20.3 Diseases Caused by Viruses and Bacteria

How do bacteria cause disease?

How do viruses cause disease?

Why are emerging diseases particularly threatening to human health?

Vocabulary

• Pathogen

• Vaccine

• Antibiotic

• Emerging disease

• Prion

Pathogen

• A Pathogen is an organism that causes disease.

• Microorganisms that cause disease are bacteria and viruses.

• Archaea do not cause disease.

How do bacteria cause disease?

• Bacteria cause disease by destroying living cells or by releasing chemicals that upset homeostasis.

Examples: Tuberculosis damages tissues in the lungs and Tetanus releases toxins that upset homeostasis

Tuberculosis

• The pathogen infects the lungs and the body’s immune response causes damage to the tissues of the lungs

• Example of disease caused by cell destruction

Tetanus

• Bacteria produce disease by releasing toxins into the system

• Spores of the pathogen enter the body and produce a toxin that blocks nerve signals

Controlling Bacteria

• There are several ways to control bacteria

• Physical removal

• Disinfection

• Food Storage

• Food Processing

• Sterilization by Heat

Physical Removal

• Washing hands with soap and water helps dislodge bacteria and viruses

• Scrub hands for 15-20 seconds will remove viruses and bacteria from your hands

Disinfectants

• Disinfectants are chemical solutions that kill bacteria and can be used to clean surfaces.

Food Storage

• Low temperatures in refrigerators and freezers slow bacterial growth

Food Processing

• Cooking food (frying, boiling, or steaming for example) can destroy bacteria.

• Example: Spinach E. Coli outbreak in 2006 raw spinach and lettuce carried disease while the cooked was safe.

Sterilization by Heat

• Heating objects to 100 degrees Celsius will kill most bacteria

• Medical equipment is heated to higher temperatures.

Preventing Disease

• In addition to controlling bacteria, many bacterial diseases can be prevented through the use of vaccines.

• A vaccine is a preparation of weakened or killed pathogens or inactivated toxins.

• This preparation helps a body produce immunity to a specific disease.

• Can prevent diseases caused by bacteria or viruses.

Treating Bacterial Diseases

• Antibiotics: drugs that are used to attack a bacterial infection. Antibiotics disrupt processes that bacteria use to survive and reproduce.

• Antibiotics are essentially selective poisons that target bacteria without damaging our cells

Antibiotic Examples

• Penicillin: disrupts the formation of peptidoglycans and weakens the cell wall of bacteria so that they rupture.

Viral Diseases

• How do viruses cause disease?• Viruses cause disease by directly destroying

living cells or by affecting cellular processes in ways that upset homeostasis

Preventing Viral Diseases

• Use of vaccines

• Example: 1950 Polio Vaccine that uses a weakened virus

• Wash your hands

• Coughing or sneezing into a tissue rather than into your hand

Treating Viral Diseases

• Cannot be treated with antibiotics

• There are some antiviral drugs, for example: Amantadine for treating the flu.

Emerging Diseases

• Emerging Diseases

• An unknown disease that appears in the human population for the first time or a well-known disease that becomes harder to control

Examples of Emerging Diseases

• Multidrug Resistant Tuberculosis

• West Nile Virus• Bird Flu

Why are emerging diseases particularly threatening to

human health?

• Emerging diseases are a threat to human health because we have poor resistance to these diseases and have not yet developed methods to control the pathogens that cause emerging diseases.

“Superbugs”

• The widespread use of antibiotics has lead to the emergence of pathogens that are resistant to the drugs we develop to fight them

• MRSA for example

Prions

Prions:

protein

infectious

particles.

Prions• Discovered in 1972 when scientists were

researching a disease in sheep called “Scrapie”

• Prions are misfolded proteins that are either ingested (eaten) or are caused by mutation

• Prions build up in nerve cells in infected people and animals until the cells no longer function.

20.3 Diseases Caused by Bacteria and Viruses