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

# 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:

# 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

## 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
- Insect repellent containing DEET
- Long sleeves, pants; tucking in pants into high socks