Week 5 Flashcards
“Great neglected disease of mankind”
pneumonia often misdiagnosed, mistreated and underestimated
high cause of mortality
Pneumonia
infection of what?
typical presenting signs/symptoms?
infection of pulmonary parenchyma from the alveoli (LOWER respiratory tract infection)
Acute, fever, tachypnea, cough, purulent sputum, lung consolidation
Pleuritic chest pain
Infiltrate on CXR
Community Acquired Pneumonia (CAP):
Typical: SYMPTOMS
purulent sputum, gram stain may show organisms, typically LOBAR infiltrate on CXR
Lobar pneumonia
what is it?
3 bugs that cause this?
intra-alveolar exudate and consolidation
S. pneumoniae (#1), Legionella, Klebsiella
Bronchopneumonia
what is it?
4 bugs that cause this?
acute inflammatory infiltrates from bronchioles into adjacent alveoli
Patchy distribution can be >1 lobe
S. pneumoniae, S. aureus, H. influenzae, Klebsiella
5 bugs that can cause typical CAP
1) Strep. Pneumoniae = #1 cause of CAP, can be secondary pneumonia after viral infection
2) H. Influenzae = often secondary pneumonia s/p virus + COPD
3) Moraxella catarrhalis
4) S. aureus = abscess, empyema, #2 most common CAP
5) Klebsiella = aspiration of enteric flora, currant jelly sputum, abscess
Community Acquired Pneumonia (CAP):
Atypical: SYMPTOMS
cough prominent +/- purulent sputum, gram stain with PMNs, but few organisms, PATCHY or DIFFUSE infiltrate on CXR
Atypical CAP Bugs
1) Mycoplasma pneumoniae
2) Chlamydophila pneumoniae
3) Legionella pneumophila = CAP, pneumonia + COPD/immunocompromised
4) Influenza, RSV, adenovirus
Interstitial pneumonia
diffuse patchy inflammation localized to interstitial areas at alveolar walls
Pneumonia caused by viruses like Influenza, RSV, and adenovirus can be complicated by ________, _________ and ______ secondary bacterial pneumonias
can be complicated by S. pneumoniae, S. aureus, and Group A strep
Fungal causes of pnuemonia (4)
Histoplasmosis, Blastomycosis, Coccidiomycosis, Aspergillus
Treatment of pneumonia:
1) Previously healthy outpatients → ?
2) Outpatients with comorbidities → ?
3) Inpatients (not ICU) → ?
4) ICU patients → ?
Previously healthy outpatients → Macrolide, Doxy
Outpatients with comorbidities → Respiratory Fluoroquinolone (levo or moxi), Macrolide + Amoxicillin/Clav
Inpatients (not ICU) → Respiratory Fluoroquinolone, Macrolide + B-lactam (3rd gen cephalosporin)
ICU patients → 3rd gen cephalosporin + respiratory fluoroquinolone or macrolide
Pneumococcal vaccine:
23-valent pneumococcal vaccine
for ADULTS: effective for bacteremia (systemic infection), not effective for pneumonia (mucosal infection)
Given to adults > 65 and asplenic patients
Pneumococcal vaccine:
13-valent pneumococcal conjugate vaccine
given to CHILDREN<5 and adults > 65 = polysaccharide capsule + protein conjugate
Haemophilus Influenzae:
gram? size? shape? Requires what for growth? capsule?
Small, gram-negative bacillus (coccobacillus)
Requires NAD (factor V), and heme (factor X) to grow on CHOCOLATE AGAR
can be encapsulated or unencapsulated
encapsulated (typeable) H. influenzae
positive quellung reaction (ab bind to bacterial capsule and can be visualized under microscope)
6 encapsulated serotypes (a-f)
Which serotype is the most virulent H. influenzae?
which is the most predominant?
Serotype b = most virulent
Serotype a is most predominant type
Unencapsulated (nontypeable) H. influenza causes what kinds of diseases?
upper respiratory tract infections (noninvasive sinusitis, otitis media)
Haemophilus Influenzae:
Virulence factors: (3)
1) Polysaccharide capsule → necessary for bug to produce invasive disease
2) Endotoxin (LPS)
3) IgA protease
Haemophilus Influenzae:
IgA protease allows this bug to do what?
colonizes upper respiratory tract, and can spread via lymphatics to seed meninges = meningitis
Haemophilus Influenzae:
Transmission
-who is particularly susceptible to infection?
aerosol droplets
Often occurs in immunosuppressed, ASPLENIC patients, and children (after maternal ab protection has declined)
Haemophilus Influenzae:
Treatment?
40% resistance to ampicillin (can use for mucosal infections)
Use 3rd gen cephalosporins for meningitis
Chloramphenicol (highly toxic though)
Haemophilus Influenzae:
Diseases (7)
1) Septic Arthritis
2) Epiglottitis → “thumbprint” sign on XR
3) Meningitis
4) Otitis media
5) Pneumonia
6) Conjunctivitis
7) Sinusitis
Haemophilus Influenzae:
Vaccine? what strain does it work against? who gets it and when?
Hib vaccine: capsular polysaccharide (polyribosylribitol phosphate, PRP) of type B strain conjugated to diphtheria toxoid
Given from 2-18 months of age
Neisseria Meningitidis
gram?
shape?
ferments what?
