[Fears of a polio resurgence in the US have health officials on
high alert. A virologist explains the history of this dreaded disease,
why its resurfacing today and what we need to do to combat it.]
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POLIO: FACTS, HISTORY AND WHY WE’RE ON HIGH ALERT  
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Rosemary Rochford
September 7, 2022
The Conversation
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_ Fears of a polio resurgence in the US have health officials on high
alert. A virologist explains the history of this dreaded disease, why
it's resurfacing today and what we need to do to combat it. _

Jonas Salk, developer of the first polio vaccine, photo: Thomas Hawk
(CC BY-NC 2.0)

 

Fears of polio gripped the U.S. in the mid-20th century
[[link removed]]. Parents were
afraid to send their children to birthday parties, public pools or any
place where children mingled. Children in wheelchairs served as a
stark reminder of the ravages of the disease.

To prevent polio outbreaks, government officials used tactics
[[link removed]] now familiar in
the era of COVID-19: They closed public spaces and shut down
restaurants, pools and other gathering places.

In 1952, two years prior to the introduction of a trial polio vaccine,
there were an estimated 58,000 cases of polio and 3,145 deaths due to
polio in the U.S. [[link removed]]. These cases
included children who were paralyzed for life. But those numbers
dropped dramatically following a widespread vaccination campaign
against polio, beginning in 1955.

By the 1970s, there were fewer than 10 cases of paralysis due to polio
[[link removed]] in the U.S.,
and the polio virus was considered eliminated from the U.S. by 1979
[[link removed]]. Since
then, collective fear of the virus has been mostly lost to history –
many people alive today are lucky enough not to know someone who has
experienced polio.

So when news broke in July 2022 that an unvaccinated adult man in New
York had contracted polio
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– the first case in the U.S. since 2013 – and developed paralysis
from the disease, it sent a ripple of fear throughout the public
health community and raised the question of whether an old foe was
making a comeback.

I am a virologist and a professor of immunology and microbiology
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and have spent my career both teaching about and doing research on how
viruses can cause disease.

There is no cure for polio. The only treatment is prevention. And the
tool for prevention is vaccination, the same tool that eliminated
polio in the U.S. in the first place
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Health experts are urging unvaccinated Americans to get vaccinated
against polio.

Life cycle of the poliovirus

Polio – or poliomyelitis – the disease
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poliovirus, which is passed from person to person through the mouth.
And while no one would knowingly ingest a virus, touching a
contaminated object like a spoon or a glass or accidentally swallowing
contaminated water can unknowingly lead to infection.

When someone is infected with the poliovirus, they shed the infectious
virus in their feces. This is why recent reports that poliovirus has
been circulating in New York City wastewater for months
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and that the virus now has been detected in three New York counties
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particularly concerning.

In August 2022, New York State Health Commissioner Mary Basset said
that the state health department is “treating the single case of
polio as just the tip of the iceberg of much greater potential spread
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“Based on earlier polio outbreaks,” she added, “New Yorkers
should know that for every one case of paralytic polio observed, there
may be hundreds of other people infected.”

A single case of polio reflects a larger potential spread of the virus
because most people infected either don’t show any symptoms or have
a very mild illness with symptoms similar to the flu
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even without symptoms, an infected person is still excreting virus in
their feces, which means they can be a source of infection to others.

The virus, which is very stable in the environment, is easily spread
through surface contamination. For this reason, hand-washing is a
critical prevention tool. Although many disinfecting agents, such as
alcohol or diluted Lysol, fail to inactivate the virus, chlorine
bleach does destroy it
[[link removed]]. This is why
public health officials started chlorinating swimming pools
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in order to inactivate the polio virus
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Typically, the human body uses stomach acid to protect against
ingested viruses
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But poliovirus can survive stomach acid to travel to your
gastrointestinal tract. There, the virus reproduces itself to
establish an infection.

What is paralytic polio?

Unfortunately, one person out of about 200 people infected with
poliovirus will develop paralysis
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Scientists still don’t know why one person is susceptible to the
paralytic disease while most are not.

