REINHARD 



of serious disease. Even the poliovirus, the most dreaded of the 

 enteroviruses, causes extensive pathology or death in only a very 

 small proportion of their hosts. This fact aids in the persistence of 

 enteroviruses; but it also makes their true bionomic status a diffi- 

 cult study because of the crj^Jtic nature of their activity. 



It is characteristic of enterovirus infection that the virus may be 

 present in large quantities in oropharyngeal secretions as well as 

 feces and intestinal secretions. Lymphoid tissue and mucosal epi- 

 thelium may be the site of propagation of virus. Usually, oropharjoi- 

 geal samples become negative for virus soon after the acute stage 

 of the disease, A notable exception to this is the case of Coxsackie 

 A- 21 infection, in which virus has been found in pharnygeal swab 

 specimens as long as 40 days after onset (Johnson et al., 1962). 

 In most enterovirus infections the virus may be shed in feces for 

 several weeks. Table IV shows duration of enteroviral excretion as 

 demonstrated by a number of workers. Rather consistently, entero- 

 viruses have been demonstrated inthefecesof a significant propor- 

 tion of individuals a month to six weeks after onset of enteroviral 

 infection (Rosen et al., 1958a; 1958b; Johnson et al,, 1962; Huebner 

 et al., 19 50). This means that the viruses may persist for a month 

 in people whose serum antibodies have reached immunologically 

 effective levels. The true duration of gastrointestinal infection is 

 not known, for recent studies have shown that treatment of feces 

 with freon, which dissociates antigen- antibody complex, may ex- 

 tend greatly the period in which virus can be detected in the healthy 

 or convalescent carrier (Howe, 1962), This prolonged carrier period 

 makes the isolation of villages in cold climates less effective in the 

 prevention of the introduction of enteroviruses, and also helps to 

 maintain the viruses within village and local area populations. 



Since the advent of the vaccines, both the formalin- inactivated 

 and attenuated types against poliomyelitis, it has become quite 

 apparent that circulating antibodies againstpoliovirusesarenosure 

 indication of permanent, solid immunity. Serologically- immune in- 

 dividuals can become reinfected with polio viruses homologous to 

 the serum antibodies and can excrete virus (Horstmannet al., 1957; 

 Fox et al., 19 58; Gelfandetal., 1960). These reinfections are usually 

 limited to the enteric tract and apparently are pathologically be- 

 nign. However, virulent virus may be excreted for extended periods, 



62 



