1 / 96

Natural History of HIV/AIDS

Natural History of HIV/AIDS. Acquired immune deficiency syndrome (AIDS) caused by Human Immunodeficiency Virus (HIV). Immune system attacked. Victim dies of secondary infections. Projected mortality by 2020 --90 million lives Responsible for about 5% of all deaths worldwide.

zaide
Download Presentation

Natural History of HIV/AIDS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Natural History of HIV/AIDS • Acquired immune deficiency syndrome (AIDS) caused by Human Immunodeficiency Virus (HIV). • Immune system attacked. Victim dies of secondary infections. • Projected mortality by 2020 --90 million lives • Responsible for about 5% of all deaths worldwide.

  2. The Human Immunodeficiency Virus • HIV, like all viruses, is an intracellular parasite • Parasitizes macrophages and T-cells of immune system • Uses cells enzymatic machinery to copy itself. Kills host cell in process.

  3. Cells HIV infects are critical to immune system function • Immune system collapse leads to AIDS. • Patient vulnerable to opportunistic infections

  4. Why is HIV hard to treat?Drug resistance. • AZT (azidothymidine) first HIV wonder drug • Works by interfering with HIV’s reverse transcriptase enzyme, which the virus uses to transcribe its viral RNA into DNA

  5. Drug resistance. • AZT similar to thymidine (one of 4 bases of DNA nucleotides) but has an azide group (N3) in place of hydroxyl group (OH). • AZT added to DNA strand prevents strand from growing. Azide blocks attachment of next nucleotide.

  6. Drug resistance. • AZT successful in tests although with serious side effects. • After only a few years patients stopped responding to treatment. • Evolution of AZT-resistant HIV in patients usually took only about 6 months.

  7. How does resistant virus differ? • Reverse transcriptase gene in resistant strains differ genetically from non-resistant strains. • Mutations located in active site of reverse transcriptase. • Selectively block binding of AZT

  8. How did resistance develop? • HIV reverse transcriptase very error prone. • Half of DNA transcripts produced contain an error (mutation). • HIV has highest mutation rate known. • There is thus VARIATION in the HIV population in a patient.

  9. How did resistance develop? • High mutation rate makes occurrence of AZT-resistant mutations almost certain. • NATURAL SELECTION now starts to act in presence of AZT

  10. Selection in action • Presence of AZT suppresses replication of non-resistant strains. • Resistant strains replicate and pass on their resistance. Resistance is HERITABLE. • AZT-resistant strains replace non-resistant strains. EVOLUTION has occurred.

  11. Other examples of natural selection • There are other examples of natural selection in action in your textbook chapter 22. You should study these too.

  12. Evidence for evolution. 1. Fossil record. Fossils show that species have changed over time. Many transitional fossils that are intermediate between extinct and modern species are known.

  13. Archaeopteryx (oldest known fossil bird)

  14. Evidence for evolution. 2. Anatomical evidence. (a) Homologous structures. Many structures, often with different functions, are made from the same ancestral parts. E.g. human arm, cat’s forelimb, bat’s wing, and whale’s flipper all contain the same bones.

  15. Homologous structures imply that organisms that may look very dissimilar in fact share a common ancestry. • Homology: similarity resulting from common ancestry.

  16. Evidence for evolution. 2. Anatomical evidence. (b) Vestigial structures. Structures with no current function but are retained by the body. Imply organisms have an evolutionary history. Human examples?

  17. Human vestigial structures Coccyx (tailbone) Appendix Wisdom teeth

  18. Evidence for evolution. 2. Anatomical evidence. (c) Jerry-rigged structures e.g. The Panda’s thumb.

  19. In Pandas, a wrist bone is modified into a “thumb” used to strip bamboo stalks. Panda’s thumb not the “best possible” solution. Natural selection has to work with the material available. Implies pandas not designed, but evolved.

  20. Evidence for evolution. 2. Anatomical evidence. (d) Developmental homologies. Embryos of different organisms display primitive features (e.g. gill slits/pharyngeal pouches, post anal tail) during development. “Old” instructions remain in our DNA

  21. Evidence for evolution. 3. Molecular evidence. All organisms share DNA/RNA as genetic material.

  22. Evidence for evolution. 3. Molecular evidence. Patterns of species relatedness based on anatomy match those derived from molecular data.

  23. Evidence for evolution. 4. Adaptive radiation and clusters of species. Many remote islands populated by different, but closely related species.

  24. Adaptive radiation: Ancestral colonist arrives on island. Absence of other species meant little competition. Descendents diversified to fill vacant niches (ecological opportunities) on the island. Speciation occurred rapidly.

  25. Example of adaptive radiation: Darwin’s Finches. 13 species of anatomically quite different, but closely related finches occur on Galapagos Islands .

  26. In absence of competitors, Darwin’s finches filled diverse ecological roles. Huge variation in beak size and diet.

  27. Evidence for Evolution • Further evidence for evolution that relates to Biogeography (distributions of animals across the planet) were discussed earlier under the heading “What Darwin observed” during the voyage of the Beagle.

  28. Chapter 23. The Evolution of Populations • Remember individual organisms do not evolve. Individuals are selected, but it is populations that evolve. • Because evolution occurs when gene pools change from one generation to the next, understanding evolution require us to understand population genetics.

  29. Some terminology • Population: All the members of one species living in single area. • Gene pool: the collection of genes in a population. It includes all the alleles of all genes in the population.

  30. Some terminology • If all individuals in a population all have the same allele for a particular gene that allele is said to be fixed in the population. • If there are 2 or more alleles for a given gene in the population then individuals may be either homozygous or heterozygous (i.e. have two copies of one allele or have two different alleles)

  31. Detecting evolution in nature • Evolution is defined as changes in the structure of gene pools from one generation to the next. • How can we tell if the gene pool changes from one generation to the next? • We can make use of a simple calculation called the Hardy-Weinberg Equilibrium

  32. Hardy-Weinberg Equilibrium • Before discussing Hardy-Weinberg need to review some basic facts about Mendelian Inheritance. • In Mendelian Inheritance alleles are shuffled each generation into new bodies in a way similar to which cards are shuffled into hands in different rounds of a card game. • The process of Mendelian Inheritance preserves genetic diversity from one generation to the next. A recessive allele may not be visible because it is hidden by the presence of a dominant allele, but it is still present.

  33. Hardy-Weinberg Equilibrium • The shuffling process occurs because an individual has two copies of any given gene (one inherited from father and one from mother), but can put only one or the other copy into a particular sperm or egg. E.g. for an individual who is heterozygous Aa 50% of sperm will contain A and 50% will contain a.

  34. Hardy-Weinberg Equilibrium • Individuals alleles thus go through a process where they are sorted into gametes (sperm or egg) which combine to form a zygote which will one day again sort alleles into gametes. • See Chapter 14 to review Mendelian Inheritance

More Related