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; California virus encephalitis;

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 La Crosse encephalitis, 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 the mosquitoes feed. Humans are dead-end hosts for the virus, meaning there is not sufficient numbers 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	Findings
La Crosse encephalitis	Presents with acute inflammation of the brain, caused by a viral infection; it may complicate into severe brain damage. Other findings include nausea, headache, vomiting in milder cases and seizures, coma, paralysis and permanent brain damage in severe cases.
Vector-borne encephalitis	Presents with acute inflammation of the brain, caused by a bacterial infection; it may complicate into severe brain damage as the inflamed brain pushes against the skull, potentially leading to mortality. See also: Tick-borne encephalitis, Eastern equine encephalitis, Western equine encephalitis, Japanese encephalitis, and West Nile encephalitis
Viral encephalitis	Presents with acute inflammation of the brain, caused by a viral infection; it may complicate into severe brain damage as the inflamed brain pushes against the skull, potentially leading to mortality. See also: Herpes simplex encephalitis and VZV encephalitis
Encephalopathy	Presents with steady depression, generalized seizures. Generally absent are fever, headache, leukocytosis, and pleocytosis; MRI often appears normal.
Meningitis	Presents with headache, altered mental status, and inflammation of the meninges, which may develop in the setting of an infection, physical injury, cancer, or certain drugs; it may have an indolent evolution, resolving on its own, or may present as an rapidly evolving inflammation, causing neurologic damage and possible mortality. See also: bacterial meningitis, viral meningitis, and fungal meningitis
Brain abscess	Presents with an abscess in the brain caused by the inflammation and accumulation of infected material from local or remote infectious areas of the body; the infectious agent may also be introduced as a result of head trauma or neurological procedures.
Acute disseminated encephalomyelitis (ADEM)	Presents with scattered foci of demyelination and perivenular inflammation; it can cause focal neurological signs and decreased ability to focus.

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 between 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. Less than 1% of cases result in mortality. However, approximately 20% of patients have residual seizures.

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.

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
• Acute flaccid myelitis
• Somnolence
• Obtundation
• Acute flaccid paralysis
• Myalgia

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 IgM antibodies.
• Persistence of IgG and neutralizing antibodies
• Confirmation of arboviral-specific neutralizing antibodies in Enzyme linked immunosorbent assay (ELISA),

commonly include enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), and plaque reduction neutralization test (PRNT)

EEG

On EEG, California encephalitis virus [disease name] 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
• Regularly changing birdbaths
• Screens on doors and windows
• When outdoors:
  • Wearing insect repellent containing DEET
  • Wearing long sleeves, pants; tucking in pants into high socks

References

CEV is closely related to La Crosse Virus.