Pathology: infectious disease Flashcards
Sources of infection (general)
Viruses - a pathogen made of nucleic acid inside a protein shell
Bacteria - a unicellular organism without a true nucleus or organelles
Protozoa - a unicellular, animal-like microorganism, not usually harmful to humans
Fungi - yeasts and molds
Helminthes - worms
Mycobacteria - type of bacteria with fungal-like properties
Prions -small proteinaceous infectious particle
Infectious diseases (general)
infection: disease caused by microorganisms, especially those that release toxins or invade body tissues
- infection differs from colonization of the body by micro-organisims in that during colonization, microbes reside harmlessly in the body or perform useful functions
- in contrast, infectious illness typically cause harm, hospital admission and death (intoxication is defined as poisoning by a drug or toxic substance)
Clinical manifestation of infectious disease (general)
Fever, chills, malaise, enlarged lymph nodes
Integumentary - pus, open wound, rash red streaks, bleeding
Cardiovascular - tachycardia, hypotension, change in pulse rate
CNS- altered level of consciousness, confusions, convulsions, headache, memory loss, photophobia, stiff neck,
GI-nausea, vomiting, diarrhea
GU (genital urinary) - dysuria, flank pain, hematuria, oliguria, urgency, frequency, nocturia (need to pee at night)
Respiratory - tachypnea, cough, dyspnea, hoarseness, sore throat, nasal drainage, decreased exercise tolerance
Classification of infection (general)
Endogenous - from within, a microorganism that was previously not pathogenic is now pathogenic. E.g. yeast
Exogenous - not from within, from a source outside the body e.g. influenza virus
Nosocomial - acquired in a health care setting e.g. staphylococcus
Transmission from the source (general)
- For infection to be transmitted, the invading organism must be transported from the infected source to a susceptible host
Portal of exit from the host include feces, urine, vomit, tears, semen, open lesions, blood
Transmission of infection pathways (general)
Microorganisms are transmitted by several possible routes
Contact - direct or indirect
Airborne - float on air currents and remain suspended for hours, small particles.
Droplet - fall out within 3 ft of source, large particles
Vehicle - through a common source such as food or water
Vector - carried by an intermediate source, usually an insect
Transmission of infection pathogen entrance (general)
ingestion Inhalation bites contact with mucosa transplacentally injections Skin to skin contact contact with blood or bodily fluids contact with contaminated articles
Infectious diseases vary as to the number or organisms and the duration of exposure required to start the infectious process in a new host (pathogenicity)
Susceptibility (general)
Can vary from person to person and depend on many factors including Age Nutritional status Hormonal balance Concurrent disease Drug use Hygiene
Chain of transmission (general)
Pathogen or agent: virus, mycobacteria, bacteria, fungi, prions
Reservoir human
Portal of exit: GU, GI, oral cavity, open lesion, semen, tears, blood, feces, urine
Transmission: contact (direct or indirect) airborne, droplet, vehicle, vector
Modes of entry: ingestion, inhalation, injection, transplacental
Susceptible host
Defense of infection (general)
- First line - mechanical barriers
- Second line - inflammation
- Third line - acquired immune response
First line of Defence
Intact skin and mucous membranes Oil and perspiration of skin Cilia in respiratory tracts Gag and coughing reflexes Peristalsis in the GI tract Flushing action of tears, saliva and mucus The presence of normal flora
2nd and 3rd line of defence
2nd - inflammatory process 3rd - immune process Include Lymphatic system Leukocytes Chemical proteins, enzymes
Defence mechanism of infection (general)
relies on mechanical integrity of epithelial surfaces as well as decontamination - removal of the pathogen
pattern of infections (general)
the invasive organism products local damage (e.g. warts)
The invasive organism is toxic (poisonous) to the host (e.g.botulism)
The invasive organism produces little local damage but has widespread effects (e.g. HIV)
Spread of infection within a host (general)
Directly - some pathogens produce enzymes that damage cell membranes, enabling them to move rapidly from cell to cell
Via natural channels such as membranes (meninges, pleura, peritoneum) and vessels (lymphatic, blood)
Through nerves or through phagocytes (e.g. herpes virus)
Mode of action (general)
Mode of action of a pathogen refers to how the organism produces a pathologic process. Great variation exists. Some intracellular pathogens, like viruses, invade cells and interfere with cellular metabolism, growth and replication. Other organisms cause cell death.
Factors affecting occurrence and spread of infection (general)
pathogenic factors
Host factors
Pathogen factors of infection (general)
virulence - the relative power and degree of pathogenicity
Dose - increased numbers are more effective
site of infection - some sites are more easily infected
Synergism between different pathogens (i.e. one organism can impair external defenses and permit another to enter)
Host factors (general)
Resistance to infection
Immune competency
Leukocyte count
Necrosis and ischemia of a tissue (e.g. anaerobic bacteria)
Diagnosis of infection (general)
- Direct visualization of organism
- Detection of microbial antigen
- Search for clues produced by the host immune response to specific micro-organisms
- Isolation of organism in culture
- Detection of specific microbial nucleotide sequences
