With the number of West Nile Virus (WNV) cases in the United States nearly doubling in the last 12 days, Center for Disease Control (CDC) officials say they are alarmed and don’t know why the disease has suddenly become so problematic.

They say for residents in Texas and across the Southwest, the urgency of control has reached a critical stage. Texas, Oklahoma and now New Mexico have more than half of the 2,192 cases of the virus reported this year and 49 of the 92 deaths attributed to the disease.

“The first known case of West Nile Virus was reported in New York City in 1999, but there were several years that went by when things settled down for a while,” reports CDC’s Janet McAllister. “But this current outbreak is unusual and we don’t know why this is happening.”

In spite of isolated cases of WNV each year, usually in the late summer months when mosquitoes breed heavily, McAllister says until now outbreaks have been limited to mostly southern states. But this year 44 states are reporting WNV cases and she says the unpredictability of the virus has researchers stumped.

“This current outbreak was unexpected. What we know about West Nile Virus is that in 13 years since it was first introduced in the United States, it has now become endemic. But until now, we have never seen such a widespread outbreak, and one that has developed so quickly,” she added.

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.

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 serious symptoms might develop that 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.

Over the last 12 days, the number of WNV cases in Texas alone has risen from 465 to nearly 900 cases. The death count in Texas has risen from 17 related deaths to 40 deaths during the same period.

Worst year ever

 "This year (2012) is now officially our worst year ever for West Nile Virus disease," said David Lakey, commissioner of the Texas Department of Health. Previously, the worst year was 2003 when Texas had 439 cases and 40 deaths, he said.

Officials say the virus lives in birds. Mosquitoes bite infected birds, become infected, and then pass the virus along to humans. Since 1999, more than 30,000 people in the United States have reported they became sick with West Nile virus. Of all the cases of WNV this year, 54 percent were classified as neuroinvasive disease (such as meningitis or encephalitis) and 46 percent were classified as non-neuroinvasive disease.

CDC officials say heavy rains from Hurricane Isaac have added to the breeding potential of infected mosquitoes across the Delta, and a warmer-than-usual winter may have added to the current outbreak.

In addition to human victims, 21 Texas counties are reporting WNV cases in animals. The specific number of each animal group was not available from the Texas Animal Health Commission (TAHC), but generally infected animals are limited to horses, cats, dogs, sheep, goats, bats, llamas, wolves, and rodents. Livestock, as a rule of thumb, are generally not affected by WMV.

Prevention is key

In rural Texas, the greatest concern is for farm and ranch workers. 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.

“Most people don’t realize that any container—from a pet dish to a potted plant, a coke can to a trash receptacle—can be a breeding ground for mosquitoes. Eliminating the breeding grounds is the best defense against spreading the disease,” reports Texas AgriLife Extension Specialist Janet Hurley.

In addition, farm and ranch workers are encouraged to wear long sleeves and pants during dusk and dawn, a prime time for mosquito feeding. In addition, wear insect repellent when heading outdoors; repair or replace screens on doors and windows, use air conditioning if possible and empty standing water from all containers on the property.