Donna Howell Medical Microbiology Gaffney High School Coming soon to a body near you - He He He! The Viruses Unit 3 Donna Howell Medical Microbiology Gaffney High School

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 1930’s, 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? DNA or RNA – that is the question! Viruses are classifed according to what type of nucleic acid core they contain: either RNA or DNA.

Further Classification Viruses can be further classified based on what part of the body is affected: Category Tissue Affected Example Diseases Dermotropic Skin and subcutaneous tissue Chicken pox, shingles, measles, mumps, smallpox, rubella, herpes simplex Neurotropic Brain and central nervous system tissue Rabies, West Nile virus, polio Viscerotropic Internal organs Yellow fever, AIDS, Hepatitis A and B, Mono, Dengue fever Pneumotropic Lungs and other respiratory structures Influenza, common cold

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: Lytic cycle – this is where the virus replicates in the host cell, and causes host cell to “lyse”, or burst to release new viruses 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: Attachment – virus attaches to host Penetration – virus enters host Uncoating – capsid removed, nucleic acid released Synthesis – parts for new viruses synthesized Assembly – parts are assembled 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 host’s 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? Touch my egg you die, buster! Viruses can be cultured in one of 3 ways: Inside a live animal Inside a fertilized chicken egg In a viral cell culture, which is a thin layer of cells in a petri dish with special nutrients

Did You Know? Shake ya tailfeathers! There is a link between in-utero exposure to flu and schizophrenia later in life!

Defenses Against Viruses Go body go! 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

Types of Vaccines I got your vaccine, baby! There are 3 types of vaccines that we use for viruses: Inactivated vaccine – those made from real inactivated virus. The genome is destroyed, but the capsid remains. Attenuated vaccine – those made from “live” viruses, but in such a low dose that it does not usually cause disease. Genetically-engineered vaccine – viral proteins are produced by yeast cells, so NO actual viruses used. Safest!

Viroids Come on viroids! An ultramicroscopic, single-stranded molecule of RNA without a protein coat. Mostly infect plants Cause stunted growth and abnormal development.

Prions I’m a mad cow – get it? 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.

Get it – horoscope, cancer, crab???? Viruses and Cancer Get it – horoscope, cancer, crab???? 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 – Burkitt’s lymphoma

HIV Virus (AIDS)

Human Papilloma Virus (Genital Warts)

Herpes Virus (Chicken Pox) Chickens don’t have pox!

Filovirus – Ebola Hemorrhagic Fever

Rotavirus – The “Stomach Bug”

HBV – Hepatitis B

Orthomyxovirus – The “Flu”

Paramyxovirus (Measles)

Picornavirus (Polio)

Rhabdovirus (Rabies)

Science is cute and cuddly, boys! The End! Science is cute and cuddly, boys!