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30 Cards in this Set
- Front
- Back
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How are animal viruses classified?
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Taxonomic criteria based on
Genomic structure DNA or RNA Single stranded or double stranded Virus particle structure Isometric Pleomorphic Helical Presence or absence of envelope |
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Some viruses are grouped by route of transmission, what types are there?
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Disease causing viruses often grouped by route of transmission
*Enteric viruses* Generally transmitted via fecal-oral route Often cause gastroenteritis Some can cause systemic disease *Respiratory viruses* Usually inhaled via infected respiratory droplets Generally remain localized in respiratory tract *Zoonotic viruses* Transmitted from animal to human via animal vector *Sexually transmitted viruses* Can causes lesions on genitalia or cause systemic infections |
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What happens during an infection? What kind of relationship does the virus have with the host?
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Outcome of infection of eukaryotic cells depends on factors independent of cell
Special importance are defense mechanisms of host Viruses may develop relationships with normal hosts No obvious disease or damage is caused to host State of balanced pathogenicity Relationships divided into two categories Acute persistent |
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What happens during acute infections?
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Usually short in duration
Host may develop long lasting immunity Result in productive infections Produce large number of viruses during replication Disease symptoms result from tissue damage and infection of new cells |
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What happens during acute infections continued?
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Reproductive cycle of animal virus can be compared to virulent bacteriophage
Essential steps include Attachment Entry into susceptible cell Targeting site of reproduction Uncoating of virion Removing protein coat exposing nucleic acid Replication nucleic acid and protein Maturation Cell lysis Spreading within host Shedding outside host Transmission to |
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What happens during persistent infections?
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Viruses continually present in host
Releases from infected cell via budding Can be divided into three categories Latent infections Chronic infections Slow infections Categories distinguished by detection of virus during period of persist |
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In persistent infections, what happens during latent infections?
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Infection is followed by symptomless period then reactivation
Infectious particles not detected until reactivation Symptoms of reactivation and initial disease may differ Example Herpes simplex viruses 1 and 2 (HSV1 and HSV2) Shingles (zoster) |
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What happens during chronic infection?
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Infectious virus can be detected at all times
Disease may be present or absent during extended times or may develop late Best know example Hepatitis B A.k.a serum hepatitis |
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What happens during slow infection?
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Infectious agent gradually increases in amount over long period of time
No significant symptoms apparent during this time Two groups of infectious agents cause slow infections Retroviruses which includes HIV |
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Viruses and human tumors?
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Double stranded DNA viruses responsible for most virus induced tumors in humans
Tumor viruses interact with host cells on one of two ways Virus can go through productive cycle and lyse cell Virus can transform cell without killing it Cancers caused by DNA viruses result from *integration of viral genome into host DNA* Transformed genes are expressed Uncontrolled growth results |
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What happens during Viral Genetic Alterations?
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Genome exchange in segmented viruses
Viruses can alter their properties via *Mutation Genetic reassortment* Genetic reassortment of viruses results from two viruses infecting the same cell Each virus incorporates segments of viral DNA One segment comes from one virion Rest of segment come from other virion Reassortment responsible fro *antigenic shift and antigenic drift* in influenza virus |
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What happens during the cultivation of host?
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Viruses multiply only inside host cell
Host cells are cultivated in the laboratory in cell culture or tissue culture Tissue culture prepared directly from an animal host is termed primary culture |
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What happens during quantitation, *plaque assay*, a method of studying viruses?
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Determines number of viruses in solution
Know volume of solution added to actively metabolizing cells Infection lyses cells and leads to clear zone or plaque surrounded by uninfected cells Each plaque represents one virion Plaques are only produced by infected cells |
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What happens during quantitatuon?
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Counting virions with electron microscope
Used with pure preparations Concentration determined by counting number of virions in sample May distinguish infective from non-infective agents |
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What are quantal assays in quantitation?
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Provides and approximate concentration
Dilutions of virus preparation administered into animal cells Chick embryos often used Endpoint is dilution at which 50% of inoculated host are infected or killed *ID50 = infective dose LD50 = lethal dose* |
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What is hemagglutination?
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Some animal viruses clump or agglutinate with red blood cells
Termed hemagglutination The highest dilution showing maximum agglutination is titer of the virus |
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What are characteristics of plant viruses?
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Number of plant diseases are caused by viruses
Can be of major economic importance Infection may be recognized via outward signs including Pigment loss Marks on leafs and fruit Tumors Stunted growth Plants generally do not recover from viral infections |
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How are plant viruses spread?
