Chapter 20: Viruses and Prokaryotes Section 20-3: Diseases Caused by Bacteria and Viruses

Bacterial Diseases Pathogens are microorganisms that cause disease All known prokaryotic pathogens are bacteria Louis Pasteur helped establish the germ theory of disease by showing bacteria responsible for many human and animal diseases Bacterial diseases produced in 2 general ways: Destroy living tissue of infected organism, directly or causing tissue damage by triggering immune system (bacteria that cause tuberculosis) Release toxins that interfere with normal activity (bacteria that cause diphtheria, botulism)

Common Human Bacterial Diseases

Controlling Bacteria Physical removal – washing hands or other surfaces under running water does not kill bacteria, but it can dislodge them (also viruses) Disinfectants – chemical solutions that kill bacteria Food storage – low temperatures slow bacterial growth, keep foods fresher than room temperature Food processing – cooking kills bacteria Heat sterilization – instruments are heated to above 100° C to kill bacteria

Preventing Bacterial Diseases Vaccines are preparations of weakened or killed pathogens or inactivated toxins When injected, vaccines prompt body to produce immunity to a specific disease

Treating Bacterial Diseases Antibiotics such as penicillin and tetracylcine block the growth and reproduction of bacteria by disrupting proteins or cellular processes specific to bacterial cells without harming host Ineffective against viral infections

Viral Diseases Produce disease by disrupting homeostasis Animal and plant diseases

Disease Mechanisms Some attack and destroy specific cells, causing disease symptoms – poliovirus Some viruses cause infected cells to change their growth and development patterns, sometimes leading to cancer

Preventing Viral Diseases Vaccines 1769- Smallpox vaccine, using cowpox virus 1880s- Anthrax and rabies 1923- tuberculosis 1950s- 2 polio vaccines, one used killed viruses and one using weakened viruses 1981- hepatitis B vaccine using recombinant DNA 2006- vaccine against human papillomavirus (HPV) Cold and flu viruses often spread by hand-to-mouth contact – wash hands, avoid contact with sick people, do not cough or sneeze on hands

Treating Viral Diseases Few antiviral drugs Attack specific viral enzymes host cells do not have

Emerging Diseases Pathogens reproduce quickly, evolve easily An unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control is called an emerging disease

Emerging Diseases Changes in lifestyle and commerce have made this a bigger issue Tend to appear suddenly, resist control methods Need better understanding of molecular structure and genetics

“Superbugs” Evolution has created many bacteria that are resistant to antibiotics In the 1940s, penicillin killed everything Widespread use of antibiotics has allowed for natural selection to favor resistance, and conjugation can transfer drug-resistant genes

MRSA

New Viruses Reproduce so quickly, so simple genetically they can jump species (SIV to HIV) Flu virus is always changing – new vaccines and variations (bird flu)

Prions 1972- Stanley Prusiner investigated cause of scrapie, an infectious disease in sheep Experiments showed clumps of protein particles in the brains of infected sheep. Prusiner called particles prions, short for “protein infectious particles” Misfolded proteins in the brain cause a chain reaction of misfolding in other normal proteins, clogging the brain tissue and causing disease Mad cow disease