Viruses How Vaccination Works Viral Diversity Viral Infection Cycle Influenza Virus Influenza Vaccines Retroviruses and HIV Genetic Impacts of Retroviruses Transposable elements Protists Eukaryotes Endosymbiosis Theory Malaria African Sleeping Sickness African Trypanosomiasis The Evolution of Multicellularity Proifera Sponges Cnidaria Bilateria Protostomes Deuterostomes Lophotrochozoa EcysozoaArthropoda Viruses Tiny non cellular parasites that infect virtually every type of cell known Cannot perform metabolism on their own meaning outside a parasitized cell and are not considered to be alive An obligate intracellular parasite Obligate because viral infection is completely dependent on host cells Intracellular because viruses must enter a host cell for replication to occur Parasite because viruses reproduce at the expense of their host cell They are not cells and are not made up of cells so they are not considered organisms They cannot manufacture their own ATP or amino acids or nucleic acids and they cannot produce proteins on their own Viruses enter a host cell take over its biosynthetic machinery and use that machinery to manufacture a new generation of viruses Outside of host cells viruses simply exist Different types of viruses are specialized for infecting particular species and types of cells Very small relative to eukaryotic or even bacterial cells Viruses are ubiquitous in natural environments greatly exceeding cellular life forms in abundance Positive sense virus the genome contains the same sequences as the mRNA required to produce viral proteins Negative sense virus The base sequences in the genome are complementary to those in viral mRNAs Ambisense Virus Some sections of the gnome are positive sense while others are negative sense Viruses Characteristics Hereditary material DNA or RNA can be single stranded or double stranded Plasma membrane is not present Cannot carry out transcription independently Even if a viral polymerase is present transcription of viral genomes requires use of ATP and nucleotides provided by host cells Cannot carry out translation independently Metabolic capabilities virtually none Organisms Characteristics Hereditary material DNA always double stranded Plasma membrane is present Can carry out transcription independently Can carry out translation independently Metabolic capabilities Extensive synthesis of ATP reduced carbon compounds vitamins lipids nucleic acids Discovery of Viruses tobacco plants 1892 Dmitri Ivanosky was studying tobacco mosaid disease which destroys the leaves of The disease was clearly infectious plants that came into contact with the sap from diseased plants were damaged as well This ability to reproduce itself eliminated the possibility that the damaging agent might be a simple toxin Ivanovsky ran an extract of diseased leaves through a very fine filter with pores small enough to trap any known type of bacteria But he found that whatever caused the disease went right through his filter By the 1930s filters could finally be manufactured with pores tiny enough to prove that viruses are particulate after all rather than being fluid in nature The earliest electron microscopes also appeared in the 1930s and viruses could at last be seen Ex Tabacco mosaic virus 4 Smallpox Is caused by the Variola virus is believed to have resulted in more human deaths throughout history than from any other single pathogen In18th century Europe 400 000 people died annually of smallpox Case fatalities ranged from 20 to 60 adults and up to 80 90 for infants Unknown in the New World smallpox devastated native American populations and was instrumental in the fall of the Aztec and Inca empires and in the European settlement of North America During the French Indian War 1754 1767 Sir Jeffrey Amherst the commander of the British forces suggested the deliberate use of smallpox to diminish the Native American population hostile to the British In 1966 the World Health Organization WHO initiated a program to eradicate smallpox from the world The last reported case of smallpox was in Somalia in October 1977 An important factor in the success of eradicating smallpox was that humans are the only host and there are no animal reservoirs for smallpox virus Currently the only official stores of Variola are in freezers of two research sites one at the Centers for Disease Control CDC in Atlanta and one at the VECTOR research facility in Russia Historical Attempts to Induce Immunity Against Smallpox Variolation Practice of inoculating someone with the virus of smallpox to produce immunity to the disease In China 16th century physicians developed the technique of variolation the deliberate infection with smallpox Dried smallpox scabs were blown into the nose of an individual who then contracted a mild form of the disease Upon recovery the individual was immune to smallpox Between 1 to 2 of those variolated died as compared to 30 who died when they contracted the disease naturally By 1700 variolation had spread to Africa India and the Ottoman Empire Inoculation The placement of something that will grow or reproduce Can provide long term immunity against re infection It takes approximately 2 weeks to mount an effective immune response to a new antigen after that the response time is much quicker leading to a period of effective immunity enhanced response also retained for many years and remains effective unless the pathogen changes its antigenic profile it evolves Edward Jenner an English physician used folk knowledge to find an alternative to variolation Recognizing that dairymaids infected with cowpox were immune to small pox Jenner deliberately infected James Phipps an eight year old boy with cowpox in 1796 He then exposed Phipps to smallpox which Phipps failed to contract After repeating the experiment on other children including his own son Jenner concluded that vaccination provided immunity to smallpox without the risks of variolation Jenner s findings were published in 1798 How Vaccination Works 1 Viral antigens are introduced into the body 2 3 4 Antigens bind to receptors on certain immune system cells These cells stimulate other immune system cells to produce antibodies to the virus Later if the host organism is exposed to actual virus particles the antibody producing cells are activated The virus particles become coated with antibodies Viruses that are coated with antibodies are destroyed by immune system cells 5 Antigen Any foreign substance usually a