8 - Infectious Diseases Flashcards
How are most skin infections initiated?
Mechanical injury of the epidermis
How are most gastrointestinal pathogens transmitted?
Fecal-oral route via contaminated food or drink
What is the body’s principal method of defending against fecal-orally transmitted infections?
Acidic gastric secretions, pancreatic enzymes, and bile detergents
What do both the skin and gut epithelial cells produce to protect against infectious disease?
IgA antibodies
How are most infections transmitted from person to person (3)?
Respiratory, fecal-oral, or sexual routes
How can infectious diseases escape from antibody-mediated host defenses?
Antigenic variation
What is the ultimate means by which infectious diseases can avoid the immune system?
Latent infection in which few if any viral genes are expressed
What is it called when viral agents have a predilection for certain types of cell to infect?
Tropism
What bacterial surface proteins bind bacteria to host cells or ECM?
Adhesins
How does tuberculosis utilize the immune system in its replication?
M. tuberculosis activates the alternative complement pathway, resulting in opsonization with C3b. Once coated with C3b, M. tuberculosis binds to the CR3 complement receptor on macrophages, enters the macrophages, and replicates within phagosomes
Describe bacterial endotoxin.
A lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria that both stimulates host immune responses and injures the host
Describe bacterial exotoxins.
Secreted bacterial proteins that cause cellular injury and disease.
What are some examples of bacterial exotoxins?
Enzymes, toxins altering intracellular signaling, neurotoxins, superantigens
What are some types of inflammatory response to infectious disease?
Suppurative, granulomatous, cytopathic-cytoproliferative reactions, tissue necrosis, scarring
How are most infectious diseases diagnosed?
Cultures, biochemical or serologic identification, and molecular diagnosis
What stain can identify most bacteria?
Gram stain
What stain can identify mycobacteria and nocardiae?
Acid-fast stain
What stain can identify fungi, legionella, and pneumocystis?
Silver stain
What stain can identify fungi and amebae?
Periodic acid-Shiff stain
What three techniques can identify all classes of infectious agents?
Antibody stains, culture, DNA probes
What are four examples of respiratory viruses with acute (transient) presentation?
Adenovirus, rhinovirus, influenza, and respiratory syncytial virus
What are four examples of digestive viruses with acute (transient) presentation?
Mumps, Rotavirus, Norovirus, and Hepatitis A-E
What are four examples of systemic viruses with acute (transient) presentation and skin eruptions?
Measles, Rubella, Varicella-zoster, HHSV 1-2
What are three examples of systemic viruses with acute (transient) presentation and hematopoietic disorders?
CMV, EBV, and HIV-1-2
What are two examples of arboviral- and hemorrhagic fever-related viruses with acute (transient) presentation?
Dengue and Yellow fever
What is an example of a viruse with acute (transient) presentation of the skin /genital warts?
HPV
What are two examples of CNS viruses with acute (transient) presentation?
Poliovirus and JC virus
What is a rare, late complication of measles?
Encephalitis
Describe mumps (type and presentation).
Acute systemic viral infection; pain and swelling of the salivary glands
Is there more than one type of mumps?
Yes: mumps parotitis, orchitis, and encephalitis
Describe poliovirus (transmission, type, presentation).
Fecal-oral; a spherical, unencapsulated RNA virus; anterior horn destruction and paralysis of limb and diaphragm
What is latency as it refers to viral genomes?
The persistence of viral genomes in cells that do not produce infectious virus
What effects can the superantigens in Staphylococcus aureus and Streptococcus pyogenes cause?
Toxic shock syndrome and food poisoning
What disease does Streptococcus pyogenes cause (respiratory)?
Pharyngitis
What disease does Corynebacterium diphtheria cause (respiratory)?
Diphtheria
What disease does Bordetella pertussis cause (respiratory)?
Pertussis
What disease does Streptococcus pneumonia cause (respiratory)?
Lobar pneumonia
What disease does Mycobacterium tuberculosis cause (respiratory)?
