What are enteroviruses?
The genus Enterovirus belongs to the Picornaviridae family and includes the following viral groups:
- Coxsackie viruses A1 to A21, A24 and B1 to 6;
- Echo Viruses 1 to 7, 9, 11 to 21, 24 to 27 and 29 to 33;
- Enteroviruses 68 to 71;
- Poliomyelitis viruses of types 1 to 3.
In the 1970s, four new enterovirus types were discovered – 68, 69, 70 and 71, which cause acute infectious diseases characterized mainly by the development of serous meningitis, acute hemorrhagic conjunctivitis and polio-like conditions.
Of the new human enteroviruses, the enterovirus type 71 has the greatest
clinical significance. It was discovered in 1969. from N. Schmidt and causes
sporadic cases with diverse clinical course – vesicular stomatitis, serous
meningitis and polio-like diseases.
Structure and cultivation.
Enteroviruses have a diameter of approximately 25-30 nm and isxohedral symmetry. They do not have envelope, and virions are relatively simple to make up – they consist of a protein capsid surrounding the single-stranded RNA genome. The genome has approximately 7500 nucleotides and contains a single open reading frame that encodes a polyprotein, which is then processed to produce the structural (capsid) proteins VP1, VP2, VP3 and VP4.
Human enteroviruses are cultured using the biological method of experimentally infecting experimental mice, and enterovirus type 71 can also reproduce in cell cultures where cytolysis (cellular degradation) is induced.
The only source of infection with enteroviruses 68 to 71 is the sick person and the infectious agents. Viral diseases occur sporadically and epidemically. Enteroviruses 68 and 69 are most commonly found in basymptomatic carriers, but type 69 is sometimes isolated from children with pneumonia.
Enterovirus 70 causes acute hemorrhagic conjunctivitis. It was isolated for the first time in 1969 to 1971 from the conjunctiva of patients in Africa and Southeast Asia.
Enterovirus 71 is isolated from patients with meningitis, encephalitis, and paralysis, whose symptoms are similar to those of polio. Outbreaks of enterovirus foot-and-mouth disease 71 occurred in China in 2008 and are related to 4,500 cases and 22 deaths in infants and young children. The main mechanism for the transmission of enterovirus 71 is fecal-oral – through contaminated hands, food, water and household items. In Bulgaria, diseases caused by this type of enterovirus were registered in 1975, when 713 persons became ill.
Pathogenesis and clinical presentation.
Enterovirus 70 causes acute hemorrhagic conjunctivitis. The source of the infection is a sick person who releases the enterovirus in large quantities with purulent exudate from the eye. The incubation period of the disease is approximately 24 hours and takes the form of small epidemics. The disease almost always goes on for 5 to 7 days, without long-term consequences and with good prognosis. However, corneal microinfection has been reported after treatment with topical steroids, which requires appropriate antimicrobial therapy.
Enterovirus type 71 causes a variety of diseases:
- polio-like conditions;
- exanthema and vesicular stomatitis;
- acute respiratory infections.
After entering the oral cavity (by fecal-oral mechanism), the virus reaches the small intestinal cells, where primary viral replication takes place. Hematogenous scattering of the virus is also possible, in which various organs and systems are damaged.
Type 71 infection usually causes mild infection in adults and children. However, children under the age of 5 are at higher risk of developing a serious infection.
- throat secretion;
Enteroviruses type 68, 69, 70 and 71 are isolated by infecting experimental animals or cell cultures.
There are kits to detect Human enterovirus. The technique is called PCR, and it is a quick method of detection of the virus