Infectious diseases - Jill Raymond PDF

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Jill Raymond...

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Infectious Disease Many infectious disease are preventable via vaccination So far, we have documented 1407 microbes that cause diseases in humans 538/1407 are bacteria (antibiotics) 317/1407 are fungi (anti-fungal meds) 287/1407 helminthes (de-wormers) 208/1407 Viruses (very few anti-viral meds) 57/1407 protozoa (parasites) (anti-protozoa meds) Infectious disease is still a major cause of disability and death worldwide Developed countries 1/10 deaths Developed countries 6/10 deaths Poverty, poor nutrient, lack of access to healthcare, overcrowding, and uncontrolled chronic diseases… 90% of infectious deaths worldwide are caused by just a few diseases… Terminology Infection = invasion or colonization of the body by a pathogenic microbe. Disease = any change from a state of health Acute disease = develops rapidly but lasts a short time  Common cold Chronic Diseases = develops slowly and continual or recurrent  Hepatitis C Latent disease = pathogen remains inactive for a period of time  Varicella –zoster virus (shingles) communicable disease = that can be spread from host to host  directly, indirectly  cold, Flu Contagious Disease = disease that easily spread from host to host  measles, chicken pox non-communicable disease = disease that cannot be spread host to host  heart disease, diabetes Epidemiology The study of where and when disease occurs Incidence = the number of new cases of a disease in a given population or area Prevalence = the total number of cases of a disease in a given population or area Endemic disease = disease that occurs at a relatedly stable frequency within a given population or area Epidemic disease = disease that occurs at a greater than normal frequency for a given population or area. Pandemic = Epidemic occurring simultaneously on more than one continent Sporadic disease = only a few cases occur Etiology Cause of an infectious disease (microbe!) Koch’s postulates

1877; use to determine the cause of an infectious disease 1. The suspected pathogen must be found in every case of the disease. 2. Isolate the pathogen and grow it in pure culture in the lab 3. Inoculate pure culture into healthy host must get same disease 4. Re-isolate the pathogen and compare it to the pure culture they must be identical

*** List Koch’s postulates*** Signs = objective manifestation of disease It can be observed/measured by others  Fever, vomiting, rash, swelling… Symptoms = subjective characteristics of disease Felt by patient  dizzy, fatigue, nausea, headache, pain Pathogenicity = ability of a microbe to cause disease Virulence = degree of pathogenicity Virulence = (pathogenicity) of a disease causing microbe Extracellular enzymes Produced by some bacterium + secreted by bacterium out into their environment Examples of extracellular enzymes: hemolysins = lyse red blood cells to access iron (blood agar) Hyaluronidase = invade deeper into tissue… Coagulase = blood clot formation Kinases = blood clot busters Collagenases = break down collagen Leukocidins = decrease phagocytosis (cellular eating by white blood cells) Toxins Chemicals that harm host tissues or trigger host immune responses that then causes damage in the host. 2 types of toxins Exotoxins Some gram-positive gram-negative can produce these Exported throughout the body via circulatory system Gene for exotoxin production would be on a plasmid Different types of exotoxins: Cytotoxins = kill the host cell or interfere host cell function  Diphtheria Neurotoxins = interfere with nerve function (synapse)  Rigid (tetanus)/ Flaccid paralysis (botulism) Endotoxins Part of outer membrane of Gram – bacteria Outer membrane made of LPS (Lipid A) Gram – bacteria die; Release Lipid A Causes: fever, inflammation, diarrhea, hemorrhage, clots, shock, death Antiphagocytic Factors Decrease phagocytosis (cellular eating)

Glycocalyx (slime layer/capsule) (loose/tight) Slippery; decrease phagocytosis Prevents fusion with lysosome Relationship between Microbe + Host Symbiosis = 2 different organisms living together 3 types of symbiosis: Mutualism = both organisms benefit  GI microbes, vaginal flora Commensalism = one organism benefits the other organism does not benefit and is not harmed  Staphylococcus Epidermis Parasitism = one organism benefits (parasite) the other organism is harmed (host) Reservoirs of infectious disease Sites where a pathogen is maintained as a source of an infectious disease 1. Animal reservoirs = zoonotic disease (animal > humans) Contact with waste of infected animal Eating infected animal Bite from infected animal 2. Human carriers = asymptomatic carriers of the infectious disease 3. Non-living reservoirs = water, soil, and food Infectious dose How many of a pathogen do you have to get to get the disease? Varies… Q fever = 1 bacterium TB; Giardia = 10 bacterium Gonorrhea = 1000 bacterium Typhoid fever = 10000 bacterium Cholera = 1000000 bacterium Portals of entry Reservoirs host 1. Broken skin = unbroken skin is an excellent barrier  wash wound with soap and water  keep wound clean(H2O2) dry 2. Mucous membrane = line of body cavities opened to the exterior  GI tract, respiratory tract, urinary tract, reproductive tract, conjunctiva 3. Placenta = connection between mom and fetus  2% pregnancies  toxoplasma gondii  Treponema pallidum (syphilis) 4. Parenteral Route = Means by which a port of entry is circumvented  deposit the pathogen directly into tissue  needle, nail, insect bite

