introduction
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This blog is set up for our CL1202 module - Microbiology B
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Picornaviridae
Sunday, February 1, 2009/ 5:07 AM
Before introducing this virus family to you, you need to know what pico means. Can't guess? It means very small in Greek! Yes, the virus family that I'll be introducing is Picornaviridae. It is a virus family containing the smallest viruses ever found!
Introduction:
The virus in this fammily are positive single stranded RNA viruses. They are the largest family of viruses. There are five genera in this family, the aphtovirus, cardiovirus, enterovirus, heptovirus and rhinovirus. For this time, we will be focusing on the rhinovirus, the common cold.
Rhinovirus:
The rhinovirus has naked virions without envelope. It has an isometric and symmetric nucleocapsid, although incomplete or empty capsids are relatively common. Its genomic RNA is infectious and can be used as a mRNA for direct gene transmission. It has a long untranslated region end of the 5' end structure(IRES), which is important for translation, virulence, and maybe encapsidation. Both ends of the genome is modified.As with the influenza virus, there are also 6 phases of reproduction.By using different cellular receptors, a picornavirus virion will attach to a host cell. The virion will uncoat and release the virus RNA into the cytoplasm of the host cell via a membrane channel. The virus replication occurs entirely in the cytoplasm. While the host cell's transcription processes are shut off to a degree, while the IRES helps to make sure that the virus transcription is unmodified. Replication then occurs. The RNA would be packaged into preformed capsids. The virus is then released, followed by cell lysis occurs.(with the exception of Hepatits A)
The rhinovirus infects the upper respiratory tract and has a short incubation of 2-3 days. When infection occurs, the endogenous IFN helps to defend the body. Although the locally synthesized IgA will decrease with time, the serum IgG will persist for years and recognize the virus if it enters the body again. It helps to remeber the virus!
Symptoms:
The main symptoms fpr the common cold are watery nasal discharge, congestion, sneezing, little or no fever. Sometimes, there might be fever, fatigue,cough and headache.
More Information:
The virus is tested out by virus culture, nasal washings, ELISA and PCR (polymerase chain reaction). The virus infects throughout the year and has a few serotypes circulating simultaneously. It is abundant in nasal discharge.
Control:
Since there is no vaccine for rhinovirus because there are too many rhinoviruses, the infected person should wash hands, avoid touching his or her eyes and nose, sneeze into a tissue and stay at home to prevent its spread.
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