Health officials at the Center for Disease Control (CDC) in Atlanta are calling the current outbreak of mosquito-transmitted West Nile Virus (WNV) disease across Texas the worst outbreak in the state’s history, causing cities across the state to launch comprehensive pesticide spraying programs in an effort to protect the public.

The death toll related to West Nile Virus in Texas this year has reached 17 so far and health officials from Austin to Atlanta are warning that number could go higher. Also at risk are farm animals, especially horses, and Texas AgriLife officials are warning farmers and ranchers to take steps now to control potential mosquito breeding grounds to protect both humans and animals.

In addition to stock ponds and water troughs in rural areas that serve as mosquito breeding grounds, officials say the problem is serious in urban areas as well. Dallas County, for example, has begun aerial spraying of pesticides to control mosquitoes for the first time in 45 years, largely because of concerns that public schools are set to open this week and next, which has alarmed parents over the dangers.

Concerns with school openings

Janet Hurley, AgriLife Extension state school integrated pest management specialist in Dallas County, says it is a valid concern, but one that can be managed.

“State law mandates that public school districts in Texas, all 1,030 of them, must have a trained integrated pest management coordinator on staff. They are trained to deal with situations such as the mosquito problems we are seeing in many parts of the state now,” she said.

West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus, which is also found in the United States. The virus can infect humans, birds, mosquitoes, horses and other mammals. The most severe type of disease for a person infected with West Nile virus is sometimes called “neuroinvasive disease” because it affects a person’s nervous system. Specific types of neuroinvasive disease include: West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis.

While most people who contract the virus experience only mild flu-like symptoms including lethargy, weakness, muscle stiffness, malaise and loss of appetite, other and more symptoms might include possible neurological signs of encephalitis (inflammation of the brain). The latter might include stumbling, staggering, abnormal posture, disorientation, muscle twitching, seizures, paralysis, and coma. In humans, those with underlying health conditions, including the elderly and extremely young, are at greater risk. In some cases, the disease can be fatal.

Health officials warn that while the summer season is nearing its end, WMV can continue to pose a health risk through the fall and winter months until a substantial freeze eliminates mosquito populations.

Half of U.S. cases in Texas

"Right now, Texas has half the West Nile cases in the nation," Dr David Lakey, Texas state health commissioner, told reporters at a press conference last week. "Dallas County has half of the cases in the state, so about a quarter of all the cases in the United States are in this county. This isn't business as usual."

According to Texas Department of Health (TDA) figures, 465 West Nile cases have been confirmed in Texas this year, including 17 related deaths, which is on track for the most cases since the disease first reached the state late last century. Ten deaths and more than 200 cases this year have been reported in Dallas County alone.

In rural Texas, WMV poses little threat to livestock, but horses and birds are subject to infection. In 2011 six cases of equine WMV were confirmed in Texas. Horses and humans are, in fact, the most likely mammals to show signs of the disease. Infections with West Nile virus have been documented in other mammals as well with evidence of illness in cats, dogs, sheep, goats, bats, llamas, wolves, and rodents.

When evaluating a cow with signs of general lethargy or neurological impairment, West

Nile Fever remains very low on the diagnostic list. But health officials warn that any evidence of neurological disease in cattle should be seriously considered.

Controlling WMV on the farm and ranch involves eliminating mosquito breeding grounds. In addition to stock ponds and water troughs, old tires, feed buckets and any other container that holds water is a potential breeding ground. In addition, overflowing septic systems can pose a serious problem.

High risk times of the day when mosquito bites are most common include early mornings and early evenings, and farm and ranch workers should use an approved insect repellant containing Deet, the most effective repellant, when working outdoors.

The CDC reports that as of August 14, 43 states have confirmed West Nile infection in people, birds or mosquitoes this year, with more than80 percent of cases from six states: Texas, Mississippi, Louisiana, Oklahoma, South Dakota and California.

The 693 human cases reported to CDC through the second week in August is the highest number for that time of year since the virus was first detected in the United States in 1999. At least 26 people have died nationwide.