-Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents.

Viruses are not Living Organisms 1.They are not made of cells 2.They are not capable of carrying out any of the “life Functions” on their own

Virology A “Virologist” is a person who studies viruses. is the study of viruses.

Viral History Dimitri Iwanowski (1892) – discovered the disease-causing juice in infected tobacco leaves was “filterable”. (it passed through the filter) Martinus Beijerinck (1898) – coined the term “virus” (poison) and confirmed they are filterable. Wendell Stanley (1935) – isolated (with the advantage of the newly developed Electron Microscope) the particle causing tobacco mosaic disease, crystallized it, and identified it as a virus.

The First Vaccination Dr. Edward Jenner's Inquiry, first published in 1798, reported how, over a period of years, he had noticed the immunity provided by cow-pox, and how he decided deliberately to introduce the disease into a patient to see if the effect could be artificially produced. Soon afterwards, he would again inoculate his patients, this time with live smallpox virus to see if the cow-pox had worked. The "healthy boy" whom Jenner, on May , first vaccinated with virus from the dairymaid Sarah Nelmes was James Phipps, who proved Jenner's point by surviving repeated unsuccessful attempts to infect him with smallpox.

Examples of Viruses ColdsPolioHerpes ChickenpoxRabiesWarts MeaslesMumpsRubella SmallpoxHepatitisShingles CowpoxHIV/AIDSHantavirus FluWest NileEbola Infectious MononucleosisCancer

Viral Structures All viruses have- A Nucleic acid core of DNA or RNA And a “ capsid ”. A capsid is a protective protein coat made of protein units called capsomeres. Some viruses also have- An Envelope, which is a membrane-like structure outside the capsid that is usually made of lipids. Projections = protein containing sugar chains that attach the virus to the host cell.

Viral Classification Viruses are grouped according to: whether they contain DNA or RNA their shape the organisms they affect their Size Etc…………

HIV (Human Immunodeficiency Virus) RNA Projections Capsid (made up of capsomeres) Envelope

The T4 Bacteriophage is a virus that destroys (eats) bacteria.

Viruses Destroy cells. The Lytic Cycle is the step by step process by which a virus destroys a cell. The Lytic Cycle has 5 steps. A) Attachment- virus connects to host cell B) Entry-nucleic acid is inserted into host cell C) Replication-viral components are made D) Assembly-new viruses are assembled E) Release-host cell membranes are destroyed by viral enzymes. New viruses are released and free to destroy other cells.

1. Attachment: virus connects to host cell 2. Entry-nucleic acid is inserted into host cell 3. Replication-viral components are made 4. Assembly-new viruses are assembled The Lytic Cycle Pathway of the T4 Bacteriophage 5. Release-host cell membranes are destroyed by viral enzymes. New viruses are released and free to destroy other cells.

The Lytic Cycle

The Lysogenic Cycle Pathway A) Attachment-virus connects to host cell B) Injection-viral nucleic acid is inserted into host cell and is incorporated into the host cell’s DNA as a Prophage. It can remain dormant for days, months, or even years. C) Host cells replicate both the host cells DNA and the Prophage. D) The “new” host cells continue to survive.

Lysogenic Cycle A) Attachment- virus connects to host cell C) Host cells replicates both the host cells DNA and the Prophage. D) The “new” host cells continue to survive. B) Injection-viral nucleic acid is inserted into host cell and is incorporated into the host cell’s DNA as a Prophage. It can remain dormant for days, months, or even years.

The Lysogenic Cycle

Radiation or chemicals can cause the lysogenic cycle to change to the lytic cycle.

The Retrovirus Pathway The retrovirus has “RNA” as its nucleic acid core, not DNA. Retroviruses contain an enzyme called reverse transcriptase. Reverse transcriptase converts RNA to DNA The viral DNA is then incorporated into the host cell’s DNA The Lytic Cycle can then take place. HIV is a Retrovirus.

Viral Specificity Most viruses require specific types of host cells. They cannot infect any other cells. For example: Rabies infects and destroys nerve cells. Hepatitis infects and destroys liver cells. HIV infects and destroys T4 lymphocytes.

Spread of Viral Diseases is called transmission. Viral diseases can be transmitted or transferred by: 1. Direct contact- touch or bites 2. Indirect contact- contaminated food, drinks or air, or contact with objects that have viral particles on them…. Doorknobs, utensils, etc..

Viruses can also be spread by Vectors Vectors are “agents” which transfer viruses from one host to another. Examples of vectors include: Mosquitoes: Which carry West Nile. Mammals: Which carry Rabies. Rodents: Which carry Hantavirus

Dual Host Viruses Dual host viruses are viruses that can exist in two very different host cell types. Example: Equine Encephalitis Horse Humans Mosquito vector

Symptoms of West Nile Fever take as little as three to twelve days to show up, and a few days to disappear. Fever Headache body ache swollen lymph glands occasionally a rash on the trunk of the body take as little as three to twelve days to show up and a few days to disappear.

Viral Disease Prevention Vaccines = the injection of materials that stimulate the immune system; many contain inactive or altered viruses Quarantine = the isolation of infected individuals, keeping them away from healthy individuals Vector Control = vaccinations of some vectors, and extermination of others

Treatment of Viral Diseases Antiviral Drugs interfere with the the synthesis of viral parts during the lytic or lysogenic cycle. Antibiotics will NOT work against viruses. They can only be used to treat bacterial diseases.

Virus Origins Viruses probably de-evolved from the first cells The first viruses could have been naked bits of nucleic acid, like viroids, that could travel from cell to cell through damaged surfaces.