Medical Meditations

[medical-meditations]

Influenza

» influenza is a negative-sense ssRNA virus with an envelope » A, B, C core types + H_N_ subtypes that undergo antigenic shift (reinfection) and drift (pandemic) » epithelial slough and damage unleashes secondary bacterial pneumonia

inhalation or contact with infected individual/contaminated object

negative ssRNA viral invasion of respiratory epithelia

epithelial apoptosis, necrosis, and sloughing

symptoms depend on age and secondary bacterial invasion

adults: fever, myalgia, fatigue

children: flu symptoms + increased GI issues

old and young: secondary bacterial pneumonia due to epithelial damage

[medical-meditations]

Polio picornavirus

» polio is a picornavirus » aseptic meningitis and poliomyelitis

oral ingestion and cellular entry via endocytosis

primary replication in lymphatic organs

lymphatic, hematogenous, and neural spread

secondary replication in motor neurons

primary replication: nonspecific flu-like sickness

lymph, blood, neural spread: aseptic meningitis

secondary replication: paralytic poliomyelitis

[medical-meditations]

Streptococcus Group B

» vagina-colonizing S. galactiae in pregnant women » FATAL pneumonia, sepsis, and meningitis in newborns

colonize vagina in pregnant individuals

bacterial passage through placenta or birth canal

migration to infant lungs without immune defense

symptoms vary by adult v. newborn

adult: mild illness symptoms

newborn: pneumonia, sepsis, meningitis

[medical-meditations]

Streptococcus Group A

» spread through infectious physical contact with secretions or lesions » scarlet fever, necrotizing fasciitis, multi-inflammatory rheumatic fever

contact with secretions or wounds of infected individual

superficial invasion to local tissue

with mucosal breakage, deep invasion to sterile sites

symptoms depend on depth of invasion and immune hypersensitivity

superficial invasion: cellulitis with fever (erysipelas), scarlet fever with strawberry tongue

deep, sterile invasion: necrotizing fasciitis, streptococcal toxic shock

immune hypersensitivity: cardiac/neural/joint rheumatic fever, acute glomerulonephritis

[medical-meditations]

Actinomyces

» occurs in men with poor dentition and anyone whose mucosal lining breaks » slow, aggressive invasion with sulfur granule drain

invades from endogenous mouth flora into mucosal breakages in any epithelial lining

slow, aggressive invasion, often polymicrobial

longstanding chronic lesions become hard, wooden, and sulfur granule-draining

symptoms occur in anyone with mucosal lining breakage

mouth mucosal breakage: "lumpy jaw" in submandibular region

thoracic mucosal breakage: chronic pneumonia or lung mass

abdominal/pelvic mucosal breakage: most aggressive progression; right ovary-targeted

IUD-mediated mucosal breakage: targets either ovary equally

[medical-meditations]

Nocardia

» found in soil and plant matter, not humans » pulmonary nocardiosis: necrotizing pneumonia and lung mass in T-cell immunocompromised individuals

inhalation from environment (not humans!)

intracellular transfer from cell to cell

dissemination to lung and CNS

multi-organ symptoms appear in T-cell immunocompromised individuals

pulmonary nocardiosis: necrotizing pneumonia and lung mass

CNS nocardiosis: brain abscess that progresses to hemiparesis and even coma

other: skin, kidney | endocarditis | mycetoma of the foot (Madura foot)

[medical-meditations]

Listeria monocytogenes

» contaminates processed meats, dairy products, soil » produces granulomatosis infantisepticum in infants » atypical meningitis and sepsis in T-cell-immunocompromised individuals

transmitted by ingestion into GI tract

intracellular actin filopod transfer from cell to cell

hematogenous dissemination with CNS and placental preference

symptoms depend on patient's immune system strength

fetus: disseminated multi-organ disease

immunocompromised: atypical sepsis and meningitis

healthy: mild fever, chills, back pain

[medical-meditations]

Echinococcus (hydatid cyst disease)

hydatid cyst disease

transmitted through exposure to dog feces

intermediate host: humans

other hosts: dogs, sheep, cattle

clinical manifestations: large, fluid-filled sacs in brain, lung, liver

treatment: albenazole

[medical-meditations]

Hookworm

anemia

transmission: skin invasion

clinical manifestations: anemia, pulmonary opacity, anorexia, abdominal pain, diarrhea

diagnosis: stool microscopy

treatment: albendazole

[medical-meditations]

Strongyloidiasis

autoinfection

Gram- bacterial pneumonia

transmission: skin invasion from soil

clinical manifestations: pneumonia Gram- superinfection, GI tract

pathogenesis: fecal-oral auto infection route » co-infection with Gram- bacterial pneumonia hosted by the worm

diagnosis: clinical presentation, eosinophilia, stool parasite

treatment: ivermectin

[medical-meditations]

Schistosomiasis

fluke in contaminated water

snail involvement in life cycle

transmission: swimming in contaminated water

clinical manifestation: swimmer's itch, Katayama fever

severe complications: cirrhosis and portal vein damage

treatment: praziquantel

[medical-meditations]

Onchocerciasias

"river blindness"

endemic to Africa

transmission: black fly bite

pathogenesis: connective tissue invasion

diagnosis: skin snips, lymph nodule biopsy

treatment: ivermectin to reduce mazzotti reaction

[medical-meditations]

