Chapter 6
Which virus causes nausea, vomiting, fever and is often associated with cruise ships? There have been outbreaks in Spokane nursing homes of this virus.
"Cruise Ship Virus" • Noroviruses -Nausea, vomiting, fever -Elderly and children-dehydration problems -Transmission-fecal oral •Ingestion of contaminated food or water •Contact with contaminated surfaces and hands -Difficult to control (survive 3 weeks on surfaces)
Treatment of Animal Viral Infections
•Examples of antiviral drugs -AZT to treat AIDS •Targets synthesis stage -HIV protease inhibitors •Interrupts assembly of virus • Interferon -shows potential for treating and preventing viral infections -Naturally occurring human product •Vaccines stimulate immunity -HPV, Chicken pox, Measles, Rubella, etc.
Synthesis of ss (-)RNA Viruses In General
•Examples: -Rabies, Ebola, Mumps, Influenza, Hantavirus •Virus has a ssRNA (-) strand genome -Must transcribe a (+) strand to serve as mRNA before they can make proteins •(+) strand transcribes additional (-) strands •(-) strand is packaged into new viruses
Synthesis of ss (+)RNA Viruses In General
•Examples: Polio, Common Cold, Hepatitis A Virus, Hand-foot-mouth disease, Rubella, Hepatitis C Virus, West Nile Virus •Virus has a (+) strand ssRNA • Use (+) strands to: • Make viral proteins • Be packaged into new viruses • Transcribe (-) strands • Use (-) strands to: • make more (+) strands
Penetration (Endocytosis vs fusion of viruses upon penetration)
•Flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid •Various mechanisms: 1. Endocytosis •entire virus engulfed by cell and enclosed in a vacuole or vesicle 2. Fusion •viral envelope directly fuses with host cell membrane
Release
•Nonenveloped and complex viruses: - released when the cell lyses or ruptures •Enveloped viruses are liberated by: - budding or exocytosis •May bud from membranes of cytoplasm, nucleus, ER or vesicles •Anywhere from 3,000 to 100,000 virions may be released, depending on the virus -Entire length of cycle- anywhere from 8 to 36 hours Release of Mature Viruses Enveloped viruses are liberated by budding or exocytosis: • Nucleocapsid binds to the membrane • A small pouch is formed • Pinching off of the pouch releases the virus with its envelope • Viruses are shed gradually without destruction of the cell
Synthesis of RNA Viruses In General
•Typically replicated and assembled in cytoplasm of host cell •Sense strand, or (+) strand -Viral RNA that can act as mRNA •Antisense strand , or (-) strand -Viral RNA that can not act as mRNA • RNA-dependent RNA polymerase (replicase) (RDRP) -makes a double-stranded RNA (complementary strand)
A few members of the Herpesviridae family
-Genus of virus: Simplexvirus Herpes -Common Name of genus member: simplex type 1 virus (HSV-1) Name of disease fever blister, cold sore -Common name of genus members: Herpes simplex type 2 virus (HSV-2) Name of disease: Genital herpes -Genus of virus: Varicellovirus -Common name of genus members: Varicella zoster virus (VZV) -Name of disease: Chickenpox, shingles -Genus of virus: Cytomegalovirus -Common name of genus members: Human cytomegalovirus (CMV) -Name of disease: CMV infections
The role of the reverse transcriptase in the replication of a retrovirus
-Retroviruses start put with + RNA and use reverse transcriptase to convert the RNA to DNA -viral DNA integrates (put in) in the host cell DNA which is called DNA provirus that comes out and stays there -Once the DNA in the host cell DNA it can be converted into RNA then eventually protein Replication of retroviruses: After a retrovirus enters a host cell, reverse transcriptase converts the retroviral RNA genome into double-stranded DNA. This viral DNA then migrates to the nucleus and becomes integrated into the host genome. Viral genes are transcribed and translated. New virus particles assemble, exit the cell, and can infect another cell.