Tuberculosis
What disease does Legionella pneumophila cause (respiratory)?
Legionnaire disease
What disease does Helicobacter pylori cause (gastrointestinal)?
Peptic ulcers
What disease do Vibrio cholerae and enterotoxigenic E. coli cause (gastrointestinal)?
Noninflammatory gastroenteritis
What disease do Shigella species, Salmonella species, Campylobacter jejuni, and enterohemorrhagic E. coli cause (gastrointestinal)?
Inflammatory gastroenteritis
What disease does Salmonella typhi cause (gastrointestinal)?
Enteric (typhoid) fever
What disease does Clostridium difficile cause (gastrointestinal)?
Psuedomembranous colitis
What disease do Neisseria meningitidis, Streptococcus pneumonia, Haemophilus influenza, and Listeria monocytogenes cause (nervous)?
Acute meningitis
What disease do Clostridium tetani and Clostridium botulinum cause (nervous)?
Paralytic intoxications, tetanus, and botulism
What disease do Escherichia coli, Pseudomonas aeruginosa, S. saprophyticus, and Enterococcus species cause (urogenital)?
UTIs
What disease does Neisseria gonorrhoeae cause (urogenital)?
Gonorrhea
What disease does Chlamydia trachomatis cause (urogenital)?
Chlamydia
What disease does Treponema pallidum cause (urogenital)?
Syphilis
What disease does Staphylococcus aureus cause (skin and adjacent soft tissue)?
Abcess, cellulitis
What disease does Streptococcus pyogenes cause (skin and adjacent soft tissue)?
Impetigo, erysipelas, necrotizing fasciitis
What disease does Clostridium perfringens cause (skin and adjacent soft tissue)?
Gas gangrene
What disease does Bacillus anthracis cause (skin and adjacent soft tissue)?
Cutaneous anthrax
What disease does Pseudomonas aeruginosa cause (skin and adjacent soft tissue)?
Burn infections
What disease does Mycobacterium leprae cause (skin and adjacent soft tissue)?
Leprosy
What disease does Yersinia pestis cause (disseminated infections)?
Plague
What disease does Borrelia burgdorferi cause (disseminated infections)?
Lyme disease
What disease does Brucella species cause (disseminated infections)?
Brucellosis (undulant fever)
What disease do Streptococcus agalactiae and Listeria monocytogenes cause (disseminated neonatal infections)?
Neonatal bacteremia, meningitis
What disease do Treponema pallidum cause (disseminated neonatal infections)?
Congenital syphilis
Describe Staphylococcus aureus.
Pyogenic, gram-positive cocci; A myriad of skin lesions (boils, carbuncles, impetigo, and scalded-skin syndrome) as well as abscesses, sepsis, osteomyelitis, pneumonia, endocarditis, food poisoning, and toxic shock syndrome
What factors are important to know about Staphylococcus aureus?
Clumping factors; alpha-, beta-, and delta-toxin; exfoliative toxins A and B; superantigens
What is a growing problem in Staphylococcus aureus infections?
Antibiotic resistance (e.g. MRSA)
What do streptococci cause?
Suppurative infections of the skin, oropharynx, lungs, and heart valves
What is distinctive about the pyogenic infection caused by Staphylococcus aureus?
Its local destruction of host tissue
What is a furuncle (boil)?
A focal suppurative inflammation of the skin and subcutaneous tissue
What is a carbuncle?
A deeper suppurative infection that spreads laterally beneath the deep subcutaneous fascia and then burrows superficially to erupt in multiple adjacent skin sinuses
What is the effect of Staphylococcus aureus that can result from the desquamation of the epidermis (most frequently in children)?
Scalded-skin syndrome (Ritter disease)
What is a very important cause of community-acquired lobar pneumonia?
Streptococcus pneumoniae
What is a characteristic finding of diptheria-induced pharyngitis?
A pseudomembrane
Describe Listeria monocytogenes.
