Residents of the Northeast and the Midwest know that ticks can carry the bacteria that cause Lyme disease. What most don’t know is that the same family of black-legged ticks can also cause other diseases that are even more dangerous.

The worst is Powassan disease, which generally kills about 10 percent of its victims and leaves half the survivors with permanent neurological damage. Only 15 cases of this rare disease have been found in New York State in the last nine years, but there is no treatment and 5 of the patients have died. Fortunately, only a small percentage of ticks in New York are infected with the Powassan virus — between 4 percent and 6 percent at sites in the hardest-hit counties, Dutchess, Putnam and Westchester. By contrast, the Lyme bacterium has been found in 35 percent to 75 percent of the ticks at sites in those areas.

Three other diseases — anaplasmosis, babesiosis and illnesses caused by a newly detected pathogen, Borrelia miyamotoi — are transmitted by the same ticks and can, to varying degrees, cause severe disability and sometimes death. In rare cases a single tick could make a person sick with several diseases at the same time, greatly complicating diagnosis.

Senator Charles Schumer, Democrat of New York, recently urged the Centers for Disease Control and Prevention to allocate resources for research to understand the Powassan virus, create a treatment and learn how to prevent further spread. It would make sense to control this virus before it becomes a major threat.