They are divided into two groups; the Enteroviruses (Poliovirus, Coxsackievirus and Echovirus) and the Rhinoviruses. There are about 63 serotypes of Enterovirus and more than 100 serotypes of Rhinovirus.

Commonly produce subclinical infections; acute disease may range from minor illness to paralytic disease.

The Enteroviruses enter via the intestinal tract and attach to receptors on intestinal epithelia. During this alimentary phase, the virus replicates in cytoplasm-> spread into the lymphatic circulation (lymphatic phase) ->bloodstream (viremic phase). The viremic phase generally marks the end of the infection but an occasional neurologic phase can lead to more severe and permanent problems.

Rhinoviruses

Sensitive to acid pH and optimal growth occurs at 33°. There are over 100 serotypes of Rhinoviruses and they produce the common cold.

PATHOGENESIS:
Infection results via the nasopharynx by direct contact. Viral replication leads to inflammation and edema, symptoms of the common cold. Inapparent infection is common.

HOST DEFENSES:
Enteroviruses: Interferon is effective against these viruses. More specifically, IgA antibodies in the intestine and saliva are protective.
Rhino: Susceptibility to the Rhinoviruses is dependent on prior exposure. Antibody of the IgA and IgG classes is important. Non-specific defenses including interferon, gastric acidity and temperature may play a major role in controlling infection.

EPIDEMIOLOGY:
Enteroviruses: Found worldwide, the enteroviruses are spread via the fecal-oral route. Most illnesses occur in the summer and fall. The virus may be carried in the throat for a week and shed in the feces for several weeks.
Rhinoviruses: Spread from person to person, usually by direct contact. Inapparent infections occur in about half. On average, most persons suffer with 2-4 colds per year during the fall and spring months and these represent different serotypes of the virus.

There are so far no vaccines invented for both enterovirus and rhinovirus which are categorised under picornaviridae as there’s too many of serotypes. Only natural recovery is possible via diagnosing a person and telling him the site of replication of the virus. For example, recovery of Enterovirus from the throat or feces is diagnostic. Recovery of Rhinoviruses is simply not practical.