 Pathogens  viruses that cause disease  Virulent  disease causing  Latent  inactive, but having the potential to be active at a later time  Antigen  the protein of a virus, which is foreign to the invaded host  Temperate  not immediately disease causing  a temperate virus introduces nucleic acid and changes the genetic code of the host ( transduction), therefore the viruses cause genetic variation within a host population, but may not cause disease.  Prion  A virus without nucleic acid.  protein infectious agent associated with several neurological diseases (scrapie; kuru; Creutzfeld-Jakob syndrome; mad cow disease)

 Maintain homeostasis  Organization  Growth and Development  Cellular organization  Heredity-- Contain genetic information  Acquire and use energy  Reproduction  Metabolism (use energy)  Responsiveness

We cannot see viruses with the naked eye Are viruses living or nonliving? Do they exhibit the characteristics of life? What characteristics of life do viruses have? video

 Obligate intracellular parasites -  they require a host cell to perform all biological functions and reproduce.  No Independent Metabolism  Smaller than the tiniest bacteria-  20 to 250 nanometers (one nanometer is one billionth of a meter)  htm htm

 Possess only one type of nucleic acid  DNA or RNA, but never both.  Eclipse Phase  period between addition of virus and the appearance of assembled virus progeny inside the cell  Some viruses still retain their infectivity, even in crystallized form

 Polio  Influenza  The common cold  herpes  smallpox  Chickenpox  ebola  human immunodeficiency virus (HIV) causing AIDS  H1N1

 The CAPSID  the protein coat that encloses the nucleic acid. This is the transport vehicle.  The CORE  made up of either DNA or RNA - this is the part that actually infects the host cell.  SURFACE PROTEINS  external protein that recognizes one or more receptor molecules on the host cell. ( The viruses ticket into a cell )  The VIRION  is the complete infective virus particle that exists outside of a host cell.

overview  Attachment  virus attaches to cell  Infection  viral nucleic acid is inserted into cell, capsid is abandoned  Replication of viral nucleic acid  viral genes are transcribed and translated by host cell  Synthesis of coat proteins  aggregate around the new strand of viral nucleic acid  Assembly of progeny viruses  hundreds are made  Bursting  liberating viral offspring to infect another cell Viral components assemble spontaneously within a host cell. The complete viral construct is called a virion. The virion is the completed, infective virus particle. A virion can be either naked, or enveloped. An enveloped virus is surrounded by a lipid bilayer where a naked virion has no layer.

 Contaminated fingers or droplets from coughs and sneezes deposit the cold virus to the front of the nasal passages.  Small doses of virus (1-30 particles) are sufficient to produce infection.  The virus is then transported to the back of the nose and onto the adenoid area by the nose itself.  The virus then attaches to a receptor (ICAM-1) which is located on the surface of nasal cells The receptor fits into a docking port on the surface of the virus After attachment, virus is taken into the cell where it starts an infection. New virus particles are produced. The infected cell dies and ruptures, releasing newly made cold virus to infect other cells in the nose and start the process over again.

 From the time a cold virus enters the nose, it takes 8-12 hours for the viral reproductive cycle to be completed and for new cold virus to be released in nasal secretions.  This interval is called the incubation period.  Cold symptoms can also begin shortly after virus is first produced in the nose (10-12 hours).  The time from the beginning of the infection to the peak of symptoms is typically hours.

 What is swine flu?  Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza viruses that causes regular outbreaks in pigs.  People do not normally get swine flu, but human infections can and do happen.  Swine flu viruses have been reported to spread from person-to-person, but in the past, this transmission was limited and not sustained beyond three people  What are the signs and symptoms of swine flu in people?  The symptoms of swine flu in people are similar to the symptoms of regular human flu and include  fever, cough, sore throat, body aches, headache, chills and fatigue.  Some people have reported diarrhea and vomiting associated with swine flu.  In the past, severe illness (pneumonia and respiratory failure) and deaths have been reported with swine flu infection in people.  Like seasonal flu, swine flu may cause a worsening of underlying chronic medical conditions.  How does swine flu spread?  Spread of this swine influenza A (H1N1) virus is thought to be happening in the same way that seasonal flu spreads.  Flu viruses are spread mainly from person to person through coughing or sneezing of people with influenza. Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose.

 Your body does have some natural ability to inhibit viral infections, which is called immunity. There are limited ways the body fights viruses:  White blood cells engulf viruses in the blood and "digest" them.  Antibodies- blood protein used to provide passive immunity to some diseases  Interferons are proteins produced by cells when exposed to a virus. This protein binds to the cell membranes of neighboring cells and "interferes" with the ability of a virus to enter the cell.

 immuneplatoon.html immuneplatoon.html

 Outside the body, the "AIDS" virus, HIV, can be destroyed with a 10% bleach solution - that is almost weak enough for you to drink.  However, once inside a host, most substances that destroy the virus are also harmful to the host.  Therefore, viral infections in animal cells can be extremely hard to cure.

 There are very few vaccines for viral infections compared to the number of vaccines developed to treat bacterial diseases.  Vaccines are a solution of weakened virus used to induce the production of antibodies.  The first viral vaccinations were for measles, mumps, and rubella.  There are now vaccines for hepatitis A and B, chickenpox, smallpox, and rabies.

 Virus vaccines are made with either inactivated or attenuated viruses.  Inactivated viruses do not replicate in a host cell.  Attenuated viruses have been genetically altered so they are not able to cause disease.

 Antiviral drugs: interfere with the synthesis of viral nucleic acid or with the formation of viral capsids during replication.  Antibiotics : specifically attack the metabolism of a bacterial cell. Since viruses use only the reproductive machinery of a cell, antibiotics are of no use in destroying viruses.