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?
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 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
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• 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.