Public health officials across Texas and New Mexico are voicing concern over the recent rapid spread of the more threatening form of a common mosquito-born illness, West Nileneuroinvasive disease (WNND).

Since Oct. 9, the total number of West Nile Virus (WNV) cases in New Mexico have risen from 20 to 33, with most, 21 of them, of the more serious West Nile neuroinvasive disease variety (WNND), which has resulted in three deaths so far. Twelve of New Mexico's WNV cases are of the simpler and milder type of the disease, known as West Nile Fever.

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In Texas, a total of 136 cases have been reported this year with most of those cropping up in the last few weeks. Of growing concern is that the majority of those cases, 79 of them, are of the more risky WNND variety that has led to nine deaths so far this year. Fifty seven of the Texas cases have been classified as West Nile fever.

According to the Center for Disease Control and Prevention in Atlanta, it is not the number of cases in the Southwest that are alarming but the large percentage of the cases that are of the more invasive and risky types of the disease.

Dr. Cedric Spak, an infectious disease specialist at Baylor Dallas Hospital, says West Nile virus is a mosquito-borne disease of the encephalitis group that was first detected in the U.S. in 1999. But he warns that West Nile neuroinvasive disease poses the biggest threat to people and animals. Symptoms for WNND can include headaches and other flu-like symptoms, but Spak said a fever higher than 102 degrees and a sense of confusion or disorientation are key signs of the more serious variety of the virus and he advises that victims should seek immediate medical attention.

Health officials say late summer and early fall rains have contributed to the rapid uptick of WNV cases across the Southwest. But, surprisingly perhaps, the number of cases so far is fewer than last year's numbers, a historic WNV year in Texas in spite of the drought. Some 1,868 WNV cases were reported in Texas in 2012 of which 844 were of the neuroinvasive strain. There were 89 fatalities attributed to WNND in Texas last year.

Researchers are still trying to determine the reasons for the increased number of neuroinvasive cases of the disease in recent weeks.

Spak advises homeowners, especially rural residents who own or stable horses, to take preventive measures designed to limit mosquito production. Standing water should be eliminated around houses and barns and standing ponds of water not used by livestock should be treated.

He further advises avoiding early morning and early evening excursions outdoors when mosquitoes are most active and says wearing long pants and shirt sleeves can help minimize the chances of exposure. He also advises using a repellant that contains DEET, picaridin, oil of lemon, eucalyptus or IR3535 when outdoors.

Horses, animals at risk as well

Health officials remind rural residents that West Nile Virus infection can not only cause fatal encephalitis (inflammation of the brain) in humans but in horses as well. Even certain domestic and wild birds can contract the disease.

A single horse from Otero County, New Mexico,has tested positive for the disease this year. Since WNV was detected in New Mexico in 2003, 438 horses have been confirmed as victims of the disease. While more rare, other animals in New Mexico have contracted the disease as well, including bovine, porcine, llama and canines. A harbor seal at the Albuquerque zoo was also diagnosed with WNV in recent years.

In Texas this year, 27 horses have been diagnosed with Wet Nile Virus.

Dr. Kristy Murray, who led the research of the 2012 Texas WNV outbreak conducted by the National School of Tropical Medicine at Baylor College of Medicine in Houston, says last year's unexpected outbreak demonstrated the need for ongoing mosquito surveillance and the necessity of developing an effective human vaccine.

She says considering the cost of acute medical care and lost productivity caused by last year's outbreak, a minimum loss of $47 million can be blamed on the 2012 incident.

"When you look at what it is costing us as a society, it’s enormous. Last year it was easily $47 million for just acute medical care, and that’s a very, very conservative estimate,” Murray said.

Texas was the epicenter last year of the largest West Nile outbreak in U.S. history.

The study indicated a historical uptick in the number of cases every three years, but it also concluded there was no obvious reason for the extreme outbreak of WNV last year. But health officials warn that the greater question may be why the ratio of the more serious neuroinvasive disease is much greater this year than for the less invasive West Nile fever cases. Even during last year's historic outbreak 844 nueroinvasive cases compares to just over 1,000 milder cases. In contrast, nearly 65 percent of WNV cases this year are nueroinvasive.

Some 135 Texas counties reported at least one WNV case last year, but the largest number of cases was reported in North Texas. Tarrant County reported 259 confirmed cases (14 percent), 396 cases were reported in Dallas (21 percent), 183 in Denton (10 percent) and 64 in Collin (3 percent), according to the study. Those four counties had a combined incidence rate of 16 cases per 100,000 population, an extremely elevated ratio compared to normal years.

Officials say with the advent of cooler weather in November, the number of confirmed cases should decrease rapidly.

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