It is rare for a person to have polio more than once.  it is much like several other common diseases, such as measles, mumps, and chicken-pox, which are also virus diseases. People who have had polio, therefore, have little reason to fear subsequent exposures to the disease.
    Long study of infectious diseases has proved that when  disease-producing bacteria or viruses attack us, out bodies
Promptly set to work making specific chemical substances to  fight these enemies. These chemical defence soldiers are
collectively called antibodies. They are generally carried in the  blood stream and many of them persist there for life, so that
any later attack by the same kind of enemy finds the body  ready to win an easy victory without suffering damage. This ability to resist infection is called immunity.
       Studies of the blood serum of the people who have had his disease have proved that the specific antibodies are already
abundant by the time the acute phase of the malady is passed.
In the case of polio victims the vitas causing the disease has been found in various parts of the body, but is comparatively
abundant in discharges from the nose and throat and most abundant of all in the bowel discharges.

    It has been noticed that to have more than one case of polio  in a family is exceptional ; and the puzzle as to where the infection actually comes from in any individual case is often impossible to solve. In attempting to reach a solution, however, body discharges of healthy family contacts of cases have many times been tested. It frequently happens that all or most of such
contacts are found to be carrying the virus without being made at all ill by it, and that they may continue to carry it much
longer than do the patients themselves. Furthermore, community-wide studies of people in polio epidemic areas have shown that carriers of the virus in such localities are very  numerous.  In fact, those best prepared to judge have estimated that during a polio epidemic any community concerned may have in it a hundred or more times as many healthy carriers as it will have cases of illness.
    Experts now believe that most polio victims become infected through exposure to healthy carriers who are not detected. This means there is no practical way to dodge the exposure, that isolating or quarantining the patient is of very little value.
     Let us look briefly at another angle of the subject of antibodies. It has been found not only that in an epidemic area there
are many healthy carriers of the virus, but also that these carriers invariably have an abundance of polio antibodies in their blood serum. In fact, extensive studies of these and other people who have never had polio in any recognizable form have shown that many teen-age children and most all adults carry a supply of polio antibodies. This is surely the chief reason why so many people who have never been ill with polio
entirely escape infection even when closely exposed to a person acutely ill with this disease. In trying to understand this
phenomenon we are forced to conclude that their resistance is due to previous exposures-perhaps quite numerous-which
led to temporary carrier states, with Or without mild illness.
These exposures also stimulated their antibody production, without showing symptoms that could be recognized as indicating polio. A large proportion of teen-agers and the great majority of adults are therefore already immune to polio.
    Unfortunately, without tedious and expensive tests we have no practical way of telling in any individual case whether or not this is so. It is probably safe to say, though, that the average adult does not stand one chance in a hundred of ever having this disease, no matter how often or how intimately exposed to




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