Gram-negative diplococcus, “coffee bean” shape
Ferments glucose and maltose (gonorrhea only ferments glucose)
Neisseria Meningitidis
vaccine? against what strains? Given to who?
Vaccine against serogroups A and C (but NOT for serogroup B strains)
quadrivalent meningococcal conjugate vaccine (excluding Type B strain)
Given to high risk individuals 2-55 - teenagers previously unvaccinated
Neisseria Meningitidis
Virulence factors:
1) Polysaccharide capsule
2) IgA protease → cleaves human IgA
3) Lipooligosaccharide
Neisseria Meningitidis
Lipooligosaccharide allows bug to do what?
induce sepsis, facilitates immune evasion
Neisseria Meningitidis
Polysaccharide capsule allows bug to do what? who is susceptible?
necessary for bug to produce invasive disease
ASPLENIC patients at increased risk for septicemia
Neisseria Meningitidis
serotypes?
9 different serotypes
A, B, and C → responsible for most disease
B = N-acetyl neuraminic acid - NON immunogenic in humans because this is in humans too
→ NO group B vaccine
Neisseria Meningitidis
Diseases (2)
1) Meningitis
2) Meningococcemia
Neisseria Meningitidis
Meningitis
- symptoms (characteristic sign?)
- who gets it?
- major complications?
most common cause of bacterial meningitis from 6mo-6yrs and young adults (high school, and college age - living in close quarters)
SX: sudden onset fever, nausea, vomiting, headache, mental status change, myalgias, petechial rash**
Waterhouse-Friderichsen Syndrome: due to LOS endotoxin
Neisseria Meningitidis
Treatment/Prophylaxis
- 3rd and 4th gen cephalosporins or penicillin G
- Not a big problem with resistance
Prophylaxis: RIFAMPIN (given to close contacts), ciprofloxacin, or ceftriaxone
Neisseria Meningitidis
Transmission
Normally colonizes nasopharynx epithelium
Transmission via respiratory droplets
Streptococcus Pneumoniae (pneumococcus)
gram? shape? grows on what agar? anaerobe/aerobe? optochin? hemolysis? catalase? quelling reaction + or -?
Gram-positive diplococcus, “lancet shaped”
Grows on blood agar
Facultative anaerobe
Optochin sensitive
Alpha-hemolytic
Catalase negative
Positive quellung reaction
Streptococcus Pneumoniae (pneumococcus)
Virulence factors (2)
1) Polysaccharide capsule → necessary for bug to produce invasive disease
2) IgA protease → colonizes respiratory tract
Streptococcus Pneumoniae (pneumococcus)
Serotypes?
90 different capsular serotypes - only 12 cause infection
Serotype H. influenza b capsule can cross react with S. pneumoniae → can get misdiagnosis of H. influenzae or S. pneumoniae
Streptococcus Pneumoniae (pneumococcus)
Diseases? (5)
1) Meningitis
2) Otitis media (in children)
3) Pneumonia (< 2 years, > 65 years) = rusty brown sputum
4) Sinusitis
5) Conjunctivitis
Streptococcus Pneumoniae (pneumococcus)
Meningitis
most common cause of bacterial meningitis in all adults
Increased risk for infection with: asthma, viral infection, smoking, asplenic, immunocompromised
Streptococcus Pneumoniae (pneumococcus)
Treatment
Alarming multidrug resistance increasing
Respiratory fluoroquinolone (levofloxacin, moxifloxacin)
B-lactam + macrolide/doxycycline
Vancomycin is only available antibiotic in some places
Mycobacteria
anaerobe or aerobe?
stable or labile?
grown on what agar?
Strict aerobes
Very stable (can remain virulent in dried sputum for 6-8 months)
Mycobacteria
Cell wall features? (4)
1) Outer lipids and proteins → used for PPD test
Very thick outer lipid layer
2) Lipoarabinomannan (LAM) layer
3) Phosphatidylinositol Mannoside (PIM) layer
4) Mycolic acids (long chain lipids)
Mycobacteria
Mycolic acids
-what stain uses this feature?
Mycolic acids (long chain lipids) → hardy, difficult to stain → ACID FAST
Ziehl-Neelsen Stain (carbol fuchsin)
Increases bacterium’s virulence
Targeted by INH
Mycobacteria Tuberculosis
acid-fast (red), obligate aerobic rod
Mycobacteria Tuberculosis
Virulence factors? (3)
Mycolic acids
Cord factor
Sulfatides
Mycobacteria Tuberculosis
Cord factor
inhibits macrophage maturation and induces TNF-a release
Mycobacteria Tuberculosis
Sulfatides
surface glycolipids that inhibit phagolysosomal fusion
Mycobacteria Tuberculosis
Transmission
airborne microscopic droplets, human-to-human spread
High risk settings: prisons, hospitals, homeless shelters
Mycobacteria Tuberculosis
Initial infection, replication, and spread →
Initial infection, replication, and spread → TB reaches alveoli and is phagocytosed by alveolar macrophages → replicates in macrophages
Carried by macs and DCs to draining lymphatics → blood → other organs
PIM, ManLAM, and SapM components of TB cell wall prevents phagosome/lysosome fusion and promotes growth within macrophages
TB granuloma (tubercle) formation:
TB in center, contains components on cell wall that promote granuloma formation
Macrophages come in and kill TB → necrotic center and formation of giant cells (fused macrophages)
T cells produce INF-y and TNF-a
Calcification and fibrosis surrounding center
Bacteria confined in “tubercles” = granulomas with epithelioid cells, giant cells, and lymphocytes + necrotic center (caseous necrosis)
What type of immunity is responsible for fighting TB?
