California encephalitis virus

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]

Synonyms and keywords: CEV; CVE; California virus encephalitis; CE virus

See also: La Crosse encephalitis

Overview

California encephalitis virus is a mild infection of the central nervous system. California encephalitis virus belongs to the Group V negative-sense ssRNA virus within the Bunyaviridae family of viruses. It is also known as an arbovirus. California encephalitis virus is usually transmitted via mosquitos to the human host. California encephalitis virus contains negative-sense viral RNA; this RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation. California encephalitis virus is contracted by the bite of an infected mosquito, primarily Aedes triseriatus. California encephalitis virus must be differentiated from other diseases that cause fever, headache, seizures, and altered mental status. There are approximately 70-115 cases of California encephalitis virus per year in the United States, most commonly affecting infants and children between the ages of 6 months and 15 years old. California encephalitis virus usually clears in 1 to 2 weeks and rarely recurs. Less than 1% of cases result in mortality. However, approximately 20% of patients have residual seizures. The diagnostic method of choice for California encephalitis virus is laboratory testing. There is no treatment for California encephalitis virus; the mainstay of therapy is supportive care.

Historical Perspective

California encephalitis virus was first discovered in 1943 in Kern County, California. In 1945, the first human cases of encephalitis were attributed to this new virus. Three cases in total were reported, and all three cases were Kern County residents. In all three cases there was strong laboratory evidence confirming infection, due to the presence of neutralizing antibodies linked to California encephalitis.

Classification

There is no classification system established for California encephalitis virus. California encephalitis virus belongs to the Group V negative-sense ssRNA virus within the Bunyaviridae family of viruses, and the genus Orthobunyavirus. California encephalitis virus is also known as an arbovirus, or an arthropod-borne virus. The California encephalitis serogroup, which contains genetically similar viruses such as the La Crosse virus, shares its name with the virus.

Pathophysiology

California encephalitis virus is usually transmitted via mosquitos to the human host. California encephalitis virus contains negative-sense viral RNA; this RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation. California encephalitis virus is made up of an enveloped virion with a helically symmetrical capsid. The envelope contains G1 glycoproteins. Neutralizing antibodies against these proteins block fusion of the virus with host cells and inhibit hemagglutination. The virus genome is over 12000 nucleotides in length and consists of three segments of various sized single-stranded RNA (negative sense and ambi-sense).

California encephalitis virus is contracted by the bite of an infected mosquito, primarily Aedes triseriatus. The virus is maintained and amplified in Aedes triseriatus populations through transovarial and venereal transmission. The virus overwinters in the mosquito egg. Amplification also occurs in chipmunks and squirrels, upon which mosquitos feed. Humans are dead-end hosts for the virus, meaning there is an insufficient amount of California encephalitis virus in the blood stream to infect a mosquito. Subsequently, the disease cannot be spread to other humans. The incubation period is 5-15 days.

Causes

California encephalitis virus causes encephalitis in humans.

Differentiating California Encephalitis Virus from other Diseases

California encephalitis virus must be differentiated from other diseases that cause fever, headache, seizures, and altered mental status, such as:

Disease	Similarities	Differentials
Meningitis	Classic triad of fever, nuchal rigidity, and altered mental status	Photophobia, phonophobia, rash associated with meningococcemia, concomitant sinusitis or otitis, swelling of the fontanelle in infants (0-6 months)
Brain abscess	Fever, headache, hemiparesis	Varies depending on the location of the abscess; clinically, visual disturbance including papilledema, decreased sensation; on imaging, a lesion demonstrates both ring enhancement and central restricted diffusion
Demyelinating diseases	Ataxia, lethargy	Multiple sclerosis: clinically, nystagmus, internuclear ophthalmoplegia, Lhermitte's 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 indistinct lesion borders
Substance abuse	Tremor, headache, altered mental status	Varies 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, hallucinations; on EKG, abnormalities in T wave, P wave, QRS complex; possible presentations include arrhythmia, dehydration, renal failure
Stroke	Ataxia, aphasia, dizziness	Varies depending on classification of stroke; presents with positional vertigo, high 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

Epidemiology and Demographics

Incidence

There are approximately 70-115 cases of California encephalitis virus per year in the United States.

Age

California encephalitis virus commonly affects individuals between 6 months old and 15 years of age.

Seasonal

The majority of California encephalitis virus cases are reported in the summer months between July and September, and peaks in August.

Geographic Location

The majority of California encephalitis virus cases are reported in the Midwestern United States, especially those living in rural and suburban settings surrounded by deciduous forests.

Risk Factors

Common risk factors in the development of California encephalitis virus include:

• Young age
• Residing or working in rural and suburban settings
• Mosquito contact
• Summer season
• Outdoor activities such as camping or hunting

Natural History, Complications, and Prognosis

Natural History

California encephalitis virus usually clears in 1 to 2 weeks and rarely recurs.

Complications

Common complications of California encephalitis virus include:

• Recurring seizures
• Coma
• Loss of basic motor skills
• Loss of coordination

Prognosis

Prognosis for California encephalitis virus is generally good, with most individuals returning to full health in 2-3 weeks. Less than 1% of cases result in mortality. However, approximately 20% of patients have residual seizures.

Diagnosis

History and Symptoms

If possible, a detailed and thorough history from the patient is necessary. In rare cases, California encephalitis virus presents with symptoms mimicking herpes simplex encephalitis. Common symptoms of California encephalitis virus include:

• Fever
• Headache
• Nausea
• Vomiting
• Seizures
• Altered mental status
• Stiff neck

Physical Examination

Common physical examination findings of California encephalitis virus include:

• Fever
• Ataxia
• Seizures
• Somnolence
• Obtundation
• Myalgia
• Acute flaccid myelitis
• Acute flaccid paralysis

This negatively-stained transmission electron micrograph (TEM) revealed the presence of numerous California encephalitis virus virions. Contained within its enveloped capsid, the genome of this Bunyaviridae family member consists of three segments of negative-sense single-stranded RNA ((-)ssRNA). From Public Health Image Library (PHIL).

Laboratory Findings

The diagnostic method of choice for California encephalitis virus is laboratory testing. Laboratory findings consistent with the diagnosis of California encephalitis virus include:

• Serologic cross-reactivity
• Presence of IgM antibodies
• Persistence of IgG and neutralizing antibodies
• Confirmation of arboviral-specific neutralizing antibodies in enzyme linked immunosorbent assay (ELISA)

EEG

On EEG, California encephalitis virus is characterized by periodic lateralizing epilepitoform discharges. However, results on imaging are not sufficient evidence to warrant California encephalitis virus diagnosis.

Treatment

Medical Therapy

There is no treatment for California encephalitis virus; the mainstay of therapy is supportive care.

Surgery

Surgical intervention is not recommended for the management of California encephalitis virus.

Prevention

There are no available vaccines against California encephalitis virus. Primary prevention strategies include:

• Removal of standing water
• Screens on doors and windows
• When outdoors, wearing:
  • Insect repellent containing DEET
  • Long sleeves, pants; tucking in pants into high socks