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Venezuelan Equine Encephalitis Workup

  • Author: Robert W Derlet, MD; Chief Editor: Burke A Cunha, MD  more...
 
Updated: Apr 15, 2016
 

Approach Considerations

Encephalitis is clinically diagnosed in 2-4% of adults and in 3-5% of children infected with the virus.

In patients presenting to the emergency department (ED) with a febrile illness, perform standard laboratory tests, including a complete blood count (CBC), electrolyte assessment, liver function tests, urinalysis, and other tests as indicated by the history and physical examination. The results of most laboratory studies in patients infected with Venezuelan equine encephalitis are nonspecific for febrile illnesses.

Electrolytes, blood glucose, renal function

Routine laboratory studies for the evaluation of an acutely ill patient with fever and headache is likely to include evaluation of electrolytes, blood glucose, and renal function.

Transaminases

Levels of transaminases, particularly serum aspartate transaminase and lactate dehydrogenase, may be elevated in Venezuelan equine encephalitis.

Liver function testing

In patients who are severely ill with Venezuelan equine encephalitis, hepatic compromise may produce abnormalities in liver synthetic function testing.

Liver function testing may reveal elevated lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) levels.

CBC count

A CBC count for analysis of the white blood cell count, hemoglobin, and platelet count is usually included in the evaluation. A decreased lymphocyte or a lymphocyte and granulocyte count 1-3 days after onset of symptoms is common.

Eosinopenia and vacuolated monocytes have been described. Lymphopenia and thrombocytopenia may also be observed.

Urinalysis and cultures

Urinalysis as part of the evaluation of other sources of infection is common. Urine culture and blood culture studies are case dependent.

Viral isolation

A specific diagnosis of Venezuelan equine encephalitis may be made with isolation of virus in the blood or from a throat swab within 1-3 days after onset of symptoms.

Lumbar puncture

Lumbar puncture with analysis of the obtained cerebrospinal fluid (CSF) is essential in reaching a diagnosis and determining the severity of illness. In patients with Venezuelan equine encephalitis, CSF analysis typically reveals a mononuclear pleocytosis of several hundred cells with a glucose concentration within the reference range.

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Serologic Studies

Sera from patients with full-blown Venezuelan equine encephalitis are usually negative for the virus, but the diagnosis can be made using serologic studies.

Enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and neutralization tests can be used to identify the virus. Immunoglobulin M (IgM) and IgG ELISA, using attenuated Venezuelan equine encephalitis as the antigen, are most sensitive but need to be followed by plaque reduction neutralization to provide diagnostic specificity. Demonstration of a 4-fold rise in serum antibody titer is also useful diagnostically.

Serum can also be sent to a laboratory with the ability to test for Venezuelan equine encephalitis and other, similar diseases using ultrasensitive qualitative detection by reverse transcription coupled real-time polymerase chain reaction (PCR) assay. Diagnostic methods also include microsphere-based immunoassay (MIA).

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Imaging Studies

Chest radiography and head computed tomography (CT) scanning may be helpful adjuncts in assessing the complications of Venezuelan equine encephalitis or in helping to eliminate other diagnostic possibilities.

Interstitial infiltrates on chest radiography indicate acute pneumonitis, which is occasionally observed in patients with Venezuelan equine encephalitis. A CT scan of the head that reveals edema or hemorrhage necessitates emergency intervention. Magnetic resonance imaging (MRI) may also be useful in establishing the diagnosis of encephalitis.

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Histologic Findings

Death due to Venezuelan equine encephalitis follows diffuse congestion and edema with hemorrhage in the brain, gastrointestinal tract, and lungs. Pathologic changes in the brain include congestion, perivascular cuffing and hemorrhage, glial nodule formation, and focal necrosis. The pathology is most prominent in the basal ganglia and substantia nigra but is also found in the cerebral cortices and deep white matter. Meningoencephalitis with necrotizing vasculitis and cerebritis has been observed in some patients. Hepatocellular degeneration and interstitial pneumonitis have been noted in fatal human infections.

Equine infections are characterized by a striking depletion of lymphocytes in the lymph nodes, spleen, and gastrointestinal tract.

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Contributor Information and Disclosures
Author

Robert W Derlet, MD Professor of Emergency Medicine, University of California at Davis School of Medicine; Chief Emeritus, Emergency Department, University of California at Davis Health System

Robert W Derlet, MD is a member of the following medical societies: American Academy of Emergency Medicine, American Association for the Advancement of Science, Infectious Diseases Society of America, Society for Academic Emergency Medicine, Wilderness Medical Society

Disclosure: Nothing to disclose.

Coauthor(s)

Iris Reyes, MD Associate Professor of Clinical Emergency Medicine, Advisory Dean, Office of Student Affairs, University of Pennsylvania School of Medicine

Iris Reyes, MD is a member of the following medical societies: American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

William H Shoff, MD, DTM&H Director, PENN Travel Medicine; Associate Professor, Department of Emergency Medicine, Hospital of the University of Pennsylvania, University of Pennsylvania School of Medicine

William H Shoff, MD, DTM&H is a member of the following medical societies: American College of Physicians, American Society of Tropical Medicine and Hygiene, International Society of Travel Medicine, Society for Academic Emergency Medicine, Wilderness Medical Society

Disclosure: Nothing to disclose.

Sarah M Perman, MD, MS Resident, Department of Emergency Medicine, University of Pennsylvania Health Systems

Sarah M Perman, MD, MS is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

John R Richards, MD, FAAEM Professor, Department of Emergency Medicine, University of California, Davis, Medical Center

John R Richards, MD, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

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

Disclosure: Received salary from Medscape for employment. for: Medscape.

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, Infectious Diseases Society of America

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.

Additional Contributors

Jerry L Mothershead, MD Medical Readiness Consultant, Medical Readiness and Response Group, Battelle Memorial Institute; Advisor, Technical Advisory Committee, Emergency Management Strategic Healthcare Group, Veteran's Health Administration; Adjunct Associate Professor, Department of Military and Emergency Medicine, Uniformed Services University of the Health Sciences

Jerry L Mothershead, MD is a member of the following medical societies: American College of Emergency Physicians, National Association of EMS Physicians

Disclosure: Nothing to disclose.

Acknowledgements

Suzanne Moore Shepherd, MD, MS, DTM&H, FACEP, FAAEM Associate Professor, Education Officer, Department of Emergency Medicine, Hospital of the University of Pennsylvania; Director of Education and Research, PENN Travel Medicine

Suzanne Moore Shepherd, MD, MS, DTM&H, FACEP, FAAEM is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American Society of Tropical Medicine and Hygiene, International Society of Travel Medicine, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

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