Enterovirus

What is Enterovirus?

Enteroviruses belong to a larger family called Picornaviridae. This group includes viruses like coxsackieviruses, rhinoviruses, polioviruses, and echoviruses. They are responsible for a range of illnesses, from the common cold to serious conditions like polio and aseptic meningitis. In fact, these viruses are among the most common sources of infection around the world.

This enterovirus family is divided into 12 groups, categorized as enteroviruses A to J (including coxsackieviruses, polioviruses, and echoviruses) and rhinoviruses A to C. Over 200 unique strains or ‘serotypes’ have been identified within this family.

The reason these viruses are called enteroviruses is because they tend to target the human digestive tract. However, the diseases they cause can vary greatly, and we don’t fully understand how all of them work.

Scientists often categorize these viruses in different ways, such as:

• Comparing rhinoviruses to other enteroviruses that are not rhinoviruses
• Comparing polioviruses to other enteroviruses that are not polioviruses
• Comparing rhinoviruses and respiratory enteroviruses to other enteroviruses that do not affect the respiratory system
• The term ‘Human enteroviruses’ (HEV) is used to refer to enteroviruses A to J, but it does not include a particular type of enterovirus (EV-I which is a camel-borne virus) or the rhinoviruses.

Unfortunately, there isn’t a vaccine or an effective treatment for diseases caused by these viruses, apart from the poliovirus vaccine. Infections usually resolve on their own, but they can lead to significant health issues and can have a major economic impact.

What Causes Enterovirus?

Enteroviruses are small viruses that belong to a family known as Picornaviridae. These viruses are about 15 to 30 nanometers in size and carry a specific type of genetic material known as positive-sense single-stranded RNA. This means that they do not contain an outer protective layer of lipid (fat), and because of a feature called an internal ribosomal entry site (IRES), they can produce proteins in a unique way.

One specific group of enteroviruses, the rhinoviruses, can infect both upper and lower parts of the respiratory system. Interestingly, unlike many other viruses in the Picornaviridae family, rhinoviruses thrive at a slightly lower temperature (33 degrees celsius). This likely explains why they frequently cause illnesses in the upper respiratory system. Research has shown that at higher temperatures, our body’s cells are more resistant to these viruses.

Other types of enteroviruses, which aren’t rhinoviruses, are often the main culprits in viral infections of the central nervous system. These viruses first infect the digestive system, and they are able to endure the very acidic environment in the stomach. This allows them to move on to infect cells in the small intestine, where they start causing problems.

A wide range of diseases can result from enterovirus infections, including polio, certain types of heart inflammation, conditions causing fever, pneumonia, illnesses causing rash and blisters like hand, foot, and mouth disease, conditions affecting the nervous system including aseptic meningitis and encephalitis, common colds, ear and sinus infections, pancreatitis, and sometimes there may be no evident symptoms.

Different types of enteroviruses are often linked with particular diseases. For example, specific types of these viruses are associated with polio, heart inflammation, eye infections, lung disease, skin infections, paralysis, respiratory problems, and certain types of meningitis.

Risk Factors and Frequency for Enterovirus

Enteroviruses are common and can cause diseases all around the world at any time of the year. These viruses are mainly found in children, but their effects, how often they occur, and how they show symptoms can differ a lot depending on the type of virus.

Non-rhinovirus enteroviruses, one type of these viruses, have different occurrence patterns based on their type. They often cause diseases during the summer. In warmer climates, these viruses can be found all year long and can cause mixed infections. Males are more often affected than females, and they also tend to have more severe illnesses. Transmission of these viruses usually happens from person to person, and it’s often through fecal-oral or fecal-hand-oral routes.

Polio, a disease similar to what these viruses cause, has been around since 2 millennium BCE. With the improvement of hygienic living conditions came a new pool of people susceptible to serious illness, leading to epidemics. The three types of polio virus, which are part of the Enterovirus C (EV-C) group, were identified, and in 1954, a vaccine was created. Vaccines for these viruses are only available for polio, and it has been effective. The western hemisphere was free of paralytic polio in 1991, but it still occurs in parts of Asia and Africa.

Coxsackieviruses and echoviruses, also a part of these viruses, are big reasons for aseptic meningitis around the world. Outbreaks of the non-rhinovirus enteroviral disease have recently occurred, with a large outbreak of Enterovirus D68 (EV-D68) happening in 2014. This outbreak not only caused respiratory symptoms but also acute flaccid paralysis, a disease marked by spinal cord gray matter lesions, in patients generally 5 years old.

Rhinoviruses, on the other hand, cause a lot of cost due to illnesses each year in the United States. They cause more than half of upper respiratory infections. Children usually experience 8 to 12 infections per year, while adults have 2 to 3 per year. These viruses peak in the spring and fall, except for Rhinovirus C viruses, which peak in the winter. Unlike non-rhinovirus enteroviruses, rhinoviruses only affect humans.

