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California Encephalitis - Symptoms, Diagnosis, and Treatment

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This article briefly discusses a viral infection caused by the California serogroup virus causing central nervous system disease. Read the article below.

Written by

Dr. Asma. N

Medically reviewed by

Dr. Abhishek Juneja

Published At May 2, 2023
Reviewed AtOctober 11, 2023


California encephalitis serogroup viruses are a group of viruses that cause disturbances in the central nervous system and were discovered in the USA, America, Australia, California, and Europe. It is the second most common domestic arbovirus (viral infection caused by infected insects), causing encephalitis (inflammation of the brain), mainly in children. The La Crosse virus is the most common virus that causes encephalitis among this serogroup. It affects healthy children of five to ten years, and males are affected more. 30 percent or more children in the endemic areas possess antibodies against california encephalitis serogroup viruses and are asymptomatic. The ratio of asymptomatic to symptomatic infections is 1000: 1. Aedes triseriatus, a mosquito species, is the vector that inhibits stagnant water. Amplifying hosts for the La Crosse virus include day-feeding chipmunks, ground squirrels, and tree squirrels.

What Is the Microbiology of California Encephalitis Serogroup Viruses?

California serogroup viruses are 90 nm thick and have a lipid envelope with two glycoproteins (Gl and G2). They have single-stranded ribonucleic acid (RNA) genomes composed of three segments, they are, small (S-RNA), medium (M-RNA), and large (L-RNA).

What Are the Types of California Encephalitis Serogroup Viruses?

Most of the viruses in this group are named for the site or region of original isolation, including California type (California, La Crosse, San Angelo, and Tahyna virus), Melao type (Melao, Jamestown canyon, and Keystone virus), trivittatus type and guaro type. California encephalitis virus mostly affects children. La Crosse virus encephalitis causes more central nervous system diseases. Jamestown Canyon virus affects mainly elderly persons and has similar clinical features as seen in the La Crosse virus.

What Is the Pathogenesis of California Encephalitis Serogroup Viruses?

Vectors which are mosquitoes, while feeding on blood, can ingest the virus, and the virus attaches to midgut epithelial cells and replicates. Barriers restrict further infection. When these viruses escape these barriers and disseminate in salivary and reproductive organs, further replication occurs, causing the mosquitoes to transmit the virus by bite.

What Are the Symptoms of California Encephalitis?

The incubation period of this virus is 7 to 15 days. Multiplication of the virus occurs in vascular endothelial and reticuloendothelial cells and spreads through blood and lymph. Infantile cases are less due to limited exposure and protective maternal antibodies. Infection is usually asymptomatic. Affected individuals can experience the following symptoms:

  • Mild febrile illness.

  • Fever (ranging from 101 °F to 106 °F), headache, nausea, and vomiting.

  • Encephalitis.

  • Meningoencephalitis.

  • Choreoathetosis (occurrence of involuntary movements).

  • Disturbance of sensorium, ranging from confusion to coma.

  • Lethargy, incoordination, focal motor abnormalities, and paralysis.

  • The most common focal seizure is lateral deviation of eyes and head toward the side of unilateral upper extremity clonic movements.

  • Focal neurologic signs include hemiparesis (inability to move on one side of the body), aphasia (a disorder that affects communication ability), dysarthria (difficulty in speaking due to weak muscles), and chorea (a disorder that causes sudden uncontrollable jerky movements).

  • Children with nervous system illnesses are typically hospitalized on the second or third day of illness. Most have malaise, restlessness, and irritability for one to three days before the onset of fever.

  • Gastrointestinal manifestations include anorexia, abdominal discomfort, nausea, and vomiting.

  • Periodic lateralizing epileptiform discharges (PLEDs) cause convulsions, intubation, epilepsy, and cognitive and memory deficits.

  • Diarrhea, sore throat, and cerebral herniation can occur rarely.

