Tick (IMAGE) Northeastern University Caption The ticks that transmit Lyme disease have multiplied aggressively over the past 20 years, and now thrive in half of all counties in the US, according to a recent study in the Journal of Medical Entomology. Credit YoungHee Jang/Northeastern University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.