Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure...
-
date post
21-Dec-2015 -
Category
Documents
-
view
230 -
download
2
Transcript of Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure...
![Page 1: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/1.jpg)
Virions, Prions, and Viroids: Infectious Agents of Animals
and PlantsTopics
Structure
Classification
Methods of study
Viral infections
Viral tumors
Human tumors
Viral host range
Prions
![Page 2: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/2.jpg)
StructureAnalogous to bacteriophages• Capsid (protein coat) made up of capsomeres• Naked vs. enveloped viruses• Attachment proteins or spikes in enveloped viruses
Distinct from bacteriophages• Segmented viruses (contain more than one RNA
molecule)• Plant viruses do not enter via receptor attachment
Shapes:IsometricHelicalPleomorphic
![Page 3: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/3.jpg)
Classification
Taxonomy in constant fluxMost common taxonomic criteria for animal viruses:
1. Genome structure (DNA or RNA, ss vs. ds, segmented or not)
2. Virus particle structure (isometric, helical, pleomorphic)
3. Presence or absence of viral envelope
Viruses infecting vertebrates are divided into 14 RNA families and 7 DNA families (Ending: -viridae)
![Page 4: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/4.jpg)
Coronavirus
• Classification: – Coronaviridae (Family) – Coronavirus (Genus)– Common cold virus (Species) (together
with rhinoviruses)
• Structure: – non-seg., lin., ssRNA, helical, env.
![Page 5: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/5.jpg)
Herpesvirus
• Classification: – Herpesviridae (Family) – Herpesvirus (Genus)– Herpes simplex type 1 / type 2 (Species)
• Structure: – non-seg., lin., dsDNA, helical, env.
http://darwin.bio.uci.edu/~faculty/wagner/movieindex.html
![Page 6: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/6.jpg)
Cells Infected with a Herpes Virus
![Page 7: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/7.jpg)
Groupings Based on Routes of Transmission
Not a taxonomic grouping – more than one family may be included in one transmission grouping
![Page 8: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/8.jpg)
Methods of Study
Much more expensive and difficult to study animal viruses than bacteriophages
• Cultivation in host cells– Living animal– Embryonated chicken eggs– Cell or tissue culture (= in
vitro)
![Page 9: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/9.jpg)
Methods of Study cont: Quantitation• Plaque assay (useful for infective and lytic viruses)
• Virion counting with EM
• Quantal assay (ID50 or LD50)
• Hemagglutination (e.g.influenza virus)
![Page 10: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/10.jpg)
Acute Viral Infections
Productive infection of relative short duration
Naked viruses usually cause cell lysis, while enveloped viruses do not
Symptoms due to localized or widespread tissue damage
Host defense mechanisms gradually eliminate virus
Examples of acute infections
Time course
![Page 11: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/11.jpg)
Mumps, Measles, Influenza, and Poliomyelitis
![Page 12: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/12.jpg)
Time Course of Acute Viral Infection
![Page 13: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/13.jpg)
HEV
![Page 14: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/14.jpg)
Reproductive Cycle
1. Attachment
2. Entry
3. Uncoating
4. Replication of NA and protein
5. Maturation of viral particles
6. Cell lysis
7. Spreading and shedding
8. Transmission to next host
![Page 15: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/15.jpg)
Transcription Strategy
![Page 16: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/16.jpg)
Mechanisms of Release
1. Cytopathic effect: Unlike virulent phages most animal viruses do not encode for cell lytic enzymes. Instead degenerative changes associated with the virus lead to cell death.
2. Budding: from plasma membrane (most common) or from Golgi apparatus. May or may not kill cell. Enveloped viruses
![Page 17: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/17.jpg)
Persistent Viral Infections
Virus continually present in body. Released by budding.
