Detection of Poliovirus Circulation by Environmental Surveillance in the Absence of Clinical Cases in Israel and the Palestinian Authority

Abstract

The global eradication of poliomyelitis, believed to be achievable around the year 2000, relies on strategies which include high routine immunization coverage and mass vaccination campaigns, along with continuous monitoring of wild-type virus circulation by using the laboratory-based acute flaccid paralysis (AFP) surveillance. Israel and the Palestinian Authority are located in a geographical region in which poliovirus is still endemic but have been free of poliomyelitis since 1988 as a result of intensive immunization programs and mass vaccination campaigns. To monitor the wild-type virus circulation, environmental surveillance of sewage samples collected monthly from 25 to 30 sites across the country was implemented in 1989 and AFP surveillance began in 1994. The sewage samples were processed in the laboratory with a double-selective tissue culture system, which enabled economical processing of large number of samples. Between 1989 and 1997, 2,294 samples were processed, and wild-type poliovirus was isolated from 17 of them in four clusters, termed “silent outbreaks,” in September 1990 (type 3), between May and September 1991 (type 1), between October 1994 and June 1995 (type 1), and in December 1996 (type 1). Fifteen of the 17 positive samples were collected in the Gaza Strip, 1 was collected in the West Bank, and 1 was collected in the Israeli city of Ashdod, located close to the Gaza Strip. The AFP surveillance system failed to detect the circulating wild-type viruses. These findings further emphasize the important role that environmental surveillance can play in monitoring the eradication of polioviruses.

Feasibility of Quantitative Environmental Surveillance in Poliovirus Eradication Strategies

“…Environmental surveillance also can retrospectively identify the circulating polioviruses in the community. Although often no clinical cases are seen in areas where these altered viruses are seen (4,16,27,44,45), a high level of awareness should be retained, because when susceptible individuals are exposed to these viruses, secondary transmission could take place and subsequently infection could occur.…”

“…In contrast, these models hypothesize that environmental surveillance even at low sampling frequencies can detect 1 infected excreting individual in a population of 10,000. Indeed, the detection of wild-type poliovirus in the environment has been described in the absence of AFP cases (16,27), but the sensitivity and specificity of environmental surveillance are difficult to assess in wild-type poliovirus outbreaks, since the onset of the epidemic and the number of asymptomatic infections are not known.…”

Pathogen Surveillance Through Monitoring of Sewer Systems

“…Surveillance of poliovirus in sewage has been used by several nations to assess the success of vaccination programs and to identify the potential need for vaccination to prevent outbreaks (Deshpande et al, 2003;Manor et al, 1999;Tambini et al, 1993). The World Health Organization has published guidelines for the environmental surveillance of poliovirus circulation (WHO, 2003).…”

“…The Public Health Laboratories of Israel have been conducting an environmental surveillance of sewage on a monthly basis since 1989 (Manor et al, 1999) to assess the spread of the wild type poliovirus strains capable of causing paralytic disease. This was done to determine the success and need for vaccination programs.…”

“…Vaccine strains have unique sequences from wild type strains of pathogens allowing easy differentiation. In addition, sequence analysis of sewage isolations has been shown useful in tracking the spread of wild type poliovirus from one country and community to another (Deshpande et al, 2003;Manor et al, 1999). This review of poliovirus is offered here as a case study and justification for the use of monitoring additional CDC select biological agents.…”