Case of St. Louis encephalitis reported in Califo…

To UNITED STATESthe Fresno County Department of Public Health (FCDPH) confirmed on September 23, 2022 the 1st positive case of the year 2022 and the death of the year of a patient by St. Louis encephalitis (LES) in the county of Fresno in California.

Reminder onSaint Louis encephalitis

L’Saint Louis encephalitis is a viral encephalitis caused by the Saint Louis encephalitis virus (SLEV), a Flavivirus transmitted by mosquitoes of the genus Culex. The mosquito becomes infected during a blood meal taken from a bird that has SLEV in its blood. Birds that live in urban and suburban areas, such as sparrows, pigeons, blue jays, and robins, are common hosts for SLEV.

Infected humans (and domestic animals) constitute a “terminal host” because they do not have enough virus in their blood to infect a mosquito. However, the amount of circulating virus can be the cause of exceptional transmission by transfusion.
The virus is present in a large geographical area from Canada to Argentina, but most of the cases described occur in the United States (cases are however rare: 5 cases of encephalitis in 2018, 15 in 2019). Periodic outbreaks have occurred in the Mississippi Valley and along the Gulf Coast of Mexico, and sporadic cases are reported throughout the United States, the Caribbean, Canada, Mexico, and Central America. In temperate areas, transmission occurs primarily in late summer and early fall, but in warmer climates transmission occurs year-round.

Most people infected with SLEV do not have symptoms.
For people with symptoms, the incubation period varies from 4 to 14 days. The disease usually begins suddenly, with fever, headache, dizziness, nausea and generalized weakness. The picture usually worsens over a period of a few days to a week. Some patients recover after this time, but others develop signs of central nervous system infection.
The severity of the disease and the risk of death increase with age. Of patients diagnosed with SLEV, 5-20% die.

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There is no vaccine against SLEV infections, nor effective antiviral treatment. The best preventative treatment is to avoid mosquito bites.

Source : ProMED.

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