The number of Lyme disease cases in Pennsylvania declined in 2018 for the first time in two years, and it may be the oak tree that gets credit for the drop.

Last year, there were 10,208 cases of the tick-borne disease in the commonwealth, down from 11,900 in 2017, the Pennsylvania Department of Health reported Friday.

The reason for the decline may lie with the number of acorns available to feed field mice, one of the lead carriers of the disease, said Nate Wardle, spokesperson for the department.

When oak trees produce a large number of acorns, it is known as a “mast” year and creates more food for squirrels and rodents. It can result in a boon for the field mice population, Wardle said. When an uninfected tick attaches itself to a mouse, it can pick up the disease when it bites to feed on the rodent’s blood.

“We are thinking we are in a low part of the mast cycle where there are fewer acorns, which helps explain the decrease in cases,” he said.

In the five-county region, only Chester County saw an increase in 2018 with 678 reported cases of Lyme disease, up from 628 in 2017. Philadelphia reported 190 cases in 2018, Montgomery County logged 463, Bucks County had 398, and Delaware County had 156, all decreases from the previous year.

The decrease was welcome news after 2017 saw an increase of nearly 500 cases from the year before, according to the department.

Since 2011, Pennsylvania has led the country in the number of Lyme disease cases, according to the U.S. Centers for Disease Control and Prevention.

That likely will not change, said Wardle. The department expects the new total to still be among the highest in the country, he said.

In 2017, approximately 59,000 cases of Lyme disease were reported to the CDC by state health departments. But that number is thought to be a fraction of the actual cases due to under-reporting, according to CDC scientists.

In general, the reported cases of vector-borne diseases in the United States caused by infected ticks, mosquitoes, and fleas has tripled from 2004 to 2016, fueled by factors including increases in rainfall, temperature, and extreme weather events driven by climate change, development in rural areas, and changing land use, according to CDC scientists.

In 2014, a Pennsylvania Task Force was formed to focus on prevention, education, awareness, and surveillance of the tick-borne illness. The following year, the state Department of Conservation and Natural Resources placed signs in the 120 state parks and 20 state forest districts warning visitors and staff about the presence of ticks.

Typical symptoms of Lyme disease, which is transmitted by ticks, can include fever, headache, fatigue, and a characteristic bull’s-eye skin rash. Most cases can be successfully treated with antibiotics.

But Lyme disease is not the only infection spread by the black-legged tick. Two cases of Powassan virus, a rare tick-related illness, were recently confirmed in North Jersey.

Officials at the Sussex County Division of Health said the disease can cause inflammation of the brain and the membranes that surround the brain and spinal cord.

If you find a tick attached to your skin, it is important to quickly remove the tick immediately and not wait for it to detach on its own. But skip the home remedies such as coating the tick with nail polish or petroleum jelly, or using heat to get it to loosen its grasp.

Tips for pulling off a tick, from the CDC

  • Grasp the tick as close to the skin’s surface as possible with tweezers.

  • Pull upward with steady, even pressure. Do not twist or jerk the tick; this can cause the mouth parts to break off and remain in the skin. If this happens, remove the mouth-parts with tweezers.

  • Once the tick has been removed, wash the bite area and your hands with rubbing alcohol or soap and water.

  • To dispose of a live tick, put it in alcohol, place it in a sealed bag, wrap it in adhesive tape, or flush it down the toilet.