Infectious Disease - Diseases Flashcards
Tetanus
Caused by gram positive, spore-forming, anaerobic rod Clostridium tetani
Produces tetanospasmin exotoxin, a protease which cleaves SNARE proteins on GABA-ergic and glycinergic (inhibitory) synaptic vesicles in the spinal cord; excessive stimulation of muscles causes spastic paralysis and trismus (lockjaw)
Toxic Shock Syndrome
S. aureus produces TSST-1 superantigen which cross-links MHC II and TCR outside of the antigen binding site, causing massive release of IFN-y and IL-2
Presents as fever, rash, and shock
Syphilis
Caused by Treponema Pallidum spirochete; blood screening by VDRL/RPR test with confirmatory testing by FTA-ABS
Primary - localized disease presenting as painless chancre
Secondary - disseminated disease presenting as maculopapular rash on palms/soles + constitutional sx (fever, non-tender lymphadenopathy)
Tertiary - end-organ failure characterized by chronic granulomatous disease, syphilitic heart disease (aortic atrophy/dilation, aortic valve incompetency), neurosyphilis (dementia, Tabes Dorsalis)
Treatment: Penicillin G
Respiratory Syncytial Virus (RSV)
RSV is a common cause of bronchiolitis in premature infants
Presents like a bad cold - low grade fever, rhinorrhea, cough, respiratory distress (apnea, tachypnea, wheezing, crackles)
Lyme Disease
Caused by infection with spirochete Borrelia burgdorferi, carried by ticks in the Northeastern US
Stage 1 is characterized by flu-like illness and erythema migrans rash (bullseye); may present with facial palsy
Stage 2 (early disseminated disease) targets skin, CNS (encephalopathy, facial nerve palsy, polyneuropathy), heart (AV node block), joints
Treatment: Ceftriaxone, doxycycline
Atypical pneumonia
Clasically caused by mycobacterium pneumoniae
Causes interstitial, “walking pneumonia” - presents as headache, non-productive cough
Diagnosed by presence of cold agglutinins (IgM)
Findings: X-ray looks worse than patient with diffuse, patchy inflammation localized to interstitial areas with distribution involving > 1 lobe
Treatment: Macrolide, doxycycline, or fluoroquinolone
Bacterial endocarditis
Most often of the mitral valve, but tricuspid valve endocarditis is associated with IV drug abuse; common pathogens: staphylococcus aureus (acute), viridans streptococci (subacute)
Presents with fever, new systolic murmur secondary to tricuspid regurgitation
Complications: May seed septic emboli from the right side of the heart, resulting in pulmonary manifestations (cough, pleuritic chest pain, diffuse pulmonary infiltrates), chordae rupture, pericarditis
Epiglottitis
Most commonly caused by H. influenzae
Presents with high fever, dysphagia, drooling, inspiratory stridor, and respiratory distress
Findings: X-ray shows thickening of epiglottis (thumbprint sign)
Pneumocystis pneumonia
Opportunistic infection caused by pneumocystis jirovecii; causes pneumonia in immunocompromised hosts - HIV or post-transplant
Presents as an acute pneumonia with fever, cough, tachypnea, and hypoxia
Findings: Diffuse interstitial pneumonia on X-ray with “ground glass” appearance
Treated with TMP-SMX
Poststreptococcal glomerulonephritis
Nephritic syndrome that develops ~10 days after pharyngitis or skin infection with nephritogenic strain of Group A b-hemolytic streptococcus
Type III hypersensitivity reaction due to deposition of antigen-antibody complexes within the glomerular basement membrane, leading to complement activation
Presents with hematuria, proteinuria, oliguria, and hypertension
Treatment: Supportive; disease is self-limited
Mononucleosis
Infection caused by the Epstein Barr Virus (HHV-4)
Presents with flu-like symptoms, increasing fatigue, lymphadenopathy, and splenomegaly
Chic
kenpox
Caused by Varicella Zoster Virus (VZV); spread by respiratory droplets and/or direct contact
Presents as a vesicular eruption appearing first on the trunk and alter on the face; “dew drop on a rose petal” lesions appear in varied stages of healing
Treatment: Usually self-limiting; may be treated with acyclovir, famciclovir, valacyclovir
Live-attenuated vaccine available
Shingles
