Academic journal article Bulletin of the World Health Organization

Can Post-Eradication Laboratory Containment of Wild Polioviruses Be Achieved? (Policy and Practice)

Academic journal article Bulletin of the World Health Organization

Can Post-Eradication Laboratory Containment of Wild Polioviruses Be Achieved? (Policy and Practice)

Article excerpt

Introduction

In May 1999 the World Health Assembly reaffirmed WHO's commitment to the eradication of poliomyelitis. All Member States were urged to move towards laboratory containment of wild poliovirus in order to prevent the reintroduction of polio from laboratories to polio-free communities (1). In December 1999, WHO distributed the Global Action Plan, linking containment steps to the global certification of eradication and subsequent decisions on post-eradication immunization strategies (2).

Over the past half-century, hundreds of laboratories have worked with various materials in which wild polioviruses were or might have been present. The logistics of identifying and disposing of or retaining such materials under appropriate biosafety conditions have prompted some to suggest that it might be easier to eradicate wild polioviruses in nature than to contain them in laboratories. The former can be verified; the latter cannot.

Absolute containment can never be assured. Questions of intentional or unintentional non-compliance could never be wholly eliminated. This and the remote possibility of the re-emergence of paralytic polio from unknown sources make it necessary to devise post-eradication strategies relating to contingencies, response plans, and vaccine stockpiles.

The prevention of inadvertent transmission to the community is a realistic goal. Such transmission can occur only if someone works under laboratory conditions that lead to the infection of himself, herself or others. We examine the opportunities for inadvertent transmission of poliovirus to the community and review the steps that are required in order to achieve biosafety levels appropriate to the risks of transmission.

Transmission of poliovirus from laboratory to community

In theory, viruses may be transmitted from laboratory to community through contaminated clothing, liquid or air effluents, or improper disposal of infectious materials. No evidence exists for poliovirus transmission by any of these routes, but the prevention of this possibility is dealt with in the WHO standards for laboratory design and biosafety practices (2). The principal challenge is to prevent transmission through unrecognized infectious laboratory workers. Such transmission can occur only if the four conditions described below are met.

Condition 1: infectious or potentially infectious materials are present in the laboratory

WHO defines wild poliovirus infectious materials as the following: stocks, isolates, cell cultures and products of laboratory research; clinical specimens from poliomyelitis patients; sewage or water samples in which wild poliovirus is present; and infected animals or specimens from such animals (2). Also considered wild for containment purposes are oral polio vaccine (OPV) derived polioviruses (VDPV) that have assumed the characteristics of wild virus in terms of neurovirulence and transmissibility (3).

Products of poliovirus replication, with virus concentrations of up to a billion infectious particles per ml, pose the highest risk. Less well recognized as laboratory risks are specimens that were collected for other purposes in which wild polioviruses may be present. Defined as potentially infectious materials, these include faeces, throat secretions, and environmental specimens collected for any purpose at a time and in an area where polio was known or suspected to be present and stored under conditions known to preserve the virus (2). The rationale for defining such materials as potentially infectious is based on the natural history of poliomyelitis. For every case of paralytic poliomyelitis, between 100 and 1000 additional poliovirus infections may go unrecognized.

The probability that a randomly collected specimen potentially harbours viable wild poliovirus hinges on whether the specimen was: collected from a person infected with poliovirus; obtained from a body site where poliovirus usually occurs, e. …

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