NEW YORK (AP) — Health officials are seeing an increases of a rare illness called rabbit fever that was beaten back decades ago.

In the last two decades, health officials saw an average of only about 125 cases each year of the illness — known to doctors as tularemia. But the government reported Thursday that there have already been 235 cases this year. That’s the most since 1984.

Officials aren’t sure why cases are up, but speculate that it may have to do with weather conditions that likely helped rodents — and the bacteria — thrive in some Western states.

Insects pick up the bacteria from rabbits and other small mammals and then spread it when they bite humans. It’s treatable with antibiotics.