Polio; infantile paralysis

Polio

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Changed on: 08.04.2019
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Poliovirus is an Enterovirus and a member of the family of Picornaviridae. It is a small, sphere-shaped, non-enveloped RNA virus with single-stranded (+) RNA and has a diameter of 25 nm. The virus is environment stable. It is also immune to many proteolytic enzymes and disinfectants. Moreover, it is resistant to lipid soluble agents, such as ether or chloroform, as a result of its lack of a phospholipid envelope. It also remains active at low pH levels (pH 3), such as gastric acid. Humans are the only reservoir for the polio Virus.

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Poliovirus is an Enterovirus and a member of the family of Picornaviridae. It is a small, sphere-shaped, non-enveloped RNA virus with single-stranded (+) RNA and has a diameter of 25 nm. The virus is environment stable. It is also immune to many proteolytic enzymes and disinfectants. Moreover, it is resistant to lipid soluble agents, such as ether or chloroform, as a result of its lack of a phospholipid envelope. It also remains active at low pH levels (pH 3), such as gastric acid. Humans are the only reservoir for the polio Virus.

More information

Transmission

The virus is usually transmitted via the faecal-oral route and reproduces on a massive scale in the epithelial cells of the intestine. As a result, 109 infectious viruses can be excreted per 100 gram of stool. Smear infections and transmission via contaminated water or food also play a role. Transmission can also occur through droplets, as the epithelial cells of the throat are also a primary place where the virus can reproduce.

Symptoms

A good 90 to 95 % of all polio virus infections are asymptomatic. However, antibodies are produced and an immune reaction is triggered.  Four to eight percent of patients will suffer of abortive poliomyelitis: following an incubation period of 7 to 14 days there will be an outbreak of the disease that lasts for about three days featuring unspecific symptoms such as fever, gastroenteritis, nausea, vomiting, lethargy, a sore throat and headaches. The cells of the central nervous system are not affected and the infection will heal completely without any long-term effects.


In one to two percent of all cases, the cells of the nervous system will be affected. This causes aseptic meningitis one week after the prodrome stage (the symptoms of the abortive phase) has subsided, in addition to high fever, stiffness in the neck, back pain and muscle spasms, although there will not be any muscle paralysis (non-paralytic poliomyelitis).

Only 0.1 to 0.5 % of all polio patients will develop paralytic poliomyelitis, the form also known as classic polio or infantile paralysis. In the more common biphasic form of the disease, the symptoms of the aseptic meningitis will subside, but fever and asymmetrical paralysis in the leg, arm, thorax, eye and abdominal muscles will suddenly appear two or three days later.

In the rarer bulbar and bulbospinal forms of poliomyelitis, the infection affects the cranial nerves and cervical spinal cord causing problems with swallowing or problems with breathing and the circulatory system. This very severe form has a negative prognosis and often ends fatally.

Long-term effects, which may last permanently, could include paresis, problems with blood circulation and skin nutrition, damage to the joints, scoliosis of the spine and deformations of the feet, as well as invalidity,. Post-poliomyelitis syndrome appears years or decades after the infection. Its symptoms include extreme tiredness, muscle pain, progressive muscle atrophy, and problems with swallowing and breathing, joint deformation, muscle tics and intolerance to cold.

Therapy

Treatment focuses on the symptoms, as there is no specific therapy with antiviral substances.

Preventative Measures - Vaccination

Basic immunisation with inactive polio vaccines (IPV) is recommended according to the vaccination calendar. The live oral polio vaccine (OPV) with weaker pathogens is not recommended in Austria because of its – albeit very small – risk of vaccine-associated poliomyelitis (VAPP).

Surveillance

Polio is a disease that must be reported. The obligation to notify the authorities about this disease applies in cases of suspicion, infections or death in line with the Austrian Epidemiology Act. The last wild polio viruses in Austria were isolated in 1980, polio viruses from vaccines were detected up to 2001. The WHO issued the polio-free certificate for Europe in 2002. 

