›Viral entry and peripheral nervous system transport
›Route of infection
›Lyssavirus (RABV) introduced through bite wound into muscle
›Initial replication in myocytes at inoculation site
›Binds to nicotinic acetylcholine receptors, NCAM, and p75 neurotrophin receptors on nerve terminals
›Retrograde axonal transport
›Virus hijacks dynein motor proteins for retrograde axonal transport
›Transport rate approximately 8-20 mm/day
›Explains incubation period inversely proportional to bite-to-brain distance
›CNS invasion and neuropathology
›Brainstem and spinal cord tropism in paralytic form
›Preferential infection of spinal cord anterior horn cells and dorsal root ganglia
›Perivascular inflammation and neuronophagia
›Negri bodies: eosinophilic cytoplasmic inclusions in hippocampal neurons and Purkinje cells — pathognomonic but may be absent in paralytic form
›Axonal Guillain-Barre-like pathology
›Paralytic rabies shows immune-mediated axonal injury in peripheral nerves
›Anti-GM1 and anti-GD1a ganglioside antibodies detected in some cases
›Suggests molecular mimicry between RABV antigens and peripheral nerve components
›Why the paralytic form occurs
›Paralytic vs furious form determinants
›Viral strain: bat variants and some dog strains preferentially produce paralytic form
›Host immune response: stronger early immune activation may modulate limbic involvement
›Route of transmission: hematogenous vs neural spread may favor different patterns
›Preserved consciousness mechanism
›Less involvement of limbic system and brainstem arousal circuits early
›Cortical involvement occurs late as virus spreads via centrifugal dissemination
›Autonomic dysfunction mechanism
›Hypothalamic and brainstem nuclei invasion
›Dysregulation of sympathetic and parasympathetic outflow
›Catecholamine surges causing cardiac arrhythmias
›Hypersalivation from excessive parasympathetic tone
Therapeutic Considerations
›PEP efficacy and timing
›PEP is nearly 100% effective when given promptly after exposure
›No documented PEP failures when correctly administered and begun promptly
›Failures occur with delayed wound care, deviation from schedule, or incorrect HRIG infiltration
›Single-visit PEP (1 dose vaccine + HRIG) being studied as simplified protocol
›PEP effectiveness window
›PEP must begin before CNS entry — once virus reaches CNS it is inaccessible to antibody
›No upper time limit for starting PEP after exposure but earlier is always better
›Why treatment fails for clinical disease
›Blood-brain barrier impermeability
›Passive antibody (HRIG, IVIG) cannot penetrate CNS once virus is established there
›Antiviral agents have poor CNS penetration
›Immune evasion
›RABV glycoprotein induces apoptosis of T lymphocytes
›Virus maintains axonal transport even in presence of systemic antibody
›Milwaukee Protocol limitations
›Theoretical basis: suppress limbic excitability, allow immune clearance
›Documented survival rate remains < 5% in published cases
›Dog-variant RABV appears less responsive than bat-variant
›Emerging therapies under investigation
›Monoclonal antibody combinations targeting RABV glycoprotein
›RVA122 and CR57 combination in animal models
›Favipiravir: broad-spectrum RNA polymerase inhibitor studied in animal models
›Intrathecal passive immunization: bypasses BBB; limited human data