AKA Herpes Zoster Virus (HZV); caused by reactivation of varicella zoster virus (VZV) infection from dorsal root ganglion secondary to chickenpox
Presents as a unilateral vesicular eruption confined to a single dermatome
Treated with Acyclovir, Famciclovir, Valacyclovir
Complications: Post-herpetic neuralgia, facial nerve palsy, retinitis
Cat scratch fever
Caused by Bartonella henselae; transmitted by bite or scratch of bacteremic cats
Presents with a primary innoculation lesion, low grade fever, and regional lymphadenopathy
Rocky Mountain Spotted Fever
Caused by gram negative cocci Rickettsia Rickettsii found in southern Atlantic US, transmitted by tick vector
Clinical triad = headache + fever + rash (vasculitis of wrists, palms, soles)
Treated with doxycycline or chloramphenicol
Rotavirus
Rotavirus = DNA Reovirus family
Most common cause of fatal diarrhea in children; common cause of acute diarrhea in US during winter months, especially in daycare centers
Causes acute nausea, vomiting, watery diarrhea, and low grade fever; self-resolves after several days but may lead to transient lactose intolerance due to destruction of lactase-producing enterocytes in the small intestine
Treatment: Fluid replacement
2 oral, live-attenuated vaccines available
Rabies
Rhabdovirus family - ssRNA; transmitted by bats, raccoons and skunks; virus migrates into CNS via retrograde transport up nerve axons from site of infection with long latency before onset of symptoms (weeks-months)
Post-exposure treatment includes wound cleaning, rabies vaccine (killed virus), +/- rabies immune globulin
Presents with fever/malaise, agitation, photo/hydrophobia, paralysis, coma, and death
Findings: Negri bodies, enlarged salivary glands
3 most common pathogens found in uncomplicated UTI
- E. coli (80%)
- Staphylococci saprophyticus (10-15%, especially sexually active women)
- Klebsiella pneumoniae
Leptospirosis
Caused by pathogen Leptospira interrogans found in water contaminated with animal urine; commonly seen in surfers in the tropics
Presents with flu-like illness, jaundice, conjunctival erythema, photophobia
Weil disease
AKA Icterohemorrhagic Leptospirosis
Severe presentation of leptospirosis with jaundice and azotemia due to liver/renal dysfunction, fever, hemorrhage, and anemia
H. pylori
Gram negative, comma-shaped rod associated with 70% of gastric ulcers and ~100% of duodenal ulcers in PUD
Associated chronic gastritis (antral) and increased risk of gastric adenocarcinoma and MALT lymphoma
Dx with urea breath test or endoscopy with biopsy
Treated with triple therapy (PPI + Bismuth + Tetracycline)
Entamoeba Histolytica
Protozoan pathogen transmitted via fecal-oral route through cysts in water
Presents with bloody diarrhea (dysentery), abdominal cramping / tenesmus, + liver abscess / RUQ pain
Findings: Serology shows protozoans with ingested RBCs; stool sample shows cysts; LFTs show elevated alk phos with ~ normal ALT, AST, and bilirubin
Treatment: Metronidazole, Iodoquinol
Enterohemorrhagic E. Coli
Serotype O157:H7 is most common; transmitted by contaminated meat/water leading to outbreaks
Non-invasive BUT produces Shiga-like toxin, which binds to rRNA in enterocytes and renal epithelial cells, inhibiting protein production and causing tissue damage
Presents with 5-10 days of bloody diarrhea, severe abdominal cramps, low grade fever; possible hemolytic uremic syndrome (thrombocytopenia + anemia + acute renal failure)
Treatment is supportive only - fluids +/- dialysis; antibiotics do not shorten course of dz and may increase risk of HUS
Schistosoma haematobium
Trematode parasite; snails are host, penetrates through skin of human to cause granuloma, fibrosis, and inflammation of liver and spleen
Chronic infection associated with squamous cell carcinoma of the bladder; presents with painless hematuria
Trx: Praziquantel
Erlichosis
Caused by parasite Erlichia Chaffeensis; transmitted by Lone Star Tick)
Presents with fever, malaise, rash
Findings: Monocytes/neutrophils with “berry-like” cytoplasmic inclusions (morulae)
Respiratory Legionellosis (Legionnaire’s Disease)
Severe pneumonia caused by gram negative Legionella; usually seen in older patients with risk factors (tobacco, alcohol, DM, chronic illness, etc.)
