The ECHO viruses (enteric cytopathogenic human orphan viruses) comprise
a subgroup of the human enteroviruses: all are infectious for human
beings. Although several may share common antigens, most are
serologically unrelated. They have been grouped together with polio-and
Coxsackie viruses because of similar physico-chemical properties, and
because they are recoverable from the alimentary tract of human beings.
Since 1951 when the first was recognized (ROBBINS et al., 1951),32 more
have been discovered. In re cent years 2 members of the group have been
placed in other categories: ECHO 10 is now reovirus type 1 (SABIN,
1959), and ECHO 28 is a rhinovirus, provisionally type 1 (TYRRELL and
CHANOOK, 1963). During the last 15 years numerous studies have brought
to light much information on the properties, ecology and natural history
of the ECHO viruses. H. Historical Resume Two conspicuous events
fostered the rapid acquisition of knowledge of ECHO viruses. The first
was aresurging interest in tissue culture methods permissive of viral
growth in vitro (ENDERs et al., 1949); the second was the introduction
of mass vaccination against poliomyelitis (FRANCIS et al., 1957). Both
events enabled further recognition and delineation of the etiology of
illnesses simulating nonparalytic poliomyelitis.