Polio 2010

Poliovirus

Over the next few weeks, Inside Vaccines will be taking a closer look at Poliomyelitis infections, exploring aspects of the history of poliomyelitis; describing environmental factors that increase the incidence of paralytic polio; considering the history and efficacy of the vaccines used against polio; and finally, exploring the campaign to eradicate polio.
First, let’s look at some basic information.

When most people think of poliomyelitis, they think of children who had lameness and leg deformities, with their legs in braces, or lying in iron lungs (old-style breathing machines, or ventilators) because they couldn’t breathe. Most people link all paralysis and lameness solely to a group of viruses called POLIOMYELITIS. The World Health Organization describes polio:

Polio is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours. The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5% to 10% die when their breathing muscles become immobilized. [1]

Now for a more accurate picture of exactly what “poliomyelitis” is.

The poliomyelitis viruses fall within a class of viruses called “human enteroviruses” [2]. Polioviruses belong to the viral family Picornaviridae [3]. There are three types: 1 Brunhilde; 2 Lansing; and 3 Leon.   Amongst these types there are hundreds of different strains. Type 1 is considered the most serious virus, followed by type 2.

Technically, a person can “get” poliomyelitis 3 times, since the types do not give cross protection to each other, but in practice, having clinical polio three times is very rare.

How is poliomyelitis virus transmitted?

Poliomyelitis is transmitted by person-to-person spread through fecal-oral and oral-oral routes, or occasionally by a common vehicle (e.g., water, milk). [4]

What happens when people are exposed to polioviruses?

When non-immune persons are exposed to wild poliovirus, inapparent infection is the most frequent outcome (72 percent). [4]

Most people won’t even be aware that they were sick.

What sort of clinical symptoms do people see?

The vast majority of symptoms fall under the category of:

1) “Abortive poliomyelitis,” also referred to as “minor illness,” is the most frequent form (24 percent) of the disease.
2) Nonparalytic poliomyelitis (including aseptic meningitis) occurs in 4 percent of patients. [4]

From the CDC Pink Book , a description of the symptoms of non-paralytic polio:

Approximately 4%–8% of polio infections consist of a minor, nonspecific illness without clinical or laboratory evidence of central nervous system invasion. This clinical presentation is known as abortive poliomyelitis, and is characterized by complete recovery in less than a week. Three syndromes observed with this form of poliovirus infection are upper respiratory tract infection (sore throat and fever), gastrointestinal disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhea), and influenza-like illness. These syndromes are indistinguishable from other viral illnesses.

Nonparalytic aseptic meningitis (symptoms of stiffness of the neck, back, and/or legs), usually following several days after a prodrome similar to that of minor illness, occurs in 1%–2% of polio infections. Increased or abnormal sensations can also occur. Typically these symptoms will last from 2 to 10 days, followed by complete recovery. (page 2) [5]

What is the proportion of people who go on to become like those people we saw in iron lungs, or with leg braces, since there doesn’t seem to very many people paralyzed or dead?

Only 1/1,000 to 1/100 infected individuals develop paralytic disease (28-30). Reports of greater ratios of paralytic infection to subclinical infection in poliomyelitis are not based on consistent case ascertainment, or are not representative of the range in the majority of literature reports. [4]

The information above, however, ONLY applies to poliomyelitis viruses  but not all poliomyelitis is actually poliomyelitis, but they don’t tell you that. I wonder why? We will … in the next post called Polio and Acute Flaccid Paralysis.”


Notes:

[1] World Health Organization. Media Centre. Fact Sheets. Poliomyelitis. http://www.who.int/mediacentre/factsheets/fs114/en

[2] Centers for Disease Control. National Center for Immunisation and Respiratory Diseases. Non-Polio Enterovirus Infections. http://www.cdc.gov/ncidod/dvrd/revb/enterovirus/non-polio_entero.htm

[3] Fields’ virology, Volume 1, By Bernard N. Fields, David Mahan Knipe, Peter M. Howley, Diane E. Griffin, 5th Edition, 2007. Accessed online via Google Books. Page 796. http://books.google.com/books?id=5O0somr0w18C&lpg=PA795&dq=Picornaviridae.&pg=PA796#v=onepage&q=Picornaviridae.&f=false

[4]  Differential Diagnosis of Acute Flaccid Paralysis and Its Role in Poliomyelitis Surveillance, Arthur Marx, Jonathan D. Glass, and Roland W. Sutter. Epidemiologic Reviews, Vol. 22, No. 2, 2000. http://epirev.oxfordjournals.org/cgi/reprint/22/2/298.pdf

[5] Epidemiology and Prevention of Vaccine-Preventable Diseases, The Pink Book: Course Textbook, 11th Edition (May 2009), Chapter 16, Poliomyelitis, page 2.  http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf

Comments

3 Comments on Polio 2010

  1. Chuck on Thu, 27th May 2010 9:31 am
  2. Excellent post. I appreciate having all factual information concerning these subjects

  3. cynic on Thu, 27th May 2010 7:20 pm
  4. How refreshing to see facts that actually are representative of history. Hopefully others will take notice to the unbiased tone in which the articles here are written.

    I look forward to the future installments.

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