VIROLOGY The Study of Viruses

Virology 1.Definition: A submicroscopic acellular pathogen composed only of protein and one type of nucleic acid.

Latin for “Poison” Can only be seen with an electron microscope; Measured in nanometers = 1 billionth of a meter; range from nanometers Pathogens = disease-causing agents Contain only 1 type of nucleic acid, either DNA or RNA, but never both Many are vector-borne = transmitted by a living organism that does NOT have the illness.

2.NOT classified as living a. NO cells ( acellular ) b. Do NOT obtain or use energy c. NO response to stimulus d. NO lifespan (do not grow, develop, and die) c. Do NOT reproduce sexually or asexually; Obligate intracellular parasites = must invade a living cell to create more viruses = cell death

3.Classification #1 characteristic = type of nucleic acid = DNA or RNA * Target host and cell type * Mode of infection = How contracted by host * Method of replication * Size and Shape

4.Shapes a. Many and varied = Icosahedral, helical, Spherical, complex Influenza Tobacco Mosaic Virus Ebola virus HIV

b.Structure of a virus Capsid * Capsid = inner protein coat that contains one type of Nucleic Acid = DNA or RNA Envelope * Envelope = outer protein and lipid layer that surrounds the capsid Glycoproteins * Glycoproteins = proteins with attached carbohydrates; can help the virus attach to its host cell. Serve as antigens to cells.

Structure: CAPSID Glycoproteins Nucleic Acid = RNA ENVELOPE

Herpes Zoster Virus Envelope Capsid DNA Glycoproteins

5.Viral Replication Viruses lack the ability to reproduce either sexually or asexually on their own. Viruses must invade a living host cell and turn the cell into a virus factory. This process results in the death of the host cell.

Two Basic Modes of Viral Reproduction a.The Lytic Cycle b. The Lysogenic Cycle

a. The Lytic Cycle A.INFECTION = Virus and/or viral genetic material enters the host cell VIRUSVIRAL GENETIC MATERIAL HOST CELL’S DNA

B.REPLICATION = Viral DNA is copied and transcribed = RNA is produced. Host cell’s DNA is destroyed

C. SYNTHESIS = The viral RNA directs the production of viral proteins to build new viral parts.

a. The Lytic Cycle E. LYSIS = the cell membrane is ruptured to release the new viruses. D. ASSEMBLY New viruses are built. E

b. The Lysogenic Cycle 1. Infection 2.Insertion = Viral DNA is inserted into the host’s DNA.

b. Lysogenic Cycle 3.Mitosis (and Cytokinesis) Host cell undergoes cell division many times = copying the viral DNA along with its own. All new daughter cells carry the viral DNA.

4. The virus then enters the Lytic Cycle (Replication, Synthesis, Assembly, & Lysis) to produce viruses. Many cells are releasing new viruses at the same time.

6. Viral Diseases Cannot be controlled by antibiotics = A drug that kills or prevents the growth of bacteria. Some can be controlled with antiviral drugs = a drug used to prevent viral attachment, interrupt viral protein synthesis, or prevent the release of new viruses.

Some can be prevented by vaccines = an injection of inactive viruses, viral proteins, or a similar virus to produce antibodies against the actual viral pathogen = immune system builds antibodies against the virus that can’t harm the cells. When the harmful virus invades the body, the immune system recognizes it immediately and antibodies attach to the virus = virus cannot infect a cell.

Viral Diseases

Chicken Pox Varicella-Zoster Virus = DNA Spread by coughing and sneezing (highly contagious), by direct contact, and by aerosolization of virus from skin lesions. A vaccine is available

Varicella-Zoster Virus

Common Cold Spread mainly by contact with the saliva or nasal secretions of an infected person, either directly or from contaminated surfaces. In aerosol form generated by coughing, sneezing. Primarily caused by Rhinoviruses = RNA virus No vaccine

Rhinovirus

AIDS = Acquired immune deficiency syndrome Caused by HIV = Human immunodeficiency virus = a RNA retro virus Spread by sexual contact, blood-to-blood, and to a fetus while in utero of an infected mother. No vaccine. Antiviral drugs to slow viral reproduction.

Human Immunodeficiency Virus

Infectious Mononucleosis Caused by the Epstein-Barr Virus; a herpesvirus = a DNA virus Spread by contact with infected saliva. No vaccine

Epstein-Barr Virus

Poliomyelitis Caused by a picornavirus = a RNA virus Spread by ingesting food or water infected with feces containing the virus. Several vaccines; Jonas Salk created the first vaccine = called the IPV.

Poliovirus

Rabies Caused by the Rhabdovirus = a RNA virus Spread by contact with the saliva of an infected mammal. Vaccines available for both human and non-human mammals.

Rhabdovirus

Yellow Fever Caused by a Flavivirus = a RNA virus Vectored by Aedes sp. of mosquitoes; saliva of the mosquito is infected with the virus. Vaccine is available

Flavivirus PATHOGEN VECTOR

EBOLA Hemorrhagic Fever Caused a Filovirus = RNA virus Spread through infected bodily fluids and contact with the skin of an infected individual. No vaccine 2009 – Discovered that Fruit Bats are the natural hosts.

Filovirus

Influenza Types A and B caused by strains of the orthomyxovirus = an RNA virus Spread mainly by contact with the saliva or nasal secretions of an infected person, either directly or from contaminated surfaces. In aerosol form generated by coughing, sneezing. Annual vaccines available. Antiviral drugs are available to shorten the duration of the disease.

Other Viral Diseases Herpes Simplex Hanta virus Measels Mumps Rubella Warts = including Human Papillomavirus Hepatitis A,B,C,D, &E Small Pox

Orthomyxovirus

H1N1 (novel Swine Flu 2009) * Classified in Genus Influenza A *Family Orthomyxoviridae *an RNA (ss) virus

H1N1 Influenza A *H1 portion of name = Identifies the specific type of antigenic glycoprotein (Haemagglutinin) that the virus has on its surface. *The purpose of this protein is to bind the virus to its specific host cell.

H1N1 Influenza A *N1 = The specific type of neurominidase enzyme found on the surface of the virus. *This protein enables the newly formed viruses to be released from the host cell.

H1N1 Influenza A *Targets cells of the respiratory system *Found to have genetic components from: -North American Swine Influenza (pig) -North American Avian Influenza (bird) -Human Influenza -Asian/European Swine Influenza (pig)

H1N1 Influenza A *Can be treated with the antiviral drugs Zanamivir (sold as Relenza) and Oseltamivir (Tamiflu) *Both of these antiviral drugs block the neuraminidase enzyme to prevent newly formed viruses from escaping the host cells and infecting new cells.