If my baby has a round, red, circular rash, could he have lyme disease?

Unlikely: To develop lyme disease, you have to be exposed to a tick bite. Infants are unlikely to get bitten by ticks.

If you child or teen has had a tick bite, or been in an area where a tick bite is possible, consider lyme disease a possibility. The red rash looks like a large target. Test results can be falsely positive or falsely negative. If a tick has been removed, it is best to go ahead and treat.

Possibly: The classic rash of lyme looks has a red center, then a normal area surrounded by a red ring. Ticks are the most likely vector of lyme, but there is strong evidence that biting flies like deerflies and horseflies can transmit lyme (see http://www.Nejm.Org/doi/full/10.1056/nejm199006143222415) and it is theorized other biting insects may also transmit it. But there are many other causes of rashes.