Infectious Disease PDF

Infectious Disease David Wagner, MD Associate Professor Department of Pathology at UNMC Email: [email protected] No financial interests to disclose  Define “opportunistic infection” and list clinical conditions in which they can occur  Describe host physical barriers...

Infectious Disease David Wagner, MD Associate Professor Department of Pathology at UNMC Email: [email protected] No financial interests to disclose  Define “opportunistic infection” and list clinical conditions in which they can occur  Describe host physical barriers to infection and how their effectiveness can be diminished  List ways in which infectious organisms spread through the body  List methods of transmission of infectious organisms from one host to another and give examples  List major categories of infectious organisms and give examples of diseases that they cause  Explain how infectious agents cause disease and how the host responds to these mechanisms  List ways that infectious organisms evade host immune defenses  Describe laboratory techniques used to help diagnose infectious diseases  Minor cause of death in developed nations  Unless in an epidemic/pandemic, i.e., COVID ◦ Public health measures ◦ Antibiotics ◦ Vaccination ◦ Nutrition ◦ Seen mostly in immunosuppressed patients  Still major cause of mortality in underdeveloped countries  Definition: Infection by an organism that would not be pathogenic in someone with a normal immune system.  Clinical setting: immunocompromised individuals ◦ Congenital immunodeficiency ◦ Drug-induced immunosuppression  Transplant patients  Cancer patients  Autoimmune disease ◦ HIV/AIDS Categories of infectious agents Prion (PrP). Abnormal forms of host protein Normally found in neurons Undergoes a conformational change with resistance to proteases which promotes conversion of normal to abnormal proteins Spread through instruments, organ donation, autopsy, surgery or blood transfusion Virus Intracellular parasite that depend on host energy/cell organelles for replication Bacteria Gram positive – thick wall that retains crystal violet Gram negative – thin cell wall Mycoplasma – no cell wall Parasite – sexual (host) and asexual reproduction (vector) Fungi Thick cell walls (chitin); yeast, hyphae or both Protozoa – single cell eukaryocytes Ectoparasites – insects or arachnids that attach to skin  Physical barriers ◦ Intact skin and mucous membranes ◦ Mechanical action--”pushing” microbes out ◦ Cilia in respiratory tract  Microbiologic barriers ◦ Normal flora that inhibit pathogen growth by competition ◦ Example: yeast infection after antibiotics  Chemical and immunologic barriers  Acid in stomach  Immune system  Skin  Respiratory tract  Urinary tract  Gastrointestinal tract  Trauma  INTACT skin is a very effective barrier to infection.  Factors predisposing to infection: ◦ Wet skin ◦ Disrupted skin  Injury/animal bites  Iatrogenic disruption (needles, catheters, surgical incisions) ◦ Damaged skin (skin disease, burns)  Mucociliary action ◦ Pathogens “swept out” of lungs and swallowed ◦ Inhibitors:  Lung disease  Tobacco smoke  Virulent bacteria and viruses  Phagocytosis by lung macrophages ◦ Inhibited by mycobacteria  Normal urinary flow washes pathogens out ◦ Inhibited by obstruction of urinary flow ◦ Diminished by shorter urethra in women  Normal vaginal bacteria inhibit pathogen growth ◦ Inhibited by indiscriminate antibiotic therapy  Defenses may be escaped by virulent pathogens  Chemical--gastric acid, bile salts, pancreatic enzymes  Immunologic--Immunoglobulin A (IgA) secreted by intestinal mucosa  Microbiologic--presence of normal gut flora  Local spread--along tissue planes ◦ Streptococcal cellulitis ◦ Staphylococcal abscesses  Lymphatic spread ◦ Swollen lymph nodes in area of infection  Hematogenous spread ◦ through blood, to distant sites throughout body ◦ “septicemia” ◦ Peritoneal spread – perforation;  Neural spread ◦ A few viruses (rabies, varicella-zoster)  Person-to-person transmission ◦ Fecal-oral route (hepatitis A, Vibrio cholerae) ◦ Respiratory (tuberculosis, legionella) ◦ Bloodborne (hepatitis B and C, HIV) ◦ Sexual (STDs) (Neisseria gonorrheae, Chlamydia)  Vector transmission (malaria, typhus)  Zoonotic transmission (trichinella, rabies)  Smallest of all microorganisms (20-30 nm)  Obligate intracellular parasites ◦ Must use cells to reproduce  Very simple structure ◦ Outer protein coat ◦ Inner nucleic acid (DNA or RNA)  Herpes virus (acyclovir, valacyclovir)  Varicella-Zoster virus (chickenpox, shingles)  Rhinovirus (common cold)  Hepatitis viruses (interferon)  Epstein-Barr virus (mononucleosis)  Influenza virus (amantadine, rimantidine)  Cytomegalovirus (CMV) (gancyclovir)  Human Papillomavirus (HPV) (warts, cervical cancer)  Virus-like nucleic acid particles  Invade bacteria, increase bacterial virulence (infectiveness) by enabling: ◦ Toxin production ◦ Antibiotic resistance  Vancomycin-resistant enterococcus (VRE)  Methicillin-resistant Staphylococcus Aureus (MRSA)  Infective protein particles ◦ The only infectious agents that do not contain nucleic acid ◦ Old designation-”slow viruses”  CNS degenerative diseases ◦ Creutzfeldt-Jakob Disease (CJD) ◦ Bovine spongioform encephalopathy (BSE)  “mad cow disease”  Smallest, simplest organisms that are capable of independent existence  Prokaryotic ◦ Cell envelope (cell wall and/or cell membrane) ◦ No nucleus ◦ Size: 0.1-10 microns ◦ Universally susceptible to antibiotics  Infectious organisms that have some properties of bacteria, lack others.  Smaller than other bacteria (