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St. Louis Encephalitis Workup

  • Author: Charurut Somboonwit, MD, FACP; Chief Editor: Burke A Cunha, MD  more...
 
Updated: Apr 16, 2015
 

Approach Considerations

The diagnostic workup of St. Louis encephalitis virus (SLEV) infection is based on clinical features, history of exposure, and epidemiologic history. According to the US Centers for Disease Control and Prevention (CDC), guidelines for the diagnosis of arboviral encephalitis include febrile illness or mild aseptic meningitis or encephalitis and 1 of the following:

  • A 4-fold increase in the antivirus antibody titer between the acute and the convalescent periods
  • Isolation of SLEV via culture or detection via nucleic acid amplification from tissue, blood, or cerebrospinal fluid (CSF)
  • Specific immunoglobulin M (IgM) antibody to SLEV

The white blood cell (WBC) count is usually not elevated. Pyuria or proteinuria may occur. More than one third of patients develop hyponatremia due to SIADH.

Antibody evaluation

Antibody titers are considered to be significant if in excess of 1:320 by hemoagglutination inhibition, 1:128 by complement fixation, 1:256 by immunofluorescence, or 1:160 by the plaque reduction neutralization test.

CSF examination

CSF examination reveals pressure that ranges from normal to mildly elevated, normal glucose levels, and protein levels that range from normal to mildly elevated. Initially, polymorphonuclear leukocytic pleocytosis occurs, followed by lymphocytic or monocytic leukocytosis. In most cases, the CSF WBC count is less than 200 cells/µL.

Serologic testing

Initial serologic testing consists of IgM capture enzyme-linked immunoassay (ELISA), microsphere-based immunoassay (MIA), and IgG enzyme-linked immunoabsorbent assay (ELISA). If the initial results are positive, further confirmatory testing may delay the reporting of final results. It is also helpful to test CSF IgM antibody for the presence of CNS infection and local antibody production.

Evaluation of fatal cases

In fatal cases, diagnosis can be confirmed via nucleic acid amplification, histopathology with immunohistochemistry, and virus culture. The specimens require specialized laboratories, including those at the CDC and a few state laboratories.

CT scanning and MRI

Neuroimaging using conventional computed tomography (CT) scanning and magnetic resonance imaging (MRI) is not helpful in establishing a diagnosis of SLEV infection.

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Histologic Findings

Microscopically, as in all viral encephalitides, widespread degeneration of single nerve cells occurs with neuronophagia and scattered foci of inflammatory necrosis involving the gray and white matter. The brain stem is relatively spared. Perivascular cuffing with lymphocytes and plasma cells occurs. Patchy infiltration of the meninges with microglial nodules also develops. Notably, no axonal or demyelinating lesions occur.

Pathologic features of St. Louis encephalitis are evident only in the CNS, although St. Louis encephalitis virus (SLEV) has been isolated from vitreous humor, lung, liver, spleen, and kidney.

Grossly, the brain and the meninges appear swollen, with widely distributed changes in the brain, mostly in the substantia nigra, thalamus, hypothalamus, cerebellum, cerebral cortex, basal ganglia, and cervical spinal cord, with more involvement of gray matter than white matter.

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Contributor Information and Disclosures
Author

Charurut Somboonwit, MD, FACP Associate Professor of Internal Medicine, Division of Infectious Disease and International Medicine, University of South Florida College of Medicine; Clinical Research and Communicable Diseases Director, USF Health and Hillsborough Health Department

Charurut Somboonwit, MD, FACP is a member of the following medical societies: American College of Physicians, American Medical Association, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Coauthor(s)

Fariba M Donovan, MD, PhD Intercoastal Medical Group

Fariba M Donovan, MD, PhD is a member of the following medical societies: American College of Physicians, American Society for Microbiology, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Joseph T Katta, DO Fellow in Infectious Disease and International Medicine, University of South Florida College of Medicine

Joseph T Katta, DO is a member of the following medical societies: American College of Physicians, American Osteopathic Association

Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Acknowledgements

John L Brusch, MD, FACP Assistant Professor of Medicine, Harvard Medical School; Consulting Staff, Department of Medicine and Infectious Disease Service, Cambridge Health Alliance

John L Brusch, MD, FACP is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Eduardo Gotuzzo, MD Adjunct Professor, Department of Medicine, University of Alabama School of Medicine

Disclosure: Nothing to disclose.

Eleftherios Mylonakis, MD Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital

Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Mary D Nettleman, MD, MS, MACP Professor and Chair, Department of Medicine, Michigan State University College of Human Medicine

Mary D Nettleman, MD, MS, MACP is a member of the following medical societies: American College of Physicians, Association of Professors of Medicine, Central Society for Clinical Research, Infectious Diseases Society of America, and Society of General Internal Medicine

Disclosure: Nothing to disclose.

Norvin Perez, MD Medical Director, Juneau Urgent and Family Care

Norvin Perez, MD is a member of the following medical societies: American College of Emergency Physicians and American Medical Association

Disclosure: Nothing to disclose.

Emad Soliman, MD, MSc Consulting Staff, Department of Neurology, St John's Riverside Hospital

Emad Soliman, MD, MSc is a member of the following medical societies: American Academy of Neurology and American Medical Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

References
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