Persistent Infections
A carrier relationship that develops in some cells •Cell harbors the virus and is not immediately lysed - from a few weeks to the remainder of the host's life - Ex. Measles may remain hidden in brain cells for many years - Eventually loss of brain function • Provirus - viral DNA incorporated into the DNA of the host • Chronic latent state - periodic activation after a period of viral inactivity - Herpes simplex viruses (Cold sores, genital herpes) or herpes zoster virus (chicken pox and shingles)
Lytic cycle vs Lysogenic cycle (prophage and temperate phage)
Bacteriophage Life Cycle • Lytic phase or lytic cycle - life cycle of bacteriophage that ends in destruction of the bacterial cell • Lysogenic cycle - bacteriophage becomes incorporated into the host cell DNA Lysogeny: The Silent Virus Infection Temperate phages: • Have the ability to undergo adsorption and penetration but do not immediately undergo replication or release • Prohage: - an inactive state in which phage DNA is inserted into the host chromosome • Induction: - activation of a prophage in a lysogenic cell to progress directly into viral replication and the lytic cycle
The name of the virus that causes infectious mononucleosis and also rarely Burkitt's lymphoma
Burkitt's Lymphoma •Unusual malignant tumor •Most common childhood cancer in Africa where malaria is common •Lab tech accidentally acquired mono while working with Burkitt's lymphoma virus •Discovered mono is caused by the same virus • Espstein-Barr virus •Causes infectious mononucleosis •More than 90% of world's the population is infected with EBV
Viral Components (Capside vs Envelope)
Capsid: (protein) • Shell surrounds the nucleic acid • Nucleocapsid: capsid and nucleic acid together Envelope • Not found in all viruses • Usually a modified piece of the host cell membrane Naked virus (non-envelope) • Consist only of a nucleocapsid Spikes • Found on both naked and enveloped viruses • Project from either the nucleocapsid or envelope • Allow viruses to dock with their host cells Virion • Fully formed virus able to establish infection in a host
The name of the virus that causes chickenpox, and its association with shingles
Chicken Pox • Varicella virus -(aka Human herpesvirus-3, varicella-zoster virus) •Vaccine preventable! •Enters respiratory system - skin cells after 2 weeks •Remains latent within body -Hides in nerve cells •Virus may be reactivated (Shingles) -Exposure to shingles may cause chickenpox
Which viruses often cause the common cold. Are cold symptoms mainly the result of our body fighting against the viruses?
Common Cold •More than 200 different viruses cause the common cold! -Most caused by Rhinoviruses •Thrive at lower temperatures •Over 99 different serotypes -Coronaviruses and Adenoviruses are also major causes -Cold symptoms: •Are mainly the result of our body fighting back against the viral invaders (inflammation of nasal mucosa)
The Viral Envelope
Composed of the membrane system of the host • Cell membrane, nuclear membrane or endoplasmic reticulum • Some of the regular membrane proteins are replaced with viral proteins • Spikes: protruding glycoproteins essential for attachment to the host cell • Envelopes are found in some, but not all viruses
DNA viruses and RNA viruses
DNA viruses •Single-stranded DNA (ss DNA) -Example: parvoviruses •Double stranded DNA (ds DNA) -Example: herpesviruses -ds DNA arrangement may be • linear •circular Nucleic Acids Positive-sense RNA (+ ssRNA) • Single-stranded RNA genomes ready for immediate translation into proteins (similar to our mRNA) Negative-sense RNA (-ssRNA) • RNA genomes that need to be converted into the proper form (+RNA) to be made into proteins Very few RNA viruses are double-stranded
Cytopathic effects vs inclusion bodies vs syncytia
Damage to the Host Cell Cytopathic effect (CPS): • Virus-induced damage to the cell that alters its microscopic appearance • Cells can become disoriented, undergo major changes in shape or size, or develop intracellular damage • Important in diagnosis of some viral infections • Inclusion bodies: - compacted masses of viruses or damaged cell organelles in the nucleus or cytoplasm • Syncytia (singular, syncytium): - fusion of multiple host cells into single large cells containing multiple nuclei
What a plaque is and know several ways in which viruses are grown in the lab?
