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Life Cycle of the Vaccinia Virus

The vaccinia virus is a pox-type virus, related to smallpox, but milder. Vaccinia is used as a live virus vaccine for smallpox. Smallpox vaccinations are generally considered safe for individuals with healthy immune systems.

  1. Initial Infection

    • Inoculation with the vaccinia virus as a live vaccine is a form of intentional infection. Vaccinia can also be spread by touching an active inoculation site before it has healed. Bandages, clothing or other contaminated items can also carry the live virus and can be considered infective. This method of transmission is referred to as inadvertent inoculation.

      Once within the host, the virus will fuse to the plasma membrane of a permissive cell in the host.

    The Cellular Stage

    • The virus will then enter into the cytoplasm of the cell. It then moves to the nucleus. The virus then gains entry to the nucleus and deposits viral DNA. The virus then replicates its genome within the nucleus. Once complete, virus particles will leave the cell, entering into the surrounding tissues and infecting other cells within the host. This is a cyclical process.

    The Infectious Stage

    • Once the virus has proliferated, it will form a vesicular lesion on the skin at the point of infection. It will then be shed into bodily secretions in the open sore. This sore contain the live virus and any contact with it can transmit the disease.

    Signs and Symptoms

    • The effects of the infection, whether intentional or inadvertent, are generally limited to the inoculation site. The vesicular lesions will remain for anywhere from 1 to 2 weeks, eventually drying out to form a scab which will fall off after approximately three weeks, leaving a characteristic scar. Vaccinia may also cause mild fever, head and joint pain, and rash.

    Diagnosis and Treatment

    • Diagnosis can be made by testing the vesicular lesions for existence of the virus. Observing the specific clinical manifestations of the disease can assist in diagnosis.

      For the most part, vaccinia reactions will generally resolve on their own. There are two known drugs that can be used to ameliorate any adverse effects from infection with vaccinia. They are Vaccinia Immune Globulin (VIG) and Cidofovir.

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