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
Opportunistic infections (general)
- an opportunistic infection is any infection that results from a defective immune system that cannot defend against pathogens normally found in the environment. these infections are usually seen in patients with impaired defenses against disease.
- Life threatening infectious disease occurs when immunity is weak or suppressed (e.g. transplant patients, AIDS patients, old age, new borns, malnourished, burn victims, etc)
Bacterial infections
Staphylococci (cocci means round, ball)
Streptococci
Pneumococci
Meningococci
Staphylococcal infections
Reference: Goodman page 316
“Staph”
Among the most common bacteria normally residing on the skin
over 30 subtypes
Cause a multitude of disease ranging from mild/asymptomatic to severe/fatal
Leading cause of nosocomial and community acquired infections
Most common - staphylococcus aureus (S.aureus)
S. aureus
Staphylococcal aureus
Extremely virulent (powerful)
Nonmotile (doesn’t move) and anaerobic
Hardy, able to survive on inanimate objects for an extended period
Can infect the blood, skin, lungs, soft tissue, joints, bones
S. aureus risk factors
Staphylococcal aureus Diabetes, chronic illness HIV positive Elderly, newborns, malnourished Surgical/burn patients prosthetics
S. aureus causes infectious diseases include
Staphylococcus causes: Osteomyelitis Respiratory tract infections Infectious arthritis Septicemia Endocarditis Toxic shock syndrome Food poisoning Skin infections (cellulitis, mastitis)
Management of infections of Staphylococcus aureus
Diagnosis - culture
Treatment - antibiotics
Prognosis is generally good although some strains of S. aureus are particularly difficult to treat
E.g. MRSA (Methicillin-resistant staphylococcus aureus, resistant to antibiotic)
Also antibiotic resistant strains are increasing
Streptococcal infections
Reference: goodman page 319
Include:
Group A - Streptococcus pyogenes (s.pyogenes)
Group B - S. agalactiae
S. pyogenes
Streptococcal pyogenes
One of the most common bacterial pathogens of human or any age
Causes many diverse disease of many diverse organs and systems
Can cause suppurative (pus making) and non-suppurative disease
Transmission - contact, droplets, foodborne
S. pyogenes causes
Streptococcal pyogenes causes
Streptococcal pharyngitis (strep throat) very common cause of sore throat occurring mostly in children
Scarlet fever - usually follows untreated strep throat and but more severe
Impetigo - skin infection that occurs in children, particularly in hot weather
Cellulitis - acute skin infection
Necrotizing fasciitis - very serious and potentially fatal infection that spreads quickly along fascial planes
S. agalactiae
Streptococcal agalactiae
Leading cause of neonatal pneumonia (vaginal, not common in adults), meningitis, sepsis
Infrequent cause of pyogenic (containing pus) disease in adults
Rapid administration of antibiotics is essential
Pregnant women are routinely screened
Pneumococcal infections
Pneumococcus or streptococcus pneumonia (S. pneumonia)
Can cause pneumonia, sepsis, otitis media, meningitis
Most common cause of community acquired pneumonia
Very young and very old particularly susceptible
Pneumococcus risk factors
Often follows influenza, viral respiratory infections
Risk factors include chronic disease and alcohol abuse, immunosuppression, etc
Most common cause of “bacterial” meningitis in adults, infants and toddlers
Meningococcal infections
Meningococci cause meningitis and septicemia
Symptoms are usually severe and can include headache, nausea, vomiting, photophobia, lethargy, rash, multiple organ failure, shock, and disseminated intravascular coagulation (DIC)
Anaerobic bacterial infections
Anaerobic bacteria are intolerant of oxygen, replicating at sites of potentially low oxygen such as necrotic, devascularized tissues. These infections are usually suppurative, causing abscess formation and tissue necrosis
Anaerobic infections cause
Diphtheria
Plague (www.merck.com/mmpe)
Botulism (www.merck.com/mmpe)
Cholera
Diphtheria
An acute pharyngeal or cutaneous infection caused by Corynebacterium diphtheria (C. diphteria)
Children are routinely vaccinated
The disease spreads by contact and secretions of nose, mouth and skin lesions
Diphtheria Symptoms
Symptoms include nonspecific skin infections (inflammation and necrosis of local tissues) or pseudomembranous pharyngitis followed by myocardial and neural tissue (heart, nerve, kidney) damage
Tx. antibiotics, prognosis good
Plague
Aka Bubonic plague or Black Death
Caused by Yersinia pestis (Y. pestis)
Symptoms are either severe pneumonia or massive lymphadenopathy with high fever often progressing to septicemia
Enlarged lymph nodes called buboes
Plague transmission
Wild rodents carry disease
Transmitted from rodents to human by the bite of a flea vector
Human to human transmission occurs by inhaling droplets from infected humans
Highly contagious
Massive human pandemics rare today due to antibiotics
Botulism
Neuromuscular poisoning caused by Clostridium botulinum
Botulism can be food-borne or wound-borne
Most frequently manifests as a severe form of food poisoning
Common sources include home-canned foods, vegetable, fish, fruits, condiments, meat, dairy
Botulism Etiology and symptoms
Bacteria produces toxin that can interfere with release of acetylcholine at peripheral nerve endings (NMJ)
Symptoms include nausea, vomiting, abdominal cramps and diarrhea followed by weakness and paralysis
Spores are common in the environment
Although the spores are heat resistant, cooking kills the toxins
A spore is a cell produced by spore-forming bacteria (bacillus) to withstand extreme conditions
It can remain viable for decades
Cholera
Acute infection of the small bowel by Vibrio cholerae
Secretes a toxin that produces copious watery diarrhea
Leads to dehydration, oliguria, and collapse (shock)
Infection is typically through water or seafood that is contaminated with the excrement of infected people
Treatment - rehydration with water and electrolytes; antibiotics
Spirochete infections
A spirochete is a slender, spiral motile bacteria that lives off dead and decaying matter in soil and water
E.g. Lyme disease, syphillis
Lyme disease
An infectious multi-systemic disorder
Caused by Borrelia burgdorferi
Vector-borne disease carried by a deer tick
Ticks carrying the bacteria can transmit to mammals by injecting saliva into the host
Symptoms include skin lesions and a “bull’s eye” rash (erythema migrans). The bacteria reach other organs through the blood and cause nausea, vomiting, neurological and arthritis-like symptoms
This disease is very common in the spring and summer in the Pacific Northwest and is the most common tick-borne disease in the states.
Treatment- antibiotics
a pathogen made of nucleic acid inside a protein shell
Virus
A unicellular organism without a true nucleus or organelles
Bacteria
A unicellular, animal like microorganism, not usually harmful to humans
Protozoa
yeasts and molds
Fungi
Worms
Helminthes
A type of bacteria with fungal-like properties
Mycobacteria
A small proteinaceous infectious particle
Prions
