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Wild polio has reappeared in Africa

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Wild polio has reappeared in Africa

This is not a defeat but a wake-up call: less than two years after the certification of eradication – and more than five years after the last confirmed case – wild polio has reappeared in Africa. On February 17, Malawian health authorities announced a probable outbreak in the capital Lilongwe, after ascertaining that the girl who was paralyzed in November 2021 had indeed been infected with the poliovirus.

The last endemic case in the African country dates back to 1992; sequencing showed that the strain detected in Lilongwe is related to the one circulated in October 2019 in Sindh province, Pakistan. Being an import case, the report does not cancel the historic milestone set by the World Health Organization (WHO) in August 2020, when the continent was declared free from the wild form of polio. Provided that, the same organization warns, the cases do not multiply in the next 12 months.

What is polio

First described in 1789, polio caused widespread epidemics over the next two centuries. It is an infectious disease caused by three different poliovirus strains, two of which have been completely eradicated. “In most cases, the infection is asymptomatic or limited to intestinal symptoms; however, in some people the virus manages to cross the gastrointestinal barrier and spread throughout the body via the blood system. If it reaches them, it can damage motor neurons, causing paralysis. more or less extensive flaccid which in many cases are irreversible “summarizes the biologist Agnese Collinoauthor of the essay “The 10-cent Disease. A History of Polio and How It Changed Our Society” (Code, 2021).

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Humans represent the only natural reservoir for the polio virus, which can affect people of all ages but mainly occurs in children under three years of age. The infection occurs via the fecal-oral route, through the ingestion of water or contaminated food or through the saliva and droplets emitted with coughs and sneezing by sick subjects or healthy carriers.

Viruses that are scary

by GIUSEPPE DEL BELLO

The eradication of poliomyelitis

Although there is no cure, the disease can be prevented: massive vaccination campaigns coordinated by the Global Polio Eradication Initiative have made it possible to eradicate the wild form of polio everywhere, except for Afghanistan and Pakistan where it remains endemic today.

“In these countries the situation is historically complex for various reasons. Firstly, the orography of the territory complicates vaccination campaigns which are mostly conducted with the door-to-door method and require a cold chain. Secondly place, some regions of the two countries are regularly crossed by nomadic populations, difficult to vaccinate, and which can spread polio from one state to another “collino begins, underlining however how the real obstacles have a different origin:” although in the last years the situation has improved, religious and political leaders have discouraged, for years, people’s participation in vaccination campaigns through the threat of fatwa? or the spread of fake news “.

It is from these countries that, from time to time, the wild form of the virus spills elsewhere, causing outbreaks in even distant regions such as Syria in 2013 or Malawi today. It is not yet clear how and when the Pakistani strain reached Lilongwe also because the resistance of the virus in the environment is relatively limited.

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The situation in Africa

Meanwhile, WHO has announced that it will support Malawi’s health authorities and step up surveillance of the disease in neighboring countries as well. “We are taking urgent steps to prevent its potential spread. With a high level of polio surveillance on the continent and the ability to quickly detect the virus, we can launch a rapid response and protect children from the debilitating impact of this disease,” he said. Matshidiso MoetiWHO regional director for Africa.

But how is it possible for a single case to cause so much havoc? “Depending on the estimates, it is estimated that flaccid paralysis affects one person out of every 100 or 200 infected who, on the other hand, escape detection because they have little or no symptoms. For this reason, a single report is sufficient to already speak of an outbreak” explains Collino .

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The vaccine-derived disease

The threat of the wild form of polio should not be confused with that of vaccine derivation. Africa is still crossed by large outbreaks of the latter, which generally occur in areas with low immunization. We currently have two distinct polio vaccines, both developed in the 1950s: the so-called Salk (IPV) and Sabin (OPV) vaccines.

“The first, administered by injection, contains an inactivated version of the virus. It cannot prevent infection but is safer and still avoids the most serious consequences of the disease,” explains Collino. “The second is taken orally and contains an attenuated, but still alive, version of the wild virus. It is more effective than Salk and prevents contagion: it is therefore the only one that can lead to eradicating polio. But in very rare cases the virus can mutate and regain pathogenic characteristics “continues the biologist.

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Together with maintaining high coverage and prophylactic vaccinations in case of outbreaks, the ultimate weapon could be called nOPV2, a new version of the more stable and safer oral Sabin vaccine.

Thanks to the first emergency procedure released in WHO history, nOPV2 was authorized in November 2020. Curiously, the same fate would befall, just a month later, another highly anticipated vaccine: Pfizer and BioNTech’s Comirnaty. But that’s another story.

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