A runny nose occurs when the membranes in the nasal passages become irritated and inflamed. The irritation causes an increase in mucus production that leads to the runny nose and nasal congestion. A fever, defined as a body temperature greater than 99.5 degree Fahrenheit when measured orally, occurs as a defense mechanism triggered by the immune system. Both of these symptoms commonly occur in response to infections such as the common cold. A high fever, however, accompanied by a runny nose may signal a more serious condition.
Pneumonia describes a condition in which the lungs become inflamed due to an infection caused by a virus, bacteria, parasite or fungus. Because pneumonia usually arises as a complication of another infection, such as the flu virus, pneumonia often begins with mild upper respiratory symptoms including a runny nose and cough, according to MayoClinic.com. As the lungs become infected, the immune system responds with inflammation and a high fever. Other symptoms of pneumonia include shortness of breath, sweating, chills, chest pain, headache, muscle pain and fatigue.
An illness known as fifth disease occurs due to an infection by the human parvovirus B19. Because 50 to 60 percent of adults have already been exposed to the virus, adults usually do not experience any symptoms, notes FifthDisease.org. That leaves infants and children as the most vulnerable population for fifth disease. Fifth disease causes a rash on the face that doctors describe as the "slapped cheek" rash. This infection also causes flu-like symptoms including a runny nose and a fever that can become high, especially in individuals with a weakened immune system.
Respiratory Syncytial Virus
Respiratory syncytial virus, usually called RSV, infects the lungs and airways, causing upper respiratory symptoms such as a runny nose, coughing and sneezing. A fever usually develops one to three days later. Most healthy individuals recover from RSV infection easily, but young children and infants are vulnerable to complications. As the most common cause of pneumonia in children under the age of 1 in the United States, according to the Centers for Disease Control and Prevention, RSV can result in inflammation of the lungs accompanied by a high fever.
Roseola describes a disease that affects infants and children between the ages of three months and 4 years, says MedlinePlus from the National Institutes of Health. Caused by the human herpesvirus 6, roseola causes a runny nose, sore throat, eye redness and a rash accompanied by a fever. The fever precedes the rash and usually lasts between three and seven days and can reach as high as 105 degree Fahrenheit, notes MedlinePlus.