Bovine Spongiform encephalopathy Mad Cow disease Closely related to scrapie in sheep Kuru in the native tribes Then discovered to be a protieneous infectious particle prion o Because no immune symptoms o Symptoms occur long after initial infection o PcP is similar to the human chromosome of PrPc Structure and Classification of Animal Viruses Viral structure o Capsid the protein coat of a virus o Nucleocapsid the nucleic acid and the protein capsid together o Capsomers defined units that when bonded covalently form the capsid o Naked if there are no additional covering the virus is deemed a naked virus o Envelope a lipid covering that surrounds the outsite of the capsid in most animal viruses Rarely found in phage bacteria Similar to the structure of the human cell membrane o Matrix protein found right inside the lipid envelope o Attachment proteins or spikes extend from the capsid or envelope Segmented viruses viruses vary in the number of genes and RNA molecules o Ex influenza has 8 RNA each coding for 8 genes Viral shapes o Isometric in which protein subunits are arranged in groups of equilateral triangles Icosahedral symmetry 20 triangular faces enclose the nucleic acid o Pleomorphic irregular shape Classification of Animal Viruses Phage is most common type o Genome structure RNA or DNA Double stranded vs single stranded Single molecule or segmented o Virus particle structure Isometric helical rod shaped or pleomorphic o Presence or absence of a viral envelope Grouping based on routes of transmission o Enteric virus Usually a fecal oral transmission Replicate in the intestinal tract and often cause gastroenteritis stomach and GI inflammation Polio replicates in the stomach making a systemic disease and not just gastroenteritis Inhaled droplets and replicate in the respiratory tract Viruses that go on to cause systemic disease are not considered respiratory mumps etc o Respiratory virus o Zoonoses of Zoonotic virus Animal to human and vice versa Vector like arthopods o Sexually transmitted disease Lesions in the genital tract Interaction of Animal Viruses and with their hosts Viral infection is a result of many factors Acute infection ends o Antibody presence o Balanced pathogenicity in which neither the virus or the host is in serious danger o Usually self limited diseases in which the host often remains localized and disappears when the disease o Short duration illnesses in which the host develops long term immunity o Cause productive infections o Coated viruses rarely cause cell lysis o Reproductive Cycle of a virus Attachment In animal viruses the surface of the virus is covered in spikes Several attachment proteins exists and they attach to the glycoprotiens located on the plasma membrane o The glycoprotiens on the cell that help the virus attach are unrelated to viral attachment normally have another major role for the cell When bind changes the viral shape and thus why a virus needs a specific receptor Entry Enveloped viruses o Fusion of the virus to the plasma membrane after binding with the host receptor o Their coats remain part of the cell membrane Involves a fusion protein on viron surface o Endocytosis o Virons are taken into the cell via vesicle o Dissolve the vesicle and exit Targeting the site of viral replication After penetration must find its place of replication The mechanism is unknown RNA polymerase enters the cell in the protein capsid because the infected cell does not have that enzyme o Replication of RNA occurs in the cytoplasm Acids are replicated and proteins are synthesized independently The large the genome the smaller number of host enzymes are utilized Maturation Release from cells This is the final assembly of the virus with its protein coat In the TMV the coat is assembled capsomer by capsomer Lipid rafts specific places in the host cell membrane that have embedded specific proteins and is an ideal place for viral maturation Most virons do not code for enzymes to lyse the cell wall instead because the viral DNA and proteins are synthesized the host cell cannot make its own and therefore dies o Cytopathic effects change in appearance of the cell normally due to cell degradation and lysis caused by viral enzymes Budding release from budding from the cell membrane o Persistant infections and may kill infected cells o First the region of budding in the membrane acquire spikes that will attach to the viron membrane o Then the inside of the membrane is coated with matrix proteins o Then the virus is enclosed by the lipid raft region enclosed in the hosts cell o Some viruses bud from other cell organelles and then use the vesicle to reach the cell membrane where they are ejected by exocytosis Shedding from host o Usually occur the same place the virus entered o i e respiratory tract etc Transmission to Other Hosts o Via routes of transmission Persistent infection o Viruses constantly in the body and are being released by budding o Remain for many years without symptoms o Latent Persistent infections in which a symptomless period is followed by a time of reactivation withan accompanying period of reactivation with symptoms Infectious particles cannot be detected until resurgence Herpes virus HV I and HV 2 Chicken pox Become latent under varying conditions Can reactivate and form shingles o Slow The population of infectious particles gradually increases over a long period of time in which no symptoms arise Lentivirus and Retroviridae retrovirus Prions are considered part of this group HIV Retrovirus DNA RNA DNA which is integrated into the host cell Attacks the T lymphocytes and macrophages Single stranded enveloped retrovirus The single stranded molecule is converted into a double stranded DNA and then integrated into the host cell with the aid of reverse transciptase as a provirus This provirus codes for polygenic or polycistronic mRNA long strands of mRNA which is translated into a polyprotien which is then cleaved by protease to yield individual proteins o Why protease inhibitors are important o Reverse transciptase has no proof reading mechanism leading to the formation of viral coats that the immune system antibodies cannot recognize Viral particles are seen or absent at all times o Chronic Heptitisis B Carrier state The state in which infectious hep B particles are continually produced and can be detected Liver cells can generate and assemble viruses as the information passes via plasmids to other liver cells Replication in hep B Uses DNA as a