ECHO viruses

In 1951, other viruses similar to polioviruses and Coxsackie viruses were discovered, but differing in the lack of pathogenicity for monkeys and newborn mice. Due to the fact that the first discovered viruses of this group were isolated from the human intestine and had a cytopathic effect, but were not associated with any diseases, they were called orphan viruses or ECHO viruses for short, which means: E - enteric; C - cytopathogenic; H - human; O - orphan.

Currently, the ECHO group includes 32 serovariants. A significant portion of them have hemagglutinating properties, and all of them reproduce well in monkey cell culture. Some ECHO virus serotypes (11, 18, 19) are among the most common pathogens of intestinal dyspepsia in humans.

The source of Coxsackie and ECHO infections is humans. Infection with viruses occurs via the fecal-oral route.

The pathogenesis of diseases caused by Coxsackie and ECHO viruses is similar to the pathogenesis of poliomyelitis. The entry points are the mucous membrane of the nose, pharynx, small intestine, in the epithelial cells of which, as well as in the lymphoid tissue, these viruses reproduce.

Affinity to lymphoid tissue is one of the characteristic features of these viruses. After reproducing, the viruses penetrate into the lymph and then into the blood, causing viremia and generalization of the infection. Further development of the disease depends on the properties of the virus, its tissue tropism, and the immunological status of the organism. Once in the bloodstream, the viruses spread hematogenously throughout the organism, selectively settling in those organs and tissues to which they have tropism. The development of poliomyelitis-like disease or serous meningitis occurs only in cases where the virus penetrates the blood-brain barrier into the central nervous system. However, this does not happen in all cases. Neurotropic properties are especially pronounced in Coxsackie viruses A 7,14, 4, 9,10 and in Coxsackie viruses B 1-5.

In the case of acute serous meningitis, the patient may experience symptoms not only of this disease, but also those associated with damage to other organs and systems of the body, which this enterovirus infection is often limited to. Therefore, a combination of various forms of enterovirus diseases in the same patient is often observed.

Due to the great similarity between polioviruses, Coxsackieviruses and ECHO viruses, they were combined into one genus Enterovirus, and in 1962 it was proposed to designate them with a species name and a specific serial number.

Later, four more enteroviruses were isolated - 68-71. Serotype 70 caused an outbreak of a new disease - acute hemorrhagic conjunctivitis. Enterovirus 71 caused an epidemic of poliomyelitis-like disease with a mortality rate of 65% in Bulgaria in 1978. The same serotype 71 caused a large outbreak of the disease in people in Taiwan, which proceeded with hemorrhagic pulmonary shock, encephalitis and a mortality rate of 20%. The hepatitis A virus isolated in 1973 also turned out to be very similar in its characteristics (size, structure, genome and epidemiological properties) to enteroviruses, so it is sometimes called enterovirus 72. In total, the genus of human enteroviruses includes 68 antigenically different serotypes, including:

• polioviruses: 1-3 (3 serotypes);
• Coxsackie A: A1-A22, A24 (23 serotypes);
• Coxsackie B: B1-B6 (6 serotypes);
• ECHO: 1-9; 11-27; 29-34 (32 serotypes);
• Human enteroviruses: 68-71 (4 serotypes).

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Diagnosis of enterovirus diseases

To diagnose diseases caused by enteroviruses, a virological method and various serological reactions are used. It should be noted that against the background of a sharp decrease in the incidence of poliomyelitis, an increase in poliomyelitis-like diseases is observed, sometimes taking the form of group outbreaks. In this regard, when diagnosing poliomyelitis, it is necessary to keep in mind the possibility of detecting Coxsackie and ECHO viruses, i.e., research must be carried out in such cases for the entire group of enteroviruses. To isolate them, intestinal contents, swabs and smears from the pharynx are used, less often cerebrospinal fluid or blood, and in the case of death of the patient, pieces of tissue from different organs are taken.

The material under study is used to infect cell cultures (polioviruses, ECHO, Coxsackie B and some Coxsackie A serovars), as well as newborn mice (Coxsackie A).

Typing of isolated viruses is carried out in neutralization reactions, RTGA, RSK, precipitation reactions, using standard mixtures of serums of various combinations. To detect antibodies in human serums in enterovirus infections, the same serological reactions are used (RN, color reactions, RTGA, RSK, precipitation reactions), but for these purposes it is necessary to have paired serums from each patient (in the acute period and 2-3 weeks after the onset of the disease). Reactions are considered positive when the antibody titer increases by at least 4 times. With these two methods, IFM is also used (to detect antibodies or antigen).

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