Cell-mediated immunity develops at 2-6 weeks dominated by TH1 cells
Infection controlled via CMI, humoral immunity does NOT play a major role, but is used as a diagnostic tool
Alveolar macrophages, monocytes, and dendritic cells: Role in TB
critical for processing and presenting antigens to T cells (CD4+ and CD8+) → activation and proliferation of CD4+ cells → differentiate to TH1 and TH2
Site of replication for TB
TH1 cells and TB
TH1 cells release ______
TH1 cells also release ______ –> activate ______ and ________ which then release ______
TH1 →
IL-2
IFN-y → activate macrophages and monocytes
Macrophages release cytokines (TNF-a)
TH2 cells release what cytokines in response to TB infection? (4)
TH2 → IL-4, IL-5, IL-10, IL-13
Pulmonary TB
(most common)
Cough (> 3 weeks)
Night sweats, chills, fever, weight loss
Hemoptysis
- Ghon focus
- Ghon Complex
- Ranke Complex
Ghon focus
granuloma located near pleura in middle or lower lobes with central caseous necrosis
Ghon complex
ghon focus + regional (usually perihilar) lymphadenopathy
Ranke complex
Ghon complex that has undergone progressive fibrosis and subsequent calcification from cell-mediated immunity (radiologically detectable)
Extrapulmonary TB:
1) Scrofula
2) Pleural or pericardial effusion
3) Kidneys → malaise, dysuria, gross hematuria, sterile pyuria
4) Pott’s disease
5) Joints (chronic arthritis)
6) CNS
scrofula
Extrapulmonary TB disease
Cervical Lymphadenitis (scrofula) = painless, chronic neck mass
Pott’s disease
Extrapulmonary TB disease of the Spine → Pott’s disease (infection of spine, destruction of intervertebral discs and vertebral bodies)
Extrapulmonary TB disease in CNS
CNS → Meningitis, granulomas in brain BASE
Miliary TB
disseminated TB
More common in HIV patients
Outcome of TB exposure:
1) 30% of those exposed are infected → 5% have early progression to primary disease (typically immunocompromised), 95% develop latent infection (immunocompetent)
2) Those that have latent disease → 5% get secondary/reactivation TB (due to reduced immune function, TNF-a therapy), and 95% will continue to contain the TB in latent form
Active TB disease
active, multiplying tubercle bacilli in the body
Positive PPD test
CXR ABNORMAL
Sputum smears and cultures usually positive
SX = cough, fever weight loss
Infectious before treatment
Reactivation TB
secondary disease
Cavitary lesions in UPPER lobes
Very infectious
Latent TB
inactive, contained tubercle bacilli in the body
Positive PPD test
CXR usually normal
Sputum smears and cultures negative
No symptoms, not infectious
PPD Test
-what causes a false positive, what causes the false negatives?
Latent TB diagnosed via PPD+ skin test (once exposed to TB, will have PPD+ for life)
False positive PPD can occur with BCG vaccine AND NON-TB mycobacteria
False negative PPD with steroid use, malnutrition, immunocompromised states
Quantiferon Gold assay
IFN-y release assay, measures IFN-y in serum released from T cells exposed to TB (does NOT cross react with PPD)
Treatment of TB
Active TB → RIPE therapy
Rifampin
Isoniazid
Pyrazinamide
Ethambutol (or streptomycin)
Prophylaxis for latent TB →?
Isoniazid (9 months) + Pyridoxine (B6)
BCG vaccination
live attenuated vaccine, induces cell-mediated immune response
TB skin test results:
1) HIV infection, contact to active TB case, abnormal CXR, or immunosuppression –> ______ mm is considered a positive PPD
2) Recent imigrants, injection drug users, children, high risk medical conditions, residents/employees of jails/nursing homes, hospitals –> ______ mm is considered a positive PPD
3) No risk -> ______ mm is considered a positive PPD
1) > 5mm
2) > 10mm
3) > 15 mm
Nontuberculous Mycobacteria
Symptoms are due to what?
causes what kind of infection?
transmission?
Constitutional symptoms due to TNF-a (NOT bug itself)
Causes chronic infections, often drug-resistant
transmission between humans, acquired from environmental sources (soil, water) via inhalation
Mycobacterium avium complex (MAC)
disease?
affects who?
how does it get into the body?
