Polio (also often called polio) is an infectious disease that primarily affects the nervous system. As confirmed by international sources such as the World Health Organization, this pathology is caused by poliovirus, a viral agent composed of RNA and a protein capsid. But what are the known types of poliomyelitis?
According to several studies, we can distinguish three serotypes (or several variants). Seriotype 2 was last identified in India in 1999, so it is now considered eradicated. Variants 1 and 3 continue to circulate among the population today. They are both highly infectious and responsible for paralytic poliomyelitis.
Distribution of poliomyelitis
The World Health Organization reports useful data to give us an idea of the distribution of the poliovirus globally. Here are a few:
- In 1988, at the beginning of the campaign to fight this disease, there were over 350,000 cases worldwide.
- Thanks to containment efforts and vaccines, only 18 cases were reported worldwide in 2018 (a reduction of 99%).
- This condition mainly affects children under five.
We could therefore say that polio is a disease of the past. Still, we must keep our guard up, as estimates indicate that if the latest outbreaks of the virus are not eradicated, more than 200,000 new cases could arise in less than 10 years.
Types of poliomyelitis
Clinical studies indicate the existence of four types of poliomyelitis with different outcomes:
- Asymptomatic: represents 90% of cases globally.
- Minor disorders: corresponds to 9% of cases and is characterized by the presence of fever, malaise, nausea, vomiting, diarrhea and constipation.
- Aseptic non-paralytic meningitis: present in a percentage that varies between 1% and 2% of cases.
- Paralytic poliomyelitis: less than 1%.
The first two develop as benign, so we will focus on aseptic non-paralytic meningitis and paralytic poliomyelitis. We explain in the following lines everything you need to know about both pathologies.
Aseptic non-paralytic meningitis
According to the scientific data available, aseptic meningitis is an infectious process that affects the tissues lining the meninges of the central nervous system (CNS), causing inflammation. It is characterized by the following symptoms:
- Headache (headache) and stiffness in the nape.
- General malaise.
- Muscle aches.
- Loss of appetite and vomiting.
According to further bibliographic sources, aseptic meningitis of viral origin (such as that caused by poliovirus) has a favorable prognosis. It is good to know that poliovirus is not the only virus that causes the onset of the disease: enteroviruses, herpesvirus or HIV have also been identified as responsible for the same.
Despite a benign course, this condition may require hospitalization and the administration of antibiotics for a certain period of time . Yes, we are talking about antibiotics although the disease is caused by a virus, in order to prevent a meningitis of bacterial origin, much more dangerous.
In this case we are talking about the most serious manifestation of poliovirus infection. Some sources estimate that one in 200 patients suffers from irreversible paralysis, among them 10% will have muscular problems of the respiratory system that will cause their death.
Diagnosis is simple, as the symptoms are particularly aggressive. Bibliographic sources report that intense myalgia (muscle pain) and limiting muscle spasms culminating in chronic limb weakness occur five days after infection. Usually, the paralysis reaches its peak within a week of the infection.
The acute mortality rate varies between 5 and 20% and there is no cure. If the subject passes the critical phase, however, the paralysis tends to improve over the years thanks to reinnervation by healthy neurons. Depending on the affected site, we can observe three types of paralytic poliomyelitis: spinal, bulbospinal and bulbar.
50% of patients who survive this severe manifestation report lifelong weakness, and between 20 and 85% of individuals who suffered from polio as a child may develop a post-polio syndrome characterized by progressive muscle atrophy.
Types of poliomyelitis: what should we keep in mind?
Polio is a disease now under control almost everywhere in the world. 90% of cases are asymptomatic, so today it is very difficult for a clinical picture associated with poliovirus to present itself.
On the other hand, there are vaccines that can be administered orally and intravenously with an efficacy equal to 99% of the total of the three dosages. Thanks to global investments to eradicate all poliovirus serotypes, polio may be a distant memory in a short time.