Comparative Virology Week 5 Lecture Notes
Comparative Virology Week 5 Lecture Notes BIOL 123 001
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BIOL 123 001
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This 11 page Class Notes was uploaded by Anastassia Erudaitius on Sunday May 1, 2016. The Class Notes belongs to BIOL 123 001 at University of California Riverside taught by Dr. Rao in Spring 2016. Since its upload, it has received 18 views. For similar materials see Virology in Biology at University of California Riverside.
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Date Created: 05/01/16
Virology Lecture 4/25/16 – Prions and Viroids Prions Viruses – the nucleic acid is the infectious part These pathogens are conventionally different from viruses, but they are studied by virologists Hershey – Chase showed DNA is the genomic material of bacteriophages Prions attack nerve and brain tissue Prions exclusively affect the brain and is found ONLY in mammals No known prion diseases in plants Transmitted only through food Prions result in a very slowly progressing disease Human Prion Disease o CJD Animal Prion disease o Found mostly in goats o CWD – found in deer, elk, and moose o BSE – found in cattle causes mad cow disease Very unusual property – they are resistant to nucleases No immune response (no production of antibodies) NO nucleic acid genome The infectious agent is the PROTEIN o In viruses however the infectious agent is the nucleic acid Prions stands for “proteinaceous infectious particle” Transmission within species o Vertical or horizontal transmission o Uncommon – foodborne Species barrier concept o They do transmit from animals to humans, and humans to animals o Unusual transmission BSE o Mainly transmitted through food o These cases mostly found in Europe o Mostly found in “beef-eating countries” U.S. and Europe o In U.S. ban on feeding cattle meat and bone meal Prions are proteins proteins are not going to replicate because proteins are made from nucleic acids o The protein binds to the normal protein in the brain, so when the prion protein is acquired it interacts with the normal protein and changes the normal protein’s conformation o The normal protein function is modified because the prion protein binds to it o Because the structure is modified it becomes highly pathogenic o The prion protein binds to a normal protein the normal protein becomes a prion protein and then it goes and binds somewhere else TSE pathogenesis o Oral route o Migrates to the nervous system o The prion attacks your NERVOUS SYSTEM o It is a very slow generating disease o Because it affects the brain, they look at the brain tissue and compare it to normal brain tissue o How does an infected individual brain tissue look? o Prp – normal protein o PrP-Sc – srapie protein Scrapie o First found in sheep o When the sheep get infected by scrapie they get very itchy Mad Cow disease o The cows are slaughtered when they are 2 years old o Since it is a slow progressing disease it is very difficult to detect in cows at 2 years of age o When they are slaughtered at 2 and the protein is present, individuals eat the infected meat and the protein enters your body the protein can bind to the regular protein in your body and change its conformation o They detected this in an 80 year old cow o If it is not well-kept meat you can get a lot of diseases the best way to avoid this is vegetarianism o They feed cows and sheep meat from other cows or sheep The dead cows or dead sheep may carry the protein and the cows/sheep eating that meat get infected because the virus spreads orally In 1997 they banned these practices to prevent this The protein is very stable – so cooking the meat may not prevent infection Beef industry is one of the biggest industries in this country Beef export from U.S. refused by Japan o Therefore a lot of times Mad Cow disease is not reported Kuru o Confined only to specific tribe o They showed very unusual symptoms instability (cannot walk), biting their own hands o Initially the scientist thought it was a genetic disorder o Ambulant stage first sedentary stage terminal stage Very long process (30-40 years) o One of the rituals of this tribe when the person dies they eat the meat of the dead they only eat women and children o That is why the disease is found manly in women and children (within families), and not in men o A child ate the meat, when he was 50 he showed symptoms of the disease Holes in the brain form from infection Treatment and Vaccination o No drugs available because it is a protein o No vaccine not easy to generate a vaccine although it is not spreading as rapidly as other diseases Feeding practices of cattle has been totally changed Transmission all mainly through feeding can be transmitted to humans if they eat infected meat Viroids Prions – no nucleic acid Viroids – free infectious nucleic acids, no capsid Genome is no more than 400 nucleic acids long Prions only in mammals – no plants Viroids are only in plants – no mammals Potato spindle tuber o Infected potatoes look like thin, spindle-like potatoes o First viroid discovered o Theodore Diener In the 70s he was working with potato spindle virus He thought it was a virus disease – he was doing assays Diener got the credit for discovering viroids, even though it was his competitor Single-stranded RNA but ssRNAs are susceptible to nucleases can be easily degraded by ribonucleases Although the host is full of the nucleases viruses are protected by the capsid Viroids however have no capsids to protect them!! o They are protected by their secondary structure o dsRNAs are resistant to