Detecting Viral Growth in Culture Degeneration and lysis of infected cells Plaques: • Clear, well-defined patches in the cell sheet • Macroscopic manifestations of cytopathic effects • Develops when viruses released from an infected cell radiate out to surrounding cells and infect them • Infection spreads gradually and symmetrically from the original point of infection Bacteriophage Plaque Assay •Phage + bacteria + melted agar •Virus-bacteria mix solidifies •Virus infects bacterium; releases new viruses -New viruses infect other bacteria in immediate vicinity •Bacteria near original viruses destroyed -Clearings or plaques seen •Uninfected bacteria-turbid background (cloudy)
The functions of the viral capsid and envelope
Functions of the Viral Capsid/Envelope: 1. Protects nucleic acids 2. May be involved in attachment to new cells 3. Help introduce the viral DNA or RNA into a suitable host cell 4. Stimulate the immune system to produce antibodies (Abs) -Abs can protect the host cells against future infections
Which hepatitis viruses cause chronic liver disease and how they may be identified in a patient
HBV HCV HDV
What the Hantavirus may cause and why it is important to disinfect a rodent-infested area prior to sweeping
Hantavirus Pulmonary Syndrome Hantavirus •Transmitted by infected -through urine, droppings, or saliva •Humans contract the disease by breathing in aerosolized virus -Rodent contamination? Wet with disinfectant before you sweep!! •Do not stir up dust by sweeping! -Lungs fill with fluids-massive inflammatory response! •Rodent control is best for prevention -No treatment or cure •Outbreaks -1993: Healthy, young adults in AZ, NM, CO, UT •Most died within several days -2012: Small outbreak at Yosemite National Park •9 campers contracted the virus, 3 adults died
Which hepatitis viruses are transmitted by fecal-oral routes and which ones are transmitted by parenteral routes (blood contact)
Hepatitis Viruses •Viruses that infect the liver may cause hepatitis. •Transmitted by fecal-oral route - HAV - HEV •Blood-borne (parenteral route) - HBV - HCV - HDV
The name of the virus that causes cold sores and why latency is important in this infection
Herpes Simplex Viruses •HSV-1 -Transmitted by oral or respiratory routes -Infection usually occurs in infancy - about 90% of the population infected - cold spores -Latent in the trigeminal nerve •HSV-2 -Transmitted primarily by sexual contact -Cause of genital herpes -Latent in the sacral nerve ganglia
Why it is important to protect pregnant women from rubella virus and what the virus may do to a fetus
Rubella (German Measles) •Vaccine-preventable disease! •Rash •Transmitted by respiratory route •Congenital rubella (infection of fetus) •Virus stops mitosis! •Miscarriage •Deafness •Cardiac abnormalities, •Retardation •Epidemic in 1964: 20,000 babies born with defects
Techniques in Cultivating and Identifying Animal Viruses
In vivo methods: viral cultivation in lab animals or embryonic bird tissues In vitro methods: viral cultivation in cell or tissue culture Primary Purposes of Viral Cultivation: • Isolate and identify viruses in clinical specimens • Prepare viruses for vaccines • Do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells
Describe the genome of the influenza virus. Know that strains are identified by the H and N spikes. What is the function of the H spike vs the N spike?
