Echovirus is one of several families of viruses that affect the gastrointestinal tract collectively called enteroviruses.The ECHO viruses‘ comprise a group of agents infectious for human beings.
History And Background of Echovirus
The first echoviruses were isolated in the early 1950’s as a result of the introduction of tissue culture techniques as an efficient tool for the isolation and study of polioviruses. During the course of studies attempting to isolate poliovirus in tissue cultures from fecal specimens, agents were found that not only were not neutralized by either poliovirus or Coxsackievirus antisera but also were incapable of inducing illness in suckling mice or in monkeys.
These new “enteric viruses” were later termed enteric cytopathogenic human orphan viruses (echo), because they were isolated predominantly from the lower alimentary tract, caused cytopathogenic changes in monkey and human cell cultures, were not pathogenic in any laboratory animal, and were human in origin. The term “orphan” was suggested because these viruses had not been associated etiologically with any disease.
At this writing 31 echovirus types are known and are numbered 1 to 33, types 10 and 28 being omitted. Type 10 was found to be considerably larger in size than other echoviruses and is now classified as reovirus type 1; type 28 was found to possess certain properties (such as inactivation at pH 3) not shared by other echoviruses and is now classified as rhinovirus 1A.
DISEASES DUE TO COXSACKIE AND ECHOVIRUS
A definitive presentation of diseases caused by Coxsackie and echoviruses is difficult, because these agents have been isolated from an ever- increasing list of specific diseases and clinical syndromes. The mere isolation of the virus from a patient’s throat or anal swab and/or the demonstration of serologic evidence of infection is not sufficient evidence to establish an etiologic relationship between the virus and the patient’s illness. Isolation of the virus from blood, cerebrospinal fluid (CSF), or diseased tissue is more meaningful evidence for an etiologic association than the above, but even more meaningful evidence may be obtained from controlled epidemiologic studies.
The establishment of an etiologic association is especially difficult with the Coxsackie and echoviruses. These viruses not only commonly cause subclinical infections but are also frequently shed in the stools for several weeks ^after either subclinical or clinically apparent, infection. Therefore an isolation could occur by chance during various periods of illness or well being. Only those specific diseases or clinical syndromes in which either satisfactorily controlled epidemiologic studies have established the etiologic relationship between Coxsackie or echovirus infections and an illness, or in which virus isolations have been made from, blood, CSF or diseased tissue will be presented in the following discussions
Epidemiology OF echoviruses.
Coxsackie and echoviruses are widely distributed throughout the world. They are found most commonly in human feces, but may also be found in the oropharynx or in nasopharyngeal washings; in patients with aseptic meningitis these agents may also be recovered from the CSF. They are resistant not only to the common antimicrobial drugs such as penicillin, streptomycin, and the tetracyclines, but also to many of the commonly used antiseptics such as 70 per cent alcohol, 5 per cent Lysol, and 1 per cent quaternary ammonium compounds. The occurrence of these infections is not influenced by sex or race.
They have been isolated from all age groups, but it is apparent that infants and children are most susceptible to infection. The prevalence of these agents in surveys of presumably normal infants and children has ranged from less than 5 per cent to 50 per cent, depending on the location of the survey. Season appears to be an important factor in the epidemiology of Coxsackie and echo vims infections, for the majority of infections occur during the summer and early autumn months. The incubation period may vary widely, but usually ranges from 2 to 15 days.
These viruses produce a broad spectrum of clinical manifestations, ranging from inapparent infection and mild undifferentiated respiratory or nonrespiratory illnesses to severe illnesses with varying involvement of the central nervous system. Illnesses associated with one or both of these agents are described in the next series of articles below