Disease: nonspecific symptoms - cough (productive or dry), fatigue, malaise, weakness, dyspnea, chest discomfort, hemoptysis
Systemic disease, multi-organ involvement
HIV patients with CD4 < 50 at HIGH RISK
NOT contagious to general population
Initial portal of entry is often GI
How can you differentiate TB vs. MAC
Distinguish from TB by presence of: anemia, high alk phos, high LDH
Diagnosis, treatment, prophylaxis of MAC
- Diagnosis: Acid-fast bacilli within macrophages on histology
- Treatment: azithromycin or clarithromycin/ethambutol
- Prophylaxis: azithromycin or clarithromycin (used in HIV CD4 < 50)
Mycobacterium kansasii
pulmonary and systemic disease - very similar to TB
Mycobacterium marinum
found in water sources
Causes papules or ulcers in lymphocutaneous pattern
Seen in aquarium cleaners, fishermen, seafood handlers
Mycobacterium abscessus
pulmonary + cutaneous disease
Mycobacterium ulcerans (Buruli ulcer)
skin disease, tissue necrosis leading to ulceration
Surgery is treatment of choice
Source = contaminated water
Mycobacterium Leprae:
Chronic infectious disease
Very slow growing
Affects peripheral nerves, skin, and mucosa
Infects monocytes
Mycobacterium Leprae:
Transmission
person-to-person (very low rate of transmission) from nasal septa
Humans and armadillos only known natural hosts
95% of people who are exposed do NOT develop disease
Mycobacterium Leprae:
2 diseases?
Leprosy (Hansen’s Disease) - affects peripheral nerves, skin, mucosa
1) Lepromatous leprosy
2) Tuberculoid Leprosy
Lepromatous leprosy
malignant form, high bacterial numbers
Strong ab response, but defect in cell-mediated immunity
SX: loss of eyebrows, thick/enlarged nares, ears, and cheeks
Severe damage and loss of nasal bone/septa and sometimes digits
Skin and nerve involvement with loss of local sensation
Tuberculoid Leprosy
self-limiting sometimes
Active cell-mediated immune response to lepromin
SX: blotchy red lesions on face, trunk, and extremities with loss of local sensation
Isoniazid
Mechanism?
activation?
distribution?
prodrug, activated by TB catalase-peroxidase enzyme (KatG)
Inhibits mycolic acid synthesis in TB cell wall
Bactericidal in growing mycobacteria, bacteriostatic in resting organisms
Can penetrate caseous cavitary lesions - very good distribution
Isoniazid
Mechanism of resistance
mutation or deletion of mycobacterial catalase-peroxidase KatG
Isoniazid
Metabolism
Acetylated in liver → produces acetylhydrazine which is HEPATOTOXIC
Isoniazid
Toxicity (5)
1) Hepatotoxic (“high acetylators”)
2) Peripheral neuropathy
3) Seizures
4) Depletes B6
5) Drug induced lupus (“slow acetylators”)
Slow vs. fast acetylators and Isoniazid
Acetylated in liver → produces acetylhydrazine which is HEPATOTOXIC
**Increased risk in patients who are “slow acetylators” → increased risk of drug induced lupus
Increase risk of hepatotoxicity if you are a “fast acetylators” and thus producing more acetylhydralizine
Rifampin
Mechanism
bactericidal (can enter cells) → effective against latent TB
Inhibits RNA polymerase initiation
Lipophilic → penetrates BBB
Rifampin
Mechanism of resistance
rapid resistance if used alone - mutation of RNA pol
Rifampin
Use (3)
TB treatment
H. influenzae prophylaxis
Meningococcal meningitis prophylaxis
Rifampin
Toxicity
1) Inducer of CYP450 (induces metabolism of itself)
Rifabutin favored of rifampin in HIV patients because LESS CYP450 stimulation
2) Stains fluids and secretions red
3) Minor hepatotoxicity
4) Dizziness, visual disturbances, nausea, vomiting, diarrhea
Ethambutol
Mechanism
inhibits carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase
Tuberculostatic to TB, but can be -cidal for other mycobacteria
Not very good at entering cells
Ethambutol (3)
optic neuropathy (reduced visual acuity, red-green color blindness, scotomas)
GI disturbance
decreased renal clearance of uric acid (gout)
Pyrazinamide
Mechanism
Acts intracellularly in acidic pH of phagolysosomes where TB is found
Prodrug converted to active form pyrazinoic acid by pyrazinamidase enzyme
Readily crosses BBB
Pyrazinamide
Mechanism of resistance
mutations in pncA gene and alterations in bacterial drug uptake
Pyrazinamide
Toxicity
1) hepatotoxicity
2) hyperuricemia
3) GI intolerance
4) fever
5) acute intermittent porphyria
Which three drugs are mycobacterial specific?
Isoniazid
Ethambutol
Pyrazinamid (?)
Which drugs are tuberculocidal?
Isoniazid
Rifampin
Pyrazinamide
Streptomycin
Which drugs are tuberculostatic?
Ethambutol
Which TB drugs have good intracellular action? Which ones do not?
Intracellular = Isoniazid, Rifampin
Ethambutol (moderate intracellular activity)
Pyrazinamide = variable intracellular
Poor intracellular = streptomycin
TB drug resistance
Monotherapy, inadequate drug regimen, or poor compliance all contribute to resistance. Can also acquire infection with a strain that is resistant
MDR and XDR TB resistance
MDR = TB resistance to at least isoniazid and rifampin
XDR-TB = TB resistant to Isoniazid and Rifampin, plus any fluoroquinolone and at least one of three injectable second line drugs
Treatment of TB - regimen?