  • La Crosse and herpes encephalitis share similar manifestations like fever, headaches, drowsiness, general weakness, coma, seizures, cerebrospinal fluid abnormalities, and computed tomography (CT) or magnetic resonance imaging (MRI) brain scan and electroencephalogram (EEG) changes.

What Is the Diagnosis of California Encephalitis?

California encephalitis is diagnosed by the following methods:

  • MRI shows focal images, which are usually confined to the temporal lobe,

  • Electroencephalograms are slow and often show focal findings, including periodic lateralizing epileptiform discharges (PLEDs). PLEDs often localize to the temporal lobe.

  • Cerebrospinal fluid (CSF) pleocytosis analysis shows lymphocytic or monocytic predominance. Cerebrospinal fluid glucose is elevated, with an increased protein level, IgM (immunoglobulin M) detection, and increased paired sera for IgG and cerebrospinal fluid erythrocythemia occurs.

  • Peripheral white blood cell counts exceed upto 10,000 per μL in the case of the La Crosse virus.

  • The diagnosis of La Crosse encephalitis can be confirmed by detecting La Crosse virus-specific IgM in serum or CSF, and reverse transcription-polymerase chain reaction (RT-PCR) can detect RNA (ribonucleic acid) of this virus.

  • Diagnosis of other California serogroup viruses requires a specific study of serology. But cross reactions develop and prevent the distinction of viruses. Therefore, a specific molecular assay for the S-RNA has been developed.

What Are the Differential Diagnosis of California Encephalitis?

The differential diagnosis of California Encephalitis are:

What Is the Treatment of California Encephalitis?

Until the diagnosis is established, healthcare should treat herpes simplex virus encephalitis. In the case of infected patients, healthcare should monitor vital signs, and in case of increased intracranial pressure, appropriate measures should be taken.

  • Seizures are treated by using an anti-convulsant medication, and at least one major anticonvulsant should be continued for approximately one year, as this appears to reduce the risk for postencephalitic epilepsy from 50 % to between 6 % and 13 %.

  • In severe cases, brain herniation can occur. It may cause death and should be managed by sedation, the elevation of the head of the bed, osmotic agents, hyperventilation, and appropriate fluid management. In addition, Haloperidol and lorazepam can treat confusion, irritability, and troublesome headaches.

What Is the Prognosis of California Encephalitis?

Recovery generally requires seven to ten days in mild cases. Almost all patients achieve normal motor, intellectual, and psychological functions within a few months. Severe encephalopathy or coma requires at least two weeks. EEG abnormalities are seen for several months in case of seizures, which resolve within a year if no seizures occur. Permanent intellectual deficits can be associated with persistent hemiparesis and epilepsy. Choreoathetosis associated with dysarthria and dysphasia may last up to a year. After the treatment, permanent motor signs and objective cognitive/learning difficulties can persist. Transplacental transmission of the La Crosse virus to the fetus is documented.

How Can California Encephalitis Be Prevented?

Prevention involves protecting susceptible humans (children under the age of 15) from the vector, avoiding staying near breeding areas in the summertime, and using full clothing and mosquito repellants. In addition, public health measures such as filling basal tree holes with concrete and removing water-containing debris from tires, old boats, and neglected troughs should be undertaken.


Most of the infected cases are asymptomatic. But children who recover may have seizures, cognitive dysfunction, weakness, or behavioral problems. In the case of the la crosse virus, fatalities are rare, about 1 % to 3 %.

Frequently Asked Questions


What Options Are Available for Treating California Encephalitis?

California encephalitis is treated with supportive care rather than a particular medication. Rehydration for nausea and vomiting, antiemetic medicines, and pain control for headaches are all important aspects of managing severe meningeal symptoms. Symptomatic alleviation during the acute phase is crucial, and bed rest is advised until the patient recovers. Patient isolation is not necessary.


Are There Any Long-Term Effects Associated With California Encephalitis?

