October 2020 - Volumes

Saint Louis Encephalitis Makes Grim Appearance

In September, Madera County California officials reported the first Saint Louis Encephalitis Virus (SLEV) mortality in the US since 2018. SLEV-related deaths are relatively uncommon. The virus had claimed just one person in the US since 2016.

The case does not necessarily indicate increased risk of contracting SLEV, while SLEV pressure on a macro level has increased over the last 20 years. Through this time last year, California had reported four cases of SLEV, none of which were fatal.That being said, less than 1% of SLEV infections are clinically apparent and the vast majority of infections go undiagnosed. The overall SLEV case-fatality ratio is between 5 to 15%.

SLEV is transmitted to humans by the same mosquito species that transmit West Nile virus (WNV). In northern California, the mosquito species that carry SLEV are Culex pipiens and Culex tarsalis.

CDC reports the risk of severe disease and SLEV fatality increases with age, and the Madera County victim was in his 90s.

Reported SLEV Cases, 2010-2019