Vaccinia
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| ICD-10 | B08.0 |
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| ICD-9 | 051.0 |
| eMedicine | med/2356 |
| iVaccinia virus | ||||||||
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Vaccinia virus (VACV or VV) is a large, complex enveloped virus belonging to the poxvirus family of viruses. It has a linear double-stranded DNA genome, which is approximately 190 kbp in length and encodes for approximately 250 genes. The dimensions of the virion are roughly 360 × 270 × 250 nm. Vaccinia virus is well-known for its role as a vaccine that eradicated the smallpox disease from our world, making it the first human disease to be successfully eradicated by mankind. This endeavour was carried out by the World Health Organization under the Smallpox Eradication Program. Post eradication of smallpox, scientists have been studying vaccinia virus to use as a tool for delivering genes into biological tissues (gene therapy and genetic engineering). Moreover, due to recent concerns about smallpox resurfacing as a possible agent for bioterrorism, scientists have renewed their interests in studying vaccinia virus.
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[edit] Basic biology
Vaccinia virus is unique amongst all DNA viruses because it replicates only in the cytoplasm of the host cell (outside of the nucleus). Therefore, the large genome is required for encoding various enzymes and proteins involved in viral DNA replication and gene transcription. During its replication cycle, VV produces several infectious forms which differ in their outer membranes: the intracellular mature virion (IMV), the intracellular enveloped virion (IEV), the cell-associated enveloped virion (CEV) and the extracellular enveloped virion (EEV). Although the issue remains contentious, the prevailing view is that the IMV consists of a single lipoprotein membrane, while the CEV and EEV are both surrounded by two membrane layers and the IEV has three envelopes. The IMV is the most abundant infectious form and is thought to be responsible for spread between hosts. On the other hand, the CEV is believed to play a role in cell-to-cell spread and the EEV is thought to be important for long range dissemination within the host organism.
[edit] Host resistance
Vaccinia contains within its genome several proteins that give the virus resistance to interferons. K3L is a protein with homology towards the protein eIF-2alpha. K3L protein inhibits the action of PKR, an activator of interferons. E3L is another protein encoded by vaccinia. E3L also inhibits PKR activation; and is also able to bind to double stranded RNA.
[edit] Origin
Vaccinia virus is closely related to the virus that causes cowpox. The precise origin of vaccinia virus is unknown due to the lack of record-tracking as the virus was repeatedly cultivated and passaged in research laboratories for many decades. The most common notion is that vaccinia virus, cowpox virus and variola virus (the causative agent for smallpox) were all derived from a common ancestral virus. There is also speculation that vaccinia virus was originally isolated from horses.
[edit] Use as a vaccine
A vaccinia virus infection is very mild and is typically asymptomatic in healthy individuals, but it may cause a mild rash and fever, with an extremely low rate of fatality. Immune responses generated from a vaccinia virus infection protects the person against a lethal smallpox infection. For this reason, vaccinia virus was, and is still being used as a live-virus vaccine against smallpox. The vaccinia virus vaccine is safe because it does not contain the smallpox virus, but occasionally certain complications and/or vaccine adverse effects may arise, especially if the vaccine is immunocompromised. In the worst case, approximately one in one million individuals will develop a fatal response to the vaccination. Currently, the vaccine is only administered to health care workers or research personnel who have a high risk of contracting vaccinia virus. Due to the present threat of smallpox-related bioterrorism, there is a possibility the vaccine may have to be widely administered again in the future. Therefore, scientists are currently developing novel vaccine strategies against smallpox which are much safer and faster to deploy during a bioterrorism event.
[edit] History
The original vaccine for smallpox, and the origin of the idea of vaccination, was cowpox, reported on by Edward Jenner in 1798. The Latin term used for cowpox was variolae vaccinae, essentially a direct translation of "cow-related pox". That term lent its name to the whole idea of vaccination. When it was realized that the virus used in smallpox vaccination was not, or was no longer, the same as the cowpox virus, the name 'vaccinia' stayed with the vaccine-related virus. (See OED.)
[edit] External links
- Smallpox and Vaccinia
- Vaccinia virus, complete genome
- Cowpox virus strain GRI-90 is the closest known match to vaccinia.
