Microbiology - Week 6 - Lecture 2 - Infection and Epidemiology 2023 PDF

INFECTION AND EPIDEMIOLOGY BMS 100 Week 6 SYMBIOTIC RELATIONSHIPS BETWEEN MICROBES AND THEIR HOSTS Symbiosis – when individuals of two or more species live in direct contact with one Mutualism (+/+): Both individuals obtain a net benefit from the interaction Commensalism (+/0): Only one individual b...

INFECTION AND EPIDEMIOLOGY BMS 100 Week 6 SYMBIOTIC RELATIONSHIPS BETWEEN MICROBES AND THEIR HOSTS Symbiosis – when individuals of two or more species live in direct contact with one Mutualism (+/+): Both individuals obtain a net benefit from the interaction Commensalism (+/0): Only one individual benefits, the other receives a neutral result Parasitism (+/-): One individual benefits, the other receives a net loss. MUTUALISM Clownfish and sea anemones Termites and gut protists Humans and Honeyguides Ants in acacia trees COMMENSALISM e.g. – Hitch-hikers e.g. – Grabbing the ‘crumbs’ from bigger animals PARASITISM Parasite derives benefit from host while harming it Same trade-off as viruses ‘face’ If it causes a disease – it’s a pathogen Tapeworm Plasmodium – ‘sleeping sickness’ HOW NORMAL MICROBIOTA BECOME OPPORTUNISTIC PATHOGENS Introduction of a member of the normal microbiota into an unusual site in the body or changes to normal microbiota populations. e.g. E. coli are mutualistic in the colon, Can cause significant disease elsewhere HOW NORMAL MICROBIOTA BECOME OPPORTUNISTIC PATHOGENS Immune suppression WHERE CAN HUMANS GET DISEASES? 1. Animal Reservoirs Transmission of pathogen from animal (wild or domestic) to humans zoonoses e.g., Lyme Disease, e.g., Salmonellosis e.g., Rabies WHERE CAN HUMANS GET DISEASES? 2. Human Carriers Humans giving disease to other humans Individuals that spread disease: carriers Big deal: asymptomatic carriers E.g., tuberculosis, syphilis, AIDS e.g., typhoid fever 300 cases in Croyden, England (1937) Originated from aymptomatic carrier WHERE CAN HUMANS GET DISEASES? 3. Non-Living Reservoirs Soil, water, food Often holding dispersal stages of pathogens Solutions: boiling water, cooking food Much more common in parts of the world with poor sanitation methods THE MOVEMENT OF MICROBES INTO HOSTS: CONTAMINATION & INFECTION Contamination: the presence of microbes in or on the body Infection: successful invasion of the body following contamination PORTALS OF ENTRY 3 major points: - Skin - Mucous Membranes - Placental - Parenteral Ear Broken skin Insect bite Conjunctiva of eye Nose Mouth Placenta Vagina Anus In males: Penis Urethra THE SKIN AS A MICROBIOTIC BARRIER Sebaceous (oil) gland Pore of sweat duct Epidermis Dermis Hair Blood capillaries Nerve fiber Nerve ending Vein Artery Sweat gland Fat cells Hair follicle MUCOUS MEMBRANES: THE PRIMARY PORTAL OF ENTRY Most common portals of entry Lining every body cavity exposed to the outside world Epithelium Conjuctiva THE PLACENTA AS A PORTAL OF ENTRY THE PARENTERAL ROUTE … not a portal of entry. Direct depositing of pathogen into tissues beneath the skin or mucous membranes Can occur through punctures (nails, thorns, needles) THE ROLE OF ADHESION IN INFECTION Adhesion factors Adhesins Recall: Biofilms TERMINOLOGY Disease (Morbidity): when infections multiply and in doing so, affect body function; any change from a state of health Symptoms: Subjective characteristics of a disease (only the patient can feel them) Signs: objective, measurable characteristics of a disease Syndrome: a group of symptoms that collectively characterizes a specific disease PATHOGENICITY AND VIRULENCE Pathogenicity: The ability to cause disease Virulence: the degree of pathogenicity Determined by virulence factors More virulent Francisella tularensis (rabbit fever) Yersinia pestis (plague) Bordetella pertussis (whooping cough) Pseudomonas aeruginosa (infections of burns) Clostridium difficile (antibiotic-induced colitis) Candida albicans (vaginitis, thrush) Lactobacilli, diphtheroids Less virulent VIRULENCE FACTORS: 1. Enzymes Secreted proteins that help pathogen dissolve chemicals or structures of the body Hyaluronidase and collagenase Bacterium Coagulase and kinase Bacterium Hyaluronidase Coagulase Clot Clotting protein Epithelial cells Kinase Collagenase Collagen layer Invasive bacteria reach epithelial surface. Bacteria