Poliomyelitis (polio)

Poliomyelitis (polio) is a contagious disease that can cause permanent disability, paralysis and death. It can be caused both by wild-type poliovirus and by circulating vaccine-derived poliovirus (cVDPV). An outbreak of either type of polio is considered an emergency that warrants a full response. As the world moves towards the elimination of polio, rapid detection and control of community cases, whether from wild-type or vaccine-derived, is extremely important. Type 2 wild poliovirus was declared eradicated in 2015. Type 3 wild poliovirus was declared eradicated in 2019. Only Type 1 wild poliovirus remains. In 2020, 84 cases of wild-type polio were reported worldwide, all of them in Afghanistan and Pakistan. Countries with low polio vaccination rates and poor water and sanitation are at risk of outbreaks caused by cVDPV. 32 countries experienced cVDPV outbreaks in 2020.

The oral polio vaccine that has brought the wild poliovirus to the brink of eradication has many benefits: the weakened vaccine virus provides better immunity in the gut, which is where polio replicates. The vaccine virus is also excreted in the stool, and in communities with low-quality sanitation, the vaccine can be spread from person to person and actually help protect the community. However, in communities with low immunization rates, as the virus is spread from one unvaccinated child to another over the course of about 12—18 months, it can mutate and take on a form that can cause paralysis just like the wild poliovirus. This mutated poliovirus can then spread in communities, leading to circulating vaccine-derived poliovirus outbreaks.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Suspected case definition: Any child under 15 years of age with acute flaccid paralysis (AFP), including Guillain-Barré syndrome, or any person of any age with paralytic illness if polio is suspected by a clinician. An AFP case is defined as presenting with recent or sudden onset of floppy paralysis or muscle weakness due to any cause.

Confirmed case definition: A final case classification can be confirmed, compatible or discarded. For more information please consult the WHO guidelines:  https://www.who.int.

In a country that has been free from polio for at least six months, a poliovirus outbreak is:

• A single case or multiple cases of poliomyelitis due to wild polio virus (WPV) or vaccine-derived polio virus (VDPV).
• A positive environmental sample for WPV or VDPV given that:
  • Two or more separate samples contain WPV/VDPV with genetic sequencing information that indicates sustained local transmission
    
    OR
  • A single sample is positive for WPV or VDPV and follow-up investigation identifies polio compatible cases or WPV or VDPV-infected persons.

• Anyone who has not been vaccinated against poliomyelitis and lives in an area where the poliovirus is circulating is at risk of contracting the disease.
• Overcrowded areas with poliovirus circulation where a person-to-person spread is easily possible. Typical at-risk areas include peri-urban slums, and camps for internally displaced persons or refugees, where minimum requirements of clean water and sanitation are not met.
• Water contaminated with human faeces, for example from sewage, septic tanks and latrines, is a source of infection. Water can also be contaminated during transport, storage and handling.
• Food and water when prepared or stored in unhygienic conditions. Raw fruits and vegetables that are washed in contaminated water. Seafood taken from contaminated water and eaten raw or insufficiently cooked.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

28 per cent (includes minor and major clinical manifestations; 24 per cent with minor illness, 4 per cent non-paralytic aseptic meningitis and less than one per cent paralysis).

Mortality rate among paralytic cases is generally 2—5 per cent among children, and 15—30 per cent among adolescents and adults.

• Children who are not vaccinated, and particularly those under the age of five years.
• Immunosuppressed persons such as those receiving chemotherapy, transplant recipients or people living with HIV/AIDS.
• People with chronic diseases such as renal disease, cancer, chronic lung or liver disease, and diabetes.
• The reasons for which a small percentage of infections result in paralysis are not clear. However, a number of risk factors that may increase the likelihood of paralysis among poliomyelitis cases include: pregnancy, strenuous exercise, injury, immune deficiency, removal of the tonsils and intramuscular injections.

Poliovirus.

Humans.

Faecal oral transmission: The virus is most often spread by the faecal-oral route. Poliovirus enters through the mouth and multiplies in the intestine. Infected individuals shed poliovirus into the environment for several weeks, where it can spread rapidly through a community, especially in areas of poor sanitation. Eating contaminated food, food that has been washed in contaminated water, or drinking water contaminated with faeces (from sewers, latrines, septic tanks or open defecation).

Droplet transmission: Sometimes poliovirus is spread through saliva from an infected person or droplets expelled when an infected person sneezes or coughs. People become infected when they inhale droplets in the air, or touch something contaminated with the infected saliva or droplets.

Transmission through objects: Sharing eating and drinking utensils can increase droplet spread. Polio in faeces can pass from one person to the mouth of another person through contaminated hands, surfaces, objects or utensils. 

7 to 10 days (range 4—35 days).

An infected person may spread the virus to others immediately before and about one to two weeks after symptoms appear. The virus can live in an infected person’s faeces for up to six weeks. It can contaminate food and water in unsanitary conditions.

• Most people who get infected with poliovirus (about 72 per cent) will not have any visible symptom.
• About one in four people with poliovirus infection will have flu-like symptoms that may include: sore throat, fever, tiredness, nausea, headache and stomach pain. These symptoms usually last two to five days then go away on their own.
• A smaller proportion of people with poliovirus infection will develop other more serious symptoms that affect the brain and spinal cord: paraesthesia (feeling of pins and needles in the legs) and meningitis (infection of the covering of the spinal cord and/or brain) occurs in about one out of 25 people with poliovirus infection.
• Paralysis (unable to move parts of the body) or weakness in the arms, legs, or both, occurs in about one out of 200 people with poliovirus infection.
• Paralysis is the most severe symptom associated with poliomyelitis because it can lead to permanent disability and death. Between 2—10 per cent of people who have paralysis from poliovirus infection die because the virus affects the muscles that help them breathe.
• Between 25 and 40 per cent of polio survivors experience post-polio syndrome, starting 15—40 years after the initial infection. Affected people can begin experiencing progressive muscle weakness of the muscles that were previously affected by the polio infection, mental and physical fatigue, joint pain, and increasing skeletal deformities such as curvature of the spine.

Polio resulting in AFP: various neurological illnesses and other diseases with paralysis.

Polio not resulting in AFP: meningitis, encephalitis, flu.

Poliovirus can be detected in specimens from the throat, and faeces (stool), and occasionally cerebrospinal fluid, by isolating the virus in cell culture or by detecting the virus by polymerase chain reaction (PCR). The virus is most likely to be isolated from stool specimens.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment or vaccine should be conducted by health professionals.

• There is no cure for poliomyelitis, but it can be prevented with a vaccine.
• There are two types of vaccines that can prevent poliomyelitis: inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV, including monovalent and bivalent vaccines).
• For people with the disease, the focus is on treating symptoms to speed up recovery and prevent complications. Supportive treatments include isolation, rest, pain relievers, portable ventilators to assist breathing, moderate exercise (physical therapy) to prevent deformity and loss of muscle function, a nutritious diet.

• Poliovirus infection can provide lifelong immunity against the disease, but this protection is limited to the serotype involved. Infection with one type does not protect an individual against infection with the other types.
• Vaccine efficacy is approximately 90 per cent for the prevention of paralysis.