My fourteen-month-old son recently had hand-foot-and-mouth virus. Is this something he can catch again, or will he be immune from future recurrences?
It's nice to have a place to ask non-urgent questions about the little ones, and as I know you -- you have seen my son in the office -- I trust your answers and advice.

The incredible human body is equipped with an immune system that staggers the imagination. In ages past, explorers charted thrilling new lands. Today, one of the most exciting frontiers of discovery is the wondrous, intricate, complex immune system silently protecting us day and night.

Two types of defense against viruses predominate in the bloodstream: humoral immunity and cellular immunity. The humoral (or one might say 'liquid') immune system attacks viruses when they are loose in the body, either in the bloodstream or in bodily secretions. The cellular immune system attempts to destroy viruses once they have taken up residence inside the body's cells.

The humoral response consists of antibodies made to specific viruses. These antibodies remain present in the circulation and secretions, hopefully eliminating the virus and protecting against future infections. The more water soluble a particular virus is, the more effective the humoral response. A good example of this is the poliovirus. Polio vaccines (and other vaccines) work precisely because they so effectively stimulate specific antibody formation. When a person is re-exposed to polio, the virus is destroyed by antibodies before infection sets in.

The cellular response consists of certain white blood cells, such as cytotoxic lymphocytes or natural killer cells, which attack and destroy our own cells that have been invaded and altered by viruses. Some viruses, such as herpes, are 'sneaky' enough to hide in our cells without changing the way they look to the cellular immune system. These viruses can remain dormant within cells for years, only to re-emerge periodically when our humoral defenses are weak and allow the viruses to get loose in the circulation once again.

Hand-foot-and-mouth syndrome is a distinct viral illness. It produces blisters in the mouth in 90% of infected children and a characteristic rash primarily on the hands, feet, or buttocks in 64% of these children. Most children are cranky, with a sore throat, decreased appetite, and/or fever. The illness typically clears within a week.

Hand-foot-and-mouth syndrome was first reported in 1956, in Australia. As far as we know, it never occurred before that time. For the next 7 years it was reported, only occasionally, in pockets dotting the globe. By 1963, however, it became a common feature of childhood worldwide.

Hand-foot-and-mouth syndrome is caused by several different viruses, including coxsackieviruses A5, A9, A10, A16, B1, B3, enterovirus 71, foot-and-mouth disease virus, and herpes simplex. The vast majority of cases, however, are caused by coxsackievirus A16.

A child with a healthy immune system will form antibodies to whichever virus caused the infection. If your son is re-exposed to the same virus, he will probably not be re-infected. He is still susceptible, in varying degrees, to the other viruses. Since 1963, most children have had one case of hand-foot-and-mouth syndrome, caused by coxsackievirus A16.

There is one other snag. While most children clear their bodies of the virus within one week, coxsackievirus A16 occasionally succeeds in hiding inside children's own cells, like herpes.