A guide to understand the disease

Poliomyelitis (polio) is a devastating disease that has historically caused paralysis and death around the world. It is caused by polioviruses, small RNA viruses that can damage cells in the nervous system

Traces of polio virus detected in London sewage: a guide to understanding the disease

Poliovirus is transmitted by respiratory droplets. Reuters

Just when we thought monkeypox would be the new virus for 2022, the UK Health Security Agency (UKHSA) declared a national incident of repeated poliovirus detection in sewage water in north and east London. Repeated positive measurements for polio suggest ongoing infection and probable transmission in the area. This is unexpected as the UK has been declared polio free since 2003. Here’s what you need to know.

Poliomyelitis (polio) is a devastating disease that has historically caused paralysis and death around the world. It is caused by polioviruses, small RNA viruses that can damage cells in the nervous system.

It is not found in animals, so, like smallpox, it can be eradicated. And thanks to effective vaccination campaigns, we are getting closer to this goal every year.

There are three types of poliovirus and infection or immunization by one type does not protect against the other. Type 1 polio virus continued to cause outbreaks, but transmission through types 2 and 3 has been successfully interrupted by vaccination.

Poliovirus is transmitted through air droplets, but it can also be caught through food or water that has been in contact with the feces of someone who has the virus.

It can survive for many days at normal temperatures. The last remaining outbreaks have been linked to areas with poor sanitation that are difficult to reach with vaccines. Afghanistan and Pakistan are the only two countries where wild polio is still endemic and the target of eradication programs to stop the spread of the virus to other countries.

Crucial role of vaccines

Vaccines have been crucial in eradicating polio. By 2021, there were fewer than 700 reported cases worldwide.

In the UK, the injected polio vaccine is used. It contains an inactivated virus (IPV) and is safe and effective at protecting the immunized person from paralysis, but it is less effective at inducing local immunity in the gut, so vaccinated people can still get infected and spread infectious virus even though they may not. show symptoms themselves.

IPV provides excellent protection for the individual but is not sufficient to control an epidemic under poor sanitation conditions. The oral polio vaccine (OPV), which contains live but attenuated virus, is ideal for this. OPV is administered drop by drop and does not require trained personnel or sterile equipment to administer it, allowing it to reach more communities.

This vaccine can induce potent gut immunity and it can prevent the spread of wild polioviruses. Since it contains a live virus, it can spread to close contacts of the immunized person and also protect them. It is also cheaper than IPV.

The disadvantage of using OPV is that the attenuated virus can mutate and in rare cases revert to paralytic variants.

OPV is cleared by our immune system within days, but this may not be the case in people with weakened immune systems who can carry the virus for longer, increasing the chance of mutations. In under-immunized countries, this can lead to circulating vaccine-derived poliovirus (VDPV). The virus detected in the London sewers was indeed of the vaccine-derived strain, VDPV type 2. There is still no wild polio virus in the UK.

Vaccine-derived polio can cause asymptomatic infection in IPV-vaccinated people, and it is excreted in the faeces because there is no local gut protection in IPV. It can therefore be detected in sewage.

Detection methods are sensitive, but a single positive reading would not raise the alarm. Type 1 VDPV was recently discovered in sewage in Kolkata. It is thought to come from an imported case of a vaccinated person with a weakened immune system who was unable to clear the vaccine strain from their body.

There are no reports of polio-related paralysis in the UK

To prevent illness, we need to make sure family members are up to date on their vaccinations, especially children who may have skipped a course of vaccinations due to the COVID pandemic. IPV is safe, free and effective in preventing polio. Unlike monkeypox vaccines which are scarce and available to high-risk groups, IPV is readily available to anyone in the UK through their GP.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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