Encephalitis

Introduction. 

Encephalitis refers to inflammation of the brain. This can be caused by many viral and bacterial pathogens. Many encephalitis viruses are also arboviruses (arthropod-borne), including West Nile virus, Western Equine Encephalitis virus (WEE), and Eastern Equine Encephalitis virus (EEE).

Summary

Cause: West Nile Virus (Flavivirus)

• Transmission: arbovirus (mosquito)
• Symptoms: mild flu-like; 20% progress to fever, headache, malaise (West Nile Fever)
• Pathogenesis:  viremia, replication in monocyte/macrophage, interferon released
• Complications: encephalitis in 1% of cases
• Treatment: supportive
• Vaccine: no
• Story: https://www.nbcnews.com/news/us-news/missouri-teenager-left-paralyzed-ventilator-west-nile-virus-rcna168761

Cause: Alphaviruses (EEE, WEE,VEE)

• Structure: Togaviruses: enveloped ('shrinkwrapped') icosahedral; +ssRNA
• Transmission: arbovirus: mosquito vector
• Reservoir: Birds (EEE, WEE) or horses & rodents (VEE)
• Symptoms: Flu-like (fever, chills, headaches)
• Pathogenesis: viremia, replication in monocyte/macrophage, interferon released
• Complications: 2nd viremia possible leading to infection of brain, liver, skin, endothelium
• Treatment: supportive
• Vaccine: available for EEE and WEE
• Story: https://www.health.ny.gov/press/releases/2024/2024-09-20_human_case_of_eee_in_ulster.htm

Cause: Other Flaviviruses (St. Louis, Russian spring-summer, Japanese)

• Transmission: arbovirus (mosquitoes & ticks)
• Reservoir: Birds (SLE, RSSE) and pigs (JE)
• Symptoms: Flu-like (fever, chills, headaches)
• Pathogenesis: viremia, replication in monocyte/macrophage, interferon released
• Complications:2nd viremia possible leading to infection of brain, liver, skin, endothelium
• Treatment:supportive
• Vaccine: Japanese & Russian spring-summer
• Story: https://pmc.ncbi.nlm.nih.gov/articles/PMC5621550/

Cause: Bunyavirus (California encephalitis, LaCrosse virus)

• Arbovirus transmitted by mosquitoes
• Zoonotic: reservoirs incl. rodents, primates, birds
• Story: https://www.neurology.org/doi/10.1212/WNL.0000000000206643

Cause: Nipah & Hendra virus

• Transmission: direct contact
• Reservoir: zoonotic (fruit bats, pigs, horses)
• Symptoms: Flu-like (fever, chills, headaches)
• Complications: encephalitis: seizures, coma, death (40 - 67%)
• Treatment: ribavirin?
• http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/nipah.htm
• Nipah story: https://www.cidrap.umn.edu/nipah/india-reports-another-fatal-nipah-virus-case
• Hendra story: https://www.health.nsw.gov.au/Infectious/controlguideline/Pages/hendra-case-summary.aspx