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Viruses infect plants through wound in plant cell wall
Viruses do not attach to specific cell receptors Once started, infection spreads from cell to cell through plasmodesmata Many viruses resistant to inactivation Viruses can be transmitted through soil contaminated by prior growth Viruses spread through grafting healthy plants to infected Viruses can spread via parasitic vine called dodder Vine establishes simultaneous connection between two plants Serves as conduit of transfer |
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Another type of infectious agent are prions, what do they do?
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*Proteinaceous* infectious agent
Linked to a number of fatal human diseases All afflictions cause brain degeneration Brain tissue develops sponge like holes Disease termed transmissible spongiform encephalopathies Symptoms may not appear for years after infection |
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How did prions evolve?
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Apparently arose following gene encoding normal prion protein
Mutation caused protein to have different folding properties Mutated protein resistant to proteases Normal protein sensitive Resists UV light and nucleases Due to lack of nucleic acid Inactivated by chemicals that denature proteins |
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Viroid are another type of infectious agent what do they do?
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Defines group of pathogens much smaller and distinctly different from viruses
Consist solely of small single-stranded RNA molecule Varies in size Have no protein coat Allows them to be resistant to proteases |
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What are some more properties of viroids?
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Replicates autonomously in susceptible cells
Single viroid capable of infecting a cell Viroid RNA is circular and resistant to nuclease digestion All identified viroids infect plants Diseases include Potato spindle tuber Chrysanthemum stunt Cadang-cadang |
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Some interesting information about viral reproduction
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(Marine) viruses are difficult to classify, since there is no single common gene among them (Rowher)
We can study marine viruses by restriction analyses, DNA-DNA hybridization, expression (mRNA) analyses, or sequencing conserved genes such as att (attachment) or DNA polymerase. Only 17 complete genome sequences of marine phage are known (Paul and Sullivan 2005) |
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What are some characteristics of Family orthomyxoviridae?
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Enveloped viruses – 80-120 nm, negative stranded RNA with
8 different segments. Allows for genetic reassortment when >1 virus infects a single cell Types A, B, and C: Significant differences in structure, genetics, organization, host range, epidemiologic and clinical characteristics Covered with surface projections or spikes -- Hemagglutinin and neuraminidase—used to subtype influenza A virus types |
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Influenza in the United States?
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Estimated 36,000 deaths annually
• Estimated 200,000 hospitalizations • Influenza vaccine recommended for ~185 million Americans annually • Coverage is yet to reach standards that is likely to prevent epidemic. – Adults > 65 years: 65.6% – Children 6-23 months: 7.4% |
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Dates to remember regarding influenza?
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1918 spanish flu 20-40 million deaths
1957 asian flu 1 million deaths 1968 hong kong flu 1 million deaths |
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what are some characteristics of Morbillivirus?
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Morbillivirus - in the Family Paramyxoviridae,
Genome: negative sense - ssRNA Host: Vertebrates related to hepatitis and distemper viruses |
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what are some characteristics of the papilloma virus?
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Papilloma viruses - Double stranded DNA viruses, usually no RNA phase. The early ORFs encode proteins which interact with the host genome to produce new viral DNA while late ORFs are activated only after viral DNA replication and encode for viral capsid proteins. All papillomaviruses are obligatory intranuclear organisms with specific tropism for keratinocytes. Three possible courses of events can follow papillomaviruses entry into cells: (1) viral DNA are maintained as intranuclear, extrachromosomal, circular DNA episomes, which replicates synchronously with the host cell, establishing a latent infection; (2) conversion from latent into productive infection with assembly of complete infective virions; (3) integration of viral DNA into host cellular genome, a phenomenon seen in HPV infections associated with malignant transformation
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Basic characeristics of viruses?
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Consist of genetic material (DNA, RNA,single or double stranded). No metabolism of their own, but rather depend on cellular machinery of host
No motility - contact hosts by diffusion Responsible for 30-40% of bacterial mortality by viral lysis Viruses can affect gene transfer, species composition |
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marine phages or viruses?
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There is a decrease of one order of magnitude between rich coastal waters and oligotrophic open ocean, a decrease of between 5- 10 fold from the euphotic zone to the upper midwaters (e.g. 500 m depth, and further decrease to abyssal depths)
Release of dissolved organic material (DOM) stimulates bacterial activity and retention of nutrients in the euphotic zone |