The majority of cases of California encephalitis affect children under the age of sixteen. Rarely, La Crosse encephalitis (a specific type of California encephalitis) can cause death or severe impairment over time. There is currently no vaccination to prevent La Crosse encephalitis virus infection or targeted antiviral therapy for clinical La Crosse encephalitis virus infection. Long-term issues may result from it include behavioral, psychological, and amnesia (memory loss), language, and speech issues (aphasia).


Is It Possible for California Encephalitis to Spread Between Individuals?

California encephalitis (CE) is spread by mosquito bites and is a reportable condition. Direct transmission through casual contact between individuals is unknown. But the virus can also spread through people who are infected, which feeds the cycle of infection in mosquitoes. Avoiding mosquito bites is essential to lower the chance of developing California encephalitis.


What Factors Increase the Risk of California Encephalitis?

Being exposed to infected mosquitoes, particularly those of the Aedes species, is the main risk factor for virus-induced California encephalitis. Arboviral encephalitis is influenced by several epidemiologic characteristics, such as

(1) the season.

(2) the geographic location,

(3) the regional climate (such as spring rainfall).

(4) the patient's age.

The Midwestern states in the United States have the greatest rate of arboviral encephalitis. Although some cases happen in the winter in subtropical endemic locations (like the Gulf States), the majority of cases happen in the late summer to early fall. Engaging in outdoor activities, particularly in woodland regions, is linked to a higher risk of infection. Children are frequently more susceptible as they lack immunity and engagement in outdoor activities.


Is There a Vaccination Available for California Encephalitis?

For viruses in the California encephalitis group, no particular antiviral medication or vaccination is available. The goal of management is symptom relief through supportive measures. Since there are no specific medical treatments for the viral infection, prevention includes taking precautions to avoid mosquito bites.


In What Ways Does California Encephalitis Differ From Other Types of Encephalitis?

The main way that California encephalitis varies from other forms of encephalitis is in how it is transmitted. The bite of an infected insect, especially an Aedes mosquito, is how it is spread. Diverse encephalitis types may be caused by viruses or autoimmune causes, and they may present with diverse clinical symptoms and means of transmission.


Can California Encephalitis Impact Pets?

Humans are the main species affected by California encephalitis, which is spread by mosquito bites. The California encephalitis virus infects both humans and small mammals, most commonly California ground squirrels. Pets such as dogs and cats are generally regarded as accidental hosts and are not known to play an important role in the development or transmission of California encephalitis. In mosquito-prone locations, it is recommended to take general precautions to shield pets from mosquito bites.


Are There Lifestyle Adjustments to Guard Against California Encephalitis?

The prevention of California encephalitis involves several measures. These include wearing long sleeves when outdoors, applying insect repellents, using spray insecticides to specifically control mosquito populations, eliminating mosquito breeding grounds, and investigating other mosquito prevention strategies like using particular essential oils' repellent qualities.


What Measures Should Be Taken if There Is Suspicion of California Encephalitis?

Receiving quick medical attention is essential if California encephalitis is suspected. Cerebrospinal fluid analysis is one type of diagnostic test that may be performed. It may be necessary to provide supportive care, such as pain relief and fever management. Preventive actions against mosquito bites should be enhanced.


How Is California Encephalitis Managed in Pediatric Cases?

The primary method of management for pediatric California encephalitis cases is supportive care. In severe circumstances, hospitalization can be necessary. It is crucial to drink enough water and control pain and fever. Priorities include monitoring for problems and giving neurological support.


What Assistance Is Available for Individuals Recovering From California Encephalitis?

Recovery from California encephalitis frequently necessitates broad assistance. To address neurological deficiencies, patients may benefit from rehabilitation therapies, such as physical and occupational therapy. Counseling and psychosocial support can improve emotional health. In treatment, supportive care is beneficial. The medications used in supportive care include those that can treat neurologic issues. When necessary, antipyretics (to reduce fever) are used. There is no vaccination or antiviral medication available for pre-exposure protection.

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Dr. Abhishek Juneja
Dr. Abhishek Juneja



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