May or may not cause disease
Carrier able to spread disease
Four categories (if more than one applies = complex infections):
1. Late complications from acute infections2. Latent infections3. Chronic infections4. Slow infections
![Page 18: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/18.jpg)
Late Complications from Acute Infections
1. Subactue sclerosing panencephalitis (SSPE) - years following measles in 1 in 300,000. Virus persistent in brain tissue with decreased transcription of viral genome. Lack of envelope protein production prevents immune response to eliminate infected cells. High Ab, low CMI. Exact mechanism unknown.
2. Progressive (pan)encephalitis following rubella
![Page 19: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/19.jpg)
Latent Infections
• Acute infection symptomless period reactivation of disease
• Symptoms of reactivation may differ from original disease
• No measurable viral particles during symptomless period
• Examples: HSV-1 and HSV-2; varicella
![Page 20: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/20.jpg)
Chickenpox- Varicella
Blister-like rash on surface of skin and mucous membranes. Blisters usually appear first on trunk and face, then spread to almost everywhere else.
![Page 21: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/21.jpg)
Shingles or Herpes Zoster
About 20 % of those people who have had chicken pox will get zoster at some time during their lives. Most people will get zoster only once.
![Page 22: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/22.jpg)
“Shingles” comes from latin cingulum, which means girdle or belt.
It occurs in an area of the skin that is supplied by the sensory fibers of a single nerve- dermatome. Rash appears as well-defined band on one side of body, or on one side of face, arms or legs.
![Page 23: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/23.jpg)
Chronic Infections
• Virus can be demonstrated at all times
• Disease may or may not be present for extended time periods or show up late (carriers!)
![Page 24: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/24.jpg)
Slow Infections
• Gradual increase of infectious agent over long time period – often no apparent symptoms for long time (=preclinical phase)
• Usually slowly progressive lethal diseases
• Examples– AIDS– Lentivirus– prions
![Page 25: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/25.jpg)
HIV: Example of Complex Infection
• Retrovirus – ssRNA, envelope
• RNA DNA (with the help of reverse transcriptase) permanent integration into host genome (=provirus)
• Polyprotein is cleaved into individual proteins with viral protease assembly of virions budding
![Page 26: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/26.jpg)
Viral Tumors (Neoplasms)• Benign
• Malignant cancer, metastasizes
• Proto-oncogenes and oncogenes are regulatory genes
• Properties of normal and transformed cells
• Only about 15% of human tumors are due to viruses
• Examples of human tumors: – Kaposi’s sarcoma (herpes virus)– Squamous cell carcinomas (HPV)– Hepatocellular carcinoma (HBV and HCV)
![Page 27: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/27.jpg)
Kaposi’s Sarcoma
Purplish lesions of a skin cancer not usually seen in young men
![Page 28: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/28.jpg)
Viral Host Range
• Mostly species – and even cell type – specific
• Exception: Zoonotic viruses are transmissible from animals (arthropods, vertebrates) to man (zoonosis) – Arboviruses (West Nile virus), rabies etc.
• Modification of host range due to – Phenotypic mixing– Genetic reassortment
![Page 29: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/29.jpg)
Genetic Reassortent
• In segmented viruses
• Simultaneous infection of one cell with 2 different types of viruses leads to exchange of genetic information
• Creation of major new influenza strains resulting in pandemics
• Antigenic shift vs. antigenic drift
![Page 30: Virions, Prions, and Viroids: Infectious Agents of Animals and Plants Topics Structure Classification Methods of study Viral infections Viral tumors Human.](https://reader031.fdocuments.us/reader031/viewer/2022031818/56649d565503460f94a341f4/html5/thumbnails/30.jpg)
Other Infectious Agents: Prions• Small proteinaceous infectious particles (resist
inactivation by procedures that modify nucleic acids)
• Prion diseases are often called spongiform encephalopathies because of the post mortem appearance of the brain with large vacuoles in the cortex and cerebellum
• Human prion diseases– CJD: Creutzfeld-Jacob Disease– BSE: Mad cow disease (BSE)– GSS: Gerstmann-Straussler-Scheinker syndrome – Kuru