“The virus is very present in the environment and if there is no effective water treatment, it is difficult to escape it”
Polio is a highly contagious infectious disease caused by a virus called “poliovirus“. There previous poliomyelitis Acute is the most common form and mainly affects children under 5 years old. “It is characterized by flaccid paralysis, loss of muscle tone which can affect muscles throughout the body“, explains Dr. Maël Bessaud from the Viral Populations and Pathogenesis unit at the Pasteur Institute.”This disease is not directly due to muscular damage but to the multiplication of a virus in the nervous system. This multiplication is at the origin of the destruction of nerve fibers“, he specifies.
History: What is the origin of polio?
“Before the vaccine era, polio was one of the most terrible scourges of childhood. In the 1980s, polio still affected several hundred thousand children worldwide each year. To defeat the disease, WHO launched the Global Polio Eradication Initiative in 1988. It is based on two pillars: surveillance, which aims to detect the circulation of poliovirus as early as possible, and vaccination of all children in the world.“, notes thePasteur Institute on its website. Today, two polio strongholds remain in Afghanistan and Pakistan and in the countries of Central Africa.It is truly a childhood disease. The virus is very present in the environment and if there is no effective water treatment, it is difficult to escape, which is why children are exposed to the virus at a very young age. This is also why it is a forgotten disease in France and other countries with a sophisticated wastewater treatment system.“, adds the specialist.
What is the mortality rate of polio in France?
“The last indigenous case in France dates back to 1988 and the last imported case dates back to 1995”recalls Maël Bessaud. The elimination of poliomyelitis was declared in Europe by the WHO in 2002. According to thePolio Association Francethe last deaths due to polio in France date back to 1978.
What causes polio?
There are three types of poliovirus that can cause polio.The virus multiplies in the intestine, so it is excreted in the stools. It is very resistant in the environment. It is transmitted directly by dirty hands for example or through contaminated water, this can be bathing water, drinking water or water used to wash food or cook for example.” explains Maël Bessaud.
What are the symptoms of polio?
“Symptomatic forms are rare. In at least 90% of cases, even 99% of cases, the infection is inapparent. Most people are infected with the virus, they excrete it through the stool and they are cured. They may have a febrile syndrome, a mild fever, sometimes diarrhea but nothing serious.“, continues the specialist. The virus only causes muscle paralysis, which is called poliomyelitis, if it reaches the central nervous system. The paralysis can be minor to extremely disabling, sometimes requiring lifelong respiratory assistance.”It is estimated that poliomyelitis occurs in 1 in 100 or even 1 in 1000 cases of contamination, it is difficult to quantify. And today, we do not know precisely why the virus reaches the central nervous system (immune deficiency, genetic causes, mechanical causes…?)“, admits the professional.
What are the consequences of polio?
“Paralysis is irreversible and the after-effects are sometimes very serious. Patients lose the use of their muscles. The disease can be fatal, due to asphyxiation, when the paralysis affects the muscles of the respiratory system.“. The disease does not kill in the majority of infections, nor does it reduce life expectancy. In young children, who have not finished growing, the disease also causes bone deformations because their development does not take place in good conditions. The Pasteur Institute also describes a syndrome “post-polio“which is characterized by new deficits that slowly progress in former patients several decades after contracting acute poliomyelitis. “The exact causes of the development of this syndrome are currently not well defined. It could be due to the persistence of the virus in some patients“, the Institute said.
The diagnosis is above all clinical.In concrete terms, the doctor observes a patient who has suddenly lost muscle tone. It is a disease that appears suddenly. The patient is doing very well and suddenly, he is paralyzed without warning signs. This is what allows the diagnosis to be made.“. Detection of poliovirus in the patient’s stools confirms the diagnosis. The systematic search for poliovirus in any child under 5 years of age presenting with paralysis is also one of the pillars of poliovirus surveillance by the WHO.
What is the treatment for polio?
“Once the paralysis is there, it is too late to act.“. The after-effects of paralysis are irreversible but physiotherapy can sometimes help in cases of mild disability. There is no curative treatment for the infection and treatment is only symptomatic: respiratory assistance, devices for affected limbs, etc.
Is there a vaccine against polio?
Only the vaccine is effective against polio. Vaccination has been mandatory in France since 1964. “There are two vaccines, developed in the 1950s and implemented in the 1960s.”.
The injectable vaccine: used today in France.These are called inactivated vaccines. The virus is grown in the laboratory, inactivated so that it is no longer infectious. This is what is injected. It has very good safety but does not protect against infections and therefore cannot eradicate the virus.“. Oral vaccine (given by mouth in the form of drops): “It is a live but attenuated virus. The vaccine infects the vaccinated person, multiplies in the intestine but will not be able to reach the central nervous system. However, the risk of developing acute polio, particularly in immunocompromised people, persists.”
Thanks to Dr. Maël Bessaud, poliovirus specialist from the Viral Populations and Pathogenesis unit at the Pasteur Institute.