The Los Angeles County Department of Public Health has confirmed the first human death of West Nile virus (WNV) infection in Los Angeles County for the 2014 season. The fatality occurred in a male in his 60s, who lived in the San Fernando Valley, had pre-existing health conditions and was hospitalized at the time of death. To date, 20 WNV infections, including 3 asymptomatic blood donors have been documented in Los Angeles County.

Public domain image/National Atlas of the United States
Public domain image/National Atlas of the United States

“Although most people bitten by a mosquito are not exposed to West Nile virus, some individuals may become infected with this disease and may experience symptoms that can last for months, or even years, such as fatigue, malaise, and depression,” said Jonathan E. Fielding, MD, MPH, Director of Public Health and Health Officer. “Residents can greatly reduce their risk of mosquito bites by following a some simple precautions, such as getting rid of pools of stagnant water around their homes, and using a repellent containing DEET when outdoors in mosquito prone areas, especially around dawn or dusk.”

In 2013, 165 human cases of WNV were reported in Los Angeles County, among the highest counts documented since 2004. Of those who showed symptoms and were reported, 122 cases required hospitalization and 9 cases were fatal. Most people with WNV infection have mild or no symptoms and do not seek medical care; therefore, the total number of WNV infections is much larger than the number reported. As of August 28, 2014, non-human WNV activity has been detected in 139 mosquito pools, 31 dead birds, and 26 sentinel chickens located all across Los Angeles County.

According to the California Department of Health, as of Tuesday there were 129 human West Nile virus cases in the state from 19 counties. They also report six deaths up to that point.

Humans contract West Nile when they are bitten by mosquitoes infected with the virus. When people are infected with West Nile, the virus will affect them one of three ways. West Nile neuroinvasive disease is the most serious type, infecting the brain and spinal cord. Neuroinvasive disease can lead to death, paralysis and brain damage. The milder viral infection is West Nile fever, in which people experience flu-like symptoms. The majority of people who contract West Nile will be asymptomatic, which means they show no symptoms. These cases are typically detected through blood donations or in the course of other routine medical tests.

About 90 percent of all cases are asymptomatic, while about 10 percent will develop West Nile fever. Only a very small number of infected individuals will show the serious symptoms associated with the neuroinvasive disease. Residents who are 65 years old and older are at higher risk for complications, but everyone is at risk for infection.