In Texas, more than half of all West Nile cases

>>> good evening. tonight it is official, the federal government says the current outbreak of one virus is the largest in the u.s. right now there are four times the usual number of cases. what's worse is very few people are exempt from this because it's now been found in just about every state in this country. some numbers here, 1100 cases in 38 states in all. texas and the lower mississippi delta area have been hit the worst. unbelievably 41 people have died from it so far. that's part of the problem, it's early in the one season. that's why the numbers from the feds today got the attention of a lot of people. we begin tonight with nbc's janet shamlian . she's just outside houston. hey, janet, good evening.

>> reporter: brian, good evening. this is the airport, one of the command centers in the battle against one. tonight after dark planes will take off from here and spray tens of thousands of acres to battle this virus from the air. the one virus, spread by infected mosquitoes, has never spread across the country this far, this fast.

>> this is the worst one outbreak in the united states .

>> reporter: the cdc reports the number of cases has almost doubled since last week. more than half are in texas , where the death toll has risen.

>> feel weak and everything, started having problems breathing. i went and laid down to see if things would get better.

>> reporter: in fact they got worse for domingo via. after 11 days at the baylor medical center , he's home, but walking with a cane and still has blurry vision.

>> they said i will get better but it's going to take some time.

>> reporter: dallas, which has most cases has after dark aerial, small planes spraying insecticide deemed safe by fda. on the ground an information campaign. standing water has become public enemy number one. it's prime breeding ground for mosquitoes.

>> what we have right now is a very serious outbreak here. what we need to do is enter the transmission cycle as quickly as we can to save lives.

>> reporter: 80% of people infected will have no thomas. dr. nancy snyderman says for others, the symptoms can progress quickly.

>> symptoms occurring 10 to 14 days after a bite. they are usually mild. fever, rash, exhaustion. if there are neurologic problems, fever, seizures, or over the age of 70, that's when you get to the hospital.

>> reporter: experts say the numbers will rise because the one season is young, not ending until late september . and the numbers are already rising. texas health officials just updated the death toll in the lone star state . it's now at 28. two more people have died.

>> unbelievable numbers. janet shamlian starting us off outside of spring, texas . janet, thanks.