DALLAS, Sept. 17, 2012— -- Brandt Leondar is learning to walk again. A single mosquito bite infected with West Nile virus has ravaged his body and his mind.
But Leondar, a 51-year-old high school band director from Grapevine, Texas, wasn't even expected to survive, and his doctor prepared the family for the worst.
"I had talked to his wife candidly," said Dr. Cedric Spak, "I told her I'm not sure which way this is going to go."
Spak is a top expert in infectious diseases at Baylor University Medical Center in Dallas. Nearly 100 victims of West Nile have been treated at Baylor this year, and Spak has watched as some of his own patients have died from the disease.
Spak admits he has few answers for those who have West Nile. "We are still unable to explain why some people get better, and others do not," he said.
Centers For Disease Control and Prevention officials announced in August that the recent outbreak of West Nile was the largest ever seen in the United States, and now it is on track to be the deadliest.
Carried by birds and mosquitoes, which have spread it across the entire country, the virus has sickened 30,000 people since it first showed up in the United States in 1999.
As of Sept. 11, there have been 2,636 cases and 118 deaths reported to the Centers For Disease Control and Prevention so far this year. Texas has seen the worst of it, with 40 percent of the nation's West Nile cases in this one state.
Since there is no cure and no vaccine for West Nile, the best hope of slowing the outbreak may be inside a laboratory in Fort Collins, Colo. Researchers at the CDC's Division of Vector-Borne Diseases are working to track this mysterious disease.
Scientists sort mosquitoes gathered in the field by species and by sex, since only females bite humans. The bugs are ground up so that they can be tested for the virus, telling researchers how fast it is spreading, and where pesticides should be used and whether or not they are working.
When used correctly, the pesticides are highly effective at killing off mosquitoes. But aerial spraying in cities such as Dallas has led to a backlash from residents who worry that the spraying may be dangerous.
Dr. Lyle Petersen, the director of the CDC's Division of Vector-Borne Diseases, is the man leading the government's battle against West Nile and maintains that spraying is safe.
"The EPA has looked at all of this, and has deemed these pesticides as being safe, Petersen told ABC's Dr. Richard Besser during a visit to the CDC lab in Fort Collins.
"We found no increased respiratory illness, or any other kind of illness," he said. "That's not unexpected, because the amount of pesticides used is often less than one ounce per acre. It's minuscule."
This is a battle that's personal for Petersen, who himself became a victim of West Nile a few years ago.
"I went out one day at dusk, no repellant, to get the mail. Three days later both my friend and I got West Nile," he said. "I mean, I'm a long distance runner and I could barely walk up the stairs for three months. It was a miserable experience."
Petersen said the best defense against West Nile is to apply insect repellent before heading out doors.
About 80 percent of those infected by a mosquito carrying West Nile will never know it -- they won't even get sick. About 1 in 150 will come down with the most severe form of West Nile, as the virus attacks the nervous system. Often the hardest hit victims are left with neurological damage that lasts a lifetime.
Joey Worley, 51, of Fairfield, Texas, narrowly escaped becoming another victim of the disease. Worley, a high school coach and marathon runner, said he began to feel flu-like symptoms after a family vacation to New Mexico. A few days later, his wife Renea called for an ambulance to take him to the emergency room.
After five days in the hospital, Joey Worley was cleared to go home. His doctor said it appears he will not suffer permanent neurological damage from the disease.
Brandt Leondar is also recovering at home -- something his doctor said he never expected because of how severe his case was. Spak said it only adds to the mystery surrounding this disease.
"It is miraculous how [Brandt is] turning around," he said.
With so few answers from medical experts, Petersen warns West Nile is here to stay.
"There's no way to get rid of it at this point," he said. "People need to realize they're at risk, and I'm a good example of that."