WNV cases see dramatic rise in August

By KARI KRAMER | East Texas Edition

In the South Central area, 346 total WNV cases have been confirmed by the state, 179 were in mosquitoes and 13 cases were found in equine. Harris County, with 247 confirmed cases of WNV, produced the highest numbers in South Central Texas. -- Staff photo by Carolyn Rost

Sept. 30, 2004 - When compared to last year's total number of West Nile Virus (WNV) cases, this year's numbers have significantly dropped in Texas - yet August saw a dramatic rise in the number of cases when compared to other monthly numbers.

According to statistics from the Texas Department of State Health Services' Zoonosis Control Division, 2003 ended with 2,759 cases of WNV confirmed in the state. Year-to-date totals for 2004 show 599 total WNV cases.

The cases include those confirmed in humans, birds, mosquitoes, horses, and "other."

A close look at this year's WNV numbers show a dramatic increase of cases in August. In Texas, at the end of July, total number of WNV cases were 33; then about six weeks later, in mid-September, WNV numbers in the state were at 496.

Other year-to-date statistics show only five cases of WNV in equine as of the end of July, but earlier this month the Texas Veterinary Diagnostics lab has tested and confirmed 29 equine cases.

The largest jump in numbers came from positive tests on mosquitoes. That number rose from just 12 confirmed cases of the virus in July, to 266 positive tests as of this September.

Dr. Fearny Hough, head of diagnostic services for the Texas Veterinary Diagnostics Lab in College Station, credited the increase in WNV numbers during August to the wet summer weather.

"What we have seen for the last two years is that it peaks in September-October. Moisture this summer has altered growth patterns of mosquitoes," said Hough.

Hough said humid weather has caused the peak for WNV to come early.

Dr. James Wright at the TDSHS Zoonosis Control office in Tyler said that not all cases of WNV are counted in the numbers that are released. He said some samples are tested at commercial labs. Commercial labs, according to Wright, may not use the same test used by state agencies, so the case, unless tested and confirmed by the state, will not be counted in the statistics. He added that some cases tested elsewhere that are found to be WNV are actually other strains of encephalitis, such as St. Louis Encephalitis, which can cause a positive WNV test in humans unless a specific screen test is ran to differentiate between the two. Any WNV case must be tested by the state, or using the same procedure as the state to be counted in the official WNV numbers.

Hough agreed, and added that in horses there is only one test, which can determine West Nile Virus, Eastern Encephalitis, Western Encephalitis and Venezuelan Encephalitis. State agencies use a screen test to confirm the presence of the IGM antibody, the antibody that confirms the strain to be WNV.

Reported WNV numbers in birds, humans, mosquitoes and horses are probably lower than the actual occurrences, according to Hough.

" There are more cases out there. They are not being sent to use for testing at the level they were in the first two years," said Hough.

Hough believes more cases are being diagnosis in other labs and not reported or sent to the state, now that lab professionals are more familiar with the virus.

"Bottom line, it's still there and it's going to stay there," said Hough, who added that vaccinations are the only way to protect equine animals from the virus.