Tick Season Begins: Latest Activity In Chester County

WEST CHESTER, PA — From the hills around Marsh Creek to the banks of French Creek and the Schuylkill River, tick season is now in full swing across Chester County.

While March and April typically mark the beginning of tick activity, random spurts of warm weather in the winter can cause ticks to emerge even earlier. This could mean that ticks are already well established in some areas.

Lyme disease incidence in ticks is currently at 27.4 in Chester County per 100,000 residents for 2026, according to the Pennsylvania Department of Health. That's notably higher than neighboring Montgomery County, which sits at 12.4, and Bucks County, which sits at 16.9.

See also: Warm PA Winters, Climate Change Could Fuel Tick Growth

Here are Chester County's rates for other infectious diseases carried by ticks, and monitored by the state:

• Anaplasmosis: 4.8
• Babesiosis: 4.08
• Erlichiosis: no data

Chester County's anaplasmosis and babeiosis rates are among the highest in the state.

The Pennsylvania Tick Research lab has tested 5,603 ticks, and found 1,175 infected with some kind of disease.

More on tick diseases

Adult ticks and nymphs can transmit tick-borne illnesses such as Lyme disease, Rocky Mountain spotted fever and a few other serious ailments.

Pennsylvania is home to four ticks which transmit disease, according to the Centers for Disease Control:

• American dog tick
  • Diseases transmitted: Tularemia, Rocky Mountain spotted fever
• Blacklegged tick
  • Diseases transmitted: Lyme disease, babesiosis, Powassan virus, relapsing fever
• Brown dog tick
  • Diseases transmitted: Rocky Mountain spotted fever (in the southwest)
• Lone Star tick
  • Heartland virus, tularemia, STARI

Lyme disease: The most notorious, Lyme disease can cause a wide range of symptoms if left untreated. This typically depends on the state of the infection, but can include fever, rash, facial paralysis, and arthritis. Other symptoms, in absence of a rash, include chills, headaches, fatigue, muscle and joint aches and swollen lymph nodes. Every state in the country has reported at least one case of Lyme disease in 2019, the latest date for which complete data is available from the Centers for Disease Control and Prevention. Lyme disease outbreaks were most common in the Northeast. Lyme disease is spread by blacklegged tick species.

Rocky Mountain spotted fever: Most people who get sick with this illness experience a fever, headache and rash. If not treated with the right antibiotic early, it can be fatal. Before tetracycline antibiotics were available, Rocky Mountain spotted fever fatality rates ranged from 20 percent to 80 percent, according to the CDC.

Cases are found throughout the continental United States, but five states, Arkansas, Missouri, North Carolina, Tennessee, and Virginia, account for more than 50 percent of Rocky Mountain spotted fever cases. Rocky Mountain spotted fever is transmitted by a variety of ticks, depending on the region of the United States.

Anaplasmosis: Symptoms are often mild and can include high fever, severe headache, chills, and muscle aches. In rare cases, untreated anaplasmosis can lead to respiratory failure. It's common in the northeast and midwest.

Babesiosis: A malaria-like disease spread by blacklegged tick bites, symptoms include fever, fatigue, and hemolytic anemia. Highest risk comes in the summers in the northeast and midwest.

Powassan virus diseases: Symptoms include fever, headache, vomiting and general weakness, usually progressing to meningoencephalitis, a very serious neurological condition resembling both meningitis and encephalitis with symptoms that include mental confusion, seizures, paralysis and palsies. If left untreated, it can lead to death. U.S. cases of Powassan virus diseases have been reported primarily in Northeast and Great Lakes states.

Ehrlichiosis: There are three strains of this illness, one of them potentially deadly. Fatal cases of ehrlichiosis are highest among children around 10 and adults around 70, according to the CDC. It’s most reported in the Southeast and South Central United States, but three states, Oklahoma, Missouri and Arkansas, account for 35 percent of all cases.