Picornaviridae, the family of the smallest RNA viruses, contains the genus Enterovirus. Species in this genus commonly infect humans and have classically been separated into polioviruses, coxsackieviruses (types A and B), enteric cytopathogenic human orphan (echo) viruses, and as yet unclassified enteric viruses. Because of recognized overlap in these viral groups, newer members of the genus are called enteroviruses (EVs), which are designated by a sequential numbering system (e.g., EV 70). Enteroviruses are environmentally resistant and infect people primarily via the fecal–oral route. After replication in submucosal lymphatic tissues, the viruses may spread systemically to various other tissues.

Dogs have been tested to determine whether they harbor a variety of human EVs because of the possible zoonotic potential (Table 22-1). Similar information is not available for cats. Dogs have been shown to be exposed to and to chronically shed human EVs; however, serologic evidence of infection does not always correlate with shedding of the viruses. Although dogs appear to become infected with these viruses, clinical signs have not been apparent. The viruses can be found in the stools for a period of months, but whether the extended shedding represents reexposure is uncertain. EVs recovered from nasopharyngeal or fecal cultures of dogs have been grown in tissue culture and cause cytopathogenic effects, primarily in monkey kidney but not canine cell lines, supporting the fact that they are human viruses. Furthermore, neutralization tests have shown them to be indistinguishable from the human isolates.^11,12 In some instances, EVs were found in canine feces that were “just passing through,” not causing infection. These viruses may have been obtained from sources contaminated by human feces. Alternatively, they may be EVs antigenically related to human EVs or other viruses neutralized by nonspecific substances in the testing sera. Newer techniques to determine viral homogeneity by genetic analysis must be performed on isolates to resolve this issue.

TABLE 22-1

Human Enteroviruses Recovered from Asymptomatic Dogs

Virus	Specimen Source	Geographic Location
Poliovirus 1	Feces	West Bengal3
	Feces	Costa Rica7
Echovirus 6	Feces	California1
	Nasopharynx, feces	New Mexico1,9,13
Echovirus 7	Feces	West Bengal3
Coxsackievirus A9, A20	Feces	Costa Rica7
Coxsackievirus B1	Nasopharynx, feces	Texas, New Mexico1,9
Coxsackievirus B3	Nasopharynx, feces	New Mexico9
Coxsackievirus B5	Nasopharynx, feces	New Mexico9
Unclassified enteroviruses	Feces	Philippines17

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