Influenza Virus •8 separate (-) ss RNA segments •H spike (attachment) •N spike (viral release) •Strains identified by H and N spikes •Certain strains usually specific for certain species •Viruses capable of genetic change Influenza Subtype Range •Hemagglutinin • Viral entry •16 variants •Human: H1, H2, H3 •Swine: H1, H3 •Equine: H3,H7 •Avian: All •Neuraminidase • Viral exit •9 variants •Human: N1, N2 •Swine: N1, N2 •Equine: N7, N9 •Avian: All 16 x 9 = 144 possible subtype combinations, 6 are most important for humans
Assembly
Mature virus particles are constructed from the growing pool of parts
Other Substances in the Virus Particle (polymerase)
May have enzymes for specific operations within the host cell: • Polymerases: synthesize DNA and RNA • Replicases: copy RNA • Reverse transcriptase: synthesizes DNA from RNA Substances from the host cell: • Arenaviruses pack along host ribosomes • Retroviruses "borrow" the host's tRNA molecules
The disease that may cause oral lesions, rash, sometimes encephalitis, and death that is vaccine-preventable
Measles •Vaccine preventable (MMR) •~400 children die every day from measles in the developing world •Transmitted by respiratory droplets •Oral lesions, sore throat, rash, occasionally encephalitis and death •Subacute sclerosing panencephalitis (SSPE): progressive neurological degeneration of the brain •2014: Outbreak in Disney, 111 cases •2015: Woman in WA died of measles
Which viruses the MMR vaccine protects against
Measles (Rubeola) and Mumps and Rubella
Describe the mechanisms of variation used by the influenza virus. Explain why there is so much genetic variation when one host is infected with 2 different influenza viruses (Figure 21.12, page 627). Know the difference between antigenic drift (gradual mutation of genes) vs antigenic shift (rapid gene reassortment)
Mechanisms of Variation: Antigenic Drift •Mutations in areas used for attachment are very rare! •Mutation of genes helps virus escape immune response! •Virus gradually changes amino acids used for antibody binding •Host antibodies don't recognize virus as well •Virus can still attach to host cells while decreasing the effectiveness of the immune response! Antigenic shift • Gene reassortment •Virus has 8 separate pieces of RNA (strands) •A strand from one influenza virus is swapped out with a strand from a different influenza virus! • Involves coinfections •Two different viruses affect a single host •Viral packaging step may accidentally produce a human influenza virus with duck RNA •Our immune system won't recognize the proteins from the duck virus! • Rapid process linked to pandemics Prevention of Influenza: Annually: 17,000-52,000 deaths in U.S. Three major types of influenza vaccines in the United States: • An intramuscular inactivated (virus won't multiply) vaccine with three strains of influenza in it • An intramuscular inactivated vaccine with four strains • A recombinant vaccine (not made in eggs for intramuscular injection) Scientists are continually researching emerging strains to attempt to prevent a pandemic
The disease that causes inflammation of salivary glands that is vaccine preventable
Mumps Vaccine-preventable (MMR) •Inflammation of salivary glands, fever muscle pain •Multiple organs may be invaded (testes, ovaries, thyroid, pancreas, meninges, heart, kidney) •U. S. Cases have increased since 2006. •Newer vaccine recommendations: 2nd dose at 4-6 years
The term genome and what types of genomes a virus may have
Nucleic Acids: At the Core of a Virus Genome: - the sum total of the genetic information Viruses contain either DNA or RNA but not both • The number of viral genes is small compared to that of a cell • Possess only the genes necessary to invade host cells and redirect their activity
What a prion is and how these diseases are caused in general (conversion of normal protein to infectious form). Would they need a DNA or RNA polymerase to replicate?
Other Noncellular Infectious Agents (1) Spongiform encephalopathies: • Implicated in chronic, persistent disease in humans and animals • Brain tissue removed from affected animals resembles a sponge Prion: (infectious proteins) • Common feature of spongiform encephalopathies • Distinct protein fibrils deposited in brain tissue of affected animals Other Noncellular Infectious Agents (2) Creutzfeldt-Jakob Disease (CJD): • Afflicts the central nervous system of humans • Causes gradual degeneration and death • Transmissible by an unknown mechanism • Several animals are victims of similar diseases: • Scrapie: sheep, mink elk • Bovine spongiform encephalopathy: cows (mad cow disease) Other Noncellular Infectious Agents (3) Prions: - Infectious proteins! NO DNA or RNA • Exact mode of infection is unknown • Protein composition of prions has revolutionized ideas of what can constitute an infectious agent • Questions about how prions replicate given that they have no nucleic acid
Which virus is vaccine preventable and may cause paralysis?
