Poliomyelitis (Polio)
Poliomyelitis, or polio, is an infectious disease of viral origin, extremely contagious, caused by three different types of polioviruses (1,2,3), belonging to the enterovirus genus.
In some countries, poor sanitary conditions, badly functioning sewage systems, difficult access to drinking water, crowded living conditions, and the absence of health surveillance systems, are among the main causes of infection. In the Western world, thanks to extensive vaccination campaigns, polio-virus infections are now under control (99% decrease in cases, since 1988).
CAUSES
The cause of polio is the poliovirus, a single-stranded RNA virus of the enterovirus genus with a capsid (the protein structure that encloses the nucleic acid), which occurs in three serotypes: PV1, PV2, PV3, which are distinguished by the composition of the capsid.
Once the virus invades the host, it moves on to the intestine, where it starts replicate, resulting in the symptoms of the disease. More specifically, it can remain in the intestines (in these cases symptoms tend to be mild or absent), or it can enter the bloodstream, reaching the central nervous system.
TRANSMISSION
Polio is an orofecal-transmitted disease, which means it can be transmitted directly through contact with the faeces or urine of infected individuals, or indirectly through ingestion of contaminated food or drink. It can also be transmitted through saliva or respiratory droplets, emitted when an infected individual coughs or sneezes. The virus can affect people at any age but, generally, the most vulnerable are children under 5 years of age.
GEOGRAPHICAL DISTRIBUTION
Thanks to the eradication program initiated in 1988, polio has become a very rare disease, particularly in industrialised countries. In some developing areas of Africa, and the Middle East, the disease is a public health problem. WHO estimates there are 200,000 cases of polio per year.
SYMPTOMS
The incubation period of polio normally ranges from 4 to 35 days.
Symptoms initially manifest as fever, weakness, headache, stiff neck, muscle pain, and vomiting. In 1% of affected individuals, the virus invades the nervous system, causing irreversible paralysis (usually in the lower limbs). 5-10% of these cases result in death due to paralysis of respiratory muscles.
DIAGNOSIS
Some of the features that allow identification of the disease are stiffness in the back and neck, back pain, difficulty breathing and swallowing, and signs of abnormal reflexes. Diagnosis can then be confirmed after testing for the specific agent in a sputum, cerebrospinal fluid, or stool sample within the first few days of disease onset.
TREATMENT
To date, there is no specific treatment for polio infections.
Treatment is supportive and based on alleviating symptoms. These include a variety of interventions, ranging from simple rest in mild cases and the use of painkillers and antipyretics for flu-like symptoms, right the way through to assisted ventilation, physiotherapy, and braces in the case of more severe problems.
PREVENTION
Polio is widespread and has a higher prevalence in places with poor hygiene conditions and countries with inadequate public health controls and governance systems. The only weapon to counter the spread of poliovirus is the vaccine, which effectively protects against all serotypes of the virus.
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