nucleases (cannot be degraded) o Even though the genome is single-stranded it can survive in the host because its seconday structure is in a double-stranded form Viroids vs Viruses o Viroids do not encode any proteins (so how to they replicate?) o Viruses encode capsid proteins o Viroids replicate using host proteins only – use host Pol o Viroid replicates in the nucleus (because it needs polymerase) Hepatitis delta virus – satellite virus associated with Hepatitis virus Virology Lecture 4/27/16 Viruses have been shown to evolve very rapidly Selection plays one of the major roles in evolution o Which mutant will win (be selected for) Viruses replicate extremely fast o TMV completes its life cycle within a few hours after infection High rates of mutation – especially common for RNA viruses New sequence is generated, and may become a new pathogen Virus in plasma – means virus in blood o For HIV – 6 hours o For hepatitis B it is 24 hours Turnover rate o HIV has a 90% daily turnover One of the reasons HIV cannot be controlled because it generates so many copies, and so many mutant, so quickly o Hepatitus B – 50% daily In table 18-1, the asterisks represent re-emerging viruses o Viruses that have been gone, but are now coming back o Polio virus is a re-emerging virus Humans are responsible for making new viruses as well Environment can affect or help virus evolution Emerging viruses – new viruses, newly entered the human population Re-emerging – viruses that reappear in the human population RNA is highly error-prone DNA errors are much lower than rate of RNA Pol errors because DNA Pol has a proofreading mechanism Antigenic drift – only nucleic substitutions Antigenic shift – entire segment is swapped with another Influenza virus underwent a lot of evolution because it has been around so long and has so many hosts o One swine can carry avian influenza, another swine can carry human influenza, the two viruses come together and generate a completely new virus this is how H1N1 developed Recombinants are different from both parents o Recombination happens within the same sequence must be homology present otherwise the Pol cannot recognize the sequence to replicate it Influenza A can infect a lot of hosts o Antigenic shift and drift can occur Humans are in contact with birds (chickens) often, and we can get influenza from birds Some viruses are highly restricted to certain species o Bats have a certain virus that used to be restricted to bats o Because of deforestation the bats came into the villages, and came in contact with humans, the virus was introduced to the human population Many viruses present in sub-tropical areas (Africa and Asia) Family size also important because if one person gets the virus they can spread it to all their family members easily Influenza mode of transmission – airborne Polio virus – transmission through food Dogs can bite you and give you rabies – it is extremely fatal Because of deforestation animals relocate to urban areas India and China have the largest populations Japan is such a small country but it is very heavily populated, but sanitation is highly regulated (it is very clean) SARS and H5N1 was spread via human travel Animals (like dogs and cats) are also carried on planes Mosquitos and other bugs can get on the plane and introduce the virus it carries to a new population Cholera gets spread very easily through water – hurricanes were a concern for the spread of cholera (as well as accumulation of mosquitos due to stagnant water) Mosquitos are very important vectors for many viruses Virology Lecture 4/29/16 – Ebola Midterm 2 is cumulative Name of Ebola came from the river (the origin) Ebola is incredibly dangerous (more dangerous than any other virus, drugs, or alcohol) Death rate is 50-90% worse than smallpox smallpox is very deadly but compared to Ebola, Ebola is worse Ebola – internally, all the organs are disintegrated whoever is infected with the virus will not survive Humans and non-humans (chimps, monkeys) get infected by Ebola Out of all 5 species the most deadly Is the ZAIRE virus o About 68% death rate compared to Reston which is 0 Very unusual looking virus particle o This virus folds differently, very unusual morphology o Looks like a snake o –ssRNA virus Like influenza Very deadly virus Lipid membrane, negative sense nucleic acid Must encode its own Pol because it is negative sense First outbreak in Congo, Ebola River -1976 o Fairly new virus o Outbreaks all reported in Africa o 2014 the virus spread o The virus began spreading very quickly Virus cases doubled in 10 days Incubation period: 2-21 days No specific symptoms to Ebola o Maculopapular rash – rash on the skin o Hemorrhage – person bleeds to death through any possible openings o Death rate 50-90% Fruit bats transmit this virus Highly contagious but not airborne Can use ELISA (because it is a protein) Can use PCR (because it has nucleic acids) No treatment fairly new virus, no vaccines Isolation is the major method used to deal with Ebola Two promising vaccines have been developed Since this virus is highly contagious: o Isolate the patient o Restricted entry o PPE – cover everything If you think a person MAY be infected with Ebola the sample must be labeled with “Suspect Ebola” Lab Sample: o Collect 4 ml blood o Wrap in tissue paper o Triple layer seal it o Put in leak-proof boxes Anytime you have a sample you must separate it from the other equipment Yellow bags are the ones they normally use under lab conditions they are autoclavable, can seal them and use them under autoclave Need BSL-4 lab to work with Ebola
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