Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 12 Mechanisms of Infectious Disease

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Infection or Colonization With Microorganisms “Infection” or “colonization” means that microorganisms are multiplying in or on the host Discussion: Do you have any infections or colonizations at this moment? –List as many as you can identify Are they normal, or are they making you ill?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Infection or Colonization With Microorganisms (cont.) Over 300 different species of bacteria live in the large intestine Bacteria and fungi live on our skin The mouth and pharynx contain many species of bacteria The vagina contains acid-producing bacteria

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Microflora The microorganisms normally living in or on your body Some are useful Many have no effect Pathogens cause disease All are capable of causing disease if your health and immunity are weakened Opportunistic pathogens

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. All interactions between humans and microorganisms are detrimental.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: Some microorganisms perform important functions for their human hosts, like producing vitamins, assisting digestion, or preventing harmful pathogens from entering the host.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents Prions –Small modified infectious host proteins –Abnormally shaped versions of your own proteins –Cause normal proteins to change their shape and become new prions –Can clump together and damage cells –Cause degenerative disease in the central nervous system, e.g., mad cow disease

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Viruses –Protein coat surrounding nucleic acid core –Have no metabolic enzymes of their own –Insert their genome into a host cell’s DNA –Use that cell’s metabolic machinery to make new viruses

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Bacteria –Cells without membrane-bound organelles (prokaryotes) –Can live independently –Use infected organism for food and shelter

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Bacteria (cont.) –Can produce toxins –Exotoxins are proteins released by bacteria –They damage or kill host cells –Endotoxins are parts of the bacterial cell wall –They cause host immune reactions

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Mycoplasmas, rickettsiae, chlamydiae –Smaller than bacteria –Mycoplasmas lack cell walls –Rickettsiae and chlamydiae have to live inside cells to metabolize, like viruses

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Fungi –Most require a cooler temperature than human core body temperature –Most infections are on the surface of the body Tinea is a fungal infection of the skin

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Infectious Agents (cont.) Parasites –Protozoa: malaria, amoebic dysentery, giardiasis –Helminths: roundworms, tapeworms, flukes –Arthropods: ticks, mosquitoes, mites, lice, fleas Trichomonas vaginalis is a protozoan that infects the vagina

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which pathogen is an intracellular parasite consisting of a protein coat surrounding a nucleic acid? a.Prion b.Virus c.Bacteria d.Protozoa

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.Virus Rationale: Viruses have no organized cellular structure like bacteria and protozoa. Viruses can only replicate inside another cell. Prions cannot reproduce at all.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion How many ways could you have become infected today? How could you have experienced: –Direct contact with a pathogen? –Ingestion of a pathogen? –Inhalation of a pathogen? –Contact with a zoonosis? –Contact with a nosocomial infection? –Contact with a fomite?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Symptomatology infection inflammatory and immune responses attack infective agent SPECIFIC: signs and symptoms of local damage and inflammation NONSPECIFIC: signs and symptoms of systemic inflammation

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario A 5-year-old boy has an ear infection. He complains of pain in his ear and cannot hear on that side When you look into his ear, you see a red, bulging eardrum with pus behind it He has a fever, sweats, and complains of joint aches Blood tests show an elevated white blood cell count Question: Use the model of symptomatology to classify these signs and symptoms

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion What stage of an infection are you in? How many people in the class are in: –The incubation stage? –The prodromal stage? –The acute stage? –The convalescent stage? –The resolution stage? How can you tell?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Terms for Infection and Damage -itis means inflammation –May or may not be due to infection -emia means in the blood Sepsis or septicemia means bacterial toxins in the blood

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Virulence Factors Make an infection more likely to cause disease –Toxins: exotoxins and endotoxins –Adhesion factors help infective organism stick to the body –Evasive factors help keep immune system from killing infective agent

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. Certain bacterial cells release proteins called endotoxins during growth.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: Exotoxins are proteins; endotoxins contain no protein (they are composed of lipids and polysaccharides). Endotoxins are not released during bacterial cell growth.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario A woman’s stomach contained the bacterium Helicobacter Pylori. For many years, the woman was healthy Then she took on a new, stressful job; moved; and began to care for her elderly parents A few months later, she began to suffer stomach pains and vomited blood She was diagnosed with a bleeding ulcer

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario (cont.) Question: How does each of these terms relate to her case? –Portal of entry –Site-specific pathogen –Opportunistic pathogen –Evasive factors –Invasive factors

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Serology After exposure to an infectious agent, the body produces antibodies Antibody titer rises IgM: rises during the acute phase, then falls IgG: remains elevated after the acute phase

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario A month-old baby is ill: Serum analysis shows that she has IgG against HIV and IgM against Pneumocystis Question: What inferences can you make?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins We have more drugs to kill bacteria than to kill viruses, and more drugs to kill viruses than to eradicate prions Question: Why has it been easier to develop antibacterial drugs than antiviral drugs? Why not use antibacterial or antiviral drugs to destroy prions? Antibacterial and Antiviral Drugs

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Antibiotics Kill Bacteria By Targeting: Cell wall synthesis Protein synthesis Nucleic acid synthesis Bacterial metabolism Bacteria Fight Back By: Inactivating antibiotics Changing antibiotic binding sites Using different metabolic pathways Changing their walls to keep antibiotics out

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Antiviral Agents Kill Viruses By: Blocking viral RNA or DNA synthesis Blocking viral binding to cells Blocking production of the protein coats (capsids) of new viruses

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question What type of infections are treated based upon the results of a Gram stain? a.Fungal b.Viral c.Bacterial d.Parasitic

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Bacterial Rationale: Bacteria are commonly classified according to Gram stain. Gram-positive and gram-negative organisms are treated with specific antibiotics that target that type of infection. For example, penicillin targets gram-positive organisms. If the cause of bacterial infection is unknown, broad-spectrum antibiotics may be prescribed, targeting both gram- positive and gram-negative organisms.