Noninfectious causes include postinfectious, postinflammatory, vasculitis, collagen vascular disorder, malignancy, paraneoplastic or drug, and toxin induced.
United States—Herpes simplex virus-1 (HSV-1), West Nile virus (WNV), and the enteroviruses are most common.
Recent vaccination—Acute disseminated encephalitis (up to 14 days after vaccination) (Table 18-1).
Location
Russia—Tickborne encephalitis (TBE)
Africa—West Nile, trypanosomes, plasmodia
Australia—West Nile, Japanese encephalitis (JE), Hendra
Europe—TBE
India—Rabies, malaria, JE
Middle East—West Nile, malaria
Central America—Eastern equine encephalitis (EEE), St. Louis encephalitis (SLE), Venezuelan Equine Encephalitis virus (VEE), Rocky Mountain spotted fever (RMSF), rabies, malaria
Southeast Asia—JE, TBE, malaria, Nipah, Gnathostoma
South America—Rickettsia, SLE, EEE, VEE, Western equine encephalitis (WEE), bartonella, malaria
Swimming—Naegleria
Tsetse flies—Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense (Africa)
Rodents—LCM, leptospirosis
Bats—Rabies, Nipah virus
Sexual activity—HIV, HSV 2
Birds—West Nile, EEE, WEE, VEE, JE, SLE
Horses—EEE, WEE, VEE, Hendra
Swine—JE, Nipah.
Raccoon—Baylisascaris procyonis
Mosquitoes—EEE, SLE, WEE, VEE, JE, Murray Valley, La Crosse
Table 18-1 Vector Borne Viruses That Cause Encephalitis
Virus
Epidemiology/Transmission
Manifestations
Diagnostic tests
Treatment
Colorado tick fever virus
Western USA, Canada.
Vector: wood tick, seasonal from March to September. Also can be transmitted by blood transfusion.
Saddleback temperature curve. Prodromal stage is followed by a petechial or maculopapular rash. 5%-10% have encephalitis
Serology/PCR
Supportive
Eastern equine encephalitis virus
Sporadic, severe course. Mosquito is the vector, birds/rodents reservoir. Summer or fall season. Atlantic/gulf states in north America are endemic. Affects children and old population disproportionately.
Can be subclinical. Symptomatic infections usually acute with rapid progression from headache, seizures to coma. Brain stem involvement is common and is associated with gaze palsies, nystagmus, and pupillary abnormalities.
High mortality.
MRI-Thalamus, basal ganglia, and brain stem involvement. CSF: higher WBC/neutrophil counts than other viruses. Protein, RBCs elevated, low glucose. CSF IgG and IgM positive. Also serum serology positive. Decreased serum sodium.
Only supportive.
Japanese encephalitis virus
Birds/swine are reservoir, vector is mosquito. Southeast Asia, Japan, China, Korea, Taiwan, India, and Australia.
Can cause a flaccid paralysis, seizures, or Parkinson-like symptoms. Nearly 1/3 mortality rate.
Serology.
CSF IgM or antigen tests.
Supportive.
Vaccine available
La Crosse virus
Seasonal from July-September. Mosquito vector, squirrel and chipmunk are reservoirs.
Affects school-age children. Areas affected are eastern, Midwest USA.
Most commonly subclinical course but can progress to fulminant fatal stage
Serology.
CSF IgM.
CSF may have increased WBCs with a PMN predominance.
Supportive
Murray Valley encephalitis virus
Australia, New Guinea. Affects children. Birds are reservoirs and mosquitoes are vectors
Rapid progression to spastic paresis and coma
Serology
Supportive
Powassan virus
Seen in New England, Canada. Has tick vector and rodent reservoir.
Can have GI symptoms
Serum or CSF IgM
Supportive
St. Louis encephalitis virus
Usually affects older adults (>50 years of age). Birds are the reservoir, with Culex mosquitoes as the vectors. Found in the United States, in addition to being found in South-Central America.
Presents early with urinary symptoms. Can have severe course with older age and can cause seizures and paresis. SIADH can occur.
Serum or CSF IgM
Supportive. interferon alpha 2b’s role.
Tick-borne encephalitis virus
Spring-summer season. Biphasic course. Found in Central Europe, Far East. Rodents are reservoir. Tick vector
Can cause myelitis, flaccid paralysis, in addition to encephalitis
Serology.
CSF IgM
Viral culture in blood in early phase
Supportive.
Effective vaccine in Europe.
Venezuelan Equine Encephalitis virus
In South and Central America, and southeastern USA (Florida). Reservoirs are rodents, horses, and birds, and vectors are mosquito. Occupational hazard, bioterrorism risk ?
Usually subclinical. Respiratory symptoms, myalgia can occur. Rarely fatal unless encephalitis occurs (20%).
Serology. Blood/pharyngeal culture. CSF IgM, PCR tests.
Supportive.
Western equine encephalitis virus
West of Mississippi, Canada, Argentina. Bird reservoir, mosquito vector.
Mainly subclinical course. The case-fatality rate is approximately 4%-10%, but is higher in infants and the elderly.
Serology IgM or CSF IgM.
Supportive
Ticks—Powassan, TBE, Lyme, Anaplasma phagocytophilum, and rickettsial illnesses
Parturient cats and farm animals—Q fever
Fall—Arboviruses and enteroviruses
Winter—Influenza
Oculomasticatory—Whipples
Parkinsonian—SLE, West Nile, JE, Nipah
Polio-like paralysis—West Nile, TBE, JE, and Enterovirus 71
Retinitis—West Nile, Cytomegalovirus (CMV), bartonella, treponemes
Rash—Zoster, West Nile, human herpes virus (HHV) 6, Herpes B, RMSF, enteroviruses, mycoplasmaRelated posts:
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