History and Physical Examination

The incubation period of California encephalitis is usually 3-7 days. A prodromal phase of 1-4 days commonly precedes the onset of encephalitis. This phase manifests as any or all of the following:

Fever
Chills
Nausea
Vomiting
Headache
Abdominal pain

The encephalitis is characterized by fever and somnolence, which may progress to obtundation. Although most patients make uneventful recoveries, electroencephalographic findings are abnormal 1-5 years later in 75% of cases, emotional lability is persistent in 10%, and epilepsy is a chronic problem in 6%-10% of all diagnosed cases. Although uncommon, frank neurologic deficit can also occur.^[3]Twenty percent of children develop focal neurologic signs (eg, asymmetrical reflexes, Babinski signs), and 10% of patients develop coma. Periodic lateralizing epileptiform discharges (PLEDS) can be seen in the temporal lobe. The total duration of illness rarely exceeds 10-14 days.

Two reports in the literature have described LaCrosse encephalitis manifesting as signs and symptoms of herpes simplex encephalitis.^{[4, 5]}

In adults, infection is asymptomatic or causes a benign febrile illness or aseptic meningitis.

Physical findings may include the following:

Fever
Lethargy
Focal neurologic findings (eg, aphasia)
Incoordination
Focal motor abnormalities
Paralysis

Complications

Complications may be associated with more severe disease. These include the following:

Epilepsy (commonest and most serious)
Cognitive and memory deficits
Lethargy
Aphasia
Incoordination
Focal motor abnormalities
Paralysis

Differential Diagnoses

HAMMON WM, REEVES WC. California encephalitis virus, a newly described agent. Calif Med. 1952 Nov. 77 (5):303-9. [QxMD MEDLINE Link].
Watts DM, Thompson WH, Yuill TM, DeFoliart GR, Hanson RP. Overwintering of La Crosse virus in Aedes triseriatus. Am J Trop Med Hyg. 1974 Jul. 23 (4):694-700. [QxMD MEDLINE Link].
McJunkin JE, de los Reyes EC, Irazuzta JE, Caceres MJ, Khan RR, Minnich LL, et al. La Crosse encephalitis in children. N Engl J Med. 2001 Mar 15. 344 (11):801-7. [QxMD MEDLINE Link].
Sokol DK, Kleiman MB, Garg BP. LaCrosse viral encephalitis mimics herpes simplex viral encephalitis. Pediatr Neurol. 2001 Nov. 25(5):413-5. [QxMD MEDLINE Link].
Wurtz R, Paleologos N. La Crosse encephalitis presenting like herpes simplex encephalitis in an immunocompromised adult. Clin Infect Dis. 2000 Oct. 31(4):1113-4. [QxMD MEDLINE Link].
Hubalek Z, Sebesta O, Pesko J, Betasova L, Blazejova H, Venclikova K, et al. Isolation of Tahyna Virus (California Encephalitis Group) From Anopheles hyrcanus (Diptera, Culicidae), a Mosquito Species New to, and Expanding in, Central Europe. J Med Entomol. 2014 Nov 1. 51 (6):1264-7. [QxMD MEDLINE Link].
Jones TF, Erwin PC, Craig AS, Baker P, Touhey KE, Patterson LE, et al. Serological survey and active surveillance for La Crosse virus infections among children in Tennessee. Clin Infect Dis. 2000 Nov. 31 (5):1284-7. [QxMD MEDLINE Link].
de los Reyes EC, McJunkin JE, Glauser TA, Tomsho M, O'Neal J. Periodic lateralized epileptiform discharges in La Crosse encephalitis, a worrisome subgroup: clinical presentation, electroencephalogram (EEG) patterns, and long-term neurologic outcome. J Child Neurol. 2008 Feb. 23(2):167-72. [QxMD MEDLINE Link].
McJunkin JE, Khan R, de los Reyes EC, Parsons DL, Minnich LL, Ashley RG, et al. Treatment of severe La Crosse encephalitis with intravenous ribavirin following diagnosis by brain biopsy. Pediatrics. 1997 Feb. 99 (2):261-7. [QxMD MEDLINE Link].
Sandler ZJ, Firpo MR, Omoba OS, Vu MN, Menachery VD, Mounce BC. Novel Ionophores Active against La Crosse Virus Identified through Rapid Antiviral Screening. Antimicrob Agents Chemother. 2020 May 21. 64 (6):[QxMD MEDLINE Link].
Conti B, Benelli G, Leonardi M, Afifi FU, Cervelli C, Profeti R, et al. Repellent effect of Salvia dorisiana, S. longifolia, and S. sclarea (Lamiaceae) essential oils against the mosquito Aedes albopictus Skuse (Diptera: Culicidae). Parasitol Res. 2012 Jul. 111(1):291-9. [QxMD MEDLINE Link].