1) Intensive phase (2 mo): isoniazid, rifampin, pyrazinamide, and ethambutol
2) Continuation phase (4-7 mo): Isoniazid, Rifampin
Opportunistic Infection
an infection that occurs in a compromised host by an organism which does not usually infect a “normal” host
Nosocomial infection
infections that occur in an institutional setting (hospital, convalescent centers, nursing homes)
Iatrogenic infection
infections resulting from the activity of a physician or other healthcare giver
Conditions that contribute to opportunistic infections: (5)
1) Granulocytopenia
2) Cellular immune dysfunction
3) Humoral immune dysfunction
4) Foreign Body
5) Surgery
Conditions that contribute to opportunistic infections:
Granulocytopenia
predispose you to what bugs?
low PMNs from chemo or radiation therapy
→ Gram negatives and staph
Conditions that contribute to opportunistic infections:
Cellular immune dysfunction
predispose you to what bugs?
AIDS, age, smoking, T-cell defects
→ Intracellular pathogens - Salmonella
→ Mycobacterium tuberculosis and avium, Listeria monocytogenes
Conditions that contribute to opportunistic infections:
Humoral immune dysfunction
predispose you to what bugs?
Agammaglobulinemia, Splenectomy
Encapsulated pathogens → S. pneumoniae, Meningococci
Conditions that contribute to opportunistic infections:
Foreign Body
predispose you to what bugs?
IV or urinary catheter, bone implant
Gram negatives, Staph
Conditions that contribute to opportunistic infections:
predispose you to what bugs?
Staph, E. Coli, Pseudomonas
3 mechanisms by which endotoxin (LPS) from gram negatives cause systemic disease?
1) Complement cascade activation → INFLAMMATION, high fever
2) Hageman Factor (XII) activation → Fibrinolysis, Hypotension
3) MACROPHAGES release TNF-a → activate factor 7 and 10 → DIC
Pseudomonas Aeruginosa:
gram? shape? lactose? oxidase? catalase? motility? synthesizes what pigments?
Gram negative bacilli Non-lactose fermenting Oxidase + Catalase + Motile Synthesizes pyoverdin and pyocyanin
pyoverdin and pyocyanin
Functions to generate ROS to kill competing microbes
→ sweet “grape-like” odor
When grown on ___________ Pseudomonas generate a blue-green pigment
Grown on King’s A and B → Blue-green pigment
Pseudomonas Aeruginosa
Virulence factors (4)
Exotoxin A
Phospholipase C: degrades plasma membrane
Pyocyanin: generates ROS
Endotoxin (LPS)
Pseudomonas Aeruginosa
Exotoxin A mechanism
inhibits host protein production by ADP-ribosylation of EF2
Pseudomonas Aeruginosa
Transmission
contact spread typically in immunocompromised patients (burn, nosocomial settings)
Widespread in moist areas of the environment and is part of normal gut flora in some people
Pseudomonas Aeruginosa
Types of infections (7)
OPPORTUNISTIC PATHOGEN
1) Chronic pneumonia (especially CF and intubated patients)
2) Sepsis (burn and chemo patients)
3) Ecthyma gangrenosum: rapidly progressive, necrotic lesion) in immunocompromised patients
4) UTI
5) Otitis Externa
6) Osteomyelitis, Septic Arthritis → secondary to nail puncture wound to the foot
7) Skin infections (“hot tub folliculitis”, burn patients)
Pseudomonas Aeruginosa
Resistance mechanisms:
High innate resistance mechanisms (many efflux pumps)
Propensity to form biofilms
Iron and Bacterial Virulence:
Nearly all bacteria require iron for growth - which two bacteria are exceptions?
what happens if you have an excess of iron in your body (e.g. hemochromatosis)
Exceptions: Lactobacilli, Treponema pallidum
If a person has really high iron, they are more susceptible to infection!
Challenges for bacteria with iron: (5)
1) Iron is poorly soluble under physiological conditions
2) Iron levels WITHIN bacteria varies 10x, while levels are highly variable outside bacteria
3) Most Fe2+ in humans is bound to transferrin or lactoferrin (only 20-30% saturated with Fe2+)
4) Excess iron is highly toxic to bacteria due to production of hydroxyl-radicals (Fenton reaction)
5) Host defences
Host defenses and Iron (3)
Shunting of iron into storage during infection (liver)
Decrease iron absorption from intestine during infection
Decrease expression of microbial iron binding compounds
Bacteria iron adaptations: (6)
1) Siderophores and high affinity uptake systems
2) Receptors to steal siderophores from normal flora bacteria
3) Reductase enzymes to free iron from host iron-binding systems
4) Receptors to bind host heme or lactoferrin and utilize their Fe directly
5) Microbial toxins to kill eukaryotic cells and release Fe
6) Proteases to degrade host iron binding proteins
Sites of Viral Replication in the Respiratory Tract
-which virus prefers to replicate in the URT?