WHO announces global eradication of wild poliovirus type 2

Global eradication of polio is deemed possible, as humans are the only reservoir of the virus and an infection or vaccination causes life-long immunity. This objective followed by the WHO as part of the global polio eradication initiative at the beginning of 1988 led to considerable success in the fight against poliomyelitis: the number of cases registered worldwide fell by 99.5 % by 2010.

The World Health Organisation (WHO) announced the global eradication of one of the three wild poliovirus serotypes, namely wild poliovirus type 2 (WPV2), on 20th September 2015. The last WPV2 case was detected in northern India in 1999. This is another milestone on the path to global eradication of poliomyelitis pathogens.

WPV3 has not been detected since November 2012 (in Nigeria). The incidence of the only endemic WPV 1 strains remaining is currently limited to Pakistan and Afghanistan.
The last case of poliomyelitis in Austria was in 1980. Since then, no wild polio virus has been detected in Austria. However, vaccinal strains – the so-called Sabin polio virus – that appear in vaccinated persons after being administered an oral vaccine have been detected, though. The National Reference Centre for Polio Viruses at AGES Vienna discovered Sabin polio viruses in eight individuals between January and September 2015, within the Austrian polio surveillance system.

The next step planned by the WHO as part of the global polio virus eradication programme will be the gradual replacement of trivalent (includes all three serotypes) oral vaccines (OPV) that are still in use with bivalent (only includes serotypes 1 and 3) oral vaccines (OPV) beginning with April 2016.

AFP Surveillance

One important demand made by the WHO is the conducting of AFP surveillance (AFP = acute flaccid paralysis), which has been carried out across all of Austria since 1998. This type of surveillance has been developed to register all AFP cases in children and teenagers up to the age of 15 centrally at the Abteilung für Infektionen, Seuchenbekämpfung und Krisenmanagement (Department for Infectious Diseases, Epidemic Control and Crisis Management) of the Austrian Federal Ministry of Health (BMG). More than 40 paediatric departments in Austria are part of this surveillance system. Two stool samples (minimum interval of the samples 24-48 hours) must be sent to the National Reference Centre for Polio within 14 days after the outbreak of the disease to isolate the virus.
 
Enterovirus Surveillance

There is also an epidemiologic laboratory network in place for Austria-wide enterovirus surveillance. Seven laboratories in Austria are part of this network and help detect evidence of enteroviruses via virus isolation or by using molecular biological methods and examining specimens from patients diagnosed with diarrhoea, meningitis or signs of paralysis. The laboratories report the number of samples tested for enteroviruses and the number of positive samples to the BMG and the National Reference Centre for Polio on a quarterly basis. All PCR positive stool specimen are forwarded to the National Reference Centre for Polio (NRZP) to isolate and classify the virus.

Additionally, a number of paediatric and pathology departments from all over Austria are also part of this surveillance system, sending stool samples from cases with neurologic symptoms or an unclear cause of death to the NRZP. The examination of specimens for enteroviruses within the surveillance system helps in the making of assessments on circulating enteroviruses and, thus, on the potential occurrence of polio in Austria.

The specimen submitted as part of the enterovirus surveillance programme are examined for free at the NRZP.

Labordiagnostik

Zum Nachweis von Polioviren eignen sich Stuhlproben, Liquor (bei ZNS-Manifestation), ferner Rachenabstriche, Rachenspülwasser, Serum (für AK-Nachweis).

Der direkte Erregernachweis erfolgt mittels Virusanzucht in Zellkultur mit anschließender Typisierung (Sequenzierung), Enterovirus-RNA wird mittels Rerverse Transkriptase-PCR (RT-PCR) bestimmt. Die Differenzierung zwischen Impf- und Wildtypstämmen erfolgt in Regionalen Referenzzentren mittels molekularbiologischen Methoden.


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