What is the appropriate diagnosis and treatment for a patient suspected of having encephalitis possibly linked to a rodent-borne illness?

Rodent-Borne Encephalitis: Diagnosis and Treatment

For suspected rodent-borne encephalitis, immediately initiate empiric IV aciclovir 10 mg/kg three times daily within 6 hours of admission while pursuing diagnostic workup including detailed exposure history, lumbar puncture with CSF PCR, and MRI brain imaging. 1

Immediate Management

Empiric Antiviral Therapy

• Start IV aciclovir (10 mg/kg three times daily) immediately if CSF/imaging suggests viral encephalitis, or within 6 hours of admission if results are unavailable or the patient is deteriorating 2, 1, 3
• Continue aciclovir even if initial CSF microscopy or imaging is normal but clinical suspicion persists 1, 3
• Reduce dose in pre-existing renal failure to prevent crystalluria and obstructive nephropathy 1, 3

Hospitalization and Monitoring

• Admit immediately to a setting with access to intensive care, neurology services, or intermediate care units 1
• Patients with decreased consciousness require urgent ICU evaluation for airway protection, ventilatory support, and management of increased intracranial pressure 1, 4

Diagnostic Workup

Critical Exposure History

When evaluating for rodent-borne encephalitis, specifically inquire about:

• Direct contact with rodents (pet squirrels, wild rodents, laboratory animals) 2
• Travel to endemic areas for Lassa fever (West Africa) or other rodent-borne viruses 2
• Occupational exposures to rodents or their excreta 2

Laboratory Investigations

• Lumbar puncture should be performed as soon as possible unless contraindicated by signs of increased intracranial pressure 2, 1
• CSF analysis must include: cell count, protein, glucose, PCR for HSV/VZV, and bacterial/fungal cultures 2
• CSF PCR results should be available within 24-48 hours 1
• Blood cultures to identify bacterial and fungal etiologies 2
• For rodent-borne pathogens specifically: serum microbiological cultures, serology, and PCR 2

Neuroimaging

• MRI is preferred over CT for detecting early changes in viral encephalitis 2, 1
• CT should only be used if MRI is unavailable or impractical 2
• Perform imaging before lumbar puncture only if there are signs of increased intracranial pressure (focal neurological deficits, papilledema, Glasgow Coma Score <9-12) 2

EEG Monitoring

• Perform EEG if non-convulsive or subtle motor seizures are suspected 2
• EEG helps distinguish organic encephalitis from primary psychiatric disease 2

Specific Rodent-Borne Pathogens

Variegated Squirrel Bornavirus 1 (VSBV1)

• Emerging pathogen identified in patients with fatal encephalitis who had contact with pet squirrels 2
• Diagnosis established through metagenomic analysis, RT-PCR, and serology 2
• Rodents represent 40% of all mammals and account for 1,700 species, making them significant reservoirs for emerging pathogens 2
• No specific treatment available; management is supportive 2

Lassa Fever Virus

• Consider in patients returning from West Africa with rodent exposure 2
• Encephalitis is an uncommon presentation; more typical is hemorrhagic fever 2
• MRI may show hypersignals with normal CSF characteristics 2
• Diagnosis confirmed by genome amplification on serum 2
• Standard protection measures are adequate for healthcare workers; no secondary transmission occurred in a documented case despite 118 contacts 2

Duration of Treatment

• Continue IV aciclovir for 14-21 days for confirmed HSV encephalitis 3
• Perform repeat lumbar puncture at completion to confirm CSF is HSV PCR-negative 3
• If CSF remains positive, continue aciclovir with weekly PCR monitoring until negative 3

Multidisciplinary Approach

Management requires involvement of:

• Neurology, infectious disease specialists, virology, microbiology 1
• Neurophysiology, neuroradiology, neurosurgery 1
• Intensive care staff 1
• Transfer to specialized neurology service within 24 hours if diagnosis is not rapidly established or patient fails to improve 1, 3

Brain Biopsy Considerations

• Brain biopsy has no role in initial assessment 2, 1
• Consider stereotactic biopsy after the first week if no diagnosis is established, especially with focal imaging abnormalities 2, 1
• An alternative diagnosis was made by biopsy in 20% of patients with suspected HSV encephalitis, half of which were treatable 2

Discharge and Follow-up

• Do not discharge without a definitive or suspected diagnosis 1
• All patients require rehabilitation assessment regardless of age 1, 4
• Arrange outpatient follow-up with plans for ongoing therapy and rehabilitation 1, 4
• Sequelae including anxiety, depression, and obsessive behaviors often become apparent after discharge 1

Key Pitfalls to Avoid

• Never delay aciclovir while awaiting diagnostic results – HSV is the most treatable cause and delays beyond 48 hours worsen outcomes 3
• Do not perform unselected CT scanning before lumbar puncture in all patients, as this causes unnecessary delays (median 18.5 vs 6 hours) 2
• Do not assume negative initial imaging excludes encephalitis – MRI may initially be normal or remain normal during illness 2
• Consider emerging rodent-borne pathogens in patients with unexplained encephalitis and rodent exposure, as these may present as sentinel cases of novel infections 2