 Viruses: Tiny particles that invade & replicate within living cells.  Bacteria: Cause disease by either breaking down the tissues of the infected organism or releasing toxins that harm the body.  Protists: Causes malaria.. Spread by mosquitoes  Worms: Parasitic worms that cause a number of serious human diseases.  Fungi: Some fungi can penetrate the outer layers of skin.. Ex. Athlete’s foot.

 Physical contact: Some diseases can be spread by direct contact. Some can be indirect contact.. Ex passed through the air or touching objects that an infected person has touched  Contaminated food & water: Food poisoning… Bacteria can grow quickly in warm, partially cooked food. Water can also carry disease.. Poor sanitation & untreated sewage.  Infected animals: Animals can spread diseases… animals that carry disease are called vectors.

 Disease: any change, other than an injury, that disrupts the normal functions of the body.  Pathogen: disease-causing agents… these are referred to as “sickness makers.”  Germ theory of disease: Infectious diseases are caused by microorganisms of different types, commonly called germs.

 Koch’s postulates: Rules that are used to identify the microorganism that causes a specific disease.  Vector: animals that carry pathogens from person to person… Example - ticks  Antibiotic: compounds that kill bacteria without harming the cells of the human or animal hosts.