The nation's medical experts have offered varying theories, or none at all, on why this year's West Nile cases appear to be centered in Dallas and Tarrant counties.
"It is not clear why we are seeing more activity than in recent years," said Dr. Marc Fischer, medical epidemiologist with the CDC's Arboviral Diseases Branch.Reliable data have been hard to come by, but by most accounts, Dallas-Fort Worth has been hit harder than most parts of the country this year.Texas reports 586 cases of West Nile virus and says 340 of those are in Dallas and Tarrant counties. Local health department officials counted 474 cases in Dallas and Tarrant counties as of Tuesday.Dr. Victor Cardenas, an epidemiology professor at the University of Texas School of Public Health, said the drought may have stymied the virus the past couple of years. But this year "is totally different.""I see the numbers often, and it's a surprise to see this happening in the northern part of Texas," he said.Jim Kennedy, a biology professor at the University of North Texas, said he believes that some factors are related to climate."Importantly, we had those mild temperatures all winter and relatively warm, mild temperatures" from March to June, he saidTemperatures were "conducive to replication of West Nile virus in mosquitoes."The state says West Nile intensity fluctuates from year to year. A combination of weather, the numbers of birds and mosquitoes that spread the virus and human behavior play a role in its prevalence. The season lasts until the first hard freeze of the year.In December, January and February, daily temperatures dipped below freezing but always climbed above 32 degrees.While the average temperatures weren't significantly different the previous winter, during Super Bowl week, there were three consecutive days when highs didn't rise above freezing, said Dennis Cavanaugh, a meteorologist with the National Weather Service office in Fort Worth.Though rainfall in the spring was roughly the same year to year, so far this summer, rainfall is 67 percent higher than last summer. From June to this point in August, 6.5 inches of rain have fallen. Last year, 3.89 inches fell during the time.Kennedy said another factor in the spike of reported cases may be that physicians in North Texas are more informed."Health-care workers are aware of the possibility some human deaths" are caused by the virus. As a result, they've increased their level of testing, he said.
West Nile virus symptoms
Most people who are infected with West Nile virus will not have any type of illness or may experience mild fever, headache and body aches before fully recovering. If illness were to occur, it would occur within 3 to 15 days of being bitten by an infected mosquito.
Symptoms
Fever, headache and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands.
In a very few individuals, particularly the elderly, the virus can affect brain tissue, cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord), but more commonly presents as a febrile illness. Symptoms of encephalitis include rapid onset of severe headache, high fever, stiff neck (in meningitis), muscle weakness, confusion and loss of consciousness
Source: Tarrant County Public Health Department
Preventing West Nile Virus
The Tarrant County Public Health Department recommends the 4Ds.
Drain standing water on your property so mosquitoes won't breed.
Use insect repellent that contains DEET.
Stay indoors at dusk and dawn when mosquitoes are most prevalent.
Dress in long sleeves and pants and spray insect repellent on the clothes.
How do you feel about aerial spraying in the effort to kill mosquitoes carrying the West Nile virus?
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