A University of Rhode Island researcher is warning of an ‘‘exceptional crisis’’ in public health after finding a record number of tick nymphs in the state. Thomas Mather directs the university’s Center for Vector-Borne Disease. He said high humidity in early summer is contributing to the higher numbers. Mather has collected data on ticks in Rhode Island for 20 years and said this summer’s survey found a ‘‘shocking’’ number of young ticks. Individuals bitten by ticks can become infected with Lyme disease, babesiosis, and other diseases.