Any living organism can contract a virus by giving parasites the opportunity to grow. Parasites feed on the nutrients of another organism which allows the virus to thrive. Once the human body detects a virus, it then creates fighter cells that attack the parasite/virus; literally, causing a war within the body. A virus can affect any part of the body causing a wide range of illnesses such as the flu, the common cold, and sexually transmitted diseases. The flu is an airborne virus that travels through tiny droplets and is formally known as Influenza. Parasites travel through the air and attack the human respiratory system. People that are initially infected with this virus pass infection on by normal day to day activity such as talking and sneezing. When a person comes in contact with the virus, unlike the common cold, the flu virus affects people almost immediately. Symptoms of this virus are very similar to the common cold but much worse. Body aches, sore throat, headache, cold sweats, muscle aches and fatigue are among the many symptoms accompanied by the virus. A viral infection in the upper respiratory tract results in the common cold. With symptoms like sore throat, sneezing, small fever, and a cough, the common cold is usually harmless and tends to clear up within a week or so. The common cold is also a virus that is spread through the air but can also be passed through direct contact. This infection takes a few days to develop symptoms; it is a gradual process unlike the flu.