Abstract
The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California. From 2003 through 2018, 6,909 human cases of WNV disease, inclusive of 326 deaths, were reported to CDPH, as well as 730 asymptomatic WNV infections identified during screening of blood and organ donors. Of these, 4,073 (59.0%) were reported as West Nile neuroinvasive disease. California’s WNV disease burden comprised 15% of all cases that were reported to the U.S. Centers for Disease Control and Prevention during this time, more than any other state. Additionally, 1,299 equine WNV cases were identified, along with detections of WNV in 23,322 dead birds, 31,695 mosquito pools, and 7,340 sentinel chickens. Annual enzootic detection of WNV typically preceded detection in humans and prompted enhanced intervention to reduce the risk of WNV transmission. Peak WNV activity occurred from July through October in the Central Valley and southern California. Less than five percent of WNV activity occurred in other regions of the state or outside of this time. WNV continues to be a major threat to public and wild avian health in California, particularly in southern California and the Central Valley during summer and early fall months. Local and state public health partners must continue statewide human and mosquito surveillance and facilitate effective mosquito control and bite prevention measures.
Highlights
West Nile virus (WNV) is a mosquito-borne flavivirus (Flaviviridae) that was introduced into New York City in 1999, rapidly spread throughout the continental United States, and was first detected in California during the summer of 2003 [1,2,3,4]
From 2003 through 2018, 6,909 human cases of WNV disease were reported in California, including 326 WNV-associated fatalities
Geographic and temporal patterns of WNV activity are influenced by climate, the distribution and abundance of mosquito vectors and reservoir birds, as well as mosquito control and public health efforts
Summary
West Nile virus (WNV) is a mosquito-borne flavivirus (Flaviviridae) that was introduced into New York City in 1999, rapidly spread throughout the continental United States, and was first detected in California during the summer of 2003 [1,2,3,4]. The virus is maintained and amplified in an enzootic transmission cycle involving mosquitoes in the genus Culex and various bird species. Humans may become infected through the bite of an infected female mosquito; in California the primary rural vector is Culex tarsalis, whereas Cx. pipiens and Cx. quinquefasciatus are the principal urban vectors in the northern and southern parts of the state, respectively. Spillover transmission has led to 50,830 reported human cases of WNV disease, inclusive of 2,330 fatalities, and more than 28,000 equine encephalitis cases across the USA since 1999 [5,6,7,8]. We have summarized WNV surveillance data collected and reported in California from 2003 through 2018
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