Waco Tribune-Herald: West Nile cases less common in suburban McLennan County

Aug. 21, 2012

Reprinted by permission of the Waco Tribune-Herald


Saturday August 18, 2012

Cases by ZIP code

76708 - 5 cases

76705 - 4

76704 - 3

76707 - 2

76710 - 2

76711 - 2

76624 - 1

76657 - 1

Source: Waco-McLennan County Health District

Reported cases of West Nile virus are more concentrated in older urban neighborhoods and absent so far from McLennan County's southern and western suburbs, a breakdown of health data by postal ZIP codes shows.

The disease has spread through ZIP codes in Waco, Bellmead and Beverly Hills, with a few cases in more rural areas, data provided by the Waco-McLennan County Health District show.

Hewitt, Woodway, Robinson, Crawford and Speegleville were among the ZIP codes that had no reported cases.

Professor Richard Duhrkopf, a mosquito biologist at Baylor University, said the mosquito species that most often carries West Nile, called culex, is commonly found in older urban areas, where tall grass and standing water are more common.

A Baylor biologist said the mosquito species called culex, which most often carries West Nile, is commonly found in older urban areas.

USDA Agricultural Research Service

The data, compiled at the Tribune-Herald 's request, represents 20 cases reported in the county this summer, starting July 22. As of Friday, the number of cases had risen to 22, but two cases lacked ZIP code information.

David Litke, the health district's environmental health coordinator, said he sees no significant pattern in where the disease strikes within the county.

"If you look at ZIP codes, there isn't any cluster effect," he said.

The data is somewhat inconclusive because many ZIP codes in McLennan County are several miles long and the number of cases is relatively small.

For example, five of the cases are within the 76708 ZIP code area, which sprawls from Windsor Drive in North Waco to China Spring.

But there were also high counts in some more compact ZIP codes, including three cases in the East Waco ZIP code of 76704 and two in the 76711 ZIP code centered around Beverly Hills. Those two ZIP codes had the highest number of cases per population.

The 76705 ZIP code, which includes Bellmead, Lacy-Lakeview and Gholson, had four cases. One of those was an 88-year-old Bellmead man who died of the infection, family members said.

Professor Richard Duhrkopf, a mosquito biologist at Baylor University who has consulted with the health district, said he's not surprised to see fewer West Nile reports in the more prosperous suburbs.

Duhrkopf said the mosquito species that most often carries West Nile, called culex, is commonly found in older urban areas, where tall grass and standing water are more common.

More affluent suburbs tend to have less mosquito habitat, he said. Lawns and lots are trimmed and generally free of debris that can collect water for a breeding ground. Also, a larger population of residents in those areas have air-conditioned homes and spend more time inside.

In a prior outbreak in the mid-2000s, Duhrkopf trapped mosquitoes from around the county and analyzed whether they had the virus.

"There was a problem around Crawford, but the most serious problems were around Bellmead, Lacy-Lakeview and Gholson," he said. He said he doesn't remember finding any infected mosquitoes around Hewitt, Robinson or Woodway.

"When I go to various places around the state to collect mosquitoes, I pretty much know where I'm going to find things," he said. "What you see in Robinson, Hewitt and Woodway -- those are not typically places I'm going to look for mosquitoes."

Duhrkopf said the favorite breeding ground of the culex mosquito is water that stands in underground storm drains. Cities such as Houston regularly hit manholes with mosquito fog.

But Duhrkopf said he doesn't think that's necessary here. He predicted the outbreak will die down as dry weather continues, then die out with a cool fall.

But the rains forecast in the next few days could reactivate mosquito populations.