Polioviruses, the causative agents of polio, were widespread worldwide before the introduction of the vaccine from 1954 onwards. In Austria, wild polioviruses were last detected in 1980.

Until the introduction of the vaccine worldwide. The consistent implementation of vaccination measures within the framework of the global polio eradication initiative of the World Health Organization (WHO) from 1988 onwards considerably reduced the occurrence of polioviruses: The Americas have been polio-free since 1994, the Western Pacific since 2000, and the WHO issued a "polio-free" certificate for the European region in 2002. Worldwide, cases of polio were only recorded in Pakistan and Afghanistan in 2017.

Human

Fecal-oral (smear infection), droplet infection, contaminated water and contaminated food

90 to 95 % of all infections with polioviruses are asymptomatic. In 4 to 8 % of all infected persons, a so-called abortive poliomyelitis occurs with fever, gastroenteritis, nausea, vomiting, fatigue, sore throat and headache. The cells of the central nervous system are not affected and the disease heals without consequences. In 1 to 2% of all infected persons, infection of the cells of the central nervous system occurs with fever, neck stiffness, back pain and muscle spasms. Only 0.1 to 0.5 % of all infected persons develop paralytic poliomyelitis, the "classic" polio.

Treatment is symptomatic, there is no specific therapy with antiviral agents.

Basic immunization with inactivated polio vaccines (IPV)

In Austria, wild polioviruses were last isolated in 1980; polio vaccine viruses could be detected sporadically until 2001.

An important requirement of the WHO is the implementation of AFP surveillance (AFP = acute flaccid paralysis), which has been carried out nationwide in Austria since 1998. There is also an epidemiological laboratory network for Austria-wide enterovirus surveillance (polioviruses are enteroviruses). By testing samples for enteroviruses within the framework of this surveillance system, statements can be made on circulating enteroviruses and thus also on the possible occurrence of polio in Austria.

Polioviruses belong to the genus Enterovirus, which are members of the Picornaviridae family. They are small, spherical, non-enveloped RNA viruses with single-stranded (+) RNA approximately 25 nm in diameter. Poliovirus is an environmentally stable virus. It is stable to many proteolytic enzymes and to a number of disinfectants. It is also resistant to lipid-soluble agents such as ether or chloroform due to the absence of a phospholipid envelope. It is not inactivated even at low pH values (pH 3), e.g. by gastric acid.

The only reservoir for polioviruses is humans. Serologically, 3 types (serovars) can be distinguished:

• Poliovirus type 1 (Brunhilde or Mahoney type) is the most common and can cause severe disease.
• Poliovirus type 2 (type Lansing) causes rather mild courses of disease
• Poliovirus type 3 (Leon type) can cause severe disease, but is relatively rare.

Transmission

The virus is usually transmitted by faecal-oral route and subsequently multiplies very massively in the intestinal epithelial cells, so that up to one billion infectious viruses can be excreted per gram of stool. Therefore, smear infection, but also transmission through contaminated water and contaminated food play a role. Since primary viral replication also occurs in the epithelial cells of the pharynx, the virus can also be transmitted by droplet infection.

Polioviruses were widespread worldwide before the introduction of the vaccine (from 1954). The consistent implementation of vaccination measures as part of the global polio eradication initiative of the WHO (World Health Organization), which began in 1988, has considerably reduced the incidence of polioviruses: The American continent has been polio-free since 1994, and in 2000 the Western Pacific region was declared polio-free. In Austria, wild polioviruses were last detected in 1980.

In 2002, the WHO issued a "polio-free" certificate for the European region. Worldwide eradication of polio is considered possible, since the pathogen's only reservoir is humans and natural infection or vaccination provides lifelong immunity.

On September 20, 2015, the World Health Organization (WHO) declared wild poliovirus type 2 (WPV2), one of three wild poliovirus serotypes, eradicated worldwide. The last WPV2 was detected in northern India in 1999. This is another milestone on the road to global poliomyelitis eradication.

