Risk Factors for Viral Encephalitis
The primary risk factors for viral encephalitis include genetic susceptibility, exposure to arthropod vectors, geographic location, age extremes, immunocompromised status, and specific viral mutations that enhance neuroinvasiveness. 1
Genetic Risk Factors
Genetic variations play a significant role in determining susceptibility to viral encephalitis:
- CCR5del32 mutation is associated with increased risk of tickborne encephalitis 1
- Mutations in TLR3 pathway genes can impair immune responses to herpes simplex virus (HSV), increasing susceptibility to HSV encephalitis 1
- Variants in TBK1 gene result in impaired toll-like receptor signaling, compromising antiviral defense mechanisms 1
- Autosomal recessive mutations affecting interferon-mediated signaling pathways increase vulnerability to viral neuroinvasion 1
Vector-Borne Transmission Risk Factors
Arthropod vectors are major transmission routes for many encephalitis-causing viruses:
- Mosquito exposure increases risk for Japanese encephalitis virus (JEV), West Nile virus (WNV), and La Crosse virus infections 1
- Tick exposure is associated with tick-borne encephalitis virus (TBEV) and Powassan virus infections 1
- Geographic location significantly impacts risk - JEV is predominant in Asia, TBEV in Europe, and WNV in North America 1
- Seasonal variations affect risk, with higher incidence during warmer months when vector activity increases 1
Host-Related Risk Factors
Individual characteristics that increase vulnerability to viral encephalitis:
- Age extremes (very young and elderly) are associated with more severe disease and poorer outcomes 2, 3
- Immunocompromised status due to HIV infection, organ transplantation, chemotherapy, or other immunosuppressive conditions 4, 5
- Lack of vaccination against preventable causes (Japanese encephalitis, tick-borne encephalitis) 6, 4
- Occupational exposures (outdoor workers, laboratory personnel handling viral agents) 1, 4
Viral Factors
Characteristics of viruses that influence encephalitis risk:
- Neurotropism - certain viruses have greater affinity for neural tissue 5, 3
- Viral mutations that enhance neuroinvasiveness or neurovirulence 1, 6
- Viral load and route of infection affect likelihood of CNS penetration 5, 4
Environmental and Behavioral Risk Factors
External factors that modify exposure risk:
- Climate change expanding the geographic range of arthropod vectors 1, 6
- Outdoor activities in endemic areas during peak vector seasons 1, 4
- Poor vector control measures in residential areas 1, 6
- International travel to endemic regions without appropriate prophylaxis 6, 4
Prevention Strategies
Based on identified risk factors, key prevention approaches include:
- Vector control programs to reduce mosquito and tick populations 1, 6
- Vaccination for preventable causes in high-risk populations and travelers to endemic areas 6, 4
- Personal protective measures (insect repellents, appropriate clothing) 1, 4
- Genetic testing may eventually identify individuals at higher risk who would benefit from targeted preventive interventions 1