July 26, 2010 — The Centers for Disease Control and Prevention (CDC) is reporting the first case of La Crosse virus (LACV) neuroinvasive disease, a rare mosquito-borne disease, to occur in Missouri since 2002.
Most LACV cases since the mid-1980s have been reported in Mid-Atlantic states, including North Carolina, Tennessee, Virginia, and West Virginia. "The reason for the increase in cases reported outside the upper Midwest is unclear but might be related to changes in diagnosis, reporting, or the ecology of the vectors," the authors suggest.
According to the case description in the CDC's Morbidity and Mortality Weekly Report, on August 7, 2009, the Missouri Department of Health and Senior Services was notified of suspected LACV neuroinvasive disease in a boy aged 8 years from northwest Missouri.
The previously healthy boy, who lived in Kansas City, Missouri, presented with headache, fatigue, nausea, vomiting, and abdominal pain and received amoxicillin for presumed streptococcal pharyngitis.
"During the next 48 hours, he continued to have vomiting and developed fever and worsening headache, prompting a second emergency department visit on July 31," Sarah Patrick, PhD, from the Missouri Department of Health and Senior Services, and colleagues write. No neurological signs were apparent, but the boy was admitted to hospital on August 1 because of suspicion of acute meningitis.
Once hospitalized, the patient received vancomycin and ceftriaxone for possible bacterial meningitis. On August 7, immunofluorescence assay results of serum and cerebrospinal fluid were positive for immunoglobulin M and immunoglobulin G against California serogroup viruses, of which LACV is the most prevalent; thus, a presumptive diagnosis of LACV was made. The CDC later confirmed the presence of LACV-neutralizing antibodies in the cerebrospinal fluid.
The patient's headache and neck and abdominal pain improved, and he was discharged on August 7. He remained healthy, and no neurologic abnormalities were detected through medical follow-up.
According to the report, the boy had been bitten multiple times by mosquitoes about a week before symptom onset, but he had not recently traveled outside of northwest Missouri.
High Clinical Suspicion
Healthcare providers serving central Kansas, Missouri, and eastern Nebraska should "maintain a high clinical suspicion for LACV among patients with unexplained meningoencephalitis during summer and fall, when mosquitoes are active," Dr. Patrick and colleagues write.
California serogroup virus neuroinvasive disease has been nationally notifiable since 1995. From 2003 to 2007, 412 neuroinvasive disease cases were reported, of which 407 (99%) were confirmed as LACV. Of the 398 LACV cases for which the outcome was known, 7 (2%) were fatal, the authors note. "The disease is likely underdiagnosed because it mimics other viral encephalitides (e.g., enteroviral and herpes virus encephalitides)."
"La Crosse virus encephalitis only occurs in children under the age of 15, and fortunately, the case fatality rate is relatively low (<3%)," noted independent commentator Samantha Soldan, PhD, from the Department of Neurology at the University of Pennsylvania, Philadelphia. "However, approximately 2% of children with LACV encephalitis will have persistent neurological sequelae including persistent paresis, attention deficit disorder, learning disabilities, and cognitive defects," she told Medscape Medical News.
Dr. Soldan added that LACV is a leading cause of pediatric encephalitis and aseptic meningitis in the Midwestern United States, where its primary vector, the eastern treehole mosquito, resides. "In recent years, LACV has spread by the invasive Asian tiger mosquito (Aedes albopictus) into Tennessee, North Carolina, West Virginia, Missouri, and Texas. Therefore, the potential emergence of LACV throughout the rest of North America is of great concern," she said.
According to Dr. Soldan, future research will be needed to determine the optimal antiviral and neuroprotective therapeutics necessary, as well as to identify factors that make developing brains more susceptible to LACV encephalitis than adult brains. "It will also be important to determine which mechanisms the virus uses to counter the host immune response," she said.
According to the CDC, LACV neuroinvasive disease was first described from La Crosse County, Wisconsin, after isolation of the virus in 1964 from brain tissue of a girl aged 4 years who had died of encephalitis in 1960.
The authors and commentator have disclosed no relevant financial relationships.
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