other viral types.pptx
- 1. SRI PARAMAKALYANI COLLEGE ( Reaccredited with B Grade with a CGPA of 2.71 in the II Cycle by NAAC Affiliated to Manonmaniam Sundaranar University, Tirunelveli) ALWARKURICHI 627 412 TAMIL NADU, INDIA POST GRADUATE & RESEARCH CENTRE - DEPARTMENT OF MICROBIOLOGY (Government Aided) II SEM - CORE –VIROLOGY UNIT – 1 VIRIODS,VIRUSOIDS AND PRIONS M.MOHAMED FAISAL REG NO: 20211232516114 I M.SC.MICROBIOLOGY ASSIGNED ON: TAKE ON : Submitted to, GUIDE: Dr.C.MARIAPPAN, Ph.D, ASSISTANT PROFESSOR, SRI PARAMAKALYANI COLLEGE, ALWARKURICHI.
- 2. LEARNING OBJECTIVES Describe viroids and their unique characteristics Describe virusoids and their unique characteristics Describe prions and their unique characteristics
- 3. VIROIDS • In 1971, Theodor Diener, a pathologist working at the Agriculture Research Service, discovered an acellular particle that he named a viroid, meaning virus. • Viroids consist only of a short strand of circular RNA capable of self-replication. • The 1st viroid discovered was found to cause potato tuber spindle disease, which causes slower sprouting and various deformities in potato plants.
- 5. • These potatoes have been infected by the potato spindle tuber viroid (PSTV), which is typically spread when infected knives are used to cut healthy potatoes, which are then planted. • Pamela Roberts, University of Florida Institute of Food and Agricultural Sciences, USDA ARS genome. • Unlike viruses, viroids do not have a protein coat to protect their genetic information.
- 6. • Viroids can result in devastating losses of commercially important agricultural food crops grown in yields and orchards. Since the discovery of PSTV, other viroids have been discovered that cause diseases in plants. • Tomato Planta Macho Viroid (TPMVd) infects tomato plants, which causes loss of chlorophyll, disgured and brittle leaves, and very small tomatoes, resulting in loss of productivity in this yield crop. • Avocado Sun Blotch Viroid (ASBVd) results in lower yields and poorer-quality fruit. • ASBVd is the smallest viroid discovered thus far that infects plants.
- 7. • Peach latent mosaic viroid (PLMVd) can cause necrosis of owner buds and branches, and wounding of ripened fruit, which leads to fungal and bacterial growth in the fruit. • PLMVd can also cause similar pathological changes in plums, nectarines, apricots, and cherries, resulting in de- creased productivity in these orchards, as well. • Viroids, in general, can be dispersed mechanically during crop maintenance or harvesting, vegetative reproduction, and possibly via seeds and insects, resulting in a severe drop in food availability and devastating economic consequences.
- 8. VIRUSOIDS • A second type of pathogenic RNA that can infect commercially important agricultural crops are the virusoids, which are subviral particles best de- scribed as non–selfreplicating sRNAs. RNA replication of virusoids is similar to that of viroids but, unlike viroids, virusoids require that the cell also be infected with a specific “helper” virus. There are currently only five described types of virusoids and their associated helper viruses. The helper viruses are all from the family of Sobemo viruses.
- 9. • An example of a helper virus is the subterranean clover mottle virus, which has an associated virusoid packaged inside the viral capsid. Once the helper virus enters the host cell, the virusoids are released and can be found free in plant cell cytoplasm, where they possess ribozyme activity. • The helper virus undergoes typical viral replication independent of the activity of the virusoid. The virusoid genomes are small, only 220 to 388 nucleotides long. A virusoid genome does not code for any proteins, but instead serves only to replicate virusoid RNA.
- 10. • Virusoids belong to a larger group of infectious agents called satellite RNAs, which are similar pathogenic RNAs found in animals. Unlike the plant virusoids, satellite RNAs may encode for proteins; however, like plant virusoids, satellite RNAs must co-infect with a helper virus to replicate. One satellite RNA that infects humans and that has been described by some scientists as a virusoid is the hepatitis delta virus (HDV), which by some reports, is also called hepatitis delta virusoid. Much larger than a plant virusoid, HDV has a circular, sRNA genome of 1,700 nucleotides and can direct the biosynthesis of HDV-associated proteins. The HDV helper virus is the hepatitis B virus (HBV). Co-infection with HBV and HDV results in more severe pathological changes in the liver during infection, which is how HDV was first discovered.
- 11. PRIONS • At one time, scientists believed that any infectious particle must contain DNA or RNA. Then, in 1982, Stanley Prusiner, a medical doctor studying scrapie (a fatal, degenerative disease in sheep) discovered that the disease was caused by proteinaceous infectious particles, or prions. Because proteins are acellular and do not contain DNA or RNA, Prusiner’s findings were originally met with resistance and skepticism. • However, his research was eventually validated, and he received the Nobel Prize in Physiology or Medicine in 1997.
- 12. • A prion is a misfolded rogue form of a normal protein (PrPc) found in the cell. This rogue prion protein (PrPsc), which may be caused by a genetic mutation or occur spontaneously, can be infectious, stimulating other endogenous normal proteins to become misfolded, forming plaques. Today, prions are known to cause various forms of transmissible spongiform encephalopathy (TSE) in human and animals.
- 14. • Endogenous normal prion protein (PrPc) is converted into the disease-causing form (PrPsc) when it encounters this variant form of the protein. PrPsc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may originate from misfolded prions consumed in food that eventually find their way into brain tissue.
- 15. • TSE is a rare degenerative disorder that affects the brain and nervous system. • The accumulation of rogue proteins causes the brain tissue to become sponge-like, killing brain cells and forming holes in the tissue , leading to brain damage, loss of motor coordination, and dementia. • Infected individuals are mentally impaired and become unable to move or speak. • There is no cure, and the disease progresses rapidly , eventually leading to death within a few months or years.
- 17. • Creutzfeldt-Jakob disease (CJD) is a fatal disease that causes degeneration of neural tissue. • (a) These brain scans compare a normal brain to one with CJD. • (b) Compared to a normal brain, the brain tissue of a CJD patient is full of sponge-like lesions, which result from abnormal formations of prion protein. • Modification of work by Dr. Laughlin Dawes
- 18. • Prions are extremely difficult to destroy because they are resistant toheat, chemicals, and radiation. Even standard sterilization procedures donot ensure the destruction of these particles. Currently, there is no treat-ment or cure for TSE disease, and contaminated meats or infected ani-mals must be handled according to federal guidelines to preventtransmission.
- 19. KEY CONCEPTS AND SUMMARY • Other acellular agents such as viroids, virusoids, and prions also cause diseases. • Viroids consist of small , naked sRNAs that cause diseases in plants. • Virusoids are sRNAs that require other helper viruses to establish an infection. • Prions are proteinaceous infectious particles that cause transmissible spongiform encephalopathies. • Prions are extremely resistant to chemicals, heat, and radiation. • There are no treatments for prion infection.
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