Polio

Overview

Polio, also known as poliomyelitis, is a viral disease primarily targeting the nervous system, specifically the spinal cord and brain stem, leading to potential paralysis, respiratory issues, and in severe cases, death. Despite a significant reduction in cases worldwide due to extensive vaccination campaigns, polio persists in regions with low immunization rates, particularly in parts of Africa, the Middle East, and southern and central Asia. The U.S. Centers for Disease Control and Prevention (CDC) advises travelers visiting these high-risk areas to receive a booster dose of the inactivated poliovirus vaccine (IPV) for lifelong immunity.

The disease is caused by three strains of the poliovirus, identified as wild poliovirus types 1, 2, and 3 (WPV1, WPV2, and WPV3). While types 2 and 3 have been successfully eradicated, type 1 continues to circulate in limited areas globally and is the most likely strain to cause paralysis. This underscores the importance of maintaining vaccination efforts to fully eliminate the threat of polio.

The way polio affects your body can vary based on the location of the virus’s multiply and attack. Types of polio include:

• Abortive poliomyelitis: Flu-like and gastrointestinal symptoms are caused by abortive poliomyelitis. It doesn’t cause long-term problems and only lasts a few days.
• Non-paralytic poliomyelitis: Swelling around the brain called aseptic meningitis can result from non-paralytic poliomyelitis. It may need you to stay in the hospital and has more symptoms than abortive poliomyelitis.
• Paralytic poliomyelitis: When the poliovirus attacks your brain and spinal cord, it results in paralytic poliomyelitis. The muscles that control your breathing, speech, swallowing, and limb movement can become paralyzed. Spinal polio or bulbar polio are the terms used to describe the areas of your body affected. Bulbospinal polio is the combination of spinal and bulbar polio.
• Polioencephalitis: The rare kind of polio that primarily affects newborns is called polioencephalitis. This results to brain edema.
• Post-polio syndrome: Post-polio syndrome occurs when polio symptoms recur years after an initial infection.

Symptoms

Polio, caused by the poliovirus, often presents without symptoms in most individuals. However, when symptoms do manifest, they can vary significantly in severity, from mild, flu-like signs to severe paralysis. Here’s a breakdown of the different forms of polio and their symptoms:

Abortive Polio: Approximately 5% of those infected experience a milder form known as abortive poliomyelitis, characterized by flu-like symptoms lasting 2 to 3 days:

• Fever
• Headache
• Muscle aches
• Sore throat
• Stomachache
• Loss of appetite
• Nausea and vomiting

Nonparalytic Polio: About 1% of poliovirus infections lead to a more severe, nonparalytic form. Symptoms are more intense and prolonged than abortive polio but do not lead to paralysis. Initial symptoms mirror severe flu, followed potentially by a second phase of symptoms after a brief improvement period:

• Neck pain or stiffness
• Arm or leg aches or stiffness
• Severe headache
• Spine and neck stiffness
• Reduced reflexes
• Muscle weakness

Paralytic Polio: This rare but severe form of polio begins like nonparalytic polio but escalates to more serious symptoms, including:

• Intense pain and extreme sensitivity to touch
• Tingling, pricking sensations
• Muscle spasms or twitching
• Weakness advancing to paralysis, typically affecting one leg most commonly, or an arm
• Severe cases may also involve:
  • Respiratory muscle paralysis
  • Difficulty swallowing

Post-Polio Syndrome: Decades after initial polio infection, some individuals may develop post-polio syndrome, characterized by:

• Progressive muscle or joint weakness and pain
• Fatigue
• Muscle wasting
• Breathing or swallowing difficulties
• Sleep-related breathing issues, like sleep apnea
• Decreased cold tolerance

Polio symptoms can resemble other viral conditions affecting the nervous system, making accurate diagnosis essential. If you’ve previously had polio and notice new or worsening symptoms, consult your healthcare provider promptly.

Causes

Polio, primarily caused by the poliovirus, targets nerve cells in the spinal cord and brain stem, affecting muscle movement without harming sensory nerves. The wild-type poliovirus, once prevalent, has been largely eradicated in many countries, with the majority of current global polio cases attributed to the vaccine-derived poliovirus (VDPV). VDPV arises in areas with low vaccination coverage, from a mutation of the weakened virus used in oral vaccines. This mutated virus can spread and evolve in under-immunized communities, occasionally causing polio in unvaccinated individuals or those with compromised immune systems, as evidenced by cases in the United States and the detection of VDPV in wastewater.

The oral polio vaccine, which contains a live but weakened virus, does not typically cause polio in vaccinated individuals. However, it can mutate and revert to a more virulent form if it circulates in populations with insufficient vaccination levels. Since 2000, the United States has exclusively used an inactivated poliovirus vaccine, eliminating the risk of VDPV. The poliovirus is highly contagious, spreading through fecal contamination or respiratory droplets, and can infect individuals through oral transmission, highlighting the importance of hygiene and comprehensive vaccination to control its spread.

Risk factors

The following risk factors for polio may include:

• Children who are under 5 years old
• Stay or visit a place with inadequate sanitation.
• Stay or visit a region where polio hasn’t been eradicated.
• Unvaccinated.