Students should be able to explain how diseases caused by viruses, bacteria, protists and fungi are spread in animals and plants. • Students should be able to explain how the spread of diseases can be reduced or prevented. • Pathogens are microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and can be spread by direct contact, by water or by air. • Bacteria and viruses may reproduce rapidly inside the body. • Bacteria may produce poisons (toxins) that damage tissues and make us feel ill. • Viruses live and reproduce inside cells, causing cell damage.