ECHO viruses
Last reviewed: 23.04.2024
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In 1951, other viruses, similar to polioviruses and Coxsackie viruses, were detected, but differed in the absence of pathogenicity for monkeys and newborn mice. Due to the fact that the first detected viruses of this group were isolated from the human intestine and possessed cytopathic action, but were not associated with any diseases, they were called orphaned or ECHO viruses, which means: E - enteric; C - cytopathogenic; H - human; O - orphan - orphan.
Currently, the ECHO group has 32 serovariants. A significant part of them has haemagglutinating properties, and all of them multiply well in the culture of monkey cells. Some serotypes of ECHO viruses (11,18,19) are among the most frequent pathogens of human intestinal dyspepsia.
The source of Coxsackie and ECHO infections is a person. Infection with viruses occurs by fecal-oral route.
The pathogenesis of diseases caused by Coxsackie and ECHO viruses is similar to the pathogenesis of poliomyelitis. The entrance gates are the mucous membrane of the nose, pharynx, small intestine, in the epithelial cells of which, as well as in the lymphoid tissue, and the multiplication of these viruses occurs.
Affinity for lymphoid tissue is one of the characteristic features of these viruses. After reproduction, the viruses enter the lymph, and then into the blood, causing viremia and generalization of the infection. The further development of the disease depends on the properties of the virus, its tissue tropism, as well as the immunological status of the organism. Getting into the flow of blood, viruses spread haematogenously throughout the body, selectively settling in those organs and tissues to which they possess tropism. The development of poliomyelitis-like disease or serous meningitis occurs only in those cases when the virus penetrates the blood-brain barrier into the central nervous system. However, this does not happen in all cases. Neurotrophic properties are especially pronounced in Coxsackie A viruses 7,14, 4, 9,10 and in Coxsackie viruses B 1-5.
In the case of acute serous meningitis, the patient may have symptoms not only of this disease, but also those associated with the damage to other organs and body systems that often restrict this enterovirus infection. Therefore, the combination of different forms of enterovirus diseases in the same patient is often observed.
Due to the fact that there is a great similarity between polioviruses, Coxsackie viruses and ECHO, they were combined into one genus Enterovirus, and in 1962 it was suggested to designate them with a specific name and a certain 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 in 1978 in Bulgaria an epidemic of poliomyelitis-like disease with a mortality rate of 65%. The same serotype 71 caused a major outbreak of people in Taiwan, with hemorrhagic pulmonary shock, encephalitis, and a 20% mortality. The virus of hepatitis A, isolated in 1973, was also very similar to enteroviruses due to its characteristics (size, structure, genome and epidemiological properties), therefore it is sometimes called enterovirus 72. The whole genus of human enteroviruses includes 68 antigenically different serotypes, including:
- polioviruses: 1-3 (3 serotypes);
- Coxsackie A: A1-A22, A24 (23 serotype);
- Coxsackie B: B1-B6 (6 serotypes);
- ECHO: 1-9; 11-27; 29-34 (32 serotype);
- human enterovirus: 68-71 (4 serotypes).
[Diagnosis of enterovirus diseases
To diagnose diseases caused by enteroviruses, use the virological method and various serological responses. It should be noted that against the backdrop of a sharp decline in the incidence of poliomyelitis, there is an increase in poliomyelitis-like diseases, which sometimes take the form of group outbreaks. In connection with this, for the diagnosis of poliomyelitis, it is necessary to bear in mind the possibility of detecting Coxsackie and ECHO viruses, that is, the study should be carried out in such cases on the whole group of enteroviruses. For their allocation, use intestinal contents, flushing and smears from the throat, less often a cerebrospinal fluid or blood, and in case of death the patient heals pieces of tissue from different organs.
The studied material is infected with 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, DSC, precipitation reaction, using reference mixtures of sera of various combinations. To detect antibodies in human sera with enterovirus infections, the same serological reactions (pH, color reactions, RTGA, RSK, precipitation reactions) are used, but for this purpose it is necessary to have paired sera from each patient (in acute period and in 2-3 weeks. From the onset of the disease). Reactions are considered positive when the antibody titer increases by at least 4 times. Two of these methods also use IFM (for detecting antibodies or antigen).