In the small subset of people that get paralytic polio, the virus can
attack [[link removed]] the lower motor
neurons found in the brain stem and spinal cord, which are important
for controlling muscles [[link removed]].
Infection of those neurons leads to the muscle paralysis that is
characteristic of paralytic polio. The legs are typically affected –
often on only one side of the body – and paralysis can range from
mild to severe. Other muscle groups can also be affected.

In the worst cases of paralytic polio, the virus can damage the
centers of the nervous system that control breathing. Respirators
known as “iron lungs”
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were early medical devices that aided those with damaged respiratory
muscles, helping them breathe until their muscles healed enough to
work on their own. Patients could die when the paralysis was severe
and sustained.

Anti-vaccination sentiments and an overall drop in routine vaccination
rates during the COVID-19 pandemic have likely contributed to the
resurfacing of the poliovirus in the U.S.

Levels of severity

Although polio can be devastating for those who contract the severe
form of it, most people’s immune systems are well-equipped to combat
it. When someone recovers from polio, researchers can detect
poliovirus-fighting antibodies in the blood
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But even long-term survivors of paralytic polio can develop late-onset
muscle weakness and fatigue
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which is known as post-polio syndrome
[[link removed]]. While the muscular effects of
post-polio syndrome are well-recognized
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associated with post-polio syndrome
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sleep disturbances, cold intolerance and difficulty swallowing.

Because post-polio syndrome is diagnosed only based on symptoms, there
is no consensus on the number of polio survivors who develop it
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but estimates range from 15% to upward of 80%
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Prevention of polio is key

The decline in polio in the U.S. and globally is a direct result of
the introduction of vaccines and the willingness of the public to
accept them. In 1988, the World Health Organization, in partnership
with Rotary International, the Centers for Disease Control and
Prevention and other national governments, launched the Global Polio
Eradication Initiative with the goal to wipe out polio worldwide
[[link removed]], as is the case with smallpox
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When this initiative was launched, there were still an estimated
350,000 children with polio in 125 countries
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In 2021, there were only six reported cases
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Two types of polio vaccine are in use worldwide. The one used in the
U.S. since 2000 [[link removed]] is an
injection made from inactivated poliovirus. Inactivation kills the
virus and prevents it from spreading. Children in the U.S. get this
shot
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at 2 months, 4 months and between 6 to 15 months of age, and it
essentially provides lifelong protection from polio.

The second vaccine type, still in use in many parts of the world, is
an attenuated – or weakened – form of the virus that is taken
orally. In places where community transmission remains significant,
like Pakistan
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the oral vaccine is preferred because it prevents people from getting
polio and also stops person-to-person transmission. In the U.S., where
person-to-person transmission of the poliovirus has been virtually
nonexistent for decades, the inactivated vaccine is preferred since
the focus is on preventing disease in the vaccinated person and
there’s less concern about spreading the virus.

But in extremely rare cases, the vaccine virus mutates after it’s
been excreted in feces. And if immunization levels fall below a
critical threshold – as is the case in some areas of the world –
this poliovirus can cause disease
[[link removed]].
The recent New York polio case has been traced back to a mutated
vaccine-derived poliovirus thought to be acquired overseas.

Most people in the U.S. are vaccinated through routine childhood
vaccinations. Because immunity to polio following vaccination is
lifelong, the CDC is not recommending booster vaccinations for the
general population
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who completed the full series. However, the CDC does recommend that
anyone who has not been vaccinated against polio virus get vaccinated,
including adults.

In my office, I keep a painting of Dr. Jonas Salk
[[link removed]], the
virologist who developed the first polio vaccine. It serves as my
reminder of the importance of biomedical research to help eliminate
human suffering caused by infectious diseases.[The Conversation]

Rosemary Rochford
[[link removed]],
Professor of Immunology and Microbiology, _University of Colorado
Anschutz Medical Campus
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This article is republished from The Conversation
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the original article
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* Science
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* Medicine
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* Polio
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* vaccines
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