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Microbiology AN INTRODUCTION B.E Pruitt & Jane J. Stein Chapter 14 Principles of Disease and Epidemiology Principles of Disease and Epidemiology • Pathology • Disease Study of disease in a state of not being healthy, change from health • Pathogens disease causing organisms • Etiology Study of the cause of a disease • Pathogenesis Development of disease • Infection Colonization or invasion of pathogens, may be microbes in the wrong place (E. coli in the urinary tract) Normal Microbiota (Flora) and the Host • Normal Flora - the normal bacteria in you and on you • Your microbiome • You have 1013 eukaryotic cells and 1014 prokaryotic cells • Most of our gut enzymes from gut microbiome • Within 8 - 12 hours of life you are colonized by normal flora (microbiota). • Breast feeding versus bottle - different organisms • Transient microbiota may be present for days, weeks, or months • Microbial antagonism • Normal microbiota overwhelm pathogens - no place for them to colonize • Intestines and vagina - excessive antibiotics disrupts balance • Vagina normally pH ~ 4 with Lactobacillus spp without can lead to Candida infections • Symbiosis is the relationship between normal microbiota and the host Symbiosis and the Host: • In commensalism, one organism is benefited and the other is unaffected. • In mutualism, both organisms benefit. • Be able to give a few examples of mutualistic bacteria • In parasitism, one organism is benefited at the expense of the other. • Some normal microbiota are opportunistic pathogens. • E. coli and urinary tract • Pneumocystis carinii and respiratory system • Streptococcus pneumoniae and pneumonia Symbiosis Normal Microbiota and the Host: • Locations of normal microbiota (flora) on and in the human body Figure 14.2 Normal Microbiota (Flora) and the Host: • Microbial antagonism is competition between microbes. • Normal microbiota protect the host by: • occupying niches that pathogens might occupy • producing acids • producing bacteriocins • Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect. • Lactobacillus spp Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.1 Figure 14.3 Koch’s Postulates: Understanding Disease. 1 Microorganisms are isolated 3 The microorganisms 2a The microorganisms are from a diseased or dead animal. are injected into a healthy laboratory animal. grown in pure culture. Colony 2b The microorganisms 4 Disease is reproduced are identified. in a laboratory animal. 5a The microorganisms are isolated from this animal and grown in pure culture. 5b Microorganisms are identified. The microorganism from the diseased host caused the same disease in a laboratory host. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. • Problems with Koch’s Postulates: • Not all diseases have bacterial etiologies • Genetic • Degenerative • Congenital • Exceptions • Not culturable • Treponema / Rickettsia / Chlamydia / viruses • Some pathogens cause many different diseases Figure 14.3.2 Classifying Infectious Diseases • Symptom A change in body function that is felt by a patient as a result of disease • Sign A change in a body that can be measured or observed as a result of disease. • Syndrome A specific group of signs and symptoms that accompany a disease. Classifying Infectious Diseases Diseases may be grouped by how spread • Communicable disease A disease that is spread from one host to another. • Contagious disease A disease that is easily spread from one host to another. • Noncommunicable disease A disease that is not transmitted from one host to another. Example: Clostridium tetani By occurrence of Disease • Incidence Fraction of a population that contracts a disease during a specific time. • Prevalence Fraction of a population having a specific disease at a given time. • Sporadic disease Disease that occurs occasionally in a population. • Endemic disease Disease constantly present in a population. • Epidemic disease Disease acquired by many hosts in a given area in a short time. Worldwide epidemic. • Pandemic disease Herd Immunity Herd immunity Immunity in most of a population. By Severity or Duration of a Disease • Acute disease Symptoms develop rapidly • Chronic disease Disease develops slowly • Subacute disease Symptoms between acute and chronic • Latent disease Disease with a period of no symptoms when the patient is inactive Shingles By Extent of Host Involvement • Local infection Pathogens limited to a small area of the body • Systemic infection An infection throughout the body • Focal infection A specific tissue type • Bacteremia Bacteria in the blood • Septicemia Growth of bacteria in the blood • Toxemia Toxins in the blood • Viremia Viruses in the blood Extent of Host Involvement • Primary infection Acute infection that causes the initial illness • Secondary infection Opportunistic infection after a primary (predisposing) infection Pneumocystis pneumonia and AIDS • Subclinical disease No noticeable signs or symptoms (inapparent infection) Hepatitis / Typhoid Mary / Polio Predisposing Factors Make the body more susceptible to disease • Inherited traits such as the sickle-cell gene • Climate and weather • Fatigue and Stress • Age • Lifestyle • Chemotherapy • Gender • urethra shorter in females therefore more UTI’s Development of Disease Stages of Disease • Incubation infection up to first symptoms may or may not be variable • Prodromal short period of early mild symptoms -- malaise • Period of Illness overt signs -- fever and chills, swollen lymph nodes, GI disturbance increase in WBC’s • Period of Decline signs and symptoms subside - susceptible to 2˚ infections • Period of Convalescence regain strength and recovery BUT may be a reservoir The Stages of a Disease Figure 14.5 Time Period of convalescence Prodromal period (mild signs or symptoms) Incubation period (no signs or symptoms) Number of microbes Figure 14.5 The stages of a disease. Period of illness Period of decline Most severe signs and symptoms Signs and symptoms Reservoirs of Infection • Reservoirs of infection are continual sources of infection. • Human — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases. • Carriers may be in pre-symptom stage or recovery of a disease - no symptoms • Animal — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Plague / psittacosis / swine flu / bird flu • Nonliving — Botulism, tetanus • Soil • Water - rivers, lakes, snow, oceans and laundry water Anthroponotic diseases (anthroponosis) • Animals contract from humans • There are many more zoonotic diseases (animal to human) than anthroponotic diseases involving animals (human to animal), but a few examples of human conditions that animals may contract include the following: • Avian influenza- human to bird, (or vice versa) • Strep throat- human to dogs (or vice versa) • Human influenza- ferrets • Tuberculosis-human to dogs, (rarely) • Ringworm- (human to animal and vice versa) Transmission of Disease • Three main routes 1. Contact - Direct or indirect 2. Vehicles - inanimate objects - e.g. waterways, air, food or drugs 3. Vectors - arthropods 1. Contact • Direct Requires close association between infected and susceptible host • Indirect Spread by fomites (inanimate objects) glass, toothbrush or clothing • Droplet Transmission via airborne droplets Transmission of Disease Figure 14.6a & 8 Transmission of Disease • 2. Vehicle Transmission by an inanimate reservoir (food, water) Shigella, cholera, airborne on dust aerosol >3’, tapeworm Staphylococci, Streptococci, tuberculosis, fungal spores -histoplasmosis, coccidiodomycosis • 3. Vectors Arthropods, especially fleas, ticks, and mosquitoes • Mechanical Arthropod carries pathogen on feet • Biological Pathogen reproduces in vector and bites host. Dengue fever, Yellow fever, Malaria, encephalitis, plague, Lyme disease RMSF Transmission of Disease Figure 14.6b, c Figure 14.7 Vehicle transmission. Water Food Air Figure 14.8 Mechanical transmission. Figure 12.31 Mosquito. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay • 5-15% of all hospital patients acquire nosocomial infections During the study period, 97 out of 333 patients acquired nosocomial infection. The frequency of nosocomial infection was 29.13%. Respiratory tract infection was seen in 29 (30.1%), urinary tract infection in 38 (39.1%) and blood stream infection in 23 (23.7%) patients. Other infections we identified were skin, soft tissue, wound and gastrointestinal tract infections.* http://www.ncbi.nlm.nih.gov/pubmed/19999200 Figure 14.7, 9 Nosocomial Hospital acquired • 5 - 15% acquire >20,000 per year die • why? • a) microbes in environment -- (lots of sick people) • b) already sick or wounded -- compromised host • c) close to people - chain of transmission • Also resistant strains - E. coli, Pseudomonas, MRSA, VRE, C. difficile enterics like Serratia • Control by aseptic techniques • Antibiotic abuse Common Causes of Nosocomial Infections Percentage of Total Infections Percentage Resistant to Antibiotics Coagulase-negative staphylococci S. aureus 15% 89% 15% 80% Enterococcus 10% 4–71% 15–25% 3–32% 13% Not reported Gram-negative rods C. difficile Relative frequency of nosocomial infections Figure 14.10 Common Causes of Nosocomial Infections Percentage of nosocomial infections Percentage resistant to antibiotics Gram + cocci 34% 28%-87% Streptoccous and Staphylococcus and VRE (Vancomycin resistant Enterococci) Gram – rods 32% 3-34% Enterics and Pseduomonas Clostridium difficile 17% Fungi 10% Clinical Focus 14.1 Nosocomial Infections Nosocomial • Hospital Associated infections Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors: • Evolution of new strains • V. cholerae O139 • Inappropriate use of antibiotics and pesticides • Antibiotic resistant strains • Changes in weather patterns • Hantavirus • Spread of human populations and travel • Ebola? Emerging Infectious Diseases • Contributing factors: • Modern transportation • West Nile virus • Ecological disaster, war, expanding human settlement • Coccidioidomycosis • Animal control measures • Lyme disease • Public Health failure • Diphtheria Epidemiology • The study of where and when diseases occur Figure 14.11 Figure 14.10 a & b Epidemiological graphs. 40,000 35,000 Number of reported cases 30,000 25,000 20,000 15,000 10,000 5,000 0 1999 2000 (a) Lyme disease cases, 1999–2010 2001 2002 2003 2004 Apr May Jun 2005 2006 2007 2008 2009 600 500 Reported cases per 100,000 people 400 300 200 100 0 Jan (b) Feb Lyme disease by month, 2009 Mar Jul Month Aug Sep Oct Nov Dec 2010 Figure 14.10c Epidemiological graphs. 120 Reported cases per 100,000 people 100 80 60 40 20 0 1948 1958 1968 1978 1988 Year Reported tuberculosis cases, 1948–2010 1998 2008 Epidemiology John Snow 1848-1849 Mapped the occurrence of cholera in London Ignaz Semmelweis 1846-1848 Florence Nightingale 1858 Showed the hand washing decreased the incidence of puerperal fever Showed that improved sanitation decreased the incidence of epidemic typhus • Descriptive Collection and analysis of data regarding occurrence of disease Snow • Analytical Comparison of a diseased group and a healthy group Nightingale • Experimental Study of a disease using controlled experiments Semmelweis • Case reporting Health care workers report specified John Snow disease to local, state, and national offices Physicians are required to report occurrence • Nationally Notifiable Diseases Table 14.7 Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the U.S. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate = number of people affected/total population in a given time period Mortality rate - number of deaths from a disease/total population in a given time