Topic 2: Picornavirus case study After completing the Picornavirus case study of Topic 2 in the Virology segment, students should be able to: . describe the structure of the Poliovirus capsid and genome. • explain the replication cycle of Poliovirus including: - the host cell receptor used and the cell types expressing that receptor. - how the virus genome enters the host cell. - how the virus' (ti)RNA competes with the cellular mRNA for translation by the ribosomes, and how the virus eliminates the competition. - how the virus' replicates its genome using an RNA-dependent RNA polymerase. - describe how the virus progeny assemble and are released from the host cell. - describe the process of virus maturation that results in an infectious virus particle. . describe the different types of diseases caused by Poliovirus. • describe the two types of Poliovirus vaccine, and explain the advantages and disadvantages of each type, how they are administered and the type of immunity they confer to the host. 1
How fast does the virus damage the host? Poliovirus is spread by fecal contamination of food or water supplies. The receptors for the virus are found on various cells in the body - initially the throat and intestine's epithelium are infected, and the infection results in local destruction of these cells. The illness here is characterized as mild. In vitro studies indicate that the replication cycle of poliovirus is complete in about ~6 hours. The most obvious cell injury is cell lysis, but prior to this, the virus specifically inhibits host cell protein synthesis. 3
How fast does the virus damage the host? Motor neurons also have receptors for poliovirus. If the virus spreads from the intestine and gets into the bloodstream, it can can infect such neurons. This happens in a very low percentage of the number of individuals infected, but it can be the most damaging form of infection. Since the virus is released by cell lysis, infected neurons are destroyed, leading to paralysis of the muscle serviced by the neurons. This result is of no value to the virus since the virus initiating neuronal infection cannot be spread to other individuals and is eventually destroyed by the immune system. Many reports of children going to bed at night seemingly well, but waking up paralyzed. 4