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The Secret Life of Vaccine Viruses: Why Do They Reproduce So Astonishingly in the Human Body?
Vaccine viruses, especially vaccinia virus (VACV), have rapidly become important tools for public health over the past few centuries with the development and widespread use of small pox vaccines. As a complex enveloped virus, the genome of vaccinia virus is approximately 190 kb long and encodes approximately 250 genes. This large and unique genome allows the vaccinia virus to reproduce astonishingly in the human body, but what are the unknown secrets hidden behind it all?
The vaccine virus replicates only in the cytoplasm of the host cell, making it uniquely different from other DNA viruses.
Structure and characteristics of vaccinia virus
The virion size of vaccinia virus is approximately 360 × 270 × 250 nanometers and has a mass of 5 to 10 femtograms (fg). Its special structure allows the virus to carry out efficient gene replication and protein synthesis processes within cells. During its infection cycle, the vaccinia virus produces a variety of infectious forms, such as intracellular mature virus (IMV), intracellular enveloped virus (IEV), cell-associated enveloped virus (CEV), and extracellular envelope. Viruses (EEV). These different viral forms play important roles in the spread of viruses, especially IMV, which is crucial in host-to-host transmission.
The transmission mechanism of viruses
Vaccinia virus is capable of replicative restart (Multiplicity Reactivation, MR). During this process, even if the viral genome is damaged, multiple viruses can interact with each other to form a viable viral genome. This property not only adds vigor to the virus's reproduction but also contributes to its continued survival within the host. In their research, scientists found that viruses affected by factors such as ultraviolet light, tap water nitrogen or gamma rays can also produce effective progeny viruses through MR, which brings them a survival advantage through the recombination and repair of viral genes.
Resistance mechanism to host
The vaccinia virus genome also contains several proteins that help it resist host interferons. The main function of these proteins is to suppress the host's immune response to the virus, which allows the vaccinia virus to multiply efficiently in the host and reduces the host's immune system's ability to recognize it. For example, proteins such as K3L and E3L can effectively inhibit the activity of PKR, further strengthening the resistance to vaccinia virus.
The history and application of vaccines
In 1796, British doctor Edward Jenner first discovered that cowpox could provide protection against small pox, laying the foundation for the development of vaccines. Over time, the vaccinia virus was gradually identified as the main component of the smallpox vaccine, although records of its origins are relatively vague. Scientists speculate that vaccinia, vaccinia, and variola viruses may have originated from the same ancestral virus, which would explain their similar properties.
The use of cowpox vaccine always revolves around one question: How to effectively protect humans without causing smallpox infection?
Current situation and future prospects
With the advancement of science and technology, the application of vaccinia virus in gene therapy and genetic engineering has also received widespread attention. The scientific community's research on vaccinia virus is not only beneficial to the prevention of small pox, but also provides new ideas for the development of modern vaccines. In the use of the modern form of the minipox vaccine, ACAM2000, and various other vaccinia virus variants, we have been able to witness the amazing vitality and adaptability of the vaccinia virus.
However, during the use of vaccines, we must also consider potential side effects and risks for groups with lower immunity. The reproductive capacity of the vaccinia virus is certainly surprising, but as a vaccine, can it truly achieve its mission of protecting humans?