Poliovirus •(ssRNA (+), non-enveloped) • Fecal-oral route -Stable at acid pH •Enters by mouth, replicates in GI tract, may infect cells of the CNS -Fever, headache, nausea, may attack nervous tissue -Post-polio syndrome (progressive muscle deterioration) develops in ~25-50% several decades after original polio attack •Efforts underway to eradicate this disease (only in humans) •Vaccine preventable! -Safer inactivated vaccine used now rather than oral
The name of the virus that is the most common cause of viral respiratory disease in infant.
Respiratory Syncytial Virus (RSV) •Most common cause of viral respiratory disease in infants -High risk: •Prematurity •Less than 6 weeks of age •Virtually all children become infected by age 2 •Epidemics in winter and early spring
What may happen to a host cell as a result of a viral infection?
Results of Viral Infections •Death of host cell = Most viruses •Proliferation of cells = Papillomavirus •Fusion of host cells = Respiratory syncytial virus •Transformation of cells = Adenovirus •No obvious changes = Rubella
Know what rotavirus causes and whether there is a vaccine to prevent this.
Rotavirus •Unusual double-stranded RNA genome •Most common cause of viral gastroenteritis -Fever, diarrhea, vomiting (~ 1 week) -2-3 million infections in U.S./yr, 70,000 hospitalizations •Over 90% infected by age 3 in U.S. •Mortality higher in less developed countries -Babies 6-24 months at risk for fatal disease -Intestinal mucosa damaged in a way that chronically compromises nutrition •Newer vaccine in 2006 -Hospital admissions have decreased by 90%
Other Noncellular Infectious Agents
Satellite viruses • Dependent on other viruses for replication • Example: the delta agent (hepatitis virus) • A naked strand of RNA that is expressed only in the presence of the hepatitis B virus • Worsens the severity of liver damage • Adeno-associated virus (AAV) • Originally thought that it could only replicate in cells infected with the adenovirus • Now found to infect cells infected with other viruses or that have had their DNA disrupted through other means
Which virus was eradicated and is now a potential bioterrorism agent?
Smallpox Variola virus -Respiratory route -Massive effort to eradicate the virus worldwide! -Last natural case occurred in Somalia in 1977 -U.S. stopped using vaccine in 1972 -Potential bioterrorism agent -All labs supposed to destroy virus -2002: CIA identified 4 countries with supplies of smallpox. -Newer vaccine used for military personnel -U.S. has a stockpile of vaccine -Can vaccinate entire U.S. population
A specific example of an organism (genus and species) that undergoes lysogenic conversion, also called phage conversion
The Danger of Lysogeny in Human Diseases Occasionally, phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human Lysogenic conversion (phage conversation): • The acquisition of a new trait from a temperate phage • Responsible for the diphtheria toxin, cholera toxin, and botulism toxin Lysogenic Conversion •Many bacteria that infect humans are lysogenized by phages. •Bad for humans! -Phage genes inserted in the bacterial chromosome may make the bacteria more pathogenic •Prophage genes may encode for toxins or enzymes that harm humans -Example: Corynebacterium diphtheriae •Diphtheria toxin-Causes disease-producing properties -Is a bacteriophage product •C. diphtheriae without the phage are harmless; C. Pharyngitis Streptococcus pyogenes: • Gram-positive coccus that grows in chains, • Untreated streptococcal infections can result in serious complications: • Scarlet fever • Rheumatic fever (affects the heart) • Glomerulonephritis (kidney damage) Streptococcal Infections •Scarlet Fever: infection with S. pyogenes strain that is itself infected with a bacteriophage. •Lysogenic virus leads to production of erythrogenic toxin -Sand-paper like rash on neck, chest, elbows and inner surfaces of thighs with high fever More Examples of Phage Conversion •Clostridium botulinum -Causes botulism -Toxin is encoded by a prophage gene •Vibrio cholerae -Causes cholera -Toxin is encoded by prophage gene in pathogenic strains
The Viral Capsid
