NEW YORK — The Centers for Disease Control and Prevention issued an early advisory in April 2026 urging Americans to guard against ticks, as weekly emergency room visits for tick bites reached their highest level for this time of year since 2017. Tick season has started earlier than usual, with a higher than average number of bites reported across the country.

"The data are telling us now is the time to take action. Ticks are out and people are getting bitten," said Alison Hinckley, a CDC Lyme disease expert.

Tick bites typically spike in May. The elevated weekly ER visit rates apply to all regions of the country except the south-central United States, according to the CDC's tracking system. About 85% of U.S. hospital emergency departments send data to the agency's tick bite surveillance system, which does not capture people who seek care outside of hospitals.

Researchers will need months to systematically sample ticks and chart changes in tick populations. Additional time will be required to determine whether there is an actual surge in Lyme disease or other illnesses, because not all tick bites result in infections.

Ticks are small, eight-legged arachnid parasites that feed on animals and sometimes people. Their numbers depend on factors including climate, deer, and mice populations, and more ticks can be seen after a mild winter. Some ticks are infected with pathogens that can cause diseases including Lyme disease, Rocky Mountain spotted fever, and alpha-gal syndrome, a red meat allergy. Lyme disease is the most common tick-borne disease, with an estimated 476,000 people treated for it each year, according to the CDC. Tick-borne infections are commonly treated with antibiotics.

"If you have a lot of exposures, there will probably be more cases of tick-related infections," said Dr. Alina Filozov, an infectious disease doctor at Middlesex Hospital in Middletown, Connecticut.

Most ticks seen in the Northeast this year have been large adult ticks, with juvenile tick nymphs expected to become more common in the coming weeks. Tiny nymphs are harder to see on people and often remain attached longer, increasing the risk of infections.

Lyme disease is named after a town in Connecticut, where residents submitted an average of 30 ticks per day for testing earlier in April 2026, according to the Connecticut Agricultural Experiment Station. Forty percent of the submitted ticks tested positive for the bacteria that cause Lyme disease, state officials said.

"Several factors have been helping tick populations expand, including unusually high numbers of mice in the last two years," said Scott Williams, a tick researcher at the Connecticut Agricultural Experiment Station. Ticks prefer warm, humid weather, and more ticks can be seen after a mild winter, contributing to the conditions researchers are monitoring in 2026.