La Crosse encephalitis, caused by the La Crosse virus (LACV), is a rare central nervous system (CNS) infection that is predominantly seen in the basins of the Mississippi and Ohio rivers, and the name was given after the first case was confirmed in La Crosse, Wisconsin [1] [2]. Humans are infected by this virus after being bitten by Aedes triseriatus, the local forest-dwelling mosquito, and a stable animal reservoir of the virus was identified to be among chipmunks and squirrels in these areas [1] [2]. For this reason, the infection is considered to be of zoonotic nature, and the summer months are when most cases are reported [3] [4] [5]. The majority of individuals who get infected by the LACV develop an asymptomatic form of illness and rough estimates suggest that approximately 1 in 1000 patients suffers from a more severe form of illness [1] [2]. La Crosse encephalitis is predominantly diagnosed in children under 15 years of age, and the incubation period symptoms appear about 3-7 days after being bitten by an infected mosquito [1] [8]. Seizures, altered mental state, cognitive impairment, and coma are main clinical features, whereas fever headaches, vomiting, and other neurological deficits (hemiparesis, dysarthria, chorea, and aphasia) are common manifestations as well [1] [4] [5] [6]. Rapid clinical deterioration, stemming from increased intracranial pressure, cerebral herniation, respiratory insufficiency requiring intubation, and status epilepticus, is encountered in a minority of cases [1] [4] [5] [6]. It must be noted that the majority of deaths by LACV occur due to La Crosse encephalitis, indicating that early recognition is vital for preventing complications [1] [4] [5]. In addition, long-term neurological sequelae are readily observed among survivors [5].

• Hyperthermia

  Effect of localized magnetic-induction hyperthermia on the brain: temperature versus intracranial pressure. Cancer 1986 ;57: 1401 - 1404 39. Nara I, Shiogai T, Hara M, Saito I. [content.nejm.org]

• Nasal Congestion

  Except for intermittent nasal congestion associated with upper respiratory infections, the infant remained healthy and exhibited appropriate growth and development through the first 6 months of life. [cdc.gov]

• Constipation

  […] depending on type of substance: prior history, drug-seeking behavior, attention-seeking behavior, paranoia, sudden panic, anxiety, hallucinations Electrolyte disturbance Fatigue, headache, nausea Varies depending on deficient ions; clinically, edema, constipation [wikidoc.org]

• Papular Rash

  In August 2006, a previously healthy woman aged 43 years in week 21 of her pregnancy was admitted to a West Virginia hospital after experiencing severe headaches, photophobia, stiff neck, fever, weakness, confusion, and a red papular rash. [cdc.gov]

• Macrocephaly

  Although no human congenital infection with a bunyavirus of the California serogroup has been reported, congenital infection with other bunyaviruses of the Bunyamwera serogroup has been associated with macrocephaly. [cdc.gov]

• Contusion

  […] blood pressure, extremity weakness Intracranial hemorrhage Headache, coma, dizziness Lobar hemorrhage, numbness, tingling, hypertension, hemorrhagic diathesis Trauma Headache, altered mental status Amnesia, loss of consciousness, dizziness, concussion, contusion [wikidoc.org]

• Behavior Problem

  Most infections are asymptomatic, and the majority of infected individuals who develop symptoms recover completely; however, up to 10% of patients develop behavioral problems or recurrent seizures. [emedicine.medscape.com]

  These included sixth-nerve palsy and hemiparesis in two, mild hemiparesis in one, speech problems in three, aphasia in one, decreased short-term memory in four, behavioral problems or dull affect in three, and poor balance in one. [content.nejm.org]

• Lhermitte's Sign

  sign ; on imaging, well-demarcated ovoid lesions with possible T1 hypointensities (“black holes”) Acute disseminated encephalomyelitis : clinically, somnolence, myoclonic movements, and hemiparesis ; on imaging, diffuse or multi-lesion enhancement, with [wikidoc.org]

The signs and symptoms of La Crosse encephalitis point to a nonspecific infection of the CNS and the differential diagnosis is often turned toward more common causes of viral encephalitis, such as herpes simplex virus (HSV) and enteroviruses [1] [5]. However, the specific geographical location is of crucial importance for including LACV as a possible cause. Thus, a detailed patient history must cover recent traveling to endemic areas of the United States (or if patients are living in these areas) and note whether mosquito bites occurred. The physical examination, if conducted properly, can immediately point to a CNS infection, in which case both laboratory and microbiological studies should be employed. A lumbar puncture will show mild lymphocytic (or sometimes neutrophilic) pleocytosis, and increased protein levels are observed in up to 30% of patients, while leukocytosis in a complete blood count (CBC) is also seen [1] [2] [5]. A definite diagnosis of La Crosse encephalitis is made after conducting one of the two microbiological procedures - serology or polymerase chain reaction (PCR) [6] [7] [8]. Identification of immunoglobulin (Ig) M or high titer IgG antibodies is a reliable and effective method, whereas detection of viral deoxyribonucleic acid (DNA) in the cerebrospinal fluid (CSF) through molecular methods, such as PCR and reverse transcriptase-PCR has increased the overall efficacy in identifying LACV in human tissue [1] [5] [6] [7] [8].

• Periodic Lateralized Epileptiform Discharges

  The aim of this study is to provide a clinical description of the largest series of children reported with periodic lateralizing epileptiform discharges (PLEDS) associated with La Cross virus encephalitis with reference to their clinical course, seizure [ncbi.nlm.nih.gov]

  lateralizing epileptiform discharges in 8, and focal epileptiform discharges in 3. [content.nejm.org]

  lateralizing epileptiform discharges • SIADH syndrome of inappropriate antidiuretic hormone • MRI magnetic resonance imaging • CDC Centers for Disease Control and Prevention • HIV human immunodeficiency virus La Crosse virus is a mosquito-borne bunyavirus [pediatrics.aappublications.org]

• Focal Epileptiform Discharges

  epileptiform discharges in 3. [content.nejm.org]

• HLA-DR5

  Of La Crosse encephalitis patients with acute-phase seizures, only 2 (7%) were positive for HLA-DR5, whereas 16 (37%) of nonseizure patients were positive for that antigen (P .025). [ncbi.nlm.nih.gov]

1. McJunkin JE, de los Reyes EC, Irazuzta JE, et al. La Crosse encephalitis in children. N Engl J Med. 2001;344(11):801-807.
2. Davis LE, Beckham JD, Tyler KL. North American encephalitic arboviruses. Neurol Clin. 2008;26(3):727-ix.
3. Lambert AJ, Fryxell RT, Freyman K, et al. Comparative Sequence Analyses of La Crosse Virus Strain Isolated from Patient with Fatal Encephalitis, Tennessee, USA . Emerg Infect Dis. 2015;21(5):833-836.
4. Haddow AD, Odoi A. The Incidence Risk, Clustering, and Clinical Presentation of La Crosse Virus Infections in the Eastern United States, 2003–2007. Rénia L, ed. PLoS One. 2009;4(7):e6145.
5. Mandell GL, Bennett JE, Dolin R. Mandel, Douglas and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, Pennsylvania: Churchill Livingstone; 2015.
6. Jones TF, Erwin PC, Craig AS, et al. Serological survey and active surveillance for La Crosse virus infections among children in Tennessee. Clin Infect Dis. 2000;31:1284-1287.
7. Lambert AJ, Nasci RS, Cropp BC, et al. Nucleic Acid Amplification Assays for Detection of La Crosse Virus RNA. J Clin Microbiol. 2005;43(4):1885-1889.
8. Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. Seventh edition. Philadelphia: Elsevier/Saunders; 2013.