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Acute Stage – the polio stage after exposure to the poliovirus, when the virus is vigorously destroying cells and the body actively responds with fever, pain, muscle spasms, unconsciousness, or paralysis. Patients were often rushed to the hospital and kept in isolation during the acute stage, usually 7–10 days.

Anterior Horn – the part of the central nervous system located at the top of the spinal column and base of the brain; location of the motor neurons most often destroyed by poliovirus.

Antibiotic – a chemical substance that can weaken or kill microorganisms (like bacteria and fungi) without significant harm to the person infected; not effective against viruses.

Antibody – a molecule produced by the body in response to a specific antigen; for example, the presence of the poliovirus in the blood provokes the body to create amino acid molecules (antibodies) to counteract it. Antigen refers to any substance that stimulates the body to make antibodies.

Attenuation – the process of weakening a virus and reducing its harmfulness; accomplished by passing the virus through different animal hosts until it is no longer strong enough to cause infection.

Clinical Trial – a research study using human volunteers to answer specific health questions. The clinical trials of the Salk vaccine used three groups: one received the vaccine, one received a placebo (harmless substance), one served as a control and was simply observed, receiving nothing. The trials were a double-blind study, meaning neither the experimenters nor the children knew who received what, with results revealed at the end of the trial.

DNA – deoxyribonucleic acid; carrier of genetic information for most organisms; made up of chains of nucleotides.

Enzyme – a protein that produces or assists in creating change in substances; a catalyst.

Epidemic – when a disease occurs suddenly and spreads quickly through a community, with numerous people affected, and then disappears; polio epidemics occurred in the summer months.

Genome – the complete set of hereditary codes (genes) contained in a species’s chromosomes.

Immune – being resistant to a particular disease; immunity can be natural (what you are born with) or acquired (either through having had the disease or artificially, through immunization).

Immunization – the process of creating immunity; vaccination with polio vaccine induces the body to produce antibodies that will protect it from future infection by poliovirus. Vaccination and inoculation are examples of immunization.

Infantile Paralysis – an older name for poliomyelitis or polio; the name was based on the observation that many infants were affected by a peculiar kind of paralysis.

Infection – when a microorganism or virus enters the body and starts reproducing itself; if the harmful agent is not stopped, disease results.

Inoculation – introduction of a disease agent into a healthy person in order to cause a mild form of the disease and create immunity.

Motor Neuron – the nerve cells of the central nervous system that control muscle movement; the poliovirus most often multiples here, destroying the motor neuron in the process.

National Immunization Days – the days, designated in a country where poliovirus is circulating, when volunteers vaccinate every child under five years of age; the children have their left pinkies marked with indelible ink to indicate that they have been vaccinated. The vaccination takes place two times a year, about six weeks apart. In January 2001, vaccinators in India immunized 150 million children during an NID.

Nobel Prize – a prestigious annual award given in six different categories to outstanding researchers, writers, and activists from around the world.

Nucleic Acid – substances that make up the proteins in a cell’s nucleus; composed of DNA or RNA nucleotides.

Nucleotide – a compound made of a base, a sugar, and a phosphate; the bits that make up nucleic acid inside a cell, including RNA and DNA.

Pandemic – an epidemic that encompasses a wide area, for instance, across nations or hemispheres.

Paralysis – loss or impairment of movement; in paralytic polio, a person’s limb muscles might not move, despite having feeling in the limb. Palsy is an old word for paralysis.

Polio – short for poliomyelitis; an acute viral disease that may include central nervous system involvement and result in paralysis and/or muscle atrophy.

Poliomyelitis – an acute viral disease that may include central nervous system involvement and result in paralysis and/or muscle atrophy.

Poliovirus – any of three serotypes of the particular virus that causes polio; it is an enterovirus, meaning it infects the gastrointestinal tract and is excreted in fecal matter.

Quarantine – to detain, isolate, or restrict commerce and interaction because of a contagious disease. Polio patients and their families were sometimes forcibly quarantined in their homes; in hospitals, patients were separated from other patients and placed in isolation wards.

Rehabilitation – restoration of activity and capacity of persons with impairment or disability; after polio, rehabilitation therapy might last from weeks to several years and include exercise, learning to use a wheelchair, and being fitted with braces.

RNA – ribonucleic acid; the molecule by which genes express themselves; the carrier of genetic information for some viruses; the part of poliovirus that replicates itself in the host cell and results in destruction.

Scientific Method – the Koch-Henle Postulates first explained in the later 19th century; with respect to polio: to prove the role of the poliovirus in disease (the hypothesis), a researcher had to identify and isolate the alleged entity (poliovirus), grow it, infect an animal with it so that it produced the same symptoms (replicate results), and then recover the same entity from the diseased animal (verify results).

Smallpox – an acute infectious disease, also called variola; causes a high fever (sometimes death) and distinct blisters on the skin that often result in permanent scars.

Synthesize – to create poliovirus artificially in the laboratory, by combining its individual components.

Vaccination – introduction of a vaccine into the body to produce immunity.

Vaccine – a substance containing some version of actual disease-causing organisms (either weakened or dead) that is used to treat or prevent disease by provoking the body to respond with antibodies. The first successful vaccine was for smallpox, in 1796.

Virology – the study of viruses and virus diseases; originated in the late 19th century.

Virus – the smallest known infectious agent; consists of either a DNA or RNA fragment protected by a protein shell (capsid); a virus cannot reproduce or act until it enters a living host cell. Viruses initially were defined by their ability to pass through a filter that stopped bacteria and other entities.

Wild-type Polio – poliovirus that occurs naturally in the environment.