These viruses are usually transferred when nasal mucosa or eye conjunctiva is directly touched. They can survive indoors at room temperature for days and can live on undisturbed skin for hours. Like respiratory enteroviruses, they are also spread through aerosols. Blowing your nose too much is linked with rhinosinusitis, which studies show is related to pressure levels while blowing your nose.

Enteroviruses have been known to cause outbreaks in healthcare settings. Observing enteroviruses is usually passive, mainly due to the large number of different types that can infect humans and also because the illnesses caused by them are often mild. However, new models that use already existing surveillance systems have been created. These, along with more accurate PCR testing, allow disease patterns to be forecasted with some accuracy, which can be important for vaccine development.

Developing a vaccine can be hard due to the limited cross-reactivity between the many types of enteroviruses, making it hard to develop vaccines that can handle multiple types. Other difficulties come from uncertainty about how vaccine-derived immunity changes over time, as seen in the poliovirus vaccine.

Signs and Symptoms of Enterovirus

Enteroviral disease symptoms are often linked to the specific type of disease. Rhinovirus, for example, can cause symptoms like fever, coughing, sneezing, runny nose, earache, sore throat, nasal congestion, and sinus pressure. It can also lead to wheezing and shortness of breath.

Other types of enteroviruses can produce different symptoms such as fever, weariness, stomach upset, rashes, swollen lymph nodes, frailty, changes in mental state, cough, sneezing, sore throat, and chest pain.

Diagnosing enteroviral disease usually depends on understanding the disease’s progress, severity of symptoms, and any risk factors. This can be determined by asking about the patient’s onset of symptoms, the type and intensity of these symptoms, whether they have been vaccinated, and if they have been exposed to certain diseases.

Patients with conditions like preterm birth, bronchopulmonary dysplasia (a chronic lung disease), weak immune system, blood disease, or diabetes can be more at risk, and this can be helpful in making treatment decisions. It doesn’t necessarily mean they will have more infections, but when they do, these infections could be more serious.

A physical exam can reveal signs of upper or lower respiratory disease, signs of meningitis, weakened muscle strength, decreased reflexes, low oxygen levels, or changes in mental state.

Testing for Enterovirus

Doctors use various methods to help diagnose enteroviruses. These viruses cause a range of illnesses, affecting various parts of the body. For respiratory diseases caused by enteroviruses, or if breathing problems are seen, abnormal findings from a chest x-ray or CT scan (which is a specialized x-ray procedure) might provide clues.

In cases where a patient exhibits changes in mental status or experiences paralysis, an MRI of the head or spinal cord could be necessary. An MRI is a scan that uses strong magnetic fields to make detailed pictures of the inside of the body.

Sample swabs taken from the nose, throat and rectum can be sent for a particular type of lab test known as a viral polymerase chain reaction (PCR). This test can identify the virus by its genetic material. Lumbar puncture, or a spinal tap, might be needed if there’s a suspicion the virus has involved the central nervous system, which comprises of the brain and spinal cord.

If a patient has chest pain or if there’s a chance of inflammation affecting the heart muscle or sac surrounding the heart (known as myopericarditis), an electrocardiogram (ECG) should be done. ECG is a simple and quick test that checks the heart’s rhythm and electrical activity.

The doctor will decide whether other specialized blood tests are required or not. These could include tests to check for kidney and liver function, complete blood count, and cardiac biomarkers (which are substances found in the blood that rise in response to heart damage).

It’s important to note that even if the virus can be identified in test samples, it doesn’t always indicate an illness — the virus could be present without causing any symptoms. If clinicians suspect an infection, they will carry out further investigations to rule out infections by bacteria, fungi, and other viruses.

Treatment Options for Enterovirus

When you catch an enterovirus, the most common treatments are intended to help manage and relieve your symptoms as your own body fights off the virus. For mild symptoms, you might take over-the-counter drugs like anti-inflammatories, acetaminophen for pain and fever, and medications to suppress coughs and clear nasal congestion. If the virus is affecting your lungs and causing severe respiratory symptoms, you may need additional oxygen or mechanical help with breathing. Those with serious conditions affecting the nervous system will need close monitoring by their doctors.

Unfortunately, there aren’t currently any antiviral drugs that are approved by the FDA specifically for treating enteroviruses. There are a few that have been trialed but failed to gain approval due to potential issues with drug interactions, resistance, and safety. For instance, a drug called pleconaril has been used in a few cases and showed some promising results, but didn’t get approval. It’s still useful though as a starting point for developing future medications.

Interestingly, a drug called Fluoxetine, which is currently approved, has been shown in lab studies to have significant activity against one particular strain of enterovirus. However, this effect is unrelated to its usual mechanism as an SSRI (a type of antidepressant), and this finding still needs to be explored further in clinical trials.