**** LIST portal of entry*** Once you enter- hang on! Giardia = suction cup

Helminthes (suckers, hooks) Virus bind to receptor on host cell Glycocalyx (slime layer/ capsule) Fimbriae Biofilm Forms when bacteria adhere to surface in an aqueous environment Bacteria excrete this sticky, glue-like substance; helps anchor them in place Dental plaque is an example of a biofilm Most research in about last 20 years About 65% of infections in the human body are biofilms UTI, Ear infections, Prostatitis, endocarditis (valves) In biofilm bacteria Quorum sensing cell to cell signaling Conjugation Difficult for immune system to fight because are lots of bacteria, different genus or species, thick Portals of Exit Usually exit same way they entered… Via secretions… Respiratory tract…exit via cough/sneeze GI tract…poop Reproductive tract…Semen/vaginal secretions Stages of infectious disease 1. Incubation Period Infection to first signs + symptoms Length depends on virulence of pathogen  Initial dose (number of pathogens)  State of host immune system  Site of infection  Quickly the pathogen divides 2. Prodromal period Not all infectious disease has this stage Short time of general signs and symptoms (fatigue, muscle aches, body aches) 3. Illness Most severe stage of an infectious disease Signs and symptoms are the most evident 4. Decline Signs and symptoms are declining 5. Convalescence Patient has recovered from their illness Signs and symptoms are gone ***Likely contagious at every stage! Modes of transmission of Infectious Disease Reservoir of infectious Disease or Portal of Exit  Portal of Entry of a new host 3 modes of Transmission

1. Contact 2. Vehicle 3. Vector Contact Transmission  Direct contact Transmission Person to person body contact between hosts Ex. Touch, kiss, sexually intercourse  Indirect contact transmission Person to person transmission via a fomite (inanimate object) Ex. Kleenex, toothbrush, glass, money  Droplet Transmission Respiratory droplets (cough/sneeze) Enter New host via eye/nose/mouth Large drops; drop quickly Travel less than three feet (up to about feet) Can’t survive outside the body Ex. Cold, flu, measles Vehicle Transmission  Airborne Transmission Small droplets Travel great distances Can survive outside of the body for extended periods of time Ex. Cough, sneeze, exhale, TB  Waterborne Transmission Fecal-oral via Contaminated water Infected person that shedding pathogen in feces  Foodborne Transmission Poorly processed food, poorly refrigerated/maintained food, poorly cooked food (Thanksgiving)  Body fluid Transmission Blood, urine, saliva Vector Transmission  Biological Vector Vector actively participates in the life cycle of the pathogen Mosquito/Plasmodium parasite  Mechanical vector Passively carries pathogen Flies, roaches (20 different pathogens on each foot) Healthcare Acquired Infections Aka Nosocomial infections Infections acquired from a healthcare setting 1 in 25 patients; 40,000 patients per day in US, 205 death per day in US Cost US $5 billion per year Use of indwelling devices, surgical procedures, injections, contamination of healthcare environment, Transmission between patients/worker, patients/patients, Patient/visitors

Overuse and inappropriate use of antibiotics  Common sites of Healthcare Acquired infections (HAI) Catheter acquired UTI (most common) Central-line associated blood stream infection Pneumonia Clostridium difficile  Healthcare facilities are a major reservoir of pathogens Weak, immunocompromised patients Handwashing with soap and water decrease transmission by 50%! Good Housekeeping  Personal protective equipment (PPE) Disposable, Handle and dispose carefully, Isolation of patients Educate patients, staff, and visitors Use antibiotics appropriately Surveillance of Healthcare Acquired Infections (HAI) Occupational exposure to blood borne pathogens OSHA estimates that 8 million workers in the US are at risk of Occupational exposure to blood borne pathogens  Blood borne Pathogens Hepatitis B Virus  HBV Hepatitis C Virus  HCV Human Immunodeficiency virus  HIV Needle sticks; OSHA estimates 800,000 a year in US half are reported (400,000) HBV Transmission from a single infected needle stick HBV has a 6-30% transmission rate  Vaccine!  Not been vaccinated; HBV immunoglobulin (antibodies) 90% effective in preventing Transmission HCV Transmission from a single infected needle stick HCV has a 1.8% Transmission rate  NO vaccine  NO HCV immunoglobulin  HCV anti-viral med ($26,000) (30 days) HIV Transmission from a single infected needle stick HIV has a 0.3% Transmission rate  NO Vaccine  NO HIV immunoglobulin  anti-viral meds right away...