sheep). The cause for this disease was unknown.
Experiments revealed clumps of tiny protein particles in the brains of infected sheep. Prusiner called these particles prions, which is short for “protein infectious particles.”
Prions are misfolded proteins in the brain that cause a chain reaction of misfolding in other normal proteins they contact, eventually clogging the brain tissue and causing disease
Many animals, humans included, can become infected with prions.

30. Mad Cow Disease