>>> important health news tonight about lyme disease . turns out it is way more common than even the experts knew. tonight, the cdc says 300,000 people get lyme disease each year from deer ticks . that's ten times more than the cdc had previously counted, partly because not all cases are reported. nearly all those 300,000 cases are in the northeast and upper midwest . nbc's chief medical editor, dr. nancy snyderman , is here with more on what you need to know about lyme disease . first, help us understand this big jump.

>> i think for a lot of us, it wasn't that surprising, because for years, we have recognized that we probably underdiagnosed this and the cdc today said they are looking at new ways of trying to figure out how many cases are in this country and this does give credence and credibility to parents wtients, who, over the years, had symptoms and frankly, doctors haven't known,put that into any bucket or category. when doctors can't do that well, they don't diagnose well.

>> we will talk about the symptoms. some mimic other illnesses but what are the they?

>> the classic is a bull's eye rash, the central point with a bull's eye and that happen 2s 4 to 36 hours after a bite. and then, flu-like symptoms, fever, aches, pain, headache. then some times, joint aches and muscle aches and when it can be misdiagnosed as arthritis. the tick bite doesn't mean you're going to get lyme disease . the black-legged tick has to be on you for 244 to 346 hours for it to really infect you. you can't infect another person. but if do you see a tick, the most important thing is to get it out with fine-nose tweezers. if you're out and about make sure you do a service, self-body tick check and if you do have symptoms, it's time to talk to your doctor about antibiotics. just because you get a tick bite doesn't mean you need antibiotics. if you have symptoms, then you get antibiotics. > how do you prevent the exposure to the ticks, so plentiful in this part of the country?

>> one of the things is just the basics we have always talked about wear light clothing, pull your socks up over your legs and for kids playing out this time of year, cut the grass, separate your backyard from longer grass or the woods with gravel or wood chips . the whole thing is to minimize exposure ahead of time and when your kids come in from playing outside, kids or grandkids, have them strip and look over their entire body. ticks like warm areas and it's important to get those ticks off within a day.

>> important information. nancy, thank you. more information about recognizing and treating lyme disease on our