A gram-positive bacillus that causes severe food-borne infections in vulnerable hosts (pregnant women, neonates, older adults, and immunosuppressed persons)
Describe bacillus anthracis.
Anthrax is characterized by necrotizing inflammatory lesions in the skin or gastrointestinal tract or systemically
What are the three types of anthrax?
Cutaneous (95% of cases), inhalational, and gastrointestinal
What are the two subunits of anthrax toxin?
Edema factor and lethal factor
Name some gram-negative bacterial infections.
Niesseria (meningitidis, gonorrhoeae), pertussis, pseudomonas, plague, chancroid
In who does Pseudomonas cause deadly infection?
People with cystic fibrosis, severe burns, or neutropenia
What kind of effects do Pseudomonas have?
Necrotizing pneumonia, bacterial vasculitis, ethycema gangrenosum
What gram-negative bacteria causes the plague?
Yersinia pestis
Are mycobacteria aeorbic or anaerobic? (Hint: think of TB)
Aerobic
What is different about the unique, waxy cell wall of mycobacteria?
They are acid-fast; they contain mycolic acid
Are mycobacteria gram-negative or gram-positive?
Weakly gram-positive
Who is most affected by TB, in the world and U.S.?
Tuberculosis flourishes wherever there is poverty, crowding, and chronic debilitating illness.
In the United States, tuberculosis is mainly a disease of older adults, immigrants from high-burden countries, racial and ethnic minorities, and people with AIDS
What is generally the only evidence of asymptomatic TB infection?
A small, fibrocalcific pulmonary nodule
What type of hypersensitivity is indicated in a positive PPD test?
Type IV
What are the steps of TB infection?
Entry into macrophages;
Replication in macrophages;
Toll-like receptors detect the PAMPs associated with TB;
TH1 cells (T-Helper 1 lymphocytes) activate bacteriocidal side of macrophages through gamma-interferon;
The TH1 response orchestrates the formation of granulomas and caseous necrosis
How long does it take in a TB infection before TH1 lymphocytes are recruited?
About 3 weeks
What is primary TB?
Primary tuberculosis is the form of disease that develops in a previously unexposed and therefore unsensitized, person (first exposure of any kind)
What is secondary TB? (2 causes)
Secondary tuberculosis is the pattern of disease that arises in a previously sensitized host
- Reactivation of a latent infection
- Exogenous reinfection
Which stages of HIV infection are associated with increased risk of TB?
All of the stages
Drainage of TB organisms through the lymphatics to the venous supply will lead to miliary TB in what organ(s)?
The lungs
Dissemination of TB organisms through the arterial supply will lead to miliary TB in what organ(s)?
Most prominently the liver, bone marrow, spleen, adrenals, meninges, kidneys, fallopian tubes, and epididymis, but could involve any organ
What type of TB infection is more common in countries where bovine TB is present and milk is not pasteurized?
GI TB
What type of necrosis is seen in TB patient granulomas? What is the cause?
Causeous; macrophage reaction to the TB
What is the name of the 1- to 1.5-cm area of gray-white inflammation as consolidation emerges in a newly infected TB patient?
A Ghon focus
What is a Ghon complex?
A combination of the parenchymal lung lesion and nodal involvement
(Ghon foci + lymph nodes)
What might be an acid-fast cause of disseminated infection in the lungs and/or GI tract that is NOT caused by Mycobacterium tuberculosis? (Mostly in immunosuppressed patients)
Mycobacterium avium complex (MAC)
Is leprosy acid-fast?
Yes, it is a mycobacterial infection.
Do Mycobacterium tuberculosis or Mycobacterium leprae secrete any exotoxins?
No, their virulence is based on properties of their cell walls.
How can M. tuberculosis and M. leprae be diagnosed in similar ways?
PPD (tuberculin) tests in TB; lepromin tests in leprosy
What are the two types of M. leprae presentation? What causes the difference?
Tuberculoid (TH1) and lepromatous (TH2); the helper T-lymphocyte response
