02.02 Viruses & Fungi

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  1. Viruses- tiny infectious agents that rely on a host cell’s machinery and metabolism in order to replicate. They tend to be host specific and they are known to infect every form of life on the planet.
    1. Six basic Stages of Viral Lytic Cycle
      1. Attachment-virus binds to cell membrane of host cell
      2. Penetration-Virus enters cell through receptor-mediated endocytosis
      3. Uncoating-viral capsid is removed
      4. Replication- Multiplication of viral genome
      5. Assemby-viral parts self assemble
      6. Release- Viruses are released through lysis of host cell.
    2. Controlling the Virus Cycle 
      1. Vaccination- expose the immune system to an attenuated version of the virus so that inthe primaryresponse creates antibodies and memory cells.
      2. Vector Control and Sanitation
      3. Antiviral chemotherapy
      4. Interferons
      5. Cytokines
  2. Fungi- a eukayotic organism that contain cell walls made of chitin and breakdown their food on before ingesting.
    1. Pathogenic examples 
      1. Candidiasis- causes thrush
      2. Aspergillosis- infects those with immuno-deficiencies.
      3. Dermatophytic and keratinophilic-attack eyes,hair, nails and skinsuch as ringworm and athlete’s foot.


Today we’re going to be talking about Viruses and Fungi.
Viruses are tiny infectious agents that are known to have infected every form of life on Earth. They tend to be host specific all though they can jump species. their only means of making more of themselves is through the use of the machinery of the host cell. Pictured here is one shape type of a virus. This is a rotavirus which is known to infect humans as well as other mammals.

So the active for of the virus life cycle is known as the lytic cycle. Lytic means to break open. There are six steps to the virus breaking open or bursting the cell it invades. Step one is attachment where the virus receptors bind to the cell membrane of the host cell. In some viral trickery, the cell invites the truly unwanted guest in through endocytosis and this is step 2 know as penetration. Once in, the damaging act begins through uncoating. The virus sheds its capsid (outer coat) releasing its genetic components. Where DNA or RNA the effects will lead to multiplication of the viral genome known as Replication. After this the virus begins assembly and once enough of these viruses have been assembled it becomes operation release. Internal viral manufacturing reaching a point of cell destruction and the lysis of the cell releases millions of virus into the host organism only to invade yet a new host cell and repeat.

So know the pathogenicity of a virus, it became imperative to learn of ways to control this beast and its cycle. One of the most effective means of accomplishing this has been through vaccines. Vaccinations are created to expose the adaptive immune response to a benign version of the virus increasing the memory identification and response time should a futuristic “real” infection occur.

Controlling exposure to the virus in more of an environmental approach is another means of controlling the virus cycle. Some viruses are transferred through hosts/vectors that are not detrimentally affected by the virus but are means in which the virus is spread. Onc common vector is the mosquito. Controlling the mosquito population is an indirect way of controlling the virus cycle. Antiviral chemotherapy like the drug tamiflu are drugs used to attack the virus in its earliest onset in hopes of preventing the virus from spreading and causing illness. Additionally, the immune system has been a beautiful model and manufacturer of special proteins like interferons and cytokines that inhibit viral replication or secrete signals to talk to immune cells to trigger the production of specific antibodies. 

Fungi are eukaryotes that can also be infectious agents. These creatures are defined by the fact that they breakdown their food sources before absorbing them… unlike humans who ingest and then digest. Although we can enjoy a good mushroom or bake with yeast there are some fungi that are pathogenic. Candidia, for example, can cause yeast infections/thrush. Aspergillosis infects those with compromised immune systems. Some fungi can thrive on the skin like ringworm and keratin like athlete’s feet and thus attack our eyes, hair, and nails.

In review viruses are non-living infectious agents that require a host cell to multiply. This invasion is known as the first part of the lytic cycle where the virus attaches then penetrates a cell, strips its’ capsid and begins to replicate its genome, reassembles itself in multitudes and releases through the rupture of the host cell’s membrane. Thus control of this cycle needed to prevent the spread of the virus. This currently is done through vaccinations, vector control and sanitation, chemotherapy against the virus and the use of adaptive immune responses such as cytokines and interferons. Lastly, we reviewed the pathogenic versions of fungi which are forms of life that have unique cell walls made of chitin and are known to break down materials prior to ingestion such as Candidia that causes thrush, or ringworm that lives off of skin.

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