Respiratory syncytial virus, known as RSV, is a respiratory virus that infects the lungs and breathing passages, according to the CDC. It's a mild, cold-like illness for most healthy people, but can be dangerous for infants and a cause of bronchiolitis and pneumonia. It can spread through coughing and sneezing and can survive on hard surfaces, such as crib rails, for hours.
Croup is caused by a virus and causes swelling in the trachea and larynx. It's most common in children 1 to 3, according to the American Academy of Family Physicians, and can be spread through coughing, sneezing, through unwashed hands, shared toys or utensils. Among symptoms, it's known for a barking cough.
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Photos:Common childhood illnesses
Hand, foot and mouth is a viral illness common among children younger than 5, according to the CDC. Symptoms include a fever and sores in the mouth, as well as a rash that may develop on the hands, feet and other parts of the body. The best ways to prevent it are washing hands, avoiding contact or sharing utensils and other items with those who are ill.