Saint Louis encephalitis

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Saint Louis encephalitis (SLE) is an arboviral infection endemic to the Americas that is caused by the Saint Louis encephalitis virus (SLEV). Before the establishment of West Nile virus, SLEV was the leading cause of Flavivirus encephalitis in North America . The incidence of SLE has since decreased significantly.

Epidemiology

SLEV received its name following the 1933 St. Louis, Missouri epidemic, having affected nearly 40% of the population . 8 genotypes have since been identified, three of which are widely distributed and prevalent across mostly eastern and central states within the United States (genotypes I and II) and South America (genotype V). In 2019, 14 cases of neuroinvasive SLEV were reported in the United States .

To a lesser extent, incidence of SLEV infection in southern South America (genotype III), Columbia (genotype IV), Panama (genotypes IV and VI), Argentina (genotype VII) and the Amazon, Brazil (genotype VIII) has been reported .

SLEV is maintained in a mosquito-bird-mosquito transmission network across a diverse range of bird species, aquatic ecosystems and locations. Mosquitoes of the Culex genus are the vector .

Clinical presentation 

Symptomatic infection occurs in <1% of exposed adults. An acute-onset, nonspecific febrile illness - malaise, myalgia, headache, nausea, cough and dizziness - precedes the development of neuroinvasive disease . Meningitis and encephalitis occur in 40% and 50% of patients under 20 years old, respectively. More than 90% of those over 60 years old develop encephalitis . Features of encephalitis most commonly include seizures, coma and reduced consciousness; tremors, myoclonic jerks, opsoclonus, nystagmus and ataxia have also been reported .

Pathology

Etiology 

Limited data evidence marked inflammatory and gliotic changes within the substantia nigra and cerebellum that are also present, to a lesser extent, diffusely throughout the brain .

Radiographic features

CT imaging and MRI are often normal; the detection of anti-SLEV IgM in the serum of CSF is crucial to diagnosis. Neuroradiological data of SLE are limited. However, MRI of 2 out of 6 cases in the 1995 Dallas, Texas endemic revealed hyperintensity within the substantia nigra, thought to represent edema .

MRI
  • T2: the degree of signal hyperintensity within the substantia nigra may be varied in terms of symmetry and laterality

Treatment and prognosis 

Only supportive treatment is available, with mortality ranging from 5-15% . The risk of death increases with age and is reported as 20% in the over-60s . There is currently no vaccine available.

Differential diagnosis

Careful history-taking and consideration of geographic location are important factors when considering SLE, as the differential diagnosis is broad, and the following list is not exhaustive.

Endemic encephalitides may present similarly:

As well as other infectious causes of meningitis and/or encephalitis:

Non-infectious etiologies should also be considered:

Siehe auch: