Taxonomy and Classification
Etymologically, the name of the genus comes from the Greek word enteron (gut), which directly indicates the primary habitat of these pathogens. The genus Enterovirus belongs to the family Picornaviridae.
There are two approaches to the taxonomy of this group:
- Historical classification divides them into polioviruses, Coxsackie viruses (groups A and B, named after the American town where they were first isolated), ECHO viruses (an acronym for Enteric cytopathogenic human orphan viruses), and numbered serotypes (68, 69, 70, and onwards).
- Modern nomenclature groups them into four main species: Enterovirus A, B, C, D, each encompassing various serotypes.
Morphology and Resistance
Enteroviruses are spherical and belong to the most simply organized viruses. Their capsid has a cubic symmetry, enclosing a single-stranded positive-sense RNA (+ssRNA).
The main structural feature is the complete absence of a lipoprotein envelope (supercapsid), as well as lipids and carbohydrates in their composition. This grants them specific resistance:
- Chemical resistance: the viruses are completely insensitive to ether, fat solvents, alcohols, phenol, and surfactants.
- Sensitivity: they are destroyed by oxidizing agents, formalin, and chlorine-containing preparations.
- Environmental survival: they persist for months in bodies of water, soil, and on fomites, withstanding a colossal pH range from 2.5 to 11.
- Physical factors: they rapidly die upon drying and exposure to ultraviolet radiation. When heated to 50 °C, inactivation occurs within 30 minutes, while boiling destroys virions instantly.
Cultivation features
In laboratory settings, most enteroviruses successfully replicate in primary and continuous human tissue cell cultures. Their presence is indicated by a pronounced cytopathic effect (CPE) or by the formation of plaques under an agar overlay.
An important exception is Coxsackie virus A, which replicates extremely poorly in cell cultures. Newborn mice are used for its identification, as well as for dividing Coxsackie viruses into groups A and B, by evaluating the pattern of pathogenicity. At the same time, ECHO viruses are completely non-pathogenic to laboratory animals.
Epidemiology and pathogenesis
The infection is widespread globally, often occurring in mass outbreaks, particularly among children. Enteroviruses are characterized by a distinct summer-autumn seasonality.
Sources of infection include sick individuals and asymptomatic virus carriers. Transmission occurs via two routes:
- Fecal-oral (primary): mediated by unwashed hands, contaminated water, food, and household items. Mechanical vector transmission by flies is also possible.
- Airborne droplet: relevant during the first 1–2 weeks of the illness when the pathogen is actively shed with nasopharyngeal mucus.
Mechanism of disease development: The virus enters through the mucous membranes of the nasopharynx or small intestine. Primary replication takes place there (in the epithelium and regional lymph nodes). Subsequently, the pathogen breaks into the bloodstream (viremia) and spreads throughout the body, settling in target organs.
Clinical Presentation, Immunity, and Diagnostics
Enteroviral infections are characterized by pronounced polymorphism. Depending on the tropism of a specific serotype, the following may develop:
- CNS involvement: poliomyelitis, serous meningitis.
- Cardromuscular disorders: myocarditis, epidemic myalgia.
- Respiratory syndromes: acute respiratory infections, "summer flu".
- Gastrointestinal issues: diarrhea and gastroenteritis.
- Cutaneous manifestations: exanthema (rash) and conjunctivitis.
Following recovery, lasting immunity is established. However, it is type-specific: it protects only against the specific serotype that caused the illness.
Virological and serological methods are used for diagnostics. Materials include nasopharyngeal swabs, feces, or cerebrospinal fluid (CSF). In serological testing, a key indicator is a 4-fold or greater rise in antibody titer when testing paired sera (the first sample is taken on days 4–5, and the second on day 14).
Briefly: answers to topical questions
Which structural proteins form the enterovirus capsid?
The enterovirus capsid is formed by four structural proteins. During viral replication, a single giant precursor—a polyprotein—is synthesized, which is subsequently cleaved into individual functional elements:
- VP1 — structural protein;
- VP2 — structural protein;
- VP3 — structural protein;
- VP4 — structural protein.
These proteins form a simple nucleocapsid with cubic symmetry, which lacks a lipoprotein envelope (supercapsid).
What specific clinical forms of disease are caused by Coxsackie viruses group B?
Coxsackie viruses group B (Coxsackie B) cause visceral pathology characterized by internal organ damage. Specific clinical forms include:
- Pleurodynia (Bornholm disease) — manifested by painful chest attacks, pleuritis, and fever;
- Myocarditis — specific cardiac involvement;
- Encephalitis — neurological manifestation of the infection;
- Poliomyelitis-like diseases — involvement of the central nervous system.
Infection of suckling mice or cell cultures is classically used to isolate these viruses.
Which cellular receptors do enteroviruses bind to upon entering the host cell?
The cited source indicates that the causative agent of acute anterior poliomyelitis, which belongs to enteroviruses, binds to lipoprotein receptors.
To memorize the main historical groups of enteroviruses, use the mnemonic PEC: Polio, ECHO, Coxsackie.
Class and exam questions
Why do enteroviruses not die when treated with alcohol?
They lack a lipid envelope (supercapsid). Because of this, alcohols, ether, and other fat solvents are ineffective against them.
Why are paired sera used for serological diagnostics?
To track the dynamics of the immune response. The diagnosis is confirmed if the antibody titer to the virus increases by 4 times or more between days 4–5 and 14 of the illness.
Can you get vaccinated against enteroviral infection?
Specific vaccine prophylaxis has been developed only against poliovirus. There are no vaccines against other enteroviruses; only non-specific protective measures are used.
What else to study on this topic
- Features of differentiating Coxsackie A and B viruses in mice
- Mechanism of the cytopathic effect during enterovirus cultivation
- Pathogenesis of poliomyelitis and motor neuron involvement
- Differences in antigenic structure: group-specific and type-specific antigens
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Other topics in the section "Picornaviruses (enteroviruses, poliomyelitis, Coxsackie, ECHO, rhinoviruses, hepatitis A)"
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