If mosquitoes weren’t bad enough already, now they’re killing people again.
The West Nile virus is making a comeback after its heyday in 2002 and 2003, resulting in 87 human deaths as of early September and almost 2,000 reported cases, according to the Centers for Disease Control and Prevention (CDC). Texas leads the country in both measures, with 888 cases recorded and 35 deaths as of Sept. 4. In 2002 and 2003, it claimed 284 and 264 lives, respectively.
Of the 1,993 cases reported nationwide as of Sept. 4, 54 percent were severe cases that affected the nervous system.
“Based on past epidemics of West Nile disease, we expect the numbers will eventually show that this year’s epidemic peaked in mid-to-late August,” said Lyle Peterson, director of the CDC’s vector-borne infectious diseases division. “Although we may be past the historical peak, we expect that a great many cases have not yet been reported largely because of the lag between when a person gets sick and when the illness is reported.”
Cases have been high in Mississippi, Louisiana, Oklahoma and South Dakota, but without a doubt the Dallas area has been the most seriously hit, with 537 cases in Dallas, Tarrant and Denton counties.
Judge Clay Jenkins has been handling Dallas County’s response as the virus claimed 13 lives and infected 313 others. The severity of the situation landed it on President Obama’s emergency briefing, Jenkins said. Jenkins declared a public health emergency Aug. 9 and began eight days of aerial spraying with the help of state and federal officials, who paid the $3 million for the flights.
• Click here to access the CDC's West Nile resource page.
•Click here to see the CDC's county-by-county map of confirmed West Nile cases, as of each Tuesday.
“It escalated very quickly,” he said. “Our ground spraying couldn’t keep up with rapid expansion of infected mosquitoes.”
Each municipality in the county decided whether to be sprayed. Municipalities totaling nearly 18 percent of the county’s population opted out of aerial spraying. The CDC found that areas that were sprayed on consecutive days were “substantially successful” in reducing the number of mosquitoes carrying West Nile, but areas that were not sprayed saw increases.
In addition to spraying, the county has been distributing out 20,000 donated cans of bug repellant to low-income residents and launching an aggressive public communication campaign to wear bug repellant and long clothes, drain standing water and limit outdoor activity at dawn and dusk.
“This is going to be an ongoing and persistent threat until the first freeze,” Jenkins said. “In the meantime, by taking appropriate steps, people can substantially mitigate or almost eliminate their risks of exposure.”
Dallas County had no indication West Nile would be such a problem, but in retrospect, the mild winter and hot summer may have, as the CDC believes, made the virus more active in the mosquitoes that were infected and extended those mosquitoes’ lives.
The additional water caused by the rains from Hurricane Isaac may not be to blame, and in fact the rains and floods likely wash away mosquito breeding grounds. Peterson said CDC analysis showed hurricanes and floods have not been found to contribute to higher incidence of West Nile, and increased numbers of mosquito bites in those affected areas are typically due to people spending more time outside.
Conversely, the extended drought that has plagued much of the Midwest has dried up a lot of water.
“A variety of environmental factors, temperature, rainfall and early onsets of spring or late onsets of spring or late onsets of fall, et cetera, can affect all of these parameters that affect transmission of West Nile virus in nature,” Peterson said. “So, it’s complicated.”
|Approximately 80 percent of people infected with West Nile virus show no symptoms, while one in 150 people infected develop a severe illness.
Those who develop a serious illness, however, are in for a rough time. More than half of confirmed West Nile infections affect the nervous system, causing meningitis and encephalitis.
Meanwhile, some environmental groups have opposed plans to combat mosquito populations via aerial spraying.
The choice to combat mosquitoes with aerial spraying in Dallas County was not without controversy, Judge Clay Jenkins said. There was some resistance to the spraying plan, particularly from bee keepers and organic farmers.
“Public safety is the most important part of this job, and our citizens were in danger,” he said. “If a gang was out in the streets killing a dozen people and hospitalizing hundreds more, sometimes with grievous injuries, people would be calling for us to take action with every tool at our disposal.”
The Centers for Disease Control and Prevention argued that not only was the amount of pesticide small — approximately one teaspoon for the size of a football field — it was sprayed mainly at the treetop level, where mosquitoes were more likely to be, tailored to mosquitoes and sprayed at night, when mosquitoes were active but other insects were dormant. It was also safe, the CDCsaid, because it was the same pesticide that is sprayed at ground level from trucks.