temperature differential between upper and lower respiratory tract → consequences for pathogenesis
Upper respiratory tract: preferential site for Rhinoviruses (exception is rhinovirus C)
The rest replicate in BOTH URT and LRT
Patterns of viral infection:
3
1) Acute infection with replication confined to respiratory mucosal surface:
2) Persistent replication on respiratory mucosal surface:
3) Systemic replication after primary replication on respiratory mucosal surface:
Acute infection with replication confined to respiratory mucosal surface: (4 viruses)
Paramyxovirus (parainfluenza)
Orthomyxovirus (Influenza)
Coronavirus
Picornavirus (rhinovirus)
Persistent replication on respiratory mucosal surface:
3 viruses
EBV
adenovirus
papillomavirus
Systemic replication after primary replication on respiratory mucosal surface: (6 viruses)
Paramyxovirus (mumps, measles) Varicella, Zoster, HHV6, CMV Rubella Picornavirus (poliovirus) Poxviruses Reoviruses
Transmission of Respiratory Viruses
fomites, aerosol transmission
Primary interaction between respiratory viruses and host occurs at EPITHELIAL surface → infection of epithelial cells → release of cytokines → symptoms
Influenza Virus
main features:
- virus family
- genome
- shape, envelope
- site of replication
orthomyxovirus
Helical, enveloped, negative segmented ssRNA
*NUCLEAR replication
Consist of Influenza A, B, and C
Influenza A
animal species
Glycoproteins have greater variability than in strain B and C
HA undergoes minor and occasional MAJOR changes - very important = ANTIGENIC SHIFT
Influenza B and C
human pathogens
B → relatively slow change in HA
C → uncommon strain
Structure of Influenza virus
Envelope → bases for classification of influenza
Neuraminidase (NA)
Hemagglutinin (HA)
Hemagglutinin (HA)
13 major antigenic types
Binds sialic acid on cells → facilitates endocytosis
Neuraminidase (NA)
9 major antigenic types, enzymatic properties
Cleaves HA-sialic acid interaction during budding to permit viral spread
Replication of Influenza virus?
what causes symptoms?
Virus replicates in ciliated epithelial cells of URT
→ Lysis and necrosis of cells
→ symptoms (fever, chills, muscular aching, headache, prostration, anorexia)
Antigenic Drift
HA and NA drift occurs via POINT MUTATIONS
Minor antigenic changes that occur continuously in host populations during interpandemic periods due to selective advantage of new strain
Occur every year → slight alterations in HA or NA → EPIDEMICS
Antigenic Shift
*ONLY Influenza A - radical change in HA and/or NA → emergence of new major antigenic variants due to GENETIC REASSORTMENT
Genetic reassortment occurs when more than 1 virus infects a cell
Exchange of RNA segments between human and animal virus → radically new HA or NA = PANDEMIC
Influenza Prevention
Vaccines target A and B but NOT C
Seasonal flu vaccine (updated yearly): bivalent, protects against seasonal A and B influenza types
1) Attenuated (intranasal)
2) Killed virus
Influenza Pathogenesis
spread primarily by aerosols
Can spread virus in absence of symptoms
Highly infectious, typically infection results in symptoms
Normally self-limited infection lasting 3-7 days
Death from primary influenza infection rare - usually due to secondary infection
Why do people usually die from influenza?
what bugs (3) are often the cause of this deadly complication?
Death from primary influenza infection rare - usually due to secondary infection
Damage to respiratory epithelium predisposes to bacterial infections → deaths
Secondary bacterial pneumonia usually caused by:
Staph aureus
H. influenzae
Strep pneumoniae
zanamivir, oseltamivir, peramivir
mechanism?
Neuraminidase inhibitors
amantadine, rimantadine
High resistance to Amantadine
M2 channel blockers
Parainfluenza virus
Main features
helical, enveloped capsid virus with negative sense ssRNA paramyxovirus
Envelope contains HA and NA
Contain viral fusion (F) surface proteins
Parainfluenza virus
viral fusion (F) surface proteins - causes what?
causes infected cells to form multinucleated giant cells (syncytia) and mediates cell entry
Parainfluenza virus
Transmission and Infection
Inhalation via aerosols → initial infection in larynx mucosa via HA and NA → progress down toward trachea and bronchial epithelium
→ Inflammation and swelling of mucous membranes → narrows lumen → can cause obstruction of inspiration and expiration
Parainfluenza virus
Diseases (2)
1) Croup
2) Pneumonia
Parainfluenza virus
Croup
(children): fever, hoarseness, barking cough upon expiration, inspiratory stridor
“Steeple sign” on XR (subglottic narrowing)
TX = glucocorticoids, nebulized epinephrine
Measles (Rubeola) virus
Main feature
Paramyxovirus
Helical, enveloped capsid virus
Negative ssRNA
Measles (Rubeola) virus
Matrix (M) Protein
regulates viral RNA synthesis and assembly
Strains that cause SSPE do NOT contain matrix (M) protein antigen
Measles (Rubeola) virus
Replication
occurs during 8-10 day incubation period - measles virus replicates and lyses respiratory epithelial cells → infection and lysis of reticuloendothelial cells
Measles (Rubeola) virus
Measles Disease
1) fever, malaise, anorexia
2) Conjunctivitis
3) Cough
4) Sore throat
5) Coryza (rhinitis)
6) Koplik’s spots
7) Rash
Measles (Rubeola) virus
Koplik’s spots:
pathognomonic for measles
1-3 mm whitish/grayish/bluish elevations with erythematous base - seen on buccal mucosa near molar teeth
Measles (Rubeola) virus
Rash of measles infection
maculopapular, blanching rash that appears days after prodrome phase
Begins on face, spreads centrifugally to involve body and extremities
RASH has NO ROLE in virus transmission
Complications of Measles infection? (4)
1) Subacute Sclerosing Panencephalitis (SSPE)
2) Acute encephalitis (Rare)
3) Giant Cell Pneumonia (only in immunosuppressed)
4) Measles and pregnancy:
Subacute Sclerosing Panencephalitis (SSPE)
Fatal, progressive degenerative disease of the central nervous system
Occurs 7-10 years after initial measles infection
Presentation: personality changes, lethargy, difficulty in school and odd behavior, progression to dementia, severe myoclonic jerking, flaccidity and decorticate rigidity
Strains that cause this do NOT contain matrix (M) protein antigen
Measles and pregnancy
infection of pregnant women with MV can result in premature labor, spontaneous abortion, low-birth weight infants
Measles prevention
live attenuated MMR vaccine
Measles transmission and replication?
