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Poliomyelitis
AN ANCIENT SCOURGE, NEARLY ELIMINATED, BUT STILL LURKING IN THE SHADOWS?
BY JOHN P. MAHER, MD, MPH
Poliomyelitis (Polio) is an ancient, highly contagious disease caused by any of three serotypes of poliovirus. It is a member of the enteroviridae genus, family picornaviridae, which have an RNA genome and are acid stable, so that the three known types (PV1, PV2, and PV3) can transit the GI tract and be shed into the environment. Transmission is generally considered “oral-fecal” (via foods, liquids, direct contact, hand-to-mouth, etc.), the efficiency of which will vary slightly with the age, personal hygiene, environmental cleanliness, dose, and health status or susceptibility of the individuals involved in the transmission events.
For all practical purposes, polio has been considered eradicated here in the U.S.A. Even when/if a case is imported, its further transmission is effectively prevented by the level of “herd immunity” among our general population – except of course if it would reach certain sub-population groups (e.g., Amish, Christian Scientists) who may avoid getting immunizations because of religious or deeply philosophical beliefs which constitute legal exemptions to state immunization laws/regulations. In third world countries, people may refuse vaccination due to fear, superstition, or pressure from political or religious extremist groups.
So, in those settings, or where people and tribes may be extremely isolated and health programs unavailable, and since only humans are hosts to this virus, it is still conceivable that until/ unless the virus is completely eradicated there could still be a resurgence of paralytic polio, depending upon the world’s political, social and economic realities.
From 1990 to 1999 there were 162 reported cases in the U.S., with an average of only 8 cases of wild virus polio per year reported here. Of those, six (6) were acquired outside the U.S., and two (2) were classified as “indeterminate” (meaning that no polio virus was isolated from the patients, and that they had no history of recent vaccination nor direct contact with a vaccine recipient). All of the remaining 154 (95%) cases were “vaccine-associated paralytic polio (VAPP) caused by the Sabin poliovirus strains in the oral polio vaccine” (more about this below). Because of the effectiveness of our American system of Public Health and the active participation of physicians, hospitals, parents and school systems, most Americans these days have had no real experience with epidemic or pandemic diseases with the current exception of the ongoing COVID-19 pandemic caused by the SARS CoV-2 virus. With the exception, perhaps, of the 10 Plagues on Pharoah’s Egypt which we pass over in silence (with apologies to Cicero and our old Latin teachers for the use of the praeteritio), all our combined histories would show only a handful of truly global prior pandemic diseases, namely: Plague, Yellow Fever, Malaria, Cholera, the 1918 Spanish Flu, and arguably Syphilis (or “the Great Pox”).
The 1950s, when this author was a teenager, were full of fear and anxiety about polio – a disease whose cause and cure were
unknown at the time and which reached epidemic and then pandemic levels across the globe, wreaking havoc with the health especially of young children. Polio was then said to be the thing Americans feared most, second only to the atomic bomb.
In the first half of the 20th century polio killed millions of people globally and left legions of others permanently paralyzed and disabled. Despite the work of Karl Landsteiner and Erwin Popper whose 1908 experiments on macaque monkeys demonstrated the transmissibility of polio by the inoculation of an extract of nervous tissue from polio patients, it still took decades of research to produce workable, usable vaccines. Meanwhile, especially in the peak summer and fall seasons, all social activities came to a screeching halt as schools, churches, theaters, playgrounds, parks and athletic events were cancelled.
By 1949, David Bodian (Johns Hopkins) identified the three types of polio virus (PV1, PV2, PV3). Jonas Salk (Univ. of Pittsburgh) subsequently developed a formalin-inactivated injectable vaccine. After some 58,000 polio cases were reported in 1952 in the US alone, in the mid-50s, Dr Salk announced the successful use of his injectable formalin-inactivated polio vaccine (IPV) and over the next five years 450 million doses were distributed, resulting in the national polio incidence declining from 18.8 per 100,000 population to only 2.2.
Unfortunately, during the 1950s, a debacle occurred when the vaccines from two pharmaceutical companies (primarily the Cutter pharmaceutical company, and to a lesser extent, Wyeth) were not completely inactivated. Their use resulted in numerous polio cases, including 250 paralytic cases, a loss of public confidence, and a decline in the vaccination rates. In 1955, the NIH created a Technical Committee on Poliomyelitis Vaccines to test and review all polio vaccines and advise the USPHS as to which lots should be released for public use. [One might wish something like that had been instituted at the start of the SARS CoV 2 pandemic to prevent much of the ensuing political hype and posturing.]
By 1961, Albert Sabin had developed his trivalent oral polio vaccine (OPV) containing all three naturally occurring live attenuated viruses (now labeled wild polioviruses, or WPV 1, 2, and 3). This improved patient acceptability, ease of administration, and had the added benefit of preventing intestinal mucosal infection with WPVs. Following its introduction polio incidence plummeted to less than 1 in 10 million population. Because of widespread immunization and the WHO’s Global Initiative to Eradicate Polio, by the end of 2007, polioviruses were limited to only four countries which had not yet succeeded in interrupting transmission (Afghanistan, India, Nigeria and Pakistan).
In 2018, the WHO reported the incidence of wild polio cases had declined by 99% from 350,000 cases in 1988, to only 33 reported cases in 2018. They also reported that WPV2 had been eradicated in 1999, and that no cases of WPV3 had been found since 2012. But lest we get too complacent, it now seems that outbreaks of circulating vaccine-derived polioviruses (cVDPVs) are more troublesome. These strains are capable of spreading through susceptible populations and “becoming manifest” in non-vaccinated or incompletely vaccinated individuals. Published data indicate that OPV shed viruses may cause 3 doses of paralytic polio per million doses given, but that contrasts with some 5,000 cases of paralysis for every million cases of natural polio infection. In nations where immunization programs have effectively reduced the occurrence of paralytic polio, as in the U.S., consideration is generally given to making the choice of going back to the use of the IPV as the vaccine of choice. cVDPVs may be rare right now but they have been increasing in recent years in low-immunization rate countries, and by 2020 were the only form of poliovirus in the African Region. In
February 2022, WHO listed 3 nations still with wild polio virus 1 (Afghanistan, Malawi, Pakistan), and 31 countries in Africa and the Middle East with cVDPVs, all currently with the
“potential for international spread.” Thus it behooves health care personnel to be aware of the differential diagnosis, not just of cases of acute flaccid paralysis (AFP) but of compatible illness syndromes in patients recently arrived in the US from endemic or at risk countries, as well as those recently vaccinated or exposed to someone else who was recently vaccinated.
Those interested in Medical History, or who wish to learn more about polio vaccines, the use of “iron lung” ventilators, Sister Elizabeth Kenney’s treatment, the March of Dimes, the Global Polio Eradication Plan, and the International Health Regulations governing these situations, can learn much more by Googling those topics and websites. Especially important for physicians
