Viruses are the smallest infectious disease and they are different because they can not live outside the body. They cause of infections like colds, flu and can cause illnesses like HIV and AIDS. Bacteria are larger than viruses and they need energy from sugars, proteins and fats from humans to survive. They can also live in the environment and can cause mild skin irritation to lethal pneumonia. Fungi are commonly found in spores and mounds and cause diseases in humans in the form of yeasts infection, they also cause skin infections and pneumonia. Parasites are a group of organisms called eukaryotes, some live within a person and some can multiply in the environment and the cause malaria and parasitic disease. Infection may cause damage to body tissue like pain, swelling, redness, heat or loss of function. Colonisation is when bacteria grows on the body in places that are exposed with out causing infection and these don't usually harm and don't need treatment. Systemic infectious affects the whole body or multiple organs and localised infection affect a specific area or organ.