Researchers are also looking into a treatment using intravenous immunoglobulin therapy, which involves injecting disease-fighting antibodies, or immunoglobulins, into the bloodstream. This could potentially help to both prevent and treat enterovirus infections.

Some people find that taking echinacea or vitamin C, which are commonly used in folk medicine, can help to slightly reduce the duration or severity of their cold symptoms caused by rhinoviruses, which are a type of enterovirus. Early supplementation with zinc can also possibly help to reduce both the length and severity of cold symptoms. However, the scientific evidence on these treatments is inconsistent. First-generation antihistamines (which usually cause drowsiness) may be used to reduce runny noses and sneezing, but won’t help with other symptoms.

If you happen to be co-infected with a bacterial or fungal pathogen, it should be treated with the appropriate antimicrobial therapy. Any existing chronic conditions like diabetes should be well-managed during this time.

Creating vaccines for enteroviruses is quite challenging due to the great many distinct types of these viruses, their limited cross-reactivity, and the unpredictability of specific types’ spread and impact. So far, only poliovirus, which is one form of enterovirus, has an effective vaccine. To maintain protection, this vaccine requires repeated booster shots.

What else can Enterovirus be?

When considering illnesses caused by enteroviruses, physicians need to consider a wide variety of conditions because these viruses can cause many different diseases. To make an accurate diagnosis, they look at how the disease presents itself.

Diseases that can resemble rhinovirus infection include:

• Influenza (flu)
• Adenovirus infection
• Streptococcal pharyngitis (strep throat)
• Haemophilus influenzae (a type of bacteria)
• Bacterial sinusitis (sinus infection)
• Allergic rhinitis (hay fever)
• Pertussis (whooping cough)
• Bronchitis
• COPD exacerbation (sudden worsening of COPD symptoms)
• Asthma exacerbation (sudden worsening of asthma symptoms)
• Pneumonia

For enteroviral infections other than rhinovirus, physicians may consider the following:

• CNS tumor (brain or spinal cord tumor)
• Guillain-Barre syndrome (a rare neurological disorder)
• Bacterial meningitis (inflammation of the protective membranes of the brain and spinal cord)
• Autoimmune disease
• Gastroenteritis (stomach flu)
• Toxic ingestion (swallowing harmful substances)

What to expect with Enterovirus

Most illnesses triggered by enteroviruses (a type of virus) are mild and will get better on their own. The seriousness of the disease often depends on the specific strain of the virus and on the person’s pre-existing health conditions and risk factors. Typically, symptoms go away within a week to two weeks, and patients fully recover.

However, some conditions like persistent encephalitis (long-lasting brain inflammation), paralytic poliomyelitis (a form of polio that causes muscle weakness or paralysis), and severe respiratory diseases leading to breathing failure can result in serious outcomes. These conditions indicate the worst prognosis, meaning they can be very challenging to treat and can significantly impact the patient’s health.

Possible Complications When Diagnosed with Enterovirus

Enteroviral infections can lead to various complications, such as secondary infections, progression to a persistent or chronic disease, permanent paralysis, damage to lung tissue, and worsening of existing health conditions. Among these, acute worsening of chronic obstructive pulmonary disease (COPD) and asthma are frequently seen issues associated with rhinoviral infections.

Since there are no officially approved treatments for enteroviruses, it is crucial to focus on reducing risk factors and preventing other infections to manage the complications effectively.

Common Complications of Enteroviral Infections:

• Development of subsequent infections
• Progression to persistent or chronic disease
• Irreversible paralysis
• Destruction of lung tissue
• Worsening of already present diseases
• Acute exacerbations of COPD and asthma (especially from rhinoviral infections)

Prevention Strategies:

• Reducing risk factors
• Preventing other infections

Preventing Enterovirus

Practices like maintaining distance from others, washing hands regularly, and keeping surroundings clean can help in preventing the spread of diseases caused by enteroviruses. These viruses often spread quickly within families, and children are usually the most likely to carry and spread them. That’s why it’s especially important for children to practice good hand hygiene, as this can significantly reduce the spread of the disease. Hospitals may also consider limiting visits from school-aged children to help control the spread.

In scenarios where there’s a large-scale outbreak in a community, it’s advisable to increase monitoring of the disease spread and implement specific action plans, like asthma care plans for rhinoviruses.

Disease outbreaks associated with enteroviruses in healthcare settings have been recorded, and they can cause significant health issues and even death. Therefore, healthcare workers should take necessary precautions, including using appropriate protective gear, when treating patients showing symptoms of enteroviral or respiratory illnesses. Wearing masks is recommended, as the virus can spread through the microscopic droplets in the air. Healthcare workers who show symptoms of the disease could possibly spread it to their patients, so it’s essential they take appropriate precautions as well.