The Pennsylvania Department of Health (DOH) has identified recent sustained increases in tick bite related emergency department visits in nearly all regions of the state. This trend was expected, as tick exposures in Pennsylvania generally increase during spring and summer months and serves as an important reminder that tickborne diseases occur seasonally in Pennsylvania. In addition, an increase in persons seeking care for Lyme disease (LD) is anticipated in the coming weeks to months as the peak period for LD is late May through early August. From April through September, health care providers should have a heightened clinical suspicion for tickborne diseases.
LD reporting in Pennsylvania is now entirely based on laboratory reports DOH receives directly from lab-based reporting, not clinical reports.
In Pennsylvania, LD is the most commonly reported tickborne disease and is usually seen during the months of May through September throughout the commonwealth. In 2020, Pennsylvania ranked sixth in the nation for the number of LD cases reported by population.
In 2021, 2,900 LD cases were reported in Pennsylvania, representing an incidence of 22.4 cases/100,000 persons. Most were reported between May and August, with 46.1% reported in June and July. Of Pennsylvania’s 67 counties, 58 reported LD, ranging from 0 cases in nine counties to 403 cases in Chester County.
It should be noted that LD was significantly underreported in 2021 due to the COVID-19 pandemic; therefore, case counts are likely significantly higher than reported and cases likely occurred in much higher numbers in all Pennsylvania counties.
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Anaplasmosis, a bacterial disease transmitted by deer ticks, has been on the rise in the United States and Pennsylvania. Anaplasmosis cases have doubled nearly every year for the past five years and are now found in almost every county in Pennsylvania.
The Pennsylvania Department of Environmental Protection (DEP) tick studies have found deer ticks infected with Anaplasma phagocytophilum in every Pennsylvania county. In 2021, Pennsylvania reported 683 anaplasmosis cases.
Several other non-Lyme tickborne diseases are also reported annually in Pennsylvania, including babesiosis, ehrlichiosis, and spotted fever rickettsiosis. Additionally, human cases of Powassan virus disease, a tickborne arbovirus, were documented in 2011 and 2017-2021. Results from the DEP tick studies conducted during 2019-2021 found additional evidence of Powassan in multiple counties.
In 2022, Pennsylvania reported its first human case of Heartland virus, an arbovirus transmitted by the lone star tick. Neighboring states have identified Bourbon virus in lone star ticks collected from the environment. Lone star ticks are established in some areas of Pennsylvania.
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