The polio virus is the causative agent of poliomyelitis, one of the most feared diseases of the twentieth century, responsible for crippling thousands of people across the globe, prior to distribution of a vaccine developed by Jonas Salk in the 1950's, according to a 2005 article published in "Annual Review of Microbiology." Three strains of polio virus have been characterized, each of which is highly infectious.
Effects of the Virus
Humans are the only species affected by the polio virus, and transmission is through the fecal, oral route. Almost 100 percent of the population may be infected in areas where the virus is endemic. The vast majority of people infected by the polio virus report no symptoms at all, but roughly 1 percent develop muscle weakness and paralysis, caused by entry of the virus into the central nervous system, according to the World Health Organization.
Biochemistry of the Virus
Polio virus is regarded as one of the simplest significant viruses, composed of a ribonucleic acid genome encapsulated by a protein coat. The virus binds to an antibody receptor on the outside of the cell in order to gain entry, using the host's biochemical machinery to replicate itself and exit the cell, according to an August 2005 article published in "Virus Research."
Three Polio Strains
The three Polio strains, PV1, PV2 and PV3 differ from one another in the nature of the protein that surrounds the riboneucleic acid genome, which in turn affects entry of these viruses into cells. PV1 is localized to India, Afganistan as well as West and Central Africa. PV2 is most likely eradicated, but was last detected in India, according to Centers for Disease control and Prevention. PV3 has been detected in only five countries Nigeria, Pakistan, Niger, India and Sudan, according to a 2005 article published in "Annual Review of Microbiology."
Vaccine Development
One method of vaccine development is to expose the body to a weakened or inactivated form of a pathogen, thus provoking a defensive immune response against the real pathogen, and this is how some polio vaccines work, according to the website Vaccine Information.
Polio Vaccine
An effective vaccine was developed against the polio virus by inactivating PV1, PV2 and PV3 using the chemical formalin, then administering the vaccine via injection. An oral vaccine was subsequently developed by inducing weakening changes in the viral genome by culturing the three strains in monkey cells for an extended period, rendering the virus less able to infect a human host, while provoking an effective immune response against the real polio virus, according to the website Polio Eradication.
References
- PubMed; "Annu Rev Microbiol"; Vaccine-Derived Polioviruses and the Endgame Strategy for Global Polio Eradication; O. Kew; Jan 2005
- PubMed; "Virus Research"; Poliovirus and Poliomyelitis: a Tale of Guts, Brains, and an Accidental Event; S. Mueller; Aug 2005
- Global Polio Eradication Initiative; Polio Vaccines
- World Health Organization; Poliomyelitis
- Vaccine Information; Polio Vaccine
