Microbiology
Summary
The Poxviridae family comprises large DNA viruses like the smallpox virus (variola virus), cowpox virus, and molluscum contagiosum virus. The poxviruses have a distinctive dumbbell-shaped core and are recognized as the largest known DNA viruses. Other unique features of these poxviruses include the ability to create their envelopes from intracellular membranes, encode their own DNA-dependent RNA polymerase, and replicate in the host cell's cytoplasm, forming inclusions known as Guarnieri bodies. This cytoplasmic replication differentiates them from many other DNA viruses which typically replicate in the nucleus.
Diseases caused by these viruses have specific features: smallpox manifests with lesions that develop uniformly, setting it apart from varicella or chickenpox lesions. Cowpox, mainly contracted from infected cow udders, was historically important for vaccine development. Molluscum contagiosum presents with flesh-colored, dome-shaped skin lesions with a central dimple, typically seen on the trunks of children. In adults, widespread molluscum contagiosum lesions may hint at immunosuppression, as observed in HIV patients.
Lesson Outline
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FAQs
Poxviruses are unique among DNA viruses due to their ability to replicate in the cytoplasm of the host cell. Their large size and complex structure that includes linear double-stranded DNA allows them to carry genes that can influence the host's immune response and support virus replication in the cytoplasm, which is unique as most DNA viruses replicate in the nucleus.
Guarnieri bodies are specific cytoplasmic inclusions found in cells infected with poxviruses. They are considered a sign of active viral replication. These bodies contain virus factories, composed of numerous virus particles and associated machinery required for replication.
Edward Jenner, an English physician, is famously known for developing the first vaccine. He observed that milkmaids who suffered from cowpox, a disease similar to smallpox but much less severe, did not get smallpox. He hypothesized that cowpox protected against smallpox and proved it by vaccinating a young boy with cowpox and later exposing him to the smallpox virus. The boy did not develop the disease, confirming Jenner's theory and leading to the development of the first successful vaccine.
The molluscum contagiosum virus is spread primarily through direct skin-to-skin contact, sharing objects such as towels or clothes, or sexual contact. It can also be spread in swimming pools. While anyone can get molluscum contagiosum, it is most common in children, people living in tropical climates, people with weakened immune systems (immunosuppression), and people with atopic dermatitis.
