Poliovirus
Poliovirus is a member of the Enterovirus genus, family Picornaviridae. Enteroviruses are transient inhabitants of the gastrointestinal tract. Poliovirus is highly contagious and causes polio or poliomyelitis. There are three poliovirus serotypes called PV1, PV2, and PV3. Immunity to one serotype does not produce significant immunity to the other serotypes.
Due to widespread polio vaccination, there have been no cases of polio caused by wild-type poliovirus originating in the United States since 1979. However, on July 21, 2022, the CDC was notified of a case of vaccine-derived poliovirus infection in a previously healthy polio-unvaccinated male from New York. The individual resided in an area of New York with a low polio vaccination rate. He was hospitalized in New York City with acute flaccid myelitis. Testing revealed infection with serotype PV2, which was genetically linked to poliovirus detected in Israel and the United Kingdom. Seventy wastewater samples tested positive in the metropolitan New York City region.
Poliovirus infects only humans. Infection is more common in infants and young children. In temperate climates, poliovirus infections are most common during summer and autumn.
Poliovirus enters through the mouth and multiplies in the oropharynx and gastrointestinal tract. The virus is usually present in nasopharyngeal secretions for 1 to 2 weeks and can be shed in stools for several weeks after infection, even in individuals with minor symptoms or no illness.
Polio has a broad spectrum of clinical manifestations. Most people who get infected with poliovirus will remain asymptomatic. The poliovirus incubation period for nonparalytic symptoms is 3 to 6 days. About 25% of individuals will experience flu-like symptoms that last for 2 to 5 days. Generally, only unvaccinated, or incompletely vaccinated individuals are at risk of developing symptomatic polio. Approximately 1 to 5% of infected individuals develop meningitis and 0.05 to 0.5% develop acute flaccid paralysis of one or more limbs without sensory or cognitive loss. Paralysis can lead to permanent disability or death secondary to respiratory failure. The onset of paralysis usually occurs 7 to 21 days after infection.
Investigation of a potential case of polio requires immediate notification of state or local health departments. Paralytic poliomyelitis can be diagnosed using clinical criteria alone; however, laboratory confirmation is useful for epidemiologic purposes. Diagnosis of nonparalytic polio is considered definitive when the presence of poliovirus is confirmed using nucleic acid amplification (NAA) or viral culture testing.
The preferred diagnostic testing methods for diagnosis and subtyping of active polio infection are viral culture or polymerase chain reaction (PCR). Culture is significantly less sensitive for the detection of poliovirus than molecular testing. At this time, poliovirus-specific molecular assays are only offered by local public health laboratories and the CDC.
The preferred specimen type is stool because pharyngeal and cerebrospinal fluid (CSF) samples often contain less virus. As poliovirus may be intermittently shed, at least two stool specimens collected 24 hours apart and within 14 days of symptom onset are recommended.
Serology may be used to detect the presence of neutralizing antibodies against poliovirus. Types 1 and 3. A positive titer indicates the presence of neutralizing antibodies to poliovirus, either as a result of vaccination or natural infection. The presence of neutralizing antibodies does not guarantee complete protection against future poliovirus infections, and protection against one type does not imply protection against other types. Observation of a fourfold increase in titer between paired acute and convalescent specimens confirms a diagnosis of poliovirus.
Healthcare providers should notify their state or local health department if polio is suspected or confirmed.
Anyone in the United States who attended public school in the last 70 years has most likely been vaccinated. Because there are no antiviral treatments for polio, vaccination is the only safeguard preventing disease.
Two types of polio vaccine are available worldwide. Oral polio vaccine (OPV) contains an attenuated poliovirus strain that induces immunity in the digestive tract. It is 95% effective in preventing symptomatic disease after 3 doses. Rarely, the attenuated virus regains its ability to infect the nervous system while replicating the GI tract, causing symptomatic polio in about 1 in 3 million vaccinees. The United States ceased used of OPV in 200, but it remains the predominant vaccine in resource-limited countries.
Since 2000, the United States, has exclusively administered inactivated poliovirus vaccine (IPV), which contains killed wild-type poliovirus of all three serotypes. It is 99% effective in preventing symptomatic disease after the recommended 3 doses and induces lifelong immunity in the bloodstream. Because it is inactivated, IPV cannot cause poliovirus infection.
References
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Vaccines and preventable diseases: vaccine-derived poliovirus.
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases: chapter 12: poliomyelitis.
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Epidemiology and prevention of vaccine-preventable diseases: poliomyelitis.
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases: chapter 22: laboratory support for surveillance of vaccine-preventable diseases.
Larkin H, What all physicians need to know about the polio resurgence in New York State, JAMA, published online August 25, 2022.
