Chapter 13 Human Host Topics • Acquire resident flora - Human Host • New born exposure - how do we - Progress of an Infection acquire our normal flora? - Epidemiology Acquire resident flora Acquire resident flora • The human body supports a wide range • Beneficial outcome of habitats – Provide nutrients (Vit K) – temperature, pH, nutrient, oxygen tension – Microbial antagonism • Wide range of microbes can inhabit – Development of immune system • Resident flora or microflora • Adverse effects – Microbes (from bacteria to sometimes – Escape immune system viruses) that inhabit but do not harm the – Multiply and disrupt tissue oportunistic! host Association between microbes and humans 1 New born exposure Progress of an Infection • Mother’s birth canal • Pathogenicity • Mother’s breast milk • Portals of entry • Bottle-feeding • Attachment • People • Surviving host defenses • Causing disease • Process of infections and disease • Portals of exit Pathogens : any organism Contamination : microorganisms capable of causing disease present on or in host Infection : multiplication of Pathogenicity : capacity to microorganisms on or in hosts produce disease Disease : disturbance in health status of host Virulence : degree or intensity of disease True pathogen Opportunistic pathogen • Cause disease in immune • Cause disease in compromised host healthy individuals • Gain access (injury) to sterile • Associated with a specific and regions recognizable disease • Examples: – Pseudomonas aeruginosa • Examples: – Staphylococcus epidermidis – Staphylococcus aureus • – E. coli 2 Opportunistic Infections: pathogens Factors that predispose a person to infections that do not cause disease under normal circumstances but under the right conditions…….can cause disease 1)Failure of host defense mechanisms – immunocompromised patients 2)Organisms at unusual sites in body 3)Disturbances in normal microflora – super-infections Virulence Portals of entry • Virulence factors (Any characteristic or • Most pathogens have specific portals on structure) entry…..and EXIT! – Ability to establish itself in the host – Skin – Gastrointestinal tract – Cause damage – Respiratory tract – Often associated with toxins – Urogenital – Placenta – Inoculum size Skin Gastrointestinal tract • Staphylococcus aureus • Salmonella, Shigella, Vibrio – Boils • Viruses – polio, hepatitis A • Protozoan – Giardia lamblia • Enter via ingestion or the anal route 3 Urogenital Respiratory tract • Numerous sexual transmitted diseases • Streptococcus pneumoniae (STDs) • Virus – human papillomavirus – Sore throat, meningitis – Genital warts • Fungi – Cryptococcus • Protozoan – Trichomonas – pneumonia – trichomoniasis • Bacteria – Neisseria gonorrhoeae – Gonorrhea • Acquire by intercourse or intimate contact Placenta • Some bacteria can penetrate the placenta barrier – Syphilis spirochete • Birth canal – Herpes simplex virus – Remember the STORCH test? 4 Portal of exit Inoculum size • Enables pathogen to spread to other hosts • Infectious dose (ID) – Respiratory – minimum number of bacteria – Salivary required to cause disease – Skin – Fecal – Low ID = high virulence – Urogenital – Blood • Persistence Mechanisms of adhesion by pathogens Attachment • Adhesion –Binding between specific molecules on both the host and pathogen • Structures –Capsules –Pili or fimbriae –Hooks or Teeth!! Causing disease Surviving host defenses • Virulence factors • Anti-phagocytic factors – Exoenzymes – Capsule – Toxins • Prevent phagocytosis – Capsule – Leukocidins • Occurrence of infection • Toxic to phagocytes - WBCs • Signs and symptoms – Some microbes survive inside phagocytes Mycobacterium tuberculosis 5 Bacterial toxins Bacteria produce toxins – • Exotoxins Endotoxins- part of the cell wall of gram-negative bacteria and are released when cells die - LPS – Gram positive and Gram negative cells – Excreted (ex. Hemolysins) Exotoxins - produced by and released from bacteria - botulinum toxin - on the other hand toxins can be – Highly toxic in small amounts used to treat disease - • Endotoxins Called neurotoxins if affect neural tissue – Gram negative cells – Membrane associated Called enterotoxins if affect digestive system • Lipopolysaccharide (LPS) Toxoids are inactivated exotoxins that are – Fever associated inactivated and used to stimulate an immune response - tetanus toxoid Bacteria release substances that damage host tissues Hemolysins - lyse red cells Leukocidins - kill white blood cells Coagulase - accelerates clotting Streptokinase - digests clots and enables bacteria to spread Hyaluronidase - digests hyaluronic acid, a glue- like substance that holds the cells together in tissues and allows the organism to penetrate to deeper tissue Endotoxins 6 Differential characteristics of bacterial Process of infections and exotoxins and endotoxins disease • Stages of Disease – Incubation – Prodromal – Invasive – Decline – Convalescence • Signs and symptoms Stages in course of infectious disease Signs and symptoms • Signs - objective evidence of disease based on observation • Symptoms – subjective evidence of disease based on the patient • Syndrome – sign and symptoms defined a particular disease Persistence • Latency – Viral • Herpes virus – Bacterial • Tuberculosis • Sequelae – long-term damage to tissues or organs Meningitis deafness 7 Epidemiology Epidemiology • The study of disease in populations – Statistics – Prevalence – total numbers of cases in – Strategies the population at any given time – Reservoir – Incidence – Number of new cases over – Carriers a defined period of time – Vectors • Center for Disease Control and – Acquisition and transmission Prevention (CDC) – Nosocomial – Koch’s postulates Statistical data can be represented graphically, and can be used to predict trends Patterns of infectious disease occurrence Reservoirs Two types of vectors • Site at which the organism remains and can potentially infect. • A) Living Reservoirs – Humans Carriers – Animals Zoonosis • B) Non-living Reservoirs – Soil – Water 8 Vectors Nonliving Reservoirs • Biological – Participates in the pathogen’s life cycle • Soil – Infected with the pathogen – Transmit bacteria, protozoa, helminths, – Transmit by bites, defecation fungi • Mechanical – Transmit spores, cysts, ova, larvae – Not part of pathogen’s life cycle • Water – similar to soil – Not infected with the pathogen Acquisition and Kinds of diseases transmission Infectious disease - caused by infectious agent Noninfectious disease - caused by some • Communicable other factor - for example a poison • Non-communicable Communicable or contagious disease - • Patterns of transmission measles, hepatitis, TB Non-communicable disease - cannot be spread from host to host - food poisoning Communicable Non-communicable • Infected host transmits an • Host acquires infectious agent infectious agent to another host – From self (compromised • Receiving host must become individual)- microflora infected – Nonliving reservoir – soil – cannot be spread from host to host!!! 9 Patterns of transmission Horizontal • Horizontal • Disease is spread through a • Vertical population from one infected • Contact - Direct person to another • Indirect Contact – Kissing, sneezing The Anatomy of a Sneeze Vertical • The disease is transmitted from parent to offspring – Ovum, sperm, placenta, milk - remember that milk also provides protection to newborn Indirect Contact Transmission • Food, water, and biological products • Direct - Kissing, sex (blood, serum, tissue), • Fomite (door knobs, toilet seats, etc.) • Droplets - Talking • Air • Vertical – Mother to fetus – Droplet nuclei (dried microscopic residue) – Aerosols (dust or moisture particles) • Vector - 10 Summary of how communicable infectious diseases are acquired Nosocomial infections • Infectious diseases that are acquired or developed from a hospital stay – Urinary tract infections – Respiratory infections – Surgical incisions Over 70% of all Nosocomial Hospital infections are caused by biofilms Most common nosocomial infections Infectious disease is due to host- microbe interaction that results in some type of insult to the host. However, the microbe is usually just trying to perpetuate itself however it can. Many diseases can be prevented. Some diseases can be cured, but not all. Then the host- microbe relationship is successful for the microbe and failing for the host. 11.