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Virus-like particles (read pages 365-366). Viroids and Prions (see virus lec. for discussion of prions) Viroids - are common plant pathogens and an emerging economic problem. They are the smallest known pathogens…..small naked, ss RNA Viroids 25 different viroid sequences have been determined and numerous variants identified. Avsunviroidae:e.g. avocado sunblotch viroid, peach latent mosaic Pospiviroidae: Subgroup 1: potato spindle tuber viroid, coconut cadang cadang viroid, tomato plant macho viroid Subgroup 2:citrus bent leaf viroid, pear blister canker viroid (< 400 nucleotides; the smallest virus is 10x bigger). • They are all single stranded covalent circles • There is extensive intramolecular base pairing (see next slide) The structure of a viroid is shown below: - lack a protein or membrane coat. - cause some plant diseases, e.g. potato spindle disease and Cadang disease of coconuts. Exactly how viroids cause disease is not understood - they don’t contain protein encoding genes. Viroids are replicated in plant cell nuclei by RNA polymerases. The seem to act like “regulatory RNAs” in plants and cause severe stunting and often death Structure of a viroid, showing how a circular single stranded RNA (246-399 nucleotides) can form a seemingly double-stranded structure…….. The Potato Spindle Tuber Viroid (PSTV) was the first viroid discovered (by T.O. Diener in 1971). This is a very serious disease of potatoes and can be spread by contaminated tools or through pollen and seeds and can infect eggplants and tomatoes as well as potatoes…. Normal potato Viroids are replicated in plant cell nuclei by RNA polymerases. The seem to act like “regulatory RNAs” in plants and cause severe stunting and often death PSTV infected potato Some excerpts from Sandra Sonada’s lecture….. Virulence Factors of Pathogens • Four categories – – – – Colonization of surface, followed by toxin production • V. cholera – Toxin activates host epithelial trans-membrane pump to cause Clefflux, with H2O following – Up to 15-20L fluid loss; if 7% loss of body wt, requires IV fluids • B. pertussis (whooping cough) – Attach to ciliated epith, toxin causes release of NO fm goblet cells – Kills ciliated epithelial cells Toxins Adhesion Factors Evasive Factors Invasive Factors Establishment of infection • Adherence • Colonization • Delivery of effector molecule Adherence Adherence • Adhesins – located on tips of pili or is component of glycocalyx or cell walls – Generally, glycoproteins or glycolipids – Binding is specific • Ex: E. coli c plasmid encoding other adhesins allow adherence to bladder epithelial cells • Hemagglutinins (remember flu lecture) on viruses that recognize receptors on cells in upper respiratory tract – Typing makes up part of categorizing flu strains Figure 19.3 Self molecule mimicry: Penetration of skin • Trauma – Deep wounds for C. tetani • Arthropods – West Nile Virus, Yellow Fever - mosquitoes S. pyogenes – capsule composed of hyaluronic acid • Hyaluronic acid – polysacch found in host tissues. Damage to the host • Exotoxins • Endotoxins Exotoxins A-B toxin, as in diphtheria Figure 19.12 Endotoxins – G -, Lipid A Endotoxin – Lipid A • Do not contain proteins, not actively released from bacteria during growth, have no enzymatic activity • Sm amt = potent activator of physiologic responses • Recognized by phagocytes, which then secrete cytokines – results in physiologic response Figure 19.14 MICROBIOLOGY - EBIO 3400 - Practice Questions 3 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. b. unmethylated. a. are rare on the skin, but more abundant deep in the nose. c. heart and lungs c. invading cells are coated and therefore marked for destruction. c. destroyed by the complement system and/or phagocytes. e. all of the above b. lipid / polysaccharide b. antigens c. give harmless bacteria a head start in colonizing mucosal surfaces in areas such as the colon. b. lysogenic (= temperate phage) e. a and b. b. electroporation. __A___uptake of naked DNA ___B__transfer of DNA by cell to cell contact ____C_transfer of DNA by viruses Briefly describe the reservoir(s), vector and pathogen (Genus species) involved in epidemics of ______ (insert any disease we have discussed into blank). (50 words or less) Plague is caused by the Gram- bacterium Yersinia pestis. The reservoirs for plague are wild rodents such as rats and prairie dogs. Fleas from the rodents are the vectors for the disease. Pneumonic plague can also be spread through the air or direct contact. 15. Briefly discuss why the incidence of West Nile Virus in Colorado dropped dramatically in 2004 compared to 2003. (50 words or less) Because the West Nile Virus isn’t passed from generation to generation of mosquito and the reservoir (birds) for the disease either die or become immune to the virus and clear it from their bodies (and therefore are no longer reservoirs).