About Poliovirus or Enterovirus
Poliovirus is identified as ss-RNA Picornavirus (single stranded picornavirus). The virus is made up of RNA genetic strands. Poliovirus when ingested passes into gastrointestinal system. The virus in most cases undergoes mutation and prevents antibody production during initial phase of infection. Mutated virus survives outside cell and in feces when discharged from human body. Mutant poliovirus remains active in feces and become the source of spread of infection.
Poliovirus is also known as Enterovirus since most infection results in enteric fever. Few cases following initial gastrointestinal symptoms continues to infect poliomyelitis or polio. In less than 1% cases polio virus affects central nervous system. The infection of central nervous system results in severe muscle weakness and paralysis, known as poliomyelitis. Poliomyelitis or polio is a disabling disease and in most cases irreversible. The disease resulting in poliomyelitis is observed in young children less than 5 to 6 years.
How Does Poliovirus Spread?
The spread of poliovirus and its infection is mainly through oral route. An infected person can transmit polioviruses through feces or mucosal secretions during the initial asymptomatic phase of disease as well 1 to 2 weeks following disappearance of symptoms. The fecal spread of poliovirus may last for several weeks in asymptomatic individual following infection, since poliovirus remains active in the tissue for several weeks.
The poliovirus or enterovirus can live in dormant condition in gastrointestinal system in few individuals and periodically discharges in feces. Food and water is often contaminated by transmission of polioviruses from feces to hand to food and water. People who don’t have symptoms can still pass the poliovirus to others and make them sick.
Spread of Poliovirus Via Fecal Oral Route:
Poliovirus or Enteroviruses are discharged in feces during initial phase of infection as well as silent asymptomatic period. The infected individual contaminates the surroundings through frequent touch of anal area or improper hand cleaning after passing stool.
Feces are carried through sewer system and treated. Sewer and domestic water pipes often lie next to each other. During work, domestic water may get contaminated with sewer water resulting in rapid spread of poliovirus or infection. Similarly, well water in villages in Asia and Africa gets contaminated with sewer water. This results in spread of poliovirus or enteroviruses and polio infection.
Spread of Poliovirus Via Sneezing and Coughing
Poliovirus are present in nasal and oral cavity during asymptomatic or initial phase of infection. Enterovirus or polioviruses are released in air during coughing and sneezing. Healthy individuals are exposed to this viral infection when they breathe infected air.
Infected child or individual may smear mucus secretion or feces over surrounding furniture which becomes a source of spread of poliovirus. Healthy individuals become carrier as soon as the infected secretion is touched. The spread of enterovirus or poliovirus occurs when food is touched with contaminated hands prior to consuming the food. Poliovirus are resistant to acid secretion of stomach.
Risk Factors of Poliovirus or Enterovirus Infection
Poliovirus or Enterovirus infection is often asymptomatic. Following conditions or risk factors increases the spread of infection and severity of symptoms of poliovirus infections.
- Immune deficient
- Pregnancy with low immunity
- Young children
- Poor sanitation
- Contaminated Water supply- Well water, sewer water and drinking water,
- Endemic places
- Laboratory worker- Handling contaminated specimen.
Symptoms of Poliovirus or Enterovirus Infection
Poliovirus or enterovirus infection is presented as either asymptomatic or symptomatic condition, mostly observed in children of age less than 5 to 6 years. Poliomyelitis is more or less not seen for last few years in North America and Europe because of effective vaccination program. Poliovirus infection in 95% individuals does not cause any symptoms.
Symptoms of poliovirus infection are observed in 5% of the patients infected with poliovirus or enterovirus. Poliovirus symptoms last for 4 to10 days but in 0.5% of patients, virus progresses to spread in central nervous system, eventually causing severe damage of motor nerves, which results in selective muscle weaknesses and paralysis.
Polioviruses after 7 to 14 days of initial symptoms in 0.5% of the infected cases rapidly replicates in reticuloendothelial system, muscles, neurons in spinal cord and medulla oblongata.
Symptoms of poliovirus infection can be seen in asymptomatic condition, non-neurological common clinical manifestation and neurological expression of neuromuscular disease.
Asymptomatic Poliovirus Infection
Most studies suggest 95% of the patients are asymptomatic following poliovirus infection and infection is considered as silent infection. Poliovirus are discharged from the system through feces and during this period, poliovirus can spread through feces and contact. Few of these patients may indicate mild to moderate muscle pain and may remain carrier of poliovirus for few weeks.
Polio Infection with Non-Neurological Symptoms
The neurological and musculoskeletal symptoms of poliovirus are not observed in 4.5% of the patient during active infection. The following symptoms, which are non-neurological, are observed for 4 to 5 days. The poliovirus spreads in upper and lower gastrointestinal (GI) mucosal epithelial cells. The upper GI infection is observed in oral cavity and esophagus. Lower GI infection is located in the stomach and intestine. Patient completely recovers from this infection but polioviruses may remain active in feces for few weeks and cause spread of polio infection.
Symptoms and Signs of Poliovirus Infection –
Paralytic or Poliomyelitis Infection-
Infection resulting in paralytic poliomyelitis is rare and seen in less than 0.5% individual suffering with enterovirus or poliovirus infection. The clinical manifestation is divided in two phases. During first phase, all poliovirus symptoms of the non-neurological phase are observed, which last for 5 to 10 days. The first phase is also known as “Non-paralytic Phase”. The second phase is characterized by symptoms depending on the area of central nervous system affected by poliovirus infection. The second phase may last for several weeks.