Taenia solium

cysticercosis with egg ingestion only

humans are intermediate AND definitive hosts

intermediate host: pigs, sheep, dogs, cats

definitive host: humans

diagnosis: stool exam or systemic radiography

treatment: albendazole (blocks microtubule assembly via tubular binding)

[medical-meditations]

[listeria, nocardia, actinomyces notes]

Rare, but interesting pathogenesis

Listeria monocytogenes

Characteristics

Gram-positive/gram-variable

pleomorphic bacillus rod/coccus

grows at cold temperatures

catalase+, oxidase-

Pathogenesis

ingestion » entry into human tissue in GI

GI co-infection may be required for intestinal wall crossing

hematogenous dissemination » preference for placenta and CNS

intracellular invasion » intracellular actin filopod rappelling into the next cell

Clinical manifestations

[adult] mild chills, fever, back pain

[untreated immunocompromised adult] milder/atypical meningitis and sepsis

[fetus] fatal disseminated multi-organ disease with granulomatosis infantisepticum and abscesses

Risk factors

contaminated processed meats, dairy and soft cheeses, vegetables and soil, dust

cantaloupe outbreak in 2011 with two brothers' arrest

age

immunocompromised, specifically T-cell mediated immunodeficiency

pregnancy (lowered T-cell immunodeficiency)

liver diseases with iron overload that listeria can scavenge

Treatment

ampicillin

gentamicin – toxic antibiotic :(

Nocardia

Characteristics

delicate, beaded filaments

weakly acid-fast staining, light orange cultures

catalase+ and super-oxide dismutase

Pathogenesis

inhalation and dissemination into lung and CNS

Clinical manifestations

[lung] acute/chronic pulmonary nocardiosis that can manifest as necrotizing pneumonia and cancer-like mass in lung

[CNS] brain abscess that looks like a tumor, hemiparesis and coma

[other sites] skin, kidney, endocarditis

contributor to mycetoma of the foot (Madura foot) that can be caused by many different species

Risk factors

soil and plant matter aerosol contact

immunocompromised, specifically T-cell immunodeficiency

chronic respiratory diseases

substance users

Treatment

Longer, CNS-penetrating antibiotics for CNS-nocardiosis

trimethoprim-sulfamethoxazole (bactram)

carbapenems

3rd generation cephalosporins

Actinomyces

Characteristics

anaerobic with bad scent

endogenous mouth flora that has tooth-like colonies

Pathogenesis

mechanical disruption of the mucosal barrier in ALL patient populations

slow, aggressive invasion of facial planes

polymicrobial infections with multiple microbes alongside it

soft lesions that turn fibrous and woody, eventually draining sulfur granules

Clinical manifestations

[cervicofacial] acute mass that progresses and disrupts facial planes ("lumpy jaw" in submandibular region)

[thoracic] chronic pneumonia or mass

[abdominal] slow, aggressive

[pelvic] if natural breakage » right ovary focus. if IUD: equal likelihood of either ovary focus

[CNS] brain abscess, meningitis

Risk factors

male gender

poor dentition

procedures that break the oral mucosal barrier

procedures that break other mucosal barriers

[medical-meditations]

[streptococci notes]

Streptococcus Group A (S. pyogenes)

Mild strep throat and skin infections (impetigo, cellulitis)

rapid, streaky cellulitis

erysipelas – cellulitis with fever & toxicity

scarlet fever – raised tongue papule and pharyngitis

Invasion to sterile sites with mucosal barrier breakage » severe disease

necrotizing fasciitis

streptococcal toxic shock syndrome

Immune hypersensitivity develops after infection

rheumatic fever: strep antibodies attack cardiac, joint, and neural tissue » incidence is going down now

rheumatic heart disease occurs as chronic sickness

acute glomerulonephritis: antibody-strep complexes cluster and deposit in kidney

Risk factors

symptomatic transmission only, peaks in winter and spring

immunocompromised/chronic illness

age

skin lesions

substance users

Treatment

penicillin-, erythromycin-, and clindamycin-susceptible

severe infections: penicillin and clindamycin that interrupts protein synthesis (lowers TOXIN synthesis)

amputate necrotizing fasciitis sites

Streptococcus Group B (S. agalactiae)

Pneumonia, sepsis, and meningitis in newborns

vaginal colonies in women that are passed to newborn lungs via placental penetration

OR vaginal colonies passed to infant in birth canal

infants have poor immune protection and develop severe symptoms above

Treatment

prophylaxis for pregnant women who test positive

treatment for pregnant women who present with symptoms

ampicillin + aminoglycosides for infected newborns

Streptococcus pneumoniae

Gram-positive, lancet-shaped diplococcus with lance-tip, alternative-pathway-blocking capsule

Pneumonia, bacteremia, sepsis, and meningitis in adults

abrupt onset pneumonia with coughing and rusty sputum

pleuritic chest pain

Most common cause of otitis media in children

Risk factors:

transmission from person to person in the winter

age

crowding

acute viral infections

chronic respiratory diseases (asthma, COPD, sickle-cell anemia, spleen loss)

aspiration-causing events

neutropenia, lymphopenia

Treatment

[archaic] horse serum antibodies when alternative pathway isn't responding due to S. pneumoniae capsule

PCV15/20 vaccination with capsule in adults

PCV13 vaccination with conjugated carrier + capsule in toddlers