produce hyaluronidase and collagenase. Extracellular enzymes Bacteria invade deeper tissues. Bacteria produce coagulase. Clot forms. Bacteria later produce kinase, dissolving clot and releasing bacteria. VIRULENCE FACTORS: 2. Toxins Chemicals that harm tissues or trigger host immune responses and cause damage. Toxemia: when toxins enter blood stream and affect many sites in the body Exotoxin Bacterium Endotoxin Exotoxin Phagocyte Phagocytized Gram- bacteria Exocytosis Endotoxin Dead Grambacteria Blood vessel Bacteria secrete exotoxins, in this case a cytotoxin. Cytotoxin kills host’s cells. Toxins Dead Gram-negative bacteria release endotoxin (lipid A), which induces effects such as fever, inflammation, diaarrhea, shock, and blood coagulation. VIRULENCE FACTORS: 3. Antiphagocytic Factors Phagocytosis – when immune system cells ‘eat’ the pathogen Phagocytosis blocked by capsule Capsule around bacterium Incomplete phagocytosis Capsule around bacterium Phagocytic vesicle Phagocyte Antiphagocytic factors Lysosome Bacteria reproduce Number of microorganisms or intensity of signs or symptoms STAGES OF INFECTIOUS DISEASES Incubation period (no signs or symptoms) Prodromal period (vague, general symptoms) Illness (most severe signs and symptoms) Time Decline (declining signs and symptoms) Convalescence (no signs or symptoms) Eyes (tears) Ear (earwax) Nose (secretions) Broken skin (blood) PORTALS OF EXIT Mouth (saliva, sputum) Skin (flakes) In females: Mammary glands (milk, secretions) Vagina (secretions, blood) Anus (feces) Seminal vesicles (semen and lubricating secretions) Urethra (urine) MODES OF INFECTIOUS DISEASE TRANSMISSION Direct Contact Transmission Indirect Contact Transmission – through fomites (inanimate objects that carry pathogens) Droplet Transmission MODES OF INFECTIOUS DISEASE TRANSMISSION Vehicle transmission Airborne transmission Waterborne transmission Foodborne transmission Bodily fluid transmission MODES OF INFECTIOUS DISEASE TRANSMISSION Vector transmission Biological Vectors Mechanical Vectors CLASSIFICATION OF INFECTIOUS DISEASE Acute Disease: develops rapidly, lasts for a short period of time (e.g., cold) Chronic Disease: develops slowly (less severe symptoms), but are continual or recurrent. (e.g. Hep C, Tuberculosis) Subacute Disease: Durations and severities in between acute and chronic. Latent Disease: pathogen remains inactive for a long period of time (e.g., herpes) CLASSIFICATION OF INFECTIOUS DISEASE Communicable Disease: when an infectious disease comes from another infective host (directly or indirectly) Contagious Disease: A communicable disease that is easily transmitted between hosts (e.g. chickenpox) Non-communicable Disease: arise outside of hosts or from normal microbiota (e.g., E. coli based disease, tetanus, acne, tooth decay) EPIDEMIOLOGY The study of where and when diseases occur, and how they spread within postulations. Not limited to disease – not used to consider injuries and deaths related to automobiles, fireworks, cigarette smoking, etc… Incidence (thousands) Incidence Year Prevalence Prevalence (thousands) INCIDENCE AND PREVALENCE OF AIDS AMONG US ADULTS REPRESENTATIVE EPIDEMIOLOGICAL DATA: INCIDENCE BY GEOGRAPHY 501 8 11 61 901 164 44 332 8 5 122 269 2853 577 188 573 569 162 82 1188 1591 255 131 671 2859 HI 38 437 530 26 460 400 354 144 235 229 100 7 1789 667 300 339 1520 VT NH MA CT RI NJ DE MD DC 4 7 283 69 35 508 25 202 80 REPRESENTATIVE EPIDEMIOLOGICAL DATA: INCIDENCE BY MONTH 2656 2490 Number of cases of shigellosis 2478 2257 1820 1250 2306 1931 1719 1369 821 2000 1825 Cases/million REPRESENTATIVE EPIDEMIOLOGICAL DATA: INCIDENCE BY AGE Age group (years) DESCRIBING DISEASE OCCURRENCES Number of cases per 100,000 individuals EPIDEMICS ARE DETERMINED BY COMPARISON OF ACTUAL CASES WITH EXPECTED CASES Disease A Epidemic 2 Epidemic 1 Disease B Time Expected number of cases Actual number of cases Disease A Actual number of cases Disease B HOSPITAL EPIDEMIOLOGY: NOSCOMIAL INFECTIONS Infections acquired by patients or health care workers when they are in health care facilities 10% of Americans get these each year Immunocompromised Presence of patients microorganisms in hospital environment Nosocomial infection Transmission of pathogens between staff and patients and among patients