Lecture 13: Flora, Diseases, and Infections

(Flora, Diseases, and Infections) Lecture 13 Normal Microbiota · normal flora = normal microbiota · animals and humans are free of microbes in utero, and acquire healthy bacteria after birth · newborns first contact with bacteria is lactobacilli from mothers vagina · with breastfeeding, exposure to environment, foods, and people; organisms are able to colonize our skin and intestinal tracts Transient Microbiota · microorganisms that may be present on body surfaces temporarily and then disappear · removed by handwashing (soap-mechanical scrubbing) · can be either pathogenic (disease causing) or nonpathogenic · do not necessarily cause disease unless special conditions prevail · fun fact: the human body contains equal or more bacterial cells than human cells How Infections Start: · pathogen finds suitable host What does Normal Flora Do? · pathogen penetrates host defenses production of PH substances, and oxygen · pathogen adheres to host cell & tissues · sometimes pathogens can produce disease without penetrating the body defenses by releasing toxins · microbial antagonism: the competition between microbial organisms for nutrients, cellular receptors, ↳ prevents overgrowth of harmful microorganisms ↳ if balance is upset, disease can result Examples of Normal Flora: eg. lactobacilli of the vagina metabolizes glycogen and lowers the PH to 3.5-4.5 (at this PH candida albicans cannot grow) eg. E. coli of the large intestine produce bacteriocins (proteins that inhibit growth of bacteria of the same or closely related species) eg. Clostridium difficile in the large intestine is usuall inhibited by normal flora ↳ broad spectrum antibiotics can remove enough normal flora that C. difficile can take over (associated with diarrhea, AAC, and PMC) Pathogen: a microorganism that can cause a disease process Primary Pathogen: · always causes disease even in healthy immunocompetent individuals · never "normal flora" eg. S. pyogenes, C. perfringens Opportunistic Pathogen: · may cause disease if given the right circumstances · can be "normal flora" eg. C. albicans, mixed diabetic foot infection Bacillus anthracis Bacillus anthracis B. anthracis can be used as a bioweapon! · primary pathogen (principle pathogen of Bacillus species) · anaerobic G+ bacillus with spores · disease of herbivores, found in soil and vegetation · spores VERY hardy 50+ years · No human to human transmission · 3 routes of infection for humans: ↳ inoculation: contact with animals or animal hides ↳ inhalation: not common "woolsorters disease" ↳ ingestion: ingestion of contaminated meat (often in Africa) -carnivorous animals, roadkill · Virulence: polypeptide capsule, spores, toxin · Pathogenesis: -plasmids responsible for acquisition of virulence factors: ↳ pX01 for toxins and pXO2 for capsule -polypeptide capsule (glutamic acid) - antiphagocytic -inert nonmetabolizing spores germinate to growing "vegetative" bacteria when conditions are right -growth of bacteria leads to production of toxin -3 components of toxin: ↳ PA (protective antigen) ↳ LF (lethal factor) ↳ EF (edema factor) must have PA and either LF or EF for toxicity Treatment: · must be started early · penicillin is the "drug of choice"but ciprofloxacin can be used if resistance is suspected · susceptible to many antibiotics: pen, cipro, tetra, macrolides, clinda, chloro Immunity and Vaccines · some animal species are naturally resistant to anthrax (dont have receptors needed) · vaccines are based on attenuated organisms or toxins from culture filtrates · human vaccine is based on the capsule, poor antigenicity · animal vaccines good for controlling disease in animals Smallpox (Poxviridae) Transmission: Orthopoxrirus, Variola virus = Smallpox · mucous membranes in upper respiratory tract · other members of the orthopoxvirus family are: · direct and indirect transmission · enveloped DNA virus · droplet transmission ↳ vaccinia, monkeypox, cowpox · vaccinia and variola virus differ in only one antigen and cross react · immunity to smallpox: immunity to monkeypox · vaccinia used in smallpox vaccines (safe) The Disease · two forms: ↳ Variola major ~ 30% mortality ↳ Variola minor ~ 1% mortality · Variola major presents in different ways: ↳ ordinary (discrete, semi-confluent, confluent) ↳ modified/mild ↳ flat and hemorrhagic (severe) · infectious, but not nearly as infectious as the flu Complications: · lesions become secondarily infected · can lead to bacteremia, sepsis, and death Treatment: · no good drug for treatment · no effect for established disease Epidemiology: · no asymptomatic carriers or subclinical disease! · no non-human reservoir Zoonosis · disease transmitted to humans from an animal · animal may be a healthy carrier or diseased · human is accidental host eg. Anthrax, Rabies, Tularemia, Chlamydia psittaci, West Nile Virus Disease Stages: · incubation period: gains pathogen, no symptoms · prodrome: pathogen starts replicating, immune response start, mild symptoms · illness: noticeable symptoms, pathogen response increases · period of decline: immune system works hard and reduces amount of pathogen · convalescence: patient regains