Media Gallery

La Crosse virus transmission cycle. The virus is maintained by vertical transmission in Aedes triseriatus mosquitoes; the virus winters in infected eggs that are usually deposited in tree holes or in artificial containers holding rainwater. Horizontal transmission (by viral amplification in small vertebrates, eg, squirrels and chipmunks, and venereally among adult mosquitoes) is required to supplement vertical transmission. The role of deer in viral amplification is uncertain. Human infections are incidental to the transmission cycle.
Brain biopsy specimen from a 7-year-old boy with severe La Crosse encephalitis (hematoxylin and eosin stain, 200X). Perivascular infiltration with mononuclear cells is present on light microscopy. This biopsy material tested positively for La Crosse virus antigen on direct immunofluorescence assay.
Left image of a CT scan of an 8-year-old boy with severe La Crosse encephalitis complicated by uncal herniation (obtained on the second hospital day) reveals brain edema with associated obliteration of perimesencephalic cisterns (arrows). On the right, a T2-weighted magnetic resonance image obtained from a 7-year-old boy with severe La Crosse encephalitis shows focal areas of increased signal intensity in the right temporoparietal and left frontotemporal regions (arrows).
La Crosse virus neuroinvasive disease cases reported in the United states from 2010-2019. Courtesy of CDC and ArboNET (https://www.cdc.gov/lac/tech/epi.html).
La Crosse virus neuroinvasive disease cases reported by state, 2010-2019. Courtesy of CDC and ArboNET (https://www.cdc.gov/lac/tech/epi.html).

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Author

Folusakin O Ayoade, MD Assistant Professor of Clinical Medicine, Division of Infectious Diseases, Department of Medicine, University of Miami, Leonard M Miller School of Medicine; Attending Physician in Infectious Diseases, Jackson Health System; Attending Physician in Infectious Diseases, University of Miami Hospital

Folusakin O Ayoade, MD is a member of the following medical societies: American College of Physicians, American Federation for Medical Research, American Medical Association, Infectious Diseases - International Research Initiative, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Coauthor(s)

Leopoldo Cordova G, MD Fellow in Infectious Diseases, University of Miami, Leonard M Miller School of Medicine

Leopoldo Cordova G, MD is a member of the following medical societies: American College of Physicians, Venezuelan Society of Infectious Diseases, Venezuelan Society of Internal 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.

Joseph F John, Jr, MD, FACP, FIDSA, FSHEA Clinical Professor of Medicine, Molecular Genetics and Microbiology, Medical University of South Carolina College of Medicine; Associate Chief of Staff for Education, Ralph H Johnson Veterans Affairs Medical Center

Joseph F John, Jr, MD, FACP, FIDSA, FSHEA is a member of the following medical societies: Charleston County Medical Association, Infectious Diseases Society of America, South Carolina Infectious Diseases Society

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America; Fellow of the Royal College of Physicians, London

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Medical Association, Association of Professors of Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, Southern Society for Clinical Investigation

Disclosure: Nothing to disclose.

Additional Contributors

Wayne E Anderson, DO, FAHS, FAAN Assistant Professor of Internal Medicine/Neurology, College of Osteopathic Medicine of the Pacific Western University of Health Sciences; Clinical Faculty in Family Medicine, Touro University College of Osteopathic Medicine; Clinical Instructor, Departments of Neurology and Pain Management, California Pacific Medical Center

Wayne E Anderson, DO, FAHS, FAAN is a member of the following medical societies: American Academy of Neurology, American Headache Society, California Medical Association, California Neurology Society, International Headache Society, San Francisco Medical Society, San Francisco Neurological Society

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, American Medical Association

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 and Translational Research, Infectious Diseases Society of America, Society of General Internal Medicine

Disclosure: Nothing to disclose.

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

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

Disclosure: Nothing to disclose.

Mohammad J Alam, MD Assistant Professor of Medicine, Departments of Internal Medicine, Infectious Disease, and Emergency Medicine, University Health, Louisiana State University School of Medicine in Shreveport; Affiliate Staff Physician, Department of Internal Medicine (Infectious Disease), Schumpert Medical Center

Mohammad J Alam, MD is a member of the following medical societies: American College of Physicians, American Medical Association, Society of Critical Care Medicine, Southern Medical Association

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors gratefully acknowledge the contributions of previous authors Eleftherios Mylonakis, MD, and Eduardo Gotuzzo, MD, to the development and writing of the source article.

California Encephalitis Clinical Presentation

History and Physical Examination

Complications

References

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