Croup, whooping cough and RSV
First of all, they are different by definition.
Croup and whooping cough are names of diseases while RSV is a special type of virus. Croup is a disease which children sometimes suffer from that makes it difficult for them to breathe and causes them to cough a lot. It is either viral or spasmodic. Whooping cough (also known as pertussis) is a bacterial infection that gets into your nose and throat. Respiratory syncytial virus (RSV) is a highly contagious illness causing some of the same symptoms as cold and flu, such as fever, runny nose, and cough.
Second, they are different in ages and genders of the infected people.
Croup is more common in boys than in girls. Babies between 3 months and 5 years of age are most at risk. Whooping Cough (pertussis), can infect babies, as well as older children and adults. Respiratory syncytial virus (RSV) is a common, and very contagious, virus that infects the respiratory tract of most children before their second birthday. Reinfection of RSV is most common among adults or vulnerable elderly people.
Third, they are different in causes and symptoms. All three conditions are contagious.
Viral croup is caused by any virus that infects your voice box and windpipe. Parainfluenza is the most common one. Whooping cough is caused by the spread of bacteria. If a person with whooping cough sneezes, laughs, or coughs, small droplets that contain the bacteria may fly through the air. One may fall ill if he breathe the air. Most often, it spreads among family members.
Croup: a "bark-sound" cough (worse at night); drooling or has trouble swallowing; constantly cranky, irritable, or uncomfortable; tired, sleepy, or hard to awaken; change of colors around one's lips, etc.
Whooping cough: a "whoop" sound is made when you gasp for air at the end of a coughing fit.
RSV: irritability and breathing problems in infants; bronchiolitis
Fourth, they are different in treatment and prevention.
For croup, you can prevent your children from getting it by paying more attention to hygiene environment. For whooping cough, vaccines like DTaP and Tdap can help prevent it in children and adults, and also help fight against tetanus and diphtheria. There is no vaccine for RSV. But a medication called palivizumab could be applied to prevent RSV infections and protect high-risk babies from developing serious complications of RSV infection.