Etiology and Epidemiology Poliovirus is an enterovirus. Of the 3 immunologically distinct poliovirus serotypes, type 1 is the most paralytogenic and the most common cause of epidemics.
Man is the only natural host for polioviruses.
The infection occurs through direct contact and is highly contagious. Extensive use of vaccines has almost eliminated the disease in developing countries. Pathology and Pathogenesis Virus enters the mouth and primary multiplication occurs in lymphoid tissues in the oropharynx and intestinal tract, mainly the ileum. Small amounts of virus reach the blood and are carried to other sites in the reticuloendothelial system, where extensive multiplication occurs. Viremia lasts several days but disappears by the time of onset, when antibodies have already developed.