PA's Warmest Winter On Record, Climate Change Could Fuel Tick Growth

PENNSYLVANIA — While warmer winters may seem, superficially at least, a mild enough consequence of climate change, the true consequences of the flux which drastically different temperatures throw the environment into may not be felt until the seasons change. For contagious disease vectors, including Pennsylvania's most notorious, the tick, this means booming populations.

This winter has been one of the warmest Pennsylvania has seen in recorded history. The average temperature this winter in Philadelphia has been 41.2 degrees, the fifth warmest in history and just shy of the 1931-32 all time record of 43.4.

But behind just being warm, many parts of Pennsylvania have seen almost zero accumulated snowfall. Both factors drive ticks to be active earlier in the season and more often, and could drive them to seek out humans with greater frequency, according to scientists.

Typically, ticks start to emerge in March. Snowfall actually helps ticks survive the winters, as it keeps them warm under the layer of leaves and duff where they burrow. But though lack of snow may mean fewer ticks survive the winter, it will drive survivors to go out to look to feed sooner. And because this winter just wasn't that cold, and because ticks can produce an "anti-freeze protein" like fish that protects them from severe cold, they could be more proliferant than ever in 2023, experts say.

RELATED: 'Ecological Mismatch': Hot Winter Wreaking Havoc On PA Environment

"Everybody is looking for the scapegoat when it comes to vector-borne diseases and ticks and tick-borne diseases," Dr. Megan Linske, with the Connecticut Agricultural Experiment Station in New Haven, told NPR. "And I think climate change is a big one."

Linske pointed to the northeast specifically.

"Without that limiting factor of winter, we're going to see more of those pop up," she told the station.

Tick populations and resulting infections from the diseases they carry have already been increasing for years in Pennsylvania and around the northeast, largely thanks to the same trends, scienstists say. Of 65,135 ticks analyzed by the Pennsylvania Tick Research Lab in 2022, 46,264 carried an infectious disease.

Ticks are not the only species impacted by one of the warmest winters in state history, however. Climate impacts migration patterns for all species, especially birds. Birds that normally would not be moving around this time of year suddenly think it's time to fly north. This further impacts the availability of breeding sites — sites which in many cases are already limited by overdevelopment and other human impacts — which can cause overcrowding and higher than usual interaction between domestic birds and migratory birds. This fuels the spread of the highly contagious avian influenza, according to recent research published in the Journal of Climate Change and Health. It's already killed 4.4 million birds in Pennsylvania.

The uusual warmth also throws the more hidden side of the delