Electron Micrographs of Different Viruses
Influenza Virus
VirusesThe structure of viruses is very simple. They are composed of genetic material surrounded by a protein coat. The genetic material is a nucleic acid, either RNA or DNA. Viruses are extremely small and cannot be seen with the unaided or naked eye; many cannot be seen even with a transmitted light microscope. The size of viruses that cause disease in humans ranges from 20 to 300 nm, so viruses typically are viewed using an electron microscope. The number of viruses on earth exceeds the population of all other life forms combined.
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Marburg Virus
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Corona Virus
Viruses cannot replicate on their own; they require a host. Once inside the host, the virus hijacks the host's cells and then uses the resources in the host's cell to replicate, or multiply. This often results in cell death, or lysis, in the host.
There are different types of viruses that are categorized by family. There are several families of RNA viruses and a few families of DNA viruses that are of importance in human epidemiology; these viruses and their families are shown on the next page. |