WPV3 has not been detected globally since November 2012 (in Nigeria). The occurrence of the only remaining endemic WPV1 strains is currently restricted to the regions of Pakistan and Afghanistan: Globally, the lowest number of poliomyelitis cases ever recorded worldwide in 2017 was only from Pakistan and Afghanistan, with 22 cases. In 2017, the WHO European Region celebrated the 15th anniversary of its certification as a polio-free region. However, as long as polioviruses circulate anywhere in the world, there is a risk of reintroduction into the European Region. Therefore, each country must continue to play its part in maintaining polio-free status and must continue to implement appropriate tasks: Ensuring high vaccination coverage to prevent the possible spread of the virus, high-quality and comprehensive enterovirus surveillance to detect early cases, and WHO-standard safe storage of polioviruses.

Symptoms

90 to 95 % of all people infected with polioviruses are asymptomatic. However, antibodies are formed and a so-called silent infection occurs. Abortive poliomyelitis occurs in 4 to 8 % of all infected persons: after an incubation period of 7 to 14 days, an illness lasting about three days develops with unspecific symptoms such as fever, gastroenteritis, nausea, vomiting, exhaustion, sore throat and headache. The cells of the central nervous system are not affected and the disease heals without consequences. However, in 1 to 2% of all infected persons, infection of the cells of the central nervous system occurs. About one week after the prodromal stage has subsided (corresponds to the symptoms of the abortive phase), aseptic meningitis develops in addition to a renewed increase in fever, neck stiffness, back pain and muscle spasms, although paralysis of the muscles is absent(non-paralytic poliomyelitis). Only 0.1 to 0.5% of all infected persons develop paralytic poliomyelitis. This is the form known as "classic polio". In the more common biphasic course, the symptoms of aseptic meningitis initially subside; after about 2 to 3 days, fever and asymmetrically distributed paralysis, especially of the leg, arm, abdominal, thoracic, and eye muscles, suddenly appear. In the less common bulbar and bulbospinal poliomyelitis, swallowing disorders or respiratory and circulatory disturbances occur due to the involvement of cranial nerves and cervical spinal cord. This severe form of poliomyelitis has a poor prognosis and a high mortality rate. Late sequelae may include paresis, circulatory and skin nutrition disorders, as well as joint damage, scoliosis of the spine and foot deformities, and disability as permanent damage. The post-poliomyelitis syndrome occurs years to decades after the onset of the disease. Its symptoms include extreme fatigue, muscle pain, progressive muscle atrophy, breathing and swallowing difficulties, joint deformities, muscle twitching and intolerance to cold.

Therapy

Treatment is symptomatic, as there is no specific therapy with antiviral agents.

Preventive measures Vaccination

Basic immunization with inactivated polio vaccines (IPV) is recommended according to the immunization calendar. The live polio vaccine ("oral vaccination") with attenuated pathogens is no longer recommended in Austria because of the - albeit very low - risk of vaccine-associated poliomyelitis (VAPP).

Surveillance

Polio is a notifiable disease. Notification is mandatory in the case of suspected cases, cases of illness or death according to the Epidemic Law. In Austria, wild polioviruses were last isolated in 1980; polio vaccine viruses could be detected sporadically until 2001. In 2002, the WHO issued a "polio-free" certificate for Europe.

AFP surveillance: An important requirement of the WHO is the implementation of AFP surveillance (AFP = acute flaccid paralysis), which has been carried out nationwide in Austria since 1998. More than 80 paediatric and neurological departments in Austria are involved in this surveillance system. In this form of surveillance, all AFP cases are to be recorded centrally in the Federal Ministry of Social Affairs, Health, Care and Consumer Protection. Two stool samples (minimum interval of sample collection 24-48 hours) are to be sent to the National Reference Centre for Polio for virus isolation within 14 days of the onset of the disease.

Enterovirus surveillance: There is an epidemiological laboratory network for Austria-wide enterovirus surveillance. Participating laboratories perform enterovirus diagnostics from various patient materials. These laboratories report the number of samples tested for enterovirus and the number of positive samples to the Ministry of Health and to the National Reference Centre for Polio on a quarterly basis. All enterovirus PCR-positive samples are forwarded to the National Reference Centre for Polio for virus isolation and typing by sequencing in accordance with the WHO recommendation.

Furthermore, paediatric departments and pathologies throughout Austria are involved in this surveillance system, sending samples of cases with neurological symptoms or with unclear cause of death to the National Reference Centre for Polio. By testing samples for enteroviruses within the framework of this surveillance system, statements can be made about circulating enteroviruses and thus also about the possible occurrence of polio in Austria. The samples sent in as part of the enterovirus surveillance programme are examined free of charge at the National Reference Centre for Polio.