Parainfluenza is a virus that can cause infections in people. Most people infected with this virus have mild symptoms including fever, cough, red eyes, or runny nose (a common cold). Some people, especially those with a weakened immune system, get very sick from this virus. They may have difficulty breathing or develop lung infections. Currently, there are no specific treatments for parainfluenza. However, a drug called DAS181 may make the virus go away faster. Researchers are interested in testing DAS181 to see if it is safe and effective against parainfluenza.