Enteroviruses are nonenveloped, icosahedral viruses whose genetic material is in the form of RNA. Therefore, they belong to the RNA viruses. They replicate in the cytoplasm of the infected host cell. As pathogens in humans, they can lead to many non-specific symptoms, especially gastrointestinal complaints and flu-like infections. The clustered occurrence of summer flu in the hot days is often due to enteroviruses. However, apart from this, they are also causative agents of known diseases such as polio (infantile paralysis) and hepatitis A.
What are enteroviruses?
Enteroviruses are a viral genus that includes a total of 9 species with many different subtypes. They are single-stranded RNA viruses, also known as pico-RNA viruses. Enteroviruses have an icosahedral shape and are on average about 25 nm in size. They are not enveloped. The genetic information of these viruses is in the form of RNA and is present as a single strand with positive polarization. Because of the positive polarization, the RNA of the viruses can be translated directly into protein when they multiply in the host cell. In contrast, DNA-containing viruses must first convert their genetic material into RNA.
Occurrence, distribution, and characteristics
Enteroviruses occur not only in humans but also in pigs, rodents, cattle, and various species of monkeys. In contrast, there is no geographic restriction of the distribution area; enteroviruses occur worldwide. However, some of the diseases they cause are much more common in developing countries, where the necessary preventive measures, such as widespread vaccination or certain hygienic standards, cannot be adequately implemented. Enteroviruses are acid-stable. The following types of enteroviruses that are significant for humans are generally distinguished: polioviruses, hepatitis A viruses, coxsackie viruses, echoviruses, and human enteroviruses 68-71 and 73. Droplet and smear infection are possible routes of transmission, with fecal-oral infection (smear infection) being much more common. It can occur, for example, via food contaminated with stool or saliva or drinking water, toys and hands. Swimming pools or lakes contaminated with feces are also a significant source of infection. Therefore, infections with enteroviruses in the temperate climate zone occur particularly frequently in summer. If a pregnant woman becomes infected with enteroviruses, she can also infect the child via the placenta, which can have serious consequences, including pneumonia in the infant. The incubation period for an infection with enteroviruses can be two to 35 days, but usually ranges between five and seven days on average. Enteroviruses multiply in the patient’s intestinal wall and mesenteric lymph nodes after infection. From there, they can enter the patient’s bloodstream; transient viremia may occur. Subsequently, infestation of almost any organ in the body is possible. Therefore, there may also be many different symptoms, which alone are not sufficient for a definite clinical diagnosis. Detection is usually by virus culture in cell culture or genetic methods such as qr-RT-PCR.
Diseases and symptoms
No fixed link exists between a type of enterovirus and a particular clinical picture. Symptoms are often nonspecific and overlap between different enteroviruses as well as other pathogens. However, some enteroviruses are particularly frequently detected in certain clinical pictures, so they are definitely considered typical. Among the most common non-specific symptoms are complaints of the gastrointestinal tract. Polioviruses, which mainly affect children, cause flu-like infections or aspetic meningitis (inflammation of the brain), possibly affecting the central nervous system. The best-known consequence of infection with polioviruses is probably polio. Symptoms of polio include fever, fatigue, headache, nausea, aching limbs, and stiff neck. However, permanent paralysis develops in only some of those infected. The most effective protection against the disease is vaccination. There is no cure for polio. Today, polio is no longer prevalent in most countries due to the good vaccination status of the population.Coxsackie viruses are also triggers of flu-like infections, but also lead to infections of the respiratory tract or the heart muscle, as well as hand-foot-and-mouth disease and Bornholm disease. Newborns and children are particularly at risk from Coxsackie viruses. Echoviruses manifest in nonspecific febrile illnesses and respiratory infections. Symptoms also include diarrhea. Echoviruses are especially often detected in aseptic meningitis and inflammation of the pericardium or myocardium. Hepatitis A virus is also known as enterovirus 72 and is the causative agent of hepatitis A. After spreading through the blood of the infected person, there is an attack on the liver, which leads to inflammation (hepatitis). The so-called human enteroviruses 68-71 and 73 usually cause acute respiratory infections. In some cases, polio-like symptoms also occur. However, most infections with enteroviruses, up to 90-95%, remain completely symptom-free and are therefore often not even noticed. The therapy of an infection with enteroviruses is symptomatic and depends strongly on which organ system is affected. Drug therapy for the causes is not yet possible. After infection with enteroviruses, the body has a permanent serotype-specific immunity to the type of virus with which infection occurred.
