Lecture 14 - Diagnosis and Control, Vaccines PDF

Diagnosis and Control Vaccines  Diagnosis of Infection AIMS OF THE CLINICAL MICROBIOLOGY LABORATORY Identification is achieved by detecting the microorganism or its products or the patient’s immune response. Specimen processing Important steps in specimen collection...

Diagnosis and Control Vaccines  Diagnosis of Infection AIMS OF THE CLINICAL MICROBIOLOGY LABORATORY Identification is achieved by detecting the microorganism or its products or the patient’s immune response. Specimen processing Important steps in specimen collection and delivery to the laboratory  CULTIVATION OF MICROORGANISMS Bacteria and fungi can be cultured on solid nutrient or liquid media Different species of bacteria and fungi have different growth requirements Growth of viruses, Chlamydia and Rickettsia requires cell or tissue cultures  IDENTIFICATION OF MICROORGANISMS GROWN IN CULTURE Bacteria and fungi are identified by colonial characteristics, cell morphology and biochemical properties.  IDENTIFICATION OF MICROORGANISMS Viruses are usually identified using serological and nucleic-acid-based tests. Mass spectrometry Microscopy - Light microscopy - Bright field microscopy - Dark field (dark ground) microscopy - Phase contrast microscopy - Fluorescence microscopy - Electron microscopy  Immunological Methods of Diagnosis Use of Monoclonal Antibodies Hybridomas are produced in the laboratory by fusing a cancerous B-cell with an antibody-secreting plasma cell. A hybridoma cell culture produces large quantities of the plasma cell’s antibodies, called monoclonal antibodies. Monoclonal antibodies are used to treat diseases and in diagnostic serological tests. Production of Monoclonal Antibodies  Immunological Methods of Diagnosis Agglutination Reactions The interaction of particulate antigens (cells that carry antigens) with antibodies leads to agglutination reactions. Diseases may be diagnosed by combining the patient’s serum with a known antigen. Hemagglutination reactions involve agglutination reactions using red blood cells. Hemagglutination reactions are used in blood typing, the diagnosis of certain diseases, and the identification of viruses. Immunological Methods of Diagnosis Agglutination Reactions Agglutination Agglutination test  Immunological Methods of Diagnosis Neutralization Reactions In neutralization reactions, the harmful effects of a bacterial exotoxin or virus are eliminated by a specific antibody. An antitoxin is an antibody produced in response to a bacterial exotoxin. The antitoxin combines with the exotoxin to neutralize it. In viral hemagglutination inhibition tests, antibodies against certain viruses can be detected by their ability to interfere with viral hemagglutination.  Immunological Methods of Diagnosis Enzyme-Linked Immunosorbent Assay (ELISA) Direct and Indirect ELISA  Principles and Effects of Vaccination Vaccine - suspension of organisms or fractions of organisms used to induce immunity. Several viral diseases are eradicated or eliminated by vaccines To create effective vaccines, the developers need to overcome a number of hurdles: understanding the most effective antigens that will cause an immune response, fully understanding the life cycle or stages of a microorganism finding effective animal models to test efficacy. Vaccines  Types of Vaccines and Their Characteristics Live attenuated vaccines consist of attenuated (weakened) microorganisms; attenuated virus vaccines generally provide lifelong immunity. Inactivated vaccines consist of killed bacteria or viruses. Subunit vaccines consist of antigenic fragments of a microorganism; these include toxoids, virus-like particles and polysaccharides. Conjugated vaccines combine the desired antigen with a protein that boosts the immune response. Nucleic acid (DNA) vaccines cause the recipient to make the antigenic protein. Recombinant vector vaccines are avirulent viruses or bacteria genetically modified to produce a desired antigen.  Vaccine Safety Vaccines are the safest and most effective means of controlling infectious diseases. Side effects vary according to vaccine but may include tenderness at the injection site, headache, fever, mild rash, and fatigue, allergic reaction and in rare cases may develop anaphylactic shock.  Epidemiology and control of infectious diseases Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems. Epidemiology is divided into observational and interventional. Observational studies are either descriptive, describing the frequency and patterns (who, where, when) of a disease in the population, or analytical (why), investigating associations between risk factors and disease. Interventional or experimental epidemiological studies are designed to test a hypothesis by allocating an exposure or intervention to one group of people but not the other and measuring the disease outcome.  Disease Prevalence and Incidence Prevalence is the number of existing cases in a population at a given point in time. Incidence is the number of new cases occurring in a population during a specified period of time. The interaction between prevalence, incidence, mortality  TRANSMISSION OF INFECTIOUS DISEASE Direct and indirect transmission The infectiousness of a disease in a population depends on several factors: The infectious agent: time between infection of a person and becoming infectious. Duration of infectiousness The probability of transmission given a contact between an infectious person and a susceptible person The number of contacts Susceptibility of the population (number of susceptible individuals and degree of susceptibility)  Time Periods of Infections The latent period is the period between infection and becoming infectious. This period is followed by the infectious period during which the infected individual is able to transmit the infectious agent. This is followed by the non-infectious period due to death or recovery. For measles the latent period is 6–9 days followed by an infectious period of 6–7 days. In contrast the latent period of hepatitis B is 13–17 days and the infectious period 19–22 days. References MIMS’ Medical Microbiology and Immunology, Chapter 33 Gerard J. Tortora, Berdell R. Funke, Christine L. Case - Microbiology_ an introduction-Pearson (2018), Chapter 18