Presentation on theme: "The Viruses Unit 3 Donna Howell Medical Microbiology Gaffney High School Coming soon to a body near you - He He He!"— Presentation transcript:
The Viruses Unit 3 Donna Howell Medical Microbiology Gaffney High School Coming soon to a body near you - He He He!
History In 1892, Dmitri Iwanowski studied the tobacco mosaic virus. He found out that this unknown agent could pass through a filter, unlike bacteria. In 1930s, Wendell Stanley found out that this unknown agent could crystallize, which means it is a chemical. In 1933, electron microscope was invented, and could see viruses by 1941.
What is a Virus? Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.
How Are Viruses Classified? Viruses are classifed according to what type of nucleic acid core they contain: either RNA or DNA. DNA or RNA – that is the question!
Further Classification CategoryTissue AffectedExample Diseases DermotropicSkin and subcutaneous tissue Chicken pox, shingles, measles, mumps, smallpox, rubella, herpes simplex NeurotropicBrain and central nervous system tissue Rabies, West Nile virus, polio ViscerotropicInternal organsYellow fever, AIDS, Hepatitis A and B, Mono, Dengue fever PneumotropicLungs and other respiratory structures Influenza, common cold Viruses can be further classified based on what part of the body is affected:
Size Of Viruses Viruses are among the smallest known infectious particles. They come in many sizes:
Did You Know? There is a connection between herpes and psychosis due to inflammation of the brain!
Shapes Of Viruses Viruses also come in many different shapes:
Components Of Viruses Capsid – the outer protein coat Capsomere – protein units that make up the capsid Genome – DNA or RNA Envelope – an enclosing structure similar to cell membrane Spikes – projections on outside of virus that allow it to attach to host cell
Viral Replication Viruses can replicate (reproduce) in one of two ways: 1.Lytic cycle – this is where the virus replicates in the host cell, and causes host cell to lyse, or burst to release new viruses 2.Lysogenic cycle – this is where the virus incorporates its DNA into the host DNA as a prophage, and replicates as host DNA replicates.
Lytic Cycle There are 6 stages of this cycle: 1.Attachment – virus attaches to host 2.Penetration – virus enters host 3.Uncoating – capsid removed, nucleic acid released 4.Synthesis – parts for new viruses synthesized 5.Assembly – parts are assembled 6.Release – host cell lyses, new viruses released Ex: Flu virus
Lysogenic Cycle This is when the virus enters the host cell, but does not replicate immediately. Instead, it incorporates its genes into the hosts genes, and then one day will complete the lytic cycle. Ex: AIDS
Viral Identification In many cases, when a virus infect a cell, it causes cell death or at least cell damage. The specific imprint that the virus leaves is called the cytopathic effect (CPE). By observing the effects under the microscope, scientists can sometimes identify the type of viral infection. Many viruses have a characteristic CPE.
How Are Viruses Cultured? Viruses can be cultured in one of 3 ways: 1.Inside a live animal 2.Inside a fertilized chicken egg 3.In a viral cell culture, which is a thin layer of cells in a petri dish with special nutrients Touch my egg you die, buster!
Did You Know? There is a link between in- utero exposure to flu and schizophrenia later in life! Shake ya tailfeathers!
Defenses Against Viruses What are some defenses against viruses? Body can produce antibodies, which attack and kill viruses. Some drugs can be used, such as interferon or AZT Can have a vaccine against a virus Go body go!
Types of Vaccines There are 3 types of vaccines that we use for viruses: 1.Inactivated vaccine – those made from real inactivated virus. The genome is destroyed, but the capsid remains. 2.Attenuated vaccine – those made from live viruses, but in such a low dose that it does not usually cause disease. 3.Genetically-engineered vaccine – viral proteins are produced by yeast cells, so NO actual viruses used. Safest! I got your vaccine, baby!
Viroids An ultramicroscopic, single-stranded molecule of RNA without a protein coat. Mostly infect plants Cause stunted growth and abnormal development. Come on viroids!
Prions Proteinaceous infectious particle (single piece of protein with no capsid) Can survive heat, radiation, and chemicals that normally inactivate viruses. Causes kuru and mad cow disease. Im a mad cow – get it?
Viruses and Cancer It is well known that certain viruses have cancer-causing abilities. Here are a few: HPV virus – cervical cancer Hepatitis B virus – liver cancer HTLV virus – leukemia Epstein-Barr virus – Burkitts lymphoma Get it – horoscope, cancer, crab????
HIV Virus (AIDS)
Human Papilloma Virus (Genital Warts)
Herpes Virus (Chicken Pox) Chickens dont have pox!