Ralph A Tripp*
Department of Infectious Diseases, University of Georgia, Athens, GA USA
Received Date: February 21, 2014; Accepted Date: February 22, 2014; Published Date: February 25, 2014
Citation: Tripp RA (2014) Addressing the Re-emergence of Poliovirus. J Antivir Antiretrovir 5:xxxiv-xxxv. doi: 10.4172/jaa.1000e116
Copyright: © 2014 Tripp RA. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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To control disease, such as polio, there is the dilemma of vaccineinduced disease and the unvaccinated. Live vaccination against polio has effectively prevented disease in most developed countries and contained polio to only a few countries where outbreaks of poliomyelitis by the wild-type strain still remain. Over the last decade, largely through the efforts of the Global Polio Eradication Initiative that involves the Centers for Disease Control (CDC), World Health Organization (WHO), the Rotary Club, the Bill and Melinda Gates Foundation and others, there has been a significant reduction in polio in endemic and spill-over countries that suggested worldwide eradication could be eventually achieved through careful surveillance and a robust immunization effort [1-3]. Although the number of people worldwide with poliomyelitis caused by wild-type poliovirus infection has decreased to very low levels due to OPV vaccination, using live oral polio vaccine to control transmission is an issue because the vaccine is excreted, and because these vaccine-derived strains can cause pathogenicity [1,4,5]. It is important to eventually discontinue OPV vaccinations and switch to IPV vaccinations , or perhaps move to a polio immunization schedule that incorporates sequential doses of IPV and OPV that could improve both humoral and intestinal immunity .
Currently, the number of OPV carriers who are the primary source of neuro virulent viruses remains unknown. Excluding the immune suppressed, poliovirus has been shown to be excreted from humans for several months after OPV vaccination [4,5,8]. OPV vaccine-derived polioviruses are routinely isolated from river or sewage waters , and silent circulation of vaccine-derived strains is a risk. At issue are “chronic excreters,” who are generally immune compromised and were vaccinated with OPV as children, who continue to shed live viruses from their intestines and upper respiratory tracts for years [10,11]. The issue of “chronic shedders” was recently highlighted in Israel, where despite very high polio vaccine compliancy rates recently identified wild poliovirus in sewage in several towns in southern Israel as well as in the West Bank and Gaza [12-14]. Despite mostly sanitary conditions in Israel, the appearance of wild type polio is nonetheless a high risk for transmission. The Israel epidemiology community rapidly identified >40 people shedding poliovirus, none of them had symptoms of paralysis, and all had been fully vaccinated with Inactivated poliovirus vaccine (IPV), which is used in routine immunizations and protects against all polio strains marking the first time that wild polio was detected without any clinical cases [12,13,15].
IPV is used my most developed countries, and if vaccines are exposed to imported polio, the findings from Israel suggest they could be at risk. It is well known that IPV provides robust humoral immunity, but poorer mucosal immunity in the gut suggesting that IPV-vaccines might still shed the virus in feces [16-19]. To stop silent polio transmission, Israel has since given nearly a million doses of OPV, and Syria administered >2 million doses. A consequence has been a rise in vaccine demand that is not being effectively addressed per worldwide needs. What is needed to bridge the poliovirus eradication program are effective antivirals. For example, once wild poliovirus transmission has been interrupted, OPV vaccination will end, leaving IPV as the only means to maintain worldwide polio eradication. Antivirals are needed to treat polio shedders and help bridge issues with vaccine manufacture and distribution, as well as outbreaks caused by accidental or deliberate release. It is clear that antiviral drugs are needed to treat the infected and protect the exposed. Unfortunately, development of a poliovirus antiviral drug will require commitment by a drug manufacturer, and this is unlikely as currently there is no commercial market and scant interest from pharmaceutical companies unless the antiviral reached across all picorna viruses, and in particular rhinoviruses, which cause substantial seasonal morbidity [20-22]. Funding is likely to come from philanthropic organizations, and government agencies that understand the public health benefits of an antiviral polio drug.