Introduction
Poliovirus is a human enterovirus, which causes a highly contagious, viral, and life-threatening disease called polio or poliomyelitis.
The name poliomyelitis originated from the Greek words “polio” and “myelon,” which mean grey and marrow, respectively.
The disease mainly affects humans, and it is transmitted through the fecal-oral route from asymptomatic carriers or patients.
In areas with poor sanitation measures, there is a rapid spread of the disease.
The most susceptible population includes young children, pregnant women, and people with a compromised immune system.
The virus belongs to the family Picornaviridae, genus enterovirus, and species enterovirus C. It is an RNA virus, which is single-stranded and positive sense.
There are three serotypes of the virus (type 1, 2, and 3), which cause the disease. They each have a different capsid protein.
Pathogenesis of Poliomyelitis
The virus enters the oropharynx and undergoes multiplication in the lymph nodes and tonsils located in the neck region. It also multiplies in the small intestines and the Payer’s patches.
After 5 days of infection, poliovirus can be recovered from stool and throat swabs of infected persons.
The virus enters the brain through the afferent nerve pathway because of its high affinity for receptors CD155, which helps the virus to attach and enter the brain cells.
It causes severe damage to the anterior horn, and it may extend to the anterior horn and motor neurons in the hypothalamus and thalamus.
In extreme cases, the virus causes death, and it is mainly due to respiratory paralysis.
Symptoms of Poliomyelitis
About 72% of the patients are asymptomatic carriers of the poliovirus, and they do not exhibit any signs (Centers for Disease Control and Prevention [CDC], 2019).
Some patients exhibit flu-like symptoms such as headache, nausea, stomach pain, tiredness, sore throat, and fever.
Such symptoms occur for two to five days and then fade.
In other instances, the patients have issues in concentration and their memory is also affected.
Moreover, they have difficulties in swallowing and experience prolonged periods of fatigue.
In severe cases, patients develop nervous signs such as paralysis, meningitis, and paresthesia.
The most severe symptom is paralysis, and it occurs in one person for every two hundred infected persons (CDC, 2019). In this case, the virus causes extreme muscle spasms in the neck, causing difficulties in breathing, and eventually, death.
Besides, patients may lose reflexes and have deformed limbs, especially at the feet, hips, and ankles, and experience muscle pains.
One out of twenty-five persons with polio develops meningitis, an infection of the spinal cord and brain (CDC, 2019).
It is possible for the virus infection to reoccur, even when someone has recovered. In post-polio syndrome, patients experience joint and muscle weaknesses, muscle wasting, pain in the muscles, breathing difficulties, and a low tolerance for cold environments.
Vaccination
In 1988, there was a consensus in the World Health Assembly to eliminate poliomyelitis (Marin et al., 2017).
Since then, there has been a rapid decline in the number of cases of wild poliovirus. This achievement was mainly because of the trivalent oral poliovirus vaccine.
The vaccine contains live, attenuated polioviruses of serotypes 1, 2, and 3.
According to Marin et al. (2017), from 2000, the United States of America started to use an inactivated vaccine against polio exclusively. As with the previous vaccine, the inactivated form is also effective against the three serotypes.
In 2013, the World Health Organization (WHO) put measures to ensure that the world would be free of polio of 2018 through the Global Polio Eradication Initiative (Thompson & Kalkowska, 2021).
One of the world’s first outstanding accomplishments in the fight against polio was eradicating serotype 2 in September 2015 (Marin et al., 2017).
With the eradication, there was a need to remove the possibility of infection by type 2 virus in the trivalent vaccine. Hence, all countries using the oral poliovirus vaccine switched to the bivalent vaccine in April 2016.
Vaccination Setbacks
Oral poliovirus vaccines have been vital in polio eradication campaigns.
However, the main setback of this type of vaccine is low vaccinations in some areas. This creates a risk for the reemergence of circulating vaccine-derived polioviruses (cVDPV), and consequently, an outbreak of poliomyelitis with similar symptoms as those seen in the case of wild polioviruses.
For instance, type 2 serotype accounts for more than 94% of cVDPV cases, and there have been over 600 polio cases since 2006 (Marin et al., 2017).
Moreover, in 2015, type 2 cVDPV was detected in sewage samples, which indicated a risk of a reemergence of the disease.
Despite the vaccines providing life-long protection against the virus, they do not stop its transmission in a population.
All children and infants should be administered the vaccine against polio. The routine entails vaccination at 2, 4, 6 months through to one and half years, and then at four to six years (Marin et al., 2017).
The final dose is administered on the fourth birthday, and it should be given after more than six months after the previous dose.
There should be a time gap of at least six months between the third and fourth dose.
The use of inactivated poliovirus vaccines should be encouraged against the oral poliovirus vaccine due to the risks associated with the continued use of the latter, such as cVDPV.
Therefore, the cessation of using oral poliovirus vaccine will help maintain high immunity levels in a population and simultaneously eliminate risks of cVDPV.
References
Centers for Disease Control and Prevention. (2019). What is polio? Web.
Marin, M., Patel, M., Oberste, S., & Pallansch, M. A. (2017). Guidance for assessment of poliovirus vaccination status and vaccination of children who have received poliovirus vaccine outside the United States. Morbidity and Mortality Weekly Report, 66(1), 23-25. Web.
Thompson, K. M., & Kalkowska, D. A. (2021). Potential future use, costs, and value of poliovirus vaccines. Risk Analysis, 41(2), 349-363. Web.