This phase is divided in 3 types of spread of poliovirus infection; spinal, bulbar and spine-bulbar.
Spinal type of poliomyelitis enterovirus infection affects motor nerves in spinal cord.
Bulbar type is caused by destruction of motor nerves in medulla oblongata and pons.
Bulbo-spinal condition is observed when poliovirus attacks motor nerve in spinal cord and medulla oblongata.
The symptoms of poliovirus infection or paralytic type during second phase of infection include:
Spinal Poliomyelitis Infection
In this type, the following symptoms of poliovirus are noted.
- Loss of Reflexes: The reflexes in extremities need active sensory and motor nerve. The poliovirus infection causes irreversible damage of motor nerves, which causes loss of reflexes in lower extremities and occasionally in upper extremity.
- Muscle Spasm and Pain: This is observed in lower back and leg. Pain is severe even at rest. Pain is not relieved with pain killers.
- Floppy Limb: Irreversible damage of motor neuron in spinal cord causes loss of muscle tone and power, which results in floppy limb.
- Muscle Paralysis- The muscles are unable to contract with voluntary or involuntary demand once the motor nerve is not physiologically functional.
- Temporary paralysis is caused by reversible motor nerve damage.
- Permanent paralysis is caused by irreversible damage.
- Deformed Limb- Muscle paralysis follows atrophy of muscles. The asymmetrical muscle atrophy and paralysis following motor cell damage causes limb deformity because of pulling of bones of joint by atrophied muscles.
- Breathing Difficulties- Contraction and relaxation of intercostal muscle and diaphragm helps to breathe. Paralysis of intercostal muscle and weaknesses in diaphragm causes breathing difficulties.
Bulbar Poliomyelitis Infection
The bulbar infection when caused by poliovirus affects cortex (brain), mid brain, pons and medulla oblongata. The cranial polio viral infection causes cranial nerve damage resulting in lack of feeling of taste, difficulties in swallowing and breathing. In this second type of poliovirus infection, the symptoms noted include the following:
Taste- Bulbar poliomyelitis affects cranial nerve which supplies sensory fibers to tongue and taste bud. The nerve damage results in lack of sensation of taste.
Swallowing- Swallowing involves contraction and relaxation of pharyngeal and esophageal muscles. The actions of these muscles are controlled by cranial nerve. The paralysis of related (8th and 10th ) cranial nerve causes inability to swallow food, which results in regurgitation and difficulties in swallowing.
Breathing- Breathing predominantly occurs because of contraction and relaxation of the diaphragm, which is controlled by the cranial nerve. As the cranial nerve gets affected, the breathing too gets affected, which may be an important symptom.
Bulbo-Spinal Poliomyelitis Infection
The poliovirus infection affects spinal and bulbar portion of central nervous system. The disease causes symptoms of spinal and bulbar poliomyelitis infection.
1 of 25 cases of the abortive or non-polio infection results in symptoms of mild to severe meningitis. Severe meningitis is very rare. Initial symptoms observed are the same as seen in abortive or non-polio infection. Later, the following symptoms are observed suggesting meningitis and further investigation is essential to initiate aggressive treatment:
Post-polio syndrome is recurrence of poliovirus or enterovirus infection often observed after 15 to 40 years following initial enterovirus infection. The symptoms include:
Treatment of Poliovirus Infection
The treatment of poliovirus or enterovirus infection mainly depends on the type of infection and the way in which it affects.
Treatment of Abortive or Non-Polio Infection
- Tylenol and non-steroidal anti-inflammatory drugs (NSAIDs) for pain and fever
- Antidiarrheal medicines
- Anti-viral treatment
Treatment of Paralytic or Poliomyelitis Infection
- Antiviral medication
- Physiotherapy and exercise
- Intermittent positive pressure ventilation is recommended if patient is unable to breath, which may be observed in patient suffering with bulbar poliomyelitis.
- Diet and fluid replacement
Prevention of Poliovirus or Enterovirus Infection
Prevention of poliovirus infection is possible by adopting high standards of personal and community hygiene. Vaccines to prevent polio infection are also available and must be taken as recommended by the physician.
- Hygiene. Wash hands thoroughly after using toilet and before handling food. Drink boiled water or treated water.
- Contact. Avoid close contact with patient who may be suffering with polio infection.
- Vaccine. Make sure to take the prescribed vaccination to build resistance to infection.
Inactivated Poliovirus (IVP)
- Series of injection from age of 2 years to 4 to 6 years.
- Safe and effective
Oral Polio Vaccine (OPV)
- Attenuated (weak) poliovirus
- Low cost
- Easy to administered oral drops
- Rarely may cause polio and paralysis
Resistance to Infection
Infection or vaccine develops immunity. The infection and vaccine produces antibodies IgG and IgM. The antibodies secreted specific to poliovirus cover the surface of endothelial cells in gastrointestinal system and also circulate in blood. The increased concentration of anti-poliovirus IgG and IgM antibodies produces immunity against Poliovirus, which helps to weaken the viruses. The white blood cells then succeed in destroying the virus. Polio vaccine was available to use since 1957.
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