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 Mycobacterium Tuberculosis

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 Clostridium tetani (C. tetani). --> tetanospasmin --> severe muscle spasms/lockjaw

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. Esherichia Coli --> release Shiga, a toxin that inhibits protein synthesis

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 Bactericidal Antibiotic: kills the bacteria Bacteriostatic Antibiotic: stops the bacteria from multiplying Selective poison: target the building of cell walls or synthesis of folic acid (two processes that bacteria perform that our cells do not), attack peptidoglycan.

Antibiotic Examples Penicillin: disrupts the formation of peptidoglycans and weakens the cell wall of bacteria so that they rupture. Sulfa Drugs stop bacteria from producing folic acid that they need to survive Tetracycline inhibits bacterial growth by stopping protein synthesis

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. Antiviral drugs attack specific enzymes that the viruses need to survive, and that human cells do not have.

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 H5N1 Bird flu is a new virus that would have to make few changes in order to jump from birds to humans and resembles the flu viruses of the past that have caused pandemics.

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