Transmitted by aeresolized droplets from environmental water source (air conditioners); no person-to-person transmission
Presents with severe pneumonia, fever, GI and CNS symptoms; milder, flu-like presentation = Pontiac Fever); antibodies can x-react with the enzyme responsible for VWF degradation leading to thrombotic thrombocytopenic purpura, intravascular hemolysis, elevated BUN/Creatinine
Dx: Presence of antigen in urine, growth on charcoal yeast extract agar
Trx: Macrolide or Fluoroquinolone
Trichomoniasis
Caused by trichomonas vaginalis; responsible for 10% of women seeking STI treatment
Presents with vaginitis - vaginal pruritis, dysuria, foul-smelling, green discharge; finding of “strawberry cervix” seen
Diagnosed by the presence of mobile, flaggelated trophozoites on discharge wet prep
Treatment: Metronidazole for patient and prophylaxis for partner
Cholera
Caused by gram negative pathogen Vibrio Cholera
Causes secretory (non-inflammatory, non-bloody) diarrhea; voluminous “rice water” stools without WBCs
Can lead to severe dehydration, electrolyte abnormalities, cardiac/renal failure
Treatment: Oral rehydration therapy
Pneumococcal pneumonia
Caused by streptococcus pneumoniae (alpha-hemolytic strep); optochin sensitive, gram positive diplococci
Most common cause of community acquired pneumonia, especially among adults 18-65 and the elderly
Presents with fever, chills, pleuritic chest pain, and cough productive of green/rusty sputum
Findings: Lobar findings on physical exam - dullness to percussion, bronchial breath sounds, egophany in a focal area, lobar consolidation on CXR
Treatment: Penicillins or cephalosporins; macrolides in allergic patients
Poliomyelitis
Caused by polio virus with fecal-oral transmission
Virus initially infects and replicates within the pharynx and small intestine causing fever, malaise, nausea, vomiting, an diarrhea; hematogenous spread to the CNS causes death of LMNs in the anterior horn of the spinal cord
Presents with LMN signs: hypotonia, muscle weakness/flaccid paralysis, hyporeflexia, muscle atrophy; most serious complications are para/quadriplegia, respiratory muscle paralysis
Nocardia
Gram positive aerobe forming branching filaments; stains weakly acid-fast positive
Normally found in soil; causes pulmonary and brain abscesses in immunocompromised patients
Treated with sulfonamides
*Often mistaken for TB due to pulmonary manifestations and weakly acid-fast staining
Candida albicans
Dimorphic yeast - can form pseudohyphae or buds; catalase positive
Common cause of mucocutaneous and systemic fungal infections including: oral/pharyngeal thrush in immunocompromised patients, vulvovaginitis, diaper rash, endocarditis in IVDUs, chronic mucocutaneous candidiasis (due to T cell deficiency), chronic granulomatous disease (due to NADPH oxidase deficiency)
Treated with Nystatin (topical) or amphotericin (systemic)
Chlamydia conjunctivitis
Transmitted from infected mother to newborn upon passage through the birth canal
Presents in the newborn several days - several weeks after birth with swollen eyelids, conjunctival inflammation, and purulent discharge
Treated prophylactically with erythromycin eye drops
Respiratory Syncytial Virus (RSV)
Most common cause of bronchiolitis and pneumonia in children; most children have been exposed by age 2
Presents with cough, tachypnea, low grade fever, and mildly decreased O2 sat; crackles and expiratory wheezes heard on auscultation
Dx: Rapid serological test for viral antigen
Pulmonary Aspergillosis
Cause of fungal pneumonia in immunocompromised (neutropenic) patients; due to Aspergillus fumigatus
Presents with pleuritic chest pain, cough, hemoptysis, and dyspnea
Measles
Caused by Rubeola (paramyxovirus)
Initially presents as cough, coryza (acute inflammation of the upper respiratory mucosa), and conjunctivitis + characteristic red, maculo-papular rash which spreads from the head downward; + Koplik (blue/white) spots of buccal mucosa
Complications:
Acute disseminated (post-infectious) encephalomyelitis
Subacute sclerosing panencephalitis
Live-attenuated vaccine available
Acute disseminated (post-infectious) encephalitis
Occurs as a rare complication of Rubeola (measles) infection
Causes multifocal inflammation and de-myelination of white matter in the brain and CNS; auto-immune mediated
Similar to MS but occurs as a single episode with fever and loss of consciousness
Subacute sclerosing panencephalitis
Occurs as a result of long-standing infection with measles (Rubeola virus)
