Student guest post by Ron Bedford.
The first week of February 2010 must have been some sort of Post Polio Syndrome (PPS) week. The New York Times ran a story about PPS on February 2nd.
On the following Saturday, during the broadcast of the 2009 AKC/Eukanuba National Championship dog show, a Labrador Retriever named Benton was honored with an AKC Humane Fund Award for Canine Excellence (ACE) in the service category for his work as an assistance dog for his owner, Margo Dietrich, a polio survivor who “lives with physical limitations due to experiencing adult-onset Post Polio Syndrome”.
Since the mid 1950s polio has been characterized as a chronic disease caused by infection with poliovirus, which was all but eradicated from the developed world through mass immunization campaigns and routine vaccination of infants. During the 1980s and 1990s, clinicians and researchers identified PPS among polio survivors who, after 10 or more years of stability, had experienced significant deterioration of their neuromuscular functioning. The Polio Today website of the Salk Institute for Biological Studies describes PPS as “a serious neuromuscular condition … Characterized by extreme fatigue and further weakness or paralysis in the limbs.” Since the onset is typically gradual with symptoms similar to other neurodegenerative diseases, PPS is not easily diagnosed. It is not uncommon for PPS to arise in people that had such a mild case of polio that they were not even aware of the infection.
This is where things start to get interesting and frustrating. Since the last great polio pandemics occurred during the 1950s and 1960s, the numbers of polio survivors are diminishing. In a study prepared for the Board of Directors of Post-Polio Health International, Lawrence C. Becker estimates that there were approximately 426,000 polio survivors living in the U.S. in 2006, 53% of whom were over the age of 65.
The cost/benefit analyses may not work in favor of those afflicted to fund the research necessary to understand the disease mechanisms and find effective treatment modalities, but polio and PPS won’t disappear any time soon. Despite the efforts of the WHO to eradicate polio worldwide, the virus remains endemic in parts of sub-Saharan Africa and the Indian subcontinent. This WHO webpage lists the countries where cases of polio have been diagnosed recently and the accompanying map shows locations of outbreaks of wild poliovirus in the last 6 months. The WHO currently estimates that there are “10 to 20 million polio survivors worldwide … one of the largest groups with physical disabilities in the world.”
There are also reports of sporadic outbreaks elsewhere, such as among communities that discourage routine vaccination of infants and among people with compromised immune systems, such as the cases described in this 2009 blog by virology Professor, Vincent Racaniello.
Whether the virus is wild type or vaccine associated, the approximately one percent of individuals infected with polio who develop paralytic symptoms will continue to suffer with the chronic phase of the disease long after being “cured” of the infection. Since the mechanism of PPS occurrence is not well understood, it should be assumed that the syndrome will continue to manifest in 20-80% of polio survivors, the current range of prevalence estimates, though Polio Today puts the estimate at 40-50%.
Recent research projects report evidence of potential immune system involvement leading to nerve tissue damage due to inflammatory processes. The causes of the inflammation are as yet unknown, but Susan Perlman, M.D., Clinical Professor of Neurology at UCLA and Ask the Expert columnist on the Polio Today website reports encouraging results in clinical trials, European studies, and her own treatment of a handful of patients with intravenously administered immunoglobulin (IVIG) to “flush out bad antibodies attacking neuromuscular junctions.”
A study by Gonzalez et al. in the Journal of Proteomics reported identification of potential protein biomarkers for PPS which, according to the authors, would aid in the diagnosis of PPS, but would also also support hypotheses of possible immune mediated inflammation and nerve damage causing the observed neurodegeneration. The researchers examined cerebrospinal fluid of PPS patients, healthy controls, negative controls with other non-inflammatory diseases, and subjects with secondary progressive multiple sclerosis. The protein expression profiles clearly distinguished the PPS patients from other subjects in the study. The authors interpret their findings to support studies with IVIG such as those referred to by Dr. Perlman. One stated potential limitation of this study is that no polio survivors without PPS were included, so it is impossible to say whether the proteomic aberrations would be specific to PPS or would be expected to identify subjects with stable neuromuscular conditions after paralytic polio as well (Gonzalez et al., 2009).
Both of these areas of study identify potentially beneficial treatments for PPS. Both are also deserving of further research and funding to find and treat the causes of this debilitating late onset consequence of an infectious cause of a chronic disease.
Gonzalez, H., Ottervald, J., Nilsson, K. C., Sjogren, N., Miliotis, T., Von Bahr, H., et al. (2009). Identification of novel candidate protein biomarkers for the post-polio syndrome – implications for diagnosis, neurodegeneration and neuroinflammation. Journal of Proteomics, 71(6), 670-681.