Cells that are in the process division are vulnerable to damage by AC electric fields that have specific frequency and field strength characteristics. The selective disruption of rapidly dividing cells can therefore be accomplished by imposing an AC electric field in a target region for extended periods of time. Some of the cells that divide while the field is applied will be damaged, but the cells that do not divide will not be harmed. This selectively damages or disrupts rapidly dividing cells like parasites, but does not harm normal cells that are not dividing.