An adult or older child is less likely to experience dehydration as quickly as an infant. Some general concepts can be used in understanding infant diseases. For more specific information, see the entries on individual diseases or disease types. Infectious disease Infections are caused by microscopic organisms that invade an infant's body and quickly begin to multiply. When the body's immune system recognizes these foreign bodies, it begins to fight against the invasion by producing an army of immune cells called antibodies.
Antibodies are chemicals produced by a kind of white blood cell.
As blood rushes to the scene of the infection, the added blood causes the infection to look red. This immune response also increases the infant's body heat, causing a higher body temperature or fever . As the antibodies destroy the microorganisms, the infection is reduced and eventually healed. The major causes of infectious diseases in infants are bacteria, viruses, and fungi. Bacteria, which live and grow naturally in and on the human body, can increase in number to the point of causing an infection.