Chapter 19-3: Diseases Caused by Bacteria and Viruses Bacteria and viruses are everywhere in nature, but only a few cause disease. Disease-causing agents are called pathogens.

Bacterial Disease in Humans Many bacteria live on and within our bodies. Growth of pathogenic bacteria disrupts the body’s equilibrium by interfering with its normal activities and producing disease.

How do bacteria cause disease? They damage the cells and tissues of the infected organism directly by breaking down the cells for food. Or they release toxins (poisons) that travel throughout the body interfering with the normal activity of the host.

Preventing Bacterial Disease Many bacterial diseases can be prevented by vaccines (a preparation of weakened or killed pathogens). When injected into the body, a vaccine may prompt the body’s immunity to the disease.

Treating Bacterial Disease If infection occurs, drugs can be used to destroy bacteria. These drugs include antibiotics, which are compounds that block the growth and reproduction of bacteria. A reason for increased human life expectancy is an increased understanding of how to prevent and cure bacterial infections.

Viral Disease in Humans Viruses produce disease by disrupting the body's normal equilibrium. How do viruses cause disease? Lytic: viruses can attack and destroy certain cells in the body, causing symptoms of the disease. Lysogenic: other viruses cause infected cells to change patterns of growth and development.

Viral Disease Prevention/Treatment Vaccines are the best protection against viral diseases, but only work if used before an infection begins. Viral diseases cannot be treated with antibiotics. Symptoms may be treated with over-the-counter medicines.

Bacterial Diseases Viral Diseases Lyme disease Tetanus Tuberculosis Bacterial meningitis Strep throat Common cold Influenza AIDS Chicken pox Hepatitis B West Nile

40-1: Infectious Disease Disease: any change, other than an injury, that disrupts the normal function of the body Can be inherited, caused by materials in the environment, or produced by pathogens (disease causing agents). Can be inherited, caused by materials in the environment (ex: cigarette smoke), or produced by pathogens (bacteria, viruses, fungi). First observed by French chemist Louis Pasteur and German bacteriologist Robert Koch

The Germ Theory of Disease Idea that infectious diseases are caused by microorganisms, or germs Observed by French chemist Louis Pasteur and German bacteriologist Robert Koch

Koch’s Postulates Series of guidelines used to identify the microorganism that causes a specific disease These rules are important because identifying pathogens that cause disease is the first step toward prevention or cures.

The Postulates (or rules) The pathogen should always be found in a sick organism, not a healthy one. It must be isolated and grown in the lab. When injected in a new host, it should cause the same original disease. The injected pathogen should be isolated from the new host and identical to the original pathogen. Do we want this slide?

Agents of Disease For many pathogens, the human body provides just the right conditions for growth. Agent Example Viruses Common cold, flu, warts Bacteria Botulism, Anthrax Protists Malaria, African Sleeping Sickness Worms Schistosoma Fungi Athletes foot, ringworm Suitable temperature, watery environment full of nutrients

Worms: Schistosoma Protists: Trypanosoma Fungi: athlete's foot Fungal spores Fungi: athlete's foot

How Diseases Are Spread Coughing, sneezing, or physical contact Contaminated food or water Vectors: infected animals that carry pathogens from person to person Malaria, lyme disease, west nile virus, rabies

Fighting Infectious Diseases Antibiotics: compound that blocks the growth and reproduction of bacteria (no effect on viruses) Over-the-Counter Drugs: treat only the symptoms, but do not actually treat the cause of the infection