Aedes albopictus serving as bridge vector in expanding territory
Aedes japonicus also implicated in some regions
Pathophysiology
Virology
Virus classification
Orthobunyavirus in the family Peribunyaviridae
California serogroup of bunyaviruses
Tripartite negative-sense RNA genome (L, M, S segments)
Transmission cycle
Primary vector: Aedes triseriatus feeds on eastern chipmunks and squirrels as amplifying hosts
Transovarial transmission maintains virus in mosquito population over winter
Humans are dead-end hosts
Neuroinvasion mechanisms
Viral entry to CNS
Hematogenous spread after initial viremia
Direct neuronal invasion via olfactory or peripheral nerve routes postulated
Neuronal injury
Direct cytopathic effect on neurons
Inflammatory response contributes to cerebral edema
Cerebral edema
Vasogenic and cytotoxic components
Hyponatremia from SIADH worsens edema
Seizure generation
Neuronal irritation from inflammation and edema
High seizure burden: seizures in majority of encephalitic cases
Disease spectrum
Clinical spectrum
Asymptomatic infection most common
Febrile illness without neurologic involvement
Aseptic meningitis in 13 to 17% of neuroinvasive cases
Encephalitis as most severe form
43% of children with neuroinvasive disease had severe disease in contemporary cohort
Therapeutic Considerations
Antiviral strategy
No FDA-approved antiviral therapy for LACV
Management is entirely supportive
Acyclovir role
Empiric use mandatory until HSE excluded
No activity against RNA viruses including LACV
Discontinue once HSV PCR confirmed negative
Ribavirin evidence base
In vitro inhibition of LACV demonstrated
Used as compassionate therapy
Randomized trial initiated but no definitive efficacy data
Not standard of care
Seizure treatment principles
Early and aggressive seizure control
Prolonged seizures worsen neuronal injury
Status epilepticus in approximately 25% of those with seizures
Continuous EEG monitoring in altered mental status
Non-convulsive status epilepticus detection
Long-term AED management guided by EEG and neurology
ICP management principles
Cerebral herniation in 2.4% of cases
Early recognition of ICP elevation critical
Osmotic therapy and positioning are first-line
Avoid hypotonic fluids universally
Prevention focus
No vaccine available for LACV
DEET-containing repellents effective against Aedes triseriatus
Protective clothing in wooded endemic areas
Elimination of standing water and tire dumps as breeding sites
Public health vector control in endemic areas
Patient Discharge Instructions
copy discharge instructions
La Crosse encephalitis discharge instructions
Activity
Rest at home for several days after discharge
No driving until seizure-free period confirmed by your doctor
Gradual return to school or work as tolerated
Medications
Take all antiseizure medications exactly as prescribed
Do not stop antiseizure medications without talking to your doctor
If you were given other medications, finish the full course as directed
Hydration and diet
Drink adequate fluids
Return to normal diet as tolerated
Avoid alcohol which lowers seizure threshold
Return to emergency room immediately if
New seizure or return of seizures
Even brief or partial seizures
Call 911 for seizure lasting more than 5 minutes
Worsening headache or sudden severe headache
Confusion, agitation, or change in behaviour
High fever returning (temperature above 38.5 C)
Persistent vomiting or inability to keep fluids down
Weakness in arms or legs or difficulty speaking
Extreme sleepiness or difficulty waking
Follow-up appointments
Neurology appointment within 2 to 4 weeks
All patients with neuroinvasive disease need neurology follow-up
Bring list of current medications to appointment
Neuropsychological testing at 3 to 6 months
Long-term cognitive and behavioral deficits occur in 19 to 54% of patients
Early identification allows for intervention
Repeat EEG if recommended by your neurologist
Important to check for ongoing brain electrical activity changes
Mosquito bite prevention
Apply DEET-containing insect repellent when outdoors
20 to 30% DEET appropriate for adults and children over 2 months
Wear long sleeves and pants in wooded areas
Eliminate standing water around your home
Empty tires, buckets, bird baths, and tree holes
Peak mosquito activity is dusk and dawn: limit outdoor exposure then
No vaccine is currently available for La Crosse encephalitis
References
Guidelines and key sources
Primary clinical evidence
Vahey GM, Lindsey NP, Staples JE, Hills SL. La Crosse Virus Disease in the United States, 2003-2019. American Journal of Tropical Medicine and Hygiene. 2021. PMID 34280142
Feng S, Feng X, Zhu W, et al. La Crosse Virus: A Comprehensive Review of Its Emerging Public Health Importance. Viral Immunology. 2025. PMID 40274395
Boutzoukas AE, Freedman DA, Koterba C, et al. La Crosse Virus Neuroinvasive Disease in Children: A Contemporary Analysis of Clinical and Neurobehavioral Outcomes. Clinical Infectious Diseases. 2023. PMID 35607778
McJunkin JE, de los Reyes EC, Irazuzta JE, et al. La Crosse Encephalitis in Children. New England Journal of Medicine. 2001. PMID 11242043
Epidemiology and vector sources
Day CA, Odoi A, Trout Fryxell R. Geographically Persistent Clusters of La Crosse Virus Disease in the Appalachian Region 2003 to 2021. PLoS Neglected Tropical Diseases. 2023. PMID 36656896
Haddow AD, Odoi A. Incidence Risk, Clustering, and Clinical Presentation of La Crosse Virus Infections in the Eastern United States, 2003-2007. PloS One. 2009. PMID 19582158
Goldman T, Hamer DH. Current Status of La Crosse Virus in North America and Potential for Future Spread. American Journal of Tropical Medicine and Hygiene. 2024. PMID 38531108
Diagnostics and laboratory references
Miller JM, Binnicker MJ, Campbell S, et al. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update IDSA and ASM. Clinical Infectious Diseases. 2024
Piantadosi A, Kanjilal S. Diagnostic Approach for Arboviral Infections in the United States. Journal of Clinical Microbiology. 2020. PMID 32938736
Dykers TI, Brown KL, Gundersen CB, Beaty BJ. Rapid Diagnosis of La Crosse Encephalitis: Detection of Specific IgM in CSF. Journal of Clinical Microbiology. 1985. PMID 3902876
Wang H, Everhart K, Oyeniran SJ, Leber AL. Detection of La Crosse Virus RNA in Clinical Specimens from Children. Journal of Clinical Virology. 2026. PMID 41619618
Treatment and outcomes references
Tyler KL. Acute Viral Encephalitis. New England Journal of Medicine. 2018. PMID 30207908
Teleron AL, Rose BK, Williams DM, Kemper SE, McJunkin JE. La Crosse Encephalitis: An Adult Case Series. American Journal of Medicine. 2016. PMID 27086496
Ouellette CP. La Crosse Virus Encephalitis in Children. Current Opinion in Infectious Diseases. 2024. PMID 39079177
Singh PG, Boutzoukas EM, Cagnina MC, Silva MA. Neuropsychological and Functional Outcome After La Crosse Encephalitis in Marine Recruit. Military Medicine. 2025. PMID 40986408
Padda H, Jacobs D, Gould CV, et al. West Nile Virus and Other Nationally Notifiable Arboviral Diseases United States 2023. MMWR. 2025. PMID 40504766
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.