The Protective Outer Shell Capsomeres: • Identical protein subunits that spontaneously self assemble to form the capsid Helical capsid: • Rod-shaped capsomeres that form a continuous helix around the nucleic acid Icosahedral capsid: • Three-dimensional, 20-sided figure with 12 evenly spaced corners The Viral Capsid Complex capsids: • Found in bacteriophage, the viruses that infect bacteria • Have multiple types of proteins • Take shapes that are not symmetrical
Adsorption
The invasion begins when the virus encounters a susceptible host and adsorbs specifically to receptor sites on the cell membrane •Adsorb: - to attach (like a virus) • Absorb: - to soak in (like a paper towel) 1. Virus encounters susceptible host cells 2. Where is adsorbs specifically to receptor sites on the cell membrane -Receptors are usually glycoproteins the cell needs for its normal function Example: Rabies virus attaches to acetylcholine receptor of nerve cells 3. Because of the exact fit required, viruses have a limited host range
Characteristics/properties of viruses (obligate intercellular)
Unique Properties of Viruses Infectious particles • Rather than organisms Active or inactive • Rather than alive or dead Obligate intracellular parasites: • Cannot multiply unless they invade a specific host cell • Must instruct the genetic and metabolic machinery of the host cell to make and release new viruses Properties of Viruses • Are not cells • Are obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals • Do not independently fulfill the characteristics of life • Are inactive macromolecules outside the host cell and active only inside host cells • Have basic structure of protein shell (capsid) surrounding nucleic acid core • Are ubiquitous in nature and have had major impact on development of biological life • Are ultramicroscopic in size, ranging from 20 nm to 1000 nm (diameter) • Can have either • Can have double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA • Carry molecules on surface that determine specificity for attachment to host cell • Multiply by taking control of host cell's genetic material and regulating the synthesis and assembly of new viruses • Lack enzymes for most metabolic processes • Lack machinery for synthesizing proteins
Cell Culture
Using Cell (Tissue) Culture Techniques Cell culture or tissue culture: -in vitro virus cultivation systems • A simple and effective way to grow populations of isolated animal cells in culture dishes • Most viruses are propagated through cell culture • Much of a virologist's work involves developing and maintaining cultures Primary Cell Cultures • Freshly isolated animal tissue is placed in a growth medium • Cells undergo mitotic division, producing a monolayer on the surface • Retain the characteristics of the original tissue from which they were derived Continuous Cell Cultures • Have altered chromosome numbers • Grow rapidly • Show changes in morphology • Can be continuously subcultured if they are given fresh nutrient media
The role of enteroviruses (mostly coxsackieviruses and echoviruses) in viral meningitis
Viral Meningitis •Termed "aseptic meningitis" -because no bacteria or fungi are found in the CSF •Caused by many different viruses -most are coxsackieviruses Echoviruses (Enteroviruses) -90% of cases are caused by enteroviruses •Spread through direct contact with respiratory secretions -Herpesviruses and mumps virus can also cause meningitis •No treatment in most cases, most recover on own
The size range of viruses and which type of microscope is needed to visualize typical viruses
Viral Size Range Ultramicroscopic size: Smaller than the average bacterium Electron microscopes are required to detect them • Parvoviruses: 0.02 μm in diameter • Mimiviruses: 450 nm in length —larger than some small bacteria • Cylindrical viruses: 0.8 μm long, but 0.015 μm in diameter
Host range
• A virus can invade its host cell only through making an exact fit with a specific host molecule • Restricted host range: hepatitis B only infects liver cells of humans • Moderately restrictive host range: poliovirus infects intestinal and nerve cells of primates • Broad host range: rabies virus infects various cells of all mammals
General phases in the life cycle of animal viruses
• Adsorption • Penetration • Uncoating • Synthesis • Assembly • Release from the host cell The host cell is absolutely necessary for viral multiplication.