health, often no symptoms, likely still infections Iceberg Model of Infection · classical diseases are common textbook diseases · mild-moderate disease are visible diseases with symptoms · under the water are asymptomatic infections that the person is unaware of Horizontal transmission: transmission from one person to another through contact, ingestion, vectors, etc. eg. Chickenpox, strep throat Vertical transmission: transfer of a pathogen from a pregnant woman to her fetus (in utero or through breast milk) eg. Streptococcus group B or rubella virus Transmission of Infections Agents ① Contact transmission a. Direct contact: person-to-person eg. Kissing, touching, sexual intercourse b. Indirect contact: agent transferred from reservoir to the susceptible host by a non-living object eg. fomites like towels, drinking cups, etc. c. Droplet transmission: microbes are spread in droplet nuclei (mucus droplets) that travel up to 1m in air eg. Sneezing ② Vehicle transmission: transmission of infection by a medium like food, water, air, blood, IV fluids eg. Hepatitus B by blood transfusion, M. tuberculosis by airborne route ③ Vectors: arthropods and bugs a. Mechanical transmission: passive transport on the vectors body eg. spread of Shigella infection on house fly feet b. Biological transmission: part of the life cycle of the microorganisms is in the arthropods body eg. Malaria and Anopheles mosquitoes Epidemiology · study: when and where diseases occur · purpose: to control disease transmission · notifiable diseases: diseases which physicians and laboratories are required to report to Public Health · Incidence: number of diseases occuring within a specified time period · Prevalence: number of diseases in the population at a particular point in time · Morbidity: incidence of specific diseases · Mortality: number of deaths from diseases Acute vs Chronic Disease · acute disease: characterized by acute inflammatory responses where the neutrophil is the predominant cell type in the infiltrate ↳ pus production eg. boil caused by Staphylococcus aureus · Chronic disease: characterized by chronic inflammatory responses where the predominant cell responders are mononuclear cells ↳ slower type of infection ↳ development of granulomas eg. tuberculosis · sub-acute disease: intermediate between acute and chronic, usually a disease process that takes a long time to develop fully eg. BSE or vCJD in humans · latent disease: causative organism may lie dormant for long periods of time before "reactivating" eg. Herpes simplex or varicella Terminology for Types of Disease · Local infection: infection limited to one site · Systemic infection: disseminated or generalized infection spread through body · Focal infection: after spread of a systemic infection through the body, the organisms stay in specific areas · Primary infection: acute and quick initial infection · Secondary infection: appears as a complication of a primary infection Bacteremia: bacteria in the blood Septicemia: multiplying bacteria in the blood (also called sepsis] Toxemia: toxins in the blood Viremia: viruses in the blood Fungemia: fungi in the blood Parasitemia: parasites in the blood Nosocomial Infections = Hospital acquired infections ↳ most common cause of nosocomial infections are due to the urinary tract (often due to catheters) Sources of Infection in Hospitals: Consequences of Hospital Infection: · hospital environment · prolonged hospital stay · other patients · health care professionals · patients own normal flora · visitors · serious illness or death · expensive antimicrobials may be needed · patient may become a carrier or source and spread the infection in the community Spread of Multi-resistant Organisms Usual Sources of Infection of Healthcare Workers: · MRSA, VRE, MRTB, etc. · soiled bedding, towels, dressings, other fomites · growing problem in health care institutions · hand washing and adherence to hygenic routines is the only way to curb the epidemic · infected patients · contaminated needles · surgical equipment thats not properly sterilized Hazards to Healthcare Workers: · diseases: infections, pose a risk for healthcare workers involved in the primary care of patients · some of the more serious of these diseases are: ↳ HIV ↳ Hepatitus A, B, C ↳ Norovirus ↳ TB and other respiratory pathogens (incl. N. meningitidis) ↳ Hemorrhagic fever viruses (eg. Lassa fever, Ebola) ↳ Tularemia, Plague ↳ SARS How to Avoid Infections: · Hand washing: the number one preventative measure · gloves, gowns, masks, goggles (PPE) · proper handling of used needles · disinfection of the environment What to do in case you become contaminated by a splash or needle stick after using it on a Hepatitus or HIV infected patient? ① Wash needlesticks and cuts with soap and water ② Flush splashes to the nose, mouth, or skin with water ③ Irrigate eyes with clean water, saline, or sterile irrigants ④ Report the incident to your supervisor ⑤ Immediately seek medical attention ↳ in the case of HIV, anti-retroviral therapy may be needed within a short time of contamination ↳ in the case of Hepatitus A or B, this may require immediate vaccination or immunoglobulin therapy