Cite This Article. A recent case of California encephalitis, a rare mosquito-borne viral disease, represents only the fourth ever reported and the first since the initial three cases in This case was diagnosed retrospectively on the basis of a rise in antibody titer between acute- and convalescent-phase serum samples. The arbovirus California encephalitis virus was first isolated in from mosquitoes collected in Kern County, California 1.
Two years later, three human cases of encephalitis were attributed to this new virus 2 ; all three cases were in residents of Kern County in the Central Valley of California. The best-documented case occurred in a 2-month-old Hispanic boy who had encephalitis and resultant developmental delay.
There was strong laboratory evidence confirming infection from the presence of neutralizing antibodies to California encephalitis, but not to St. Louis encephalitis virus or western equine encephalomyelitis virus. Serum from a 7-year-old boy hospitalized with encephalitis also had neutralizing antibodies to California encephalitis.
Serologic tests were inconclusive in a third possible case in a year-old agricultural worker with mild encephalitis; neutralizing antibodies against both California encephalitis and St. Louis encephalitis were detected. Since the original virus was isolated, other viruses have been isolated that are closely related to California encephalitis. This group of related viruses is now classified as the California serogroup, one of 16 serogroups within the genus Bunyavirus , family Bunyaviridae.
Several other human pathogens e. Little human disease was associated with these viruses until , but now California serogroup virus infections are the most commonly reported cause of arboviral encephalitis in the United States.
From to , approximately three times as many reported human cases of arboviral encephalitis were caused by California serogroup viruses as were reported for western equine encephalomyelitis virus, St.
Louis encephalitis, and eastern equine encephalomyelitis viruses combined 3. However, since the three original cases from California, no further cases of human disease caused by the prototype California encephalitis had been reported 4. Campbell et al. In June , a year-old man who lived in Marin County, California, became ill with blurred vision and dizziness.
Eight days after the onset of symptoms, he visited his primary physician. A physical examination was remarkable only for nystagmus. Laboratory studies included leukocytes 8.
A magnetic resonance image and arteriogram were normal. One month after the initial visit, the patient no longer complained of blurred vision or vertigo, and nystagmus had disappeared. Two years after the episode, he had no neurologic sequelae. The patient lived in a suburban area of Marin County, approximately 1 km from a large brackish marsh bordering San Francisco Bay. He had traveled outside the United States the previous February, when he had visited Egypt and several Caribbean islands.
He had not traveled outside California between this time and the onset of his illness in June, 4 months later. Indirect immunofluorescence antibody tests were negative for St. Louis encephalitis and Western equine encephalomyelitis virus, as were serum samples taken 8 and 16 days after onset of illness. California encephalitis-related arboviruses included in the tests were snowshoe hare, La Crosse, Jamestown Canyon, Morro Bay, and Tahyna.
Tahyna, an important California serogroup virus widely distributed in Europe and Asia, was included because of the patient's travel history. Northway, Main Drain, and Lokern viruses, members of the Bunyamwera serogroup occurring in California, were also included, as were Western equine encephalomyelitis virus and St.
Louis encephalitis. The sera were tested by plaque reduction-serum dilution neutralization with African green monkey kidney Vero cell cultures, according to the protocol of Campbell et al. These may include recurrent seizures, hemiparesis partial paralysis of one side of the body , and cognitive and neurobehavioral abnormalities. Skip to Main Content. Go to TN. Print This Page. Go to Search. Doxycycline was initiated, and serologic tests were conducted for Bartonella , Borrelia , Coxiella , and Anaplasma species and for Powassan virus, JCV, and SSHV; tests were also conducted to rule out paraneoplastic process and autoimmune causes.
By August 12, the patient was afebrile but remained confused. On August 18, PCR was negative for herpes simplex virus in CSF, and an electroencephalograph revealed no periodic lateralizing epileptiform discharges; acyclovir was discontinued. Initial serologic test results were negative, and the patient showed no autoimmune or paraneoplastic markers. Confirmatory PRNT titers for both viruses and the absence of IgM in the acute-phase serum suggest prior exposure to a CSG virus associated with the etiologic pathogen in this case.
Secondary infections with orthobunyaviruses may result in a gradual or delayed rise in IgM, with neutralizing antibodies already detectable early after symptom onset, as documented in other cases involving CSG viruses 9. Results for all other serologic tests were negative, leading to a modification of the diagnosis to confirmed CSG viral encephalitis. On September 9, the patient was transferred to a nursing home. The patient, who was totally dependent for personal care and instrumental activities of daily living, was diagnosed with postencephalitic dementia.
Drebot, unpub. As such, there is need for increased awareness that these viruses are circulating during the mosquito season and may be associated with human disease. Although most CSG infections result in mild illness, this case further highlights that these viruses can cause severe and debilitating neuroinvasive disease.
Patients who seek medical care for febrile or encephalitic clinical symptoms and who have possible or known exposures to mosquito vectors should be considered for CSG virus testing. JCV and SSHV infection should be considered in the differential diagnosis for such patients during the spring, summer, and fall. His primary research interests include zoonoses, harm reduction, tuberculosis, and glycosylation.
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Dimitrova, K. Holloway, K. Makowski, D. Safronetz, M.
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