Polio Virology, Symptoms, Vaccines, and Eradication

What virus causes polio?

An RNA enterovirus (poliovirus).

What are the three wild poliovirus types?

WPV1, WPV2, and WPV3.

Which wild poliovirus type remains endemic?

WPV1.

When were wild poliovirus types 2 and 3 declared eradicated?

2015 and 2019, respectively.

What is the principal route of polio transmission?

Fecal-oral transmission, especially with poor sanitation.

What other body fluid can spread polio?

Saliva.

Where does poliovirus initially enter and replicate?

Cells in the throat or intestines, then lymphatic tissue.

What proportion of polio infections have no symptoms?

Approximately 75%.

What are the usual mild symptoms of polio?

Fever, malaise, headache, sore throat, and vomiting.

Approximately what percentage develop severe nervous-system symptoms?

About 1%.

What does spinal polio affect?

The spinal cord; it can paralyze limbs and breathing muscles.

What does bulbar polio affect?

The brainstem; it can impair facial muscles, breathing, and heartbeat.

What is bulbospinal polio?

A combination of spinal and bulbar polio.

What device historically assisted breathing in severe polio?

An iron lung.

When can damaged nerve cells recover?

Potentially within 4-6 weeks if damaged rather than destroyed.

What happens when poliovirus destroys nerve cells?

Paralysis or disability may be permanent.

What does paralysis remaining after one year suggest?

It is likely permanent.

How is polio treated?

No cure; supportive care, rehabilitation, and sometimes breathing assistance.

Who developed the oral polio vaccine?

Albert Sabin.

What type of virus is in the oral polio vaccine?

Live attenuated (weakened) virus.

What rare risk is associated with the oral polio vaccine?

Vaccine-derived polio from mutation and circulation of weakened virus.

Who developed the injected inactivated polio vaccine?

Jonas Salk.

Why cannot the inactivated polio vaccine cause polio?

Its virus is inactivated.

When did the global eradication campaign start?

1988.

What two countries are remaining wild-polio reservoirs?

Pakistan and Afghanistan.

What did the 1952 US outbreak cause?

About 58,000 cases, 3,145 deaths, and 21,269 people left with disability.

How long can poliovirus be found in feces?

Up to six weeks in some cases.

When is polio particularly infectious relative to symptoms?

Roughly 7-10 days before and after symptoms appear.