Poliovirus

Poliovirus
Virus classification
Group:	ssRNA viruses IV
Family:	Picornaviridae;
Genus:	Enterovirus;
Sero complex:	Poliovirus;

Main Article

Discussion

Description and significance

Poliovirus is an enteroviruses which is a RNA virus that is stable and survive in acidic conditions. Poliovirus was first isolated by Karl Landersteiner and Erwin Popper in 1909. They proved that a virus caused the paralysis and not a bacterium. Karl Landsteiner presented that the cause of poliomyelitis could be experimentally transmitted to monkeys by injecting them with material that was made by grinding up the spinal cords of children who died from poliomyelitis.

Poliovirus

Genome structure

Poliovirus is made up of a RNA genome and a protein capsid. The RNA genome is a linear, single-stranded, positive-strand RNA and it is approximately 7,500 nucleotides long. The viral component is about 300 Ångström wide with icosahdral symmetry. Poliovirus is composed of carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. Poliovirus assembles its RNA genes and its protective protein capsid from these elements. Poliovirus has three serotypes; PV1, PV2, and PV3. There are many strains of each serotype. The three serotypes are highly infectious, but differ in the protein capsid. PV1 is the most common serotype. Poliovirus is commonly known as the most important and basic virus because of its short genome and simple structure.

Cell structure and metabolism

The cellular life cycle of poliovirus begins by binding of a poliovirion to the host cell surface receptor, CD155 (1). Destabilization of the virus capsid which is receptor dependent mediates the uncoating of the viral RNA (2). Cellular phosphodiesterase cleaves the viral protein VPg and translation of the viral RNA occurs by a cap-independent (IRES-mediated) mechanism (3). Proteolytic processing of the viral polyprotein produces mature structural and non-structural proteins (4). The positive-sense RNA serves as template for complementary negative-strand synthesis, which produces a double-stranded RNA (replicative form, RF) (5). Initiation of many positive strands from a single negative strand produces the partially single-stranded replicative intermediate (RI) (6). The newly synthesized positive-sense RNA molecules can serve as templates for translation (7) or associate with capsid precursors to undergo encapsidation and the maturation cleavage of VP0 (8), which produces virions. The infected cell bursts and releases infectious viruses into the bloodstream(9). [1]

Ecology

Humans are the exclusive natural host for poliovirus. It cannot naturally infect other species. Monkeys and chimpanzees can be infected with poliovirus experimentally, but not naturally. Poliovirus is spread through sewage by infected people who pass their faeces.

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

Poliovirus causes the viral disease, poliomyelitis. Poliomyelitis is an extremely infectious disease. Humans are the exclusive natural host for poliovirus. It cannot naturally infect other species. The virus takes over the nervous system and can cause paralysis in hours. Poliovirus enters the body through the mouth and replicates in the throat and intestine. Once the virus remains stable in the intestine, it can enter the blood stream and pass onto the central nervous system.

As poliovirus replicates, it damages motor neurons which control the muscles for swallowing, circulation, respiration, and the trunk, arms, and legs. The damage of the motor neurons are irreversible and can cause a condition known as acute flaccid paralysis (AFP) which affects the limbs. Paralysis involving the trunk and muscles of the thorax and abdomen can result in quadriplegia. For bulbar polio, a more severe case of polio, poliovirus attacks the motor neurons of the brain stem which cause difficulty in swallowing and speaking. Without respiratory support, bulbar polio can lead to death. In the 1940s and 50s, people infected with polio that affected their respiratory muscles were treated with "iron lungs" - metal cylinders that were worked like a pair of bellows to regulate breathing and keep them alive. Today the positive pressure ventilator replaced the iron lung.

In countries with poor sanitation, poliovirus can be spread to others by faeces of people who are infected by the virus. It can also infect vaccinated people; they will not develop polio, but can carry this virus in their gastrointestinal tract and pass it on to others.

Symptoms of infected individuals include headache, fever, vomitting, stiffness and pain in the neck and back. Poliovirus can also lead to paralysis, commonly in the legs. Some people infected with this virus do not have any symptoms and aren't aware they have been infected.

Unfortunately, there is no known cure for poliomyelitis.

(How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.)

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

First Animal Model Developed for Oral Infection of Human Poliovirus

In the August 2007 issue of Journal of Virology, it was reported that researchers developed an animal model for oral poliovirus infection. Researchers were trying to find new ways to prevent the spread of the virus in countries with poor conditions. In the study, the mice that lacked the interferon receptor gene (IFNAR) and carried the human poliovirus receptor gene were affected by the oral ingestion of poliovirus. Nine days after the ingestion, the mice died and the poliovirus was found in their small intestines and digestive tracts. The mice that expressed the interferon receptor gene (IFNAR) were found to be less affected by the virus. These results show that the interferon receptor gene (IFNAR) is significant in determining how permissive the poliovirus is in the digestive tract as well as the production of virus-specific immune responses to the virus by the oral route. The researchers stated, “Thus, hPVR-Tg/IfnarKO are considered to be the first oral infection model for poliovirus.”