Stage 1 - Behavior/personality changes, decreased memory
Stage 2 - Myoclonic spasms, increasing memory impairment
Stage 3 - Blindness, mutism, coma; fatal
Can be chronically managed (not cured) in Stage 1 with interferon, Ribavirin
Whooping Cough
Caused by gram negative rod bordatella pertussis
Produces pertussis toxin; toxin inhibits Gi, leading to overactivity of adenylate cyclase with increased production of cAMP; this leads to inhibition of phagocytosis and survival of the microbe
Presents as cough on expiration and “whooping” on inspiration
Meningococcal Meningitis
Caused by N. meningidites - 2nd most common causative organism in young adults
Presents with headache, malaise, pain with flexion and extension of the neck, + petechial / maculopapular rash on the extremities (with meningococcemia)
Labs: CSF shows elevated WBCs (primarily neutrophils), elevated protein, low glucose
Diagnosed by CSF culture on Thayer-Martin agar
Diptheria
Caused by the gram positive rod Corynebacterium diptheriae via a pro-phage encoded exotoxin which inhibits protein synthesis via ADP-ribosylation of EF-2
Presents with pseudomembranous pharyngitis, cervical lymphadenopathy, dysphagia
Toxoid vaccine preventable
Molluscum Contagiosum
Caused by the poxvirus
Presents as flesh-colored nodules
Transmitted to the trunk by swimming pools and towels (especially in kids) or to the genitals by sexual contact
Otitis Externa
AKA “Swimmer’s Ear,” often caused by Pseudomonas
Presents with ear pain, fever, erythema and tenderness of the external auricle and mandibular area
Progressive Multifocal Leukoencephalopathy (PML)
An opportunistic infection caused by re-activation of latent JC virus in the CNS
Seen in advanced AIDS patients with CD4 < 200; causes destruction of oligodendrocytes with demyelination of white matter
Presents with initial visual field deficits, mental status changes, and weakness; progresses to blindness, dementia, coma, and death within 6 months
CSF fluid analysis is unremarkable; MRI shows non-enhancing lesions
Bacterial Vaginosis
Caused by Gardernella vaginalis infection - gram-variable, pleomorphic rod
Presents as gray vaginal discharge with a fishy odor; associated with sexual activity but NOT sexually transmitted
Microscopy shows clue cells
Treated with metronidazole or clindamycin
Mucormycosis
Non-septate, branching fungal infection of the nasal cavity and sinuses
Seen mostly in ketoacidotic patients due to increased concentrations of glucose and ketones
Presents with headache, fever, facial pain, nasal discharge
Risk of meningitis if fungi penetrate through cribiform plate into CSF space
Treated with Amphotericin B
Hepatitis E
RNA Hepevirus; transmitted via fecal-oral route, common in Sub-Saharan Africa
Presents acutely with nausea, vomiting, and abdominal pain associated with low-grade fever
High mortality in pregnant women
Staphylococcal toxic shock syndrome
Caused by release of TSST-1 toxin by S. aureus; TSST-1 is a super-antigen that non-specifically cross-links MHCII and TCR leading to clonal T-cell proliferation with massive release of IFN-y and IL-2
Presnts with fever, hypotension, desquamating rash, and end organ damage
Mumps
A paramyxovirus clasically infecting the parotid glands and testes
Presents with swollen neck and parotid glands, orchitis, and asceptic meningitis; risk of infertility, especially after puberty
Brucella Melitensis
Intracellular, gram negative coccobacilli; acid fast
Enters the body through contaminated milk or direct contact with infected live stock
Presents with undulating fever, weakness, loss of appetite
Tularemia
Caused by intracellular, gram negative rod Francisella Tularensis; carried by rabbits, transmitted to humans by flea or tick bite
Presents as a well-demarcated, ulcerative lesion with a black base
Actinomyces israelli
Gram positive anaerobe found in normal oral flora
Causes orofacial abscesses which drain yellow pus that demonstrates “sulfur granules”
Treated with IV penacillin x 2-4 weeks followed by oral penicillin or amoxicillin x 6-12 months
St. Louis Encephalitis
Due to an arthropod-transmitted Flavivirus; most commonly seen in the Mississippi River Valley
Most common cause of epidemic encephalitis in the US; also causes meningitis
Treatment is supportive; no specific antiviral medications exist
Chagas Disease
Caused by South American protozoa Trypanosoma cruzi; transmitted by the painless bite of the Reduviid bug (“kissing bug”)
Presents as dilated cardiomyopathy, megacolon, megaesophagus
Romana sign characteristic of acute phase