Synthesis: Replication and Protein Production
Viral nucleic acid takes control over the host's synthetic and metabolic machinery • Mechanism varies depending on whether the virus is a DNA or RNA virus - RNA viruses replicate in the cytoplasm - DNA viruses replicate in the nucleus
List three methods used to identify viruses
Virus Identification •Methods to identify viruses: -Look for cytopathic effects -Perform serological tests •Detect antibodies against viruses in a patient •Use antibodies to identify viruses in neutralization tests, ELISAs, Western blot - Nucleic acid testing •PCR •RFLP's
Understand what a bacteriophage is and how lysogeny and phage conversion (lysogenic conversion) can cause harm to humans.
Viruses That Infect Bacteria Bacteriophage: • Discovered in 1915 by Frederick Twort and Felix d'Herelle • Parasitize every known bacterial species • Often make the bacteria they infect more pathogenic for humans "T-even" bacteriophage infect Escherichia coli • T-2 and T-4 • Most widely studied bacteriophage • Go through similar stages as animal viruses Bacteriophage Life Cycle • Lytic phase or - life cycle of bacteriophage that ends in destruction of the bacterial cell • Lysogenic cycle - bacteriophage becomes incorporated into the host cell DNA
Know what an oncogenic virus can cause, and the characteristics of a transformed cell. List a few examples of oncoviruses.
Viruses and Cancer Oncogenic viruses: • Experts estimate that up to 13% of human cancers are caused by viruses • Papillomavirus, Epstein-Barr virus, Hepatitis B virus, HTLV Transformation: • Virus carries genes that directly cause cancer • Virus produces proteins that induce a loss of growth regulation in the cell Properties of Transformed Cells -Increased rate of growth -Alterations in chromosomes -Changes in cell surface molecules -Divide indefinitely, unlike normal cells
Why antibiotics are ineffective against a virus?
Viruses mutate at a rapid rate Difficult to design therapies against viruses Scientists focus on developing vaccines against viruses since so few antiviral drugs are available and antibiotics are ineffective Treatment of Animal Viral Infections •Antibiotics and viruses: -Antibiotics are designed to target bacterial structures - viruses lack bacterial structures (cell wall, 70s ribosomes etc.), so ANTIBIOTICS ARE INEFFECTIVE!!! •Antiviral drugs and viruses: -Antiviral drugs block virus replication •target one of the steps in the viral life cycle -Effective in some viruses
An example of a latent viral infection
cold sores
Hepatitis B and C Virus
• Enveloped DNA virus • Signs and symptoms: • Fever, chills, malaise, anorexia, abdominal discomfort, diarrhea, nausea • Rashes and arthritis may occur • Cause of hepatocellular carcinoma • Transmitted by minute amounts of blood • Sharing a toothbrush, razor, needlesticks, etc. can transmit HBV • An effective vaccine is available • Especially important for health-care workers! Hepatitis B Virus: Why are children vaccinated? • Higher risks of long-terms infection and disease in children! • Chronic infections may result in: • 90% of neonates infected at birth • 30% of children infected between ages 1-5 • 6% of persons infected after the age of 5 • Chronic infections: • Liver Cancer • Mortality rate: 15-25% Hepatitis C Virus • Silent epidemic: 3.5 million Americans infected • Signs and symptoms: • Similar to hepatitis B virus • 75 to 85% remain infected indefinitely • Transmission and epidemiology: • Blood transfusions, needle sharing • Treatment: • No vaccine available • Two-drug regimen: Sofosbuvir (a nucleotide analog that "fools" the RNA polymerase of the virus) and simeprevir (a protease inhibitor)
viroids
• Virus-like agent that parasitizes plants • Very small • About one-tenth the size of an average virus (100-300 nucleotides) • Composed only of naked strands of RNA —lack a capsid or other type of coating • Significant pathogens in economically important plants: tomatoes, potatoes, cucumbers, citrus trees, and chrysanthemums (Other Noncellular Infectious Agents)
Synthesis of DNA Viruses In General
•DNA virus enters host cell nucleus -DNA enters nucleus and is transcribed into RNA -The RNA becomes a message for synthesizing viral proteins (translation) -Using host nucleotides, new viral DNA is synthesized
Uncoating
•Enzymes in the vacuole dissolve the envelope and capsid •The virus is now uncoated -nucleic acid released into cytoplasm
