Definition and references

• Definition: Poliovirus is a class of risk 2 (or Risk Group 2 or Hazard group 2) non-envelopped RNA enterovirus. Enteroviruses are one of the genera belonging to the Picornavirus family, wich are very small, icosahedral, nonenveloped ss (+)RNA viruses. Humans are the only natural hosts for polioviruses. A specific protein receptor on susceptible human cells (CD155) allows the attachment and entry of poliovirus. The virus infects cells of the oropharynx, the tonsils, the lymph nodes of the neck, and the small intestines. Infection progresses through cycles of virus replication. Once infection is established in the gastrointestinal tract, poliovirus can invade the central nervous system by penetrating the blood/brain barrier or by spreading along nerve fibres.

• Polioviruses are defined by standard neutralization tests with specific antisera. There are three types of wild poliovirus*:
  • Type 1 causes paralysis in about 1 in 200 infections;
  • Type 2 was last recorded in 1999;
  • Type 3 is found only in northern Nigeria, Afghanistan, Pakistan and India. It is less virulent than type 1, causing paralysis in about 1 in 1000 cases.

  *These 3 serotypes of poliovirus have no common poliovirus antigen. They have identical physical properties and their genomic base sequences share 36 - 52% homology. Antigenic variants of types 1 and 2 have been reported, but these antigenic differences do not affect the capacity of antibodies induced by one strain to protect against other strains of the same type. Despite these minor differences, polioviruses show marked antigenic stability.

• Definitions from the WHO Global Action Plan for Laboratory Containment of Wild Polioviruses:
• Polioviruses: human enteroviruses that exist as three well-defined serotypes, which infect cells via a specific receptor (PVR:CD155).
• Wild polioviruses: field isolates and reference strains derived from polioviruses known or believed to have circulated persistently in the community.
• Oral poliovirus vaccine strains: attenuated polioviruses approved for use in oral vaccines by national control authorities.
• Vaccine-derived polioviruses: progeny of approved oral poliovirus vaccine strains.
• Poliovirus survival in the environment

Poliovirus is resistant to inactivation by common laboratory disinfectants such as alcohol and cresols. The virus is rapidly destroyed by exposure to temperatures of 50°C or more, autoclaving or incineration. It is readily inactivated by dilute solutions of formaldehyde or free residual chlorine (bleach), ultraviolet light, heat and drying. Inactivation is slowed by the presence of extraneous organic matter. Chlorine bleach (0.5%) is the recommended disinfectant for laboratories working with polioviruses.
Under stable laboratory conditions, poliovirus in clinical or environmental specimens may survive at freezing temperatures for many years, under refrigeration for many months, and at room temperatures for days or weeks. Rates of poliovirus inactivation in nature are greatly influenced by the immediate environment. It has been estimated that poliovirus infectivity in soil decreases by 90% every 20 days in winter and every 1.5 days in summer, and that at ambient temperatures a 90% decrease in infectivity occurs in sewage every 26 days, in freshwater every 5.5 days, and in seawater every 2.5 days.

• Infectious dose

Infectious dose by ingestion of wild type 1 poliovirus in children: 2 pfu

• Mode of transmission and environmental risk

Poliovirus is transmitted from person to person either through droplets from the upper respiratory tract during the early days of infection or, more commonly, through the ingestion of faecal contaminated material in circumstances of poor hygiene. In theory, polioviruses may be transmitted to persons outside the laboratory through contaminated laboratory effluents released into sewage, solid wastes transported to landfills, spent air exhausted to surroundings, or contaminated workers’ skin or clothing.

• Laboratory containment

In the pre-certification phase of Region as poliomyelitis-free, laboratories must institute enhanced biosafety level–2 (BSL-2/polio) procedures for safe handling of all such infectious or potentially infectious materials. See: WHO global action plan for laboratory containment of wild polioviruses. Second edition. Department of Vaccines and Biologicals. World Health Organization, Geneva, 2003. (WHO/V&B/03.11). When poliomyelitis is eradicated every effort must be made to ensure that wild poliovirus is not similarly transmitted from the laboratory to an increasingly susceptible community.

References:

Reported laboratory poliovirus acquired infections

• Gear JHS, Rodger LM. Poliomyelitis in northern Rhodesia with special reference to an outbreak occurring on the Roan Antelope Copper Mine,
  Luanshya in 1946. South African Medical Journal. 1946; 20: 670-3.
• Wenner HP & Paul JR. Fatal infection with poliomyelitis virus in a laboratory technician. Am J Med Sci. 1947; 213: 9-1
• Beller K. Laboratoriumsinfektion mit dem Lansing-Virus. Zbl Bakt I Abt Orig. 1949; 153: 269-273
• Sabin AB & Ward R. Poliomyelitis in a laboratory worker exposed to the virus. Science 1941; 94: 113-114
• Pike RM. Laboratory associated infections: summary and analysis of 3921 cases. Health Laboratory Science. 1976; 13:105-14.
• Pike RM. Laboratory-associated infections: incidence, fatalities, causes and preventions. Annual Review of Microbiology. 1979;33: 5.
• Miller BM, et al. Laboratory safety: principles and practices. Washington DC: American Society for Microbiology.1986. p. 322.
• Sewell DL. Laboratory-associated infections and biosafety. Clinical Microbiology Review. 1995; 389-405.
• A wild-type 1 strain used for IPV production was documented as being transmitted from a worker in a vaccine production facility to
  his young son: Mulders MN, Reimerink JHJ, Koopmans MPG, van Loon AM, van der Avoort HGAM. Genetic analysis of wild type poliovirus importation into the Netherlands (1979-1995). Journal of Infectious Diseases. 1997; 176: 617-24.
• In another incident a child was reported to have been infected with a prototype strain of type 3 commonly used in laboratories for research and IPV vaccine production. The source of this infection was not determined (found in WHO global action plan for laboratory containment of wild polioviruses, Second edition: WHO/V&B/03.11)

Infectious dose

- Wedum AG, Barkley WE & Hellman A. Handling infectious agents. J Am Vet Med Assoc. 1972; 161: 1557-1567.

General references

- World Health Organization: Poliomyelitis