Transmission via respiratory droplets, is HIGHLY CONTAGIOUS
Replicates in nasopharynx and moves to lymph nodes → VIREMIA (5-7 days after exposure)
EXTENSIVE generalized virus infection in lymphoid tissue/skin
Measles Histological examination signs:
Lymphoid organs show fused lymphocytes (Warthin Finkeldey Giant Cells) + paracortical hyperplasia
Treatment of measles virus infection?
Treatment: supportive, can try Vitamin A
Rubella
Main features
(not a respiratory virus): aka German Measles
icosahedral
enveloped
nonsegmented, positive sense ssRNA
Togavirus
Rubella
Disease
German Measles aka “3 day measles”
Low grade fever and lymphadenopathy 1-5 days prior to rash
RASH
Rubella
Characteristic rash?
maculopapular rash, begins on face, spreads to extremities
Antibody mediated
Present for 3 days
Pregnancy and Rubella:
Manifestations in women
Women infected get postauricular and occipital lymphadenopathy with maculopapular rash
Congenital rubella
occurs with infection during FIRST trimester
PDA, cataracts, sensorineural deafness
Pulmonary artery hypoplasia
Microcephaly
Purpuric “blueberry muffin” rash (dermal erythropoiesis)
Rubella
Prevention
MMR live-attenuated vaccine
Rubella
Transmission
aerosol droplets or transplacentally
Aerosol infection of nasopharynx → 14-21 day incubation period with replication in local lymph nodes → prodrome
Mumps
Main Features:
Paramyxovirus
Helical, enveloped capsid virus
Negative ssRNA
Mumps
Structure
Fusion (F) surface protein
causes infected cells to form multinucleated giant cells (syncytia)
Mumps
Prevention
MMR live attenuated vaccine → immunity for life
Mumps
Tranmission
Transmission via respiratory droplets
Humans are ONLY natural reservoir
Less infectious than measles and chickenpox
Mumps
invasion and replication
Invades URT epithelium via hemagglutinin envelope proteins → local lymph nodes → VIREMIA
2-3 week incubation period → inflammation and edema of glandular tissue, spread to meninges
Mumps Disease
Parotitis → elevated serum amylase, leukopenia, lymphocytosis
Orchitis
Meningitis (aseptic) and encephalitis
Acute pancreatitis
Mumps - treatment?
supportive
RSV
Main features?
Paramyxovirus
Helical, enveloped capsid virus
Negative sense ssRNA
RSV
Structure (2 main proteins and their function)
Viral fusion (F) protein → infected cells fuse and form syncytia
Protein G → allow attachment to bronchiolar and alveolar epithelium → necrosis and inflammation of bronchioles and alveoli
RSV
Disease
Lower respiratory tract disease (Infant Bronchiolitis, Pneumonia)
One of the most common causes of pneumonia in children and bronchiolitis (especially children)
→ Affects many children UNDER 6 months of age
Can cause bronchitis, pneumonia, and croup
RSV
Diagnosis (3 ways)
- epidemiology
- nasal swab tests to detect RSV antigen
- histology of cells from LRT
RSV - Prevention
1 drug and its mechanism/use
Palivizumab: monoclonal antibody used for prophylaxis in immunocompromised at high risk for RSV Targets F (fusion) protein of RSV → inhibit cell entry
RSV transmission
Transmission via respiratory droplets
RSV treatment - 1 drug and its mechanism/use
Ribavirin: purine nucleoside analog
Used in severe cases of RSV in immunocompromised patients
Orthomyxoviruses
- viruses that belong to this family?
- replication?
- genome?
- envelope?
Influenza: A, B, and C
Nuclear replication
Segmented (-) sense RNA
Enveloped
Paramyxoviruses
viruses that belong to this family?
Paramyxovirus: Mumps, Parainfluenza
Morbillivirus: Measles
Pneumovirus: RSV
Paramyxoviruses
- replication?
- genome?
- envelope?
Cytoplasmic replication
No polarity to their infection (can come in/go out both apical or basal side)
Non-segmented (-) sense RNA
LITTLE genetic variation
Enveloped
How do the glycoproteins on paramyxoviruses differ from those on orthomyxoviruses
Glycoproteins: do not form such prominent spikes as on influenza virus
HN - Hemagglutinin + Neuraminidase activities
Measles → H protein (no neuraminidase activity)
RSV → G protein (neither activity
Virus cultivation (2 ways we do this)
1) growth in tissue culture cells
2) cytopathic effects (CPE)
Growth in tissue culture cells:
3 steps
1) Cells in culture → add patients sample to cells → cells will become infected if patient is infected
2) Anti-virus Ab added → binds infected cells
3) Fluorophore-labeled anti-IgG Ab → lights up if present
Cytopathic effects
provides evidence of presence of infectious virus
Tests for virus antigen - 4 tests that do this
1) Western blot
2) immunofluorescence assay
3) hemadsorption
4) rapid immunoassays
Hemadsorption
what does it test?
how do tests results differ for infected vs. uninfected cells?
Tissue culture cells + RBCs
Uninfected → No RBC binding (Hemadsorption negative)
Infected → RBC binding to infected tissue culture cells (Hemadsorption positive)
-tests for virus antigen
Tests for virus nucleic acid
3 tests that do this
PCR
RT-PCR
Multiplex PCR (qualitative vs. quantitative)
RT-PCR
4 steps
Reverse Transcription PCR
1) viral ssRNA reverse transcribed into cDNA
2) cDNA/RNA hybrid then melted to separate RNA and cDNA
3) Add specific viral primer + DNA polymerase → synthesis of second strand cDNA
4) dsDNA melted and amplified for detection → run on gel and look for dsDNA of a specific size
What does RT PCR look for?
what is it used to screen?
*used to screen donated blood for virus
Tests for virus nucleic acid
Tests for virus-specific antibody
1) ELISA
2) Virus-Specific IgM or IgG Capture ELISA
3) Western blot
4) Hemagglutination Inhibition
5) Hemadsorption Inhibition Test
ELISA
3 steps
what does it test for?
1) Each well coated with virus antigen → patient sample added to well (may or may not contain Abs specific for antigen in well)
2) Enzyme linked anti-human IgM or IgG added to well
3) Add enzyme substrate - if enzyme present, will produce color change
Tests for virus-specific antibody
Virus-Specific IgM or IgG Capture ELISA
1) Each well coated with anti-human IgM or IgG
2) Add patient sample, all IgM (or IgG) Abs bound in well
3) Virus antigen added
4) Enzyme linked anti-virus antigen Ab added to well
5) Add enzyme substrate → color change if enzyme present
Hemadsorption Inhibition Test
- test results for infected vs. non-infected
- tests for what?
Infected cells in tissue culture + RBCs → RBC binding to viral surface protein
Infected cells + RBCs + Abs to cells (specific for specific viral proteins)→ NO RBC binding because specific antibodies have blocked RBC binding
CONFIRMS infection via a specific virus
Do NOT know that this virus is the cause of the patient’s illness
Hemagglutination Inhibition Test
serological confirmation that isolated virus was associated with patient’s disease
tests for virus specific antibody
Hemagglutination Inhibition Test
test results for infected vs. non-infected
RBCs + virus → Hemagglutination (network formation)
-When hemagglutination occurs that shows there are NO antiviral antibodies present in the patient’s serum (aka not cause of patient’s disease)
RBCs + virus + Ab → No hemagglutination (Ab binds virus, prevents RBC binding with virus)
Adenoviruses
main features
linear dsDNA virus, icosahedral, non-enveloped
- Very common, most are asymptomatic
- Different serotypes associated with different diseases
- Can be reactivated during immunosuppression (AIDS)
- Virus can shed for long periods after infection, asymptomatic
Adenoviruses
Mode of entry and replication
virus binds via hemagglutinin and enters and lyses mucosal cells
Adenoviruses
Diseases (7)
Acute respiratory disease and pneumonia
- Conjunctivitis
- Common cold
Acute hemorrhagic cystitis
Gastroenteritis (day care - not as common as rotavirus)
Myocarditis
More serious clinically in immunosuppressed)
Rhinovirus
main features
picornavirus family
Linear positive sense ssRNA virus, naked, icosahedral capsid
Rhinovirus
Mode of entry and replication
Binds ICAM-1 of URT epithelial cells → spreads locally WITHOUT killing cells → local inflammation, increase ICAM-1 expression
Acid LABILE (does not cause GI disease)
Preferentially replicates at cooler temp (33 C) in nose/upper airways
Rhinovirus
Diseases (3)
1) Most common cause of URT (e.g. “cold”)
- Generally self-limiting
2) Otitis media
3) Exacerbations of chronic pulmonary disease
Coronavirus
main features
Large +ssRNA, enveloped, non segmented, helical capsule
Unstable in environment
Coronavirus
Diseases (3)
Can cause systemic disease
1) Common cold (second most common cause)
2) Severe acute respiratory syndrome (SARS)
3) Middle East Respiratory Syndrome (MERS)
