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ID20 Infectious Diseases
CNS Infections
Toronto Notes 2019
Antimicrobial therapy (e.g. metronidazole) may fail to treat C. tetani unless adequate wound debridement is performed
Treatment
• generalsupportivecare
• monitorvitalsignscarefully
• IVacyclovirempiricallyuntilHSVencephalitisruledout
Generalized Tetanus
• seePediatrics,P4
Etiology and Pathophysiology
• causedbyClostridiumtetani:motile,sporeforming,anaerobicGram-positivebacillus
• foundinsoil,splinters,rustynails,GItract(humansandanimals)
• traumaticimplantationofsporesintotissueswithlowoxygenation(e.g.puncturewounds,burns,
nonsterile surgeries or deliveries)
• uponinoculation,sporestransformintoC.tetanibacillithatproducetetanustoxin
■ toxintravelsviaretrogradeaxonaltransporttotheCNSwhereitirreversiblybindspresynapticneurons to prevent the release of inhibitory neurotransmitters (e.g. GABA)
■ neteffectisthedisinhibitionofspinalmotorreflexeswhichresultsintetanyandautonomichyperactivity
Clinical Presentation
• generalizedtetanus
■ initially present with painful spasms of masseters (trismus or “lockjaw”)
■ sustained contraction of skeletal muscle with periodic painful muscle spasms (triggered by sensory
stimuli, e.g. loud noises)
■ paralysis descends to involve large muscle groups (neck, abdomen)
■ apnea, respiratory failure, and death secondary to tonic contraction of pharyngeal and respiratory
muscles
• autonomichyperactivity
■ diaphoresis, tachycardia, HTN, fever as illness progresses
Investigations
• primarilyaclinicaldiagnosis,oftenalthoughnotalwayswithahistoryofatraumaticwoundandlackof immunization
• culturewounds,creatinekinase(CK)maybeelevated
Treatment
• stoptoxinproduction
■ wound debridement to clear necrotic tissue and spores
■ antimicrobial therapy: IV metronidazole; IV penicillin G is an effective alternative
• neutralizeunboundtoxinwithtetanusimmuneglobulin(TIg)
• supportivetherapy:intubation,spasmolyticmedications(benzodiazepines),quietenvironment,cooling
blanket
• controlautonomicdysfunction:α-andβ-blockade(e.g.labetalol),magnesiumsulfate
Prevention
• infectionwithC.tetanidoesnotproduceimmunity–vaccinatepatientsondiagnosis • tetanustoxoidvaccination(seePediatrics,P4andEmergencyMedicine,ER17)
Rabies
Definition
• acuteprogressiveencephalitiscausedbyRNAvirus(genusLyssavirusoftheRhabdoviridaefamily)
Etiology and Pathophysiology
• anymammalcantransmittherabiesvirus
■ most commonly transmitted by raccoon, skunk, bat, fox, cat, and dog; monkeys also a risk in the
developing world
• transmission:breachingofskinbyteethordirectcontactofinfectioustissue(saliva,neuraltissue)with
skin or mucous membranes
■ almost all cases due to bites
■ animals can be carriers for several days before manifest signs of disease
• virustravelsviaretrogradeaxonaltransportfromPNStoCNS
• virusmultipliesrapidlyinbrain,thenspreadstootherorgans,includingsalivaryglands
• developmentofclinicalsignsoccurssimultaneouslywithexcretionofrabiesvirusinsaliva
■ infected animal can transmit rabies virus as soon as it shows signs of disease
Clinical Presentation
• fivestagesofdisease 1. incubation period
■ 1-3 mo on average (can range from days to years)