California Drought Boosts West Nile Threat

West Nile

California’s three-year old drought has had a terrible impact on the normally agriculture-rich state. It would seem counter-intuitive with a dearth of water that mosquitos would be an issue. Yet, the California drought has actually increased the West Nile virus threat and public health officials are reporting significant boosts in the numbers of cases being reported.

There are now approximately 375 human cases of West Nile virus reported in the state, according to California public health officials. That is more than double the rate that had been diagnosed by this time last year and more than three times the five-year average. Of the 300-plus people infected in the state, 12 have died so far.

Normally mosquitos depend on water to breed, so the drought would normally have reduced the threat. However, the warm weather in some areas leads to more insects, particularly the southern house mosquito, which can be a West Nile carrier. In addition, when there is less water, birds and insects seek out the same sources of water and there interaction further spreads the virus.

Drought conditions have helped pools of water that are stagnant and stinky. In parts of the state, rainwater collection vessels are sitting with untouched water have become breeding grounds. In addition, there are many foreclosed properties with abandoned pools where water is attracting insets.

Some parts of the state, like Orange County, are West Nile hot spots. There have been 116 cases of West Nile identified in the county so far this year. Local officials have attempted to spray pools to fight the insects.

The San Fernando Valley (SFV) section of Los Angeles County – particularly Sherman Oaks, Encino and Canoga Park – are also experiencing a higher than average infection rate. The SFV has typically experienced more cases of West Nile than the rest of the county. One reasons is that the valley tends to be hotter temperature-wise. It also has a lot of swimming pools, spas and other sources of water.

While the numbers of cases in Orange and Los Angeles counties are high, those counties are heavily populated. Some less populated area in Northern California are experience a greater concentration and percentage of their population impacts. For example, Glenn County (located north of Sacramento) has the highest West Nile infection rate, according to state health officials, at 35 cases per 100,000 people. By comparison, the Orange County rate is approximately 4 cases per 100,000 residents.

California residents, particularly in those counties known to have a West Nile virus problem, are encouraged to make sure there is no stagnant water around their homes, such as a birdbath or unused kiddie pool. The officials also encourage used of insect repellent or wearing long sleeves and pants (which is not very practical while the area still has summer weather).

The situation in California is similar to the West Nile virus epidemic that affected the Dallas-Forth Worth area is 2012. There was a drought condition and high temperatures, like in Southern California that lead to boosts in that state’s West Nile threat. There were close to 2,000 cases of West Nile reported in that part of Texas that year and 89 people died. So far this year, Texas has the second largest infection rate in the country with 98 cases reported so far, nothing like what was experienced two years ago.

By Dyanne Weiss

Los Angeles Times
Los Angeles Times
Washington Post
U.S. Centers for Disease Control and Prevention

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