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The Nature Of Disease Controlling Disease


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The Nature Of Disease Controlling Disease

  1. 1. Controlling Disease To control infectious disease we must consider such aspects as: The origin of the outbreak (especially the natural reservoir) Its mode of transmission within the population The possible methods that can be employed to contain it Photo: CDC
  2. 2. Preventing the Spread of Disease The best method of disease control is to prevent the disease spreading in the first place. The four main methods by which the spread of infectious disease is controlled are through: Photo: CDC Modifying the Behavioral control environment Treatment Immunization
  3. 3. Modifying the Environment All pathogens require certain conditions for growth, reproduction, and transmission. By modifying the environment to make it less suitable for pathogens, most infectious diseases can be controlled. Examples include Draining swampy ground to eliminate breeding sites for Photo: CDC mosquitoes carrying malaria and dengue fever. Spraying disinfectants to sterilize potentially contaminated surfaces. Workers spray drainage ditches with insecticide to kill mosquitoes
  4. 4. Effective Sanitation The development of effective sanitation, sewage treatment, and the treatment of drinking water has virtually eliminated dangerous waterborne diseases from developed countries. These practices disrupt the normal infection cycle of pathogens transmitted through the fecal-oral route, such as those causing typhoid fever and cholera.
  5. 5. Behavioral Control Transmission of disease can be prevented or significantly reduced by adopting ‘safe’ behaviors. Examples include: Using condoms to reduce the spread of sexually transmitted diseases. Establishing quarantine and isolation procedures to prevent the spread of disease from other countries. Adopting appropriate personal hygiene practices, such as washing your hands after going to the toilet and before handling food.
  6. 6. Immunization Vaccination or immunization is a procedure that provides artificially acquired active immunity for the person receiving it. A vaccine is a suspension of microorganisms (or portions of them) which protects people from disease by inducing immunity. Photo: CDC Vaccines that are effective against bacteria and viruses have been produced, but to date there are no useful vaccines for humans against protozoa, roundworms, flatworms, or fungi. Photo: CDC/WHO The last known person in the world to have smallpox, 23 year old Ali Maow Maalin (photo), from Merka, Somalia. Smallpox was eradicated due to a vigorous vaccination program.
  7. 7. Types of Vaccine There are two basic types of vaccine: subunit vaccines and whole-agent vaccines. Recombinant vaccines Subunit Vaccine Contains some part Toxoids or product of micro- organisms that can Conjugated produce an immune response vaccines Acellular vaccines Photo: CDC Attenuated Whole-Agent (weakened) Vaccine Contains whole, nonvirulent microorganisms Inactivated (killed)
  8. 8. Subunit Vaccines 1 Subunit vaccines contain some product of, or fragments of, microorganisms. These are capable of providing an immune response in the person receiving the vaccine. Yeast makes Recombinant Vaccines viral proteins Produced using genetic engineering techniques when other microbes (bacteria and yeast) are genetically altered to make Inactivated the desired antigenic fraction. toxins Conjugated Vaccines Toxoid Some pathogens produce polysaccharide attached capsules that are poorly antigenic, especially in young children. To enhance their effectiveness, they are combined with proteins such as toxoids Polysaccharide from other pathogens. from pathogen
  9. 9. Subunit Vaccines 2 Toxoids Heat, iodine or formaldehyde Toxoids are bacterial toxins that have been inactivated by heat or chemicals. When injected, the toxoid stimulates the production of antitoxins. Acellular Vaccines These are produced by fragmentation of a conventional whole-agent vaccine and collecting only those portions containing Antigenic the desired antigens. fragments of bacterial cells
  10. 10. Whole Agent Vaccines Whole agent vaccines contain complete microorganisms that are nonvirulent (not capable of causing disease). Inactivated: whole agent is inactivated by treatment with They may be either inactivated formalin or other chemicals whole or attenuated. Many attenuated viruses provide recipients with life-long immunity (without the need for booster shots). An effectiveness of 95% is not Mutated DNA unusual. One danger of such vaccines is that these live viruses can back-mutate to a virulent form. Attenuated: The agent is alive, but has been significantly weakened. They are usually derived from strains where mutations have accumulated during long-term cell culture.
  11. 11. DNA Vaccines Using genetic material to produce vaccines is one of the promising new fields of vaccine research. Unlike traditional vaccines (which contain either whole or parts of a pathogen), genetic vaccines contain only the gene for producing an antigen from the pathogen. When this gene is expressed in a patient the protein Malaria produced elicits an immune response. Genetic vaccines are currently being developed and trialed to immunize people against: Malaria Herpes simplex HIV Hepatitis B Herpes simplex Hepatitis B Rabies HIV Rabies Cancer Cancer
  12. 12. Producing a DNA Vaccine 1 Plasmid is isolated from Gene for the a harmless bacterium. antigen is removed from the pathogenic or cancerous cell Antigen gene is spliced into the plasmid and the plasmid is inserted back into the bacterium. The recombinant bacteria are allowed to grow and reproduce on an agar plate.
  13. 13. Producing a DNA Vaccine 2 The isolated antigen gene is delivered to the patient using direct injection or via a gene gun. Expression of the gene in the patient produces a protein that elicits an immune response.
  14. 14. Antimicrobial Drugs Antimicrobial drugs include synthetic (manufactured) drugs as well as drugs produced by bacteria and fungi, called antibiotics. Antibiotics are produced naturally by microorganisms as a means of inhibiting competitor microbes around them (a form of antibiosis, hence the name applied to the drugs). Photo: CDC The first antibiotic, called penicillin, was discovered in 1928 by Alexander Fleming. Agar plate with Since then, similar inhibitory reactions between colonies bacterial colonies growing on solid media have been commonly observed. and antibiotic discs Antibiotics are actually rather easy to discover, but few of them are of any medical or commercial value.
  15. 15. Antimicrobial Effectiveness 1 To be effective, antimicrobial drugs must often act inside the host so their effect on the host’s cells and tissues is important. The ideal antimicrobial drug has selective toxicity, killing the harmful organism without damaging the host. Some antimicrobial drugs have a narrow spectrum of activity and affect only a limited number of microbial types. Photo: CDC The wrong antibiotic can allow infections such as this ulcer to get out of control
  16. 16. Antimicrobial Effectiveness 2 Other drugs affect a large variety of microbes and are therefore called broad-spectrum drugs. The identity of a pathogen is not always known. Therefore a broad- spectrum drug may be prescribed in order to save valuable time. However there is a disadvantage with this practice. Broad spectrum drugs not only target the pathogen, but also the host’s normal microbial Photo: CDC community (flora). Staphylcoccus aureus infection The sticky looking substance is a polysaccharide biofilm, which protects the bacteria from antibiotics. Some strains of staph. have developed resistance to multiple antibiotics. The wide use of broad-spectrum antibiotics has contributed to this.
  17. 17. Antimicrobial Activity Spectrum of antimicrobial activity of a number of chemotherapeutic drugs Prokaryotes Gram-Negative Gram-Positive Rickettsias/ Mycobacteria Viruses Bacteria Bacteria Chlamydias Penicillin Tetracycline Acyclovir Streptomycin Isoniazid
  18. 18. Antimicrobial Activity Spectrum of antimicrobial activity of a number of chemotherapeutic drugs Eukaryotes Tapeworms/ Fungi Protozoa Flukes Nicosamide Ketoconazole (tapeworms) Mefloquine (malaria) Praziquantel (flukes)
  19. 19. How Antimicrobial Drugs Work Antimicrobial drugs disrupt the functioning of a bacterial cell in the following ways: Inhibited Protein Synthesis Damaged Cell Walls Translation is disrupted. The synthesis of new cell walls Examples: erythromycin, during cell division is inhibited. tetracyclines, chloramphenicol, Examples: penicillin, vancomycin, streptomycin cephalosporins, bacitracin Damaged Plasma Membrane Inhibition of Enzyme Activity The plasma membrane may be Inhibit Gene Copying The synthesis of essential ruptured. Examples: nystatin, DNA replication and transcription metabolites is inhibited. miconazole, polymyxin B, are interfered with. Examples: Examples: sulfanilamide, amphotericin B Rifampin, Quinolones trimethoprim
  20. 20. Monoclonal Antibodies A monoclonal antibody is an artificially produced antibody that neutralizes only one specific protein (antigen). Monoclonal antibodies are produced by stimulating the production of B-cells in mice injected with the antigen. These B-cells produce an antibody against the antigen. B-cells can be isolated and made to fuse with immortal tumor cells. They can then be cultured indefinitely in a suitable growing medium. Monoclonal antibodies are useful for 3 reasons: They are totally uniform (i.e. clones). They can be produced in large quantities. Photo: CDC They are highly specific. Monoclonal antibodies chemically linked to a fluorescent dye to detect the presence of gonorrhea
  21. 21. Making Monoclonal Antibodies A mouse is injected with a foreign protein (antigen). Pure tumor cells are harvested from culture The mouse’s B-cells produce an antibody to recognize the antigen. A few days later, antibody- producing B-cells are taken Some of the mouse cells fuse from the mouse’s spleen. with tumor cells to make hybrid Hybridoma cells cells called hybridomas. The mouse cells and tumor cells are mixed Mouse cell and together in suspension. tumor cell fusing Unfused cell The mixture of cells is placed in Hybridomas are screened for a selective medium that allows antibody production. They are then only hybrid cells to grow. cultured to produce large numbers of monoclonal antibodies.
  22. 22. The World Health Organization Founded in 1948, the World Health Organization (WHO) is a specialized agency of the United Nations WHO promotes technical cooperation for health among nations, carries out programs to control and eradicate disease, and strives to improve the quality of human life. WHO has four main functions: To give worldwide guidance in the field of health To set global standards for health To cooperate with governments in strengthening national health programs To develop and transfer appropriate health technology, information and standards A major event in WHO's first 50 years was the global eradication of smallpox.
  23. 23. The Role of the CDC The Center for Disease Control and Prevention (CDC) is an agency of the US Department of Health and Human Services. In today's global environment, new diseases have the potential to spread across the world in a matter of days, or even hours, making early detection and action more important than ever. The CDC plays a critical role in investigating, monitoring and controlling these diseases, traveling at a moment's notice to investigate outbreaks worldwide. CDC and Zairian scientists take samples from animals collected near Kikwit, Zaire, 1995. These samples were sent back to CDC in Atlanta for testing to search for the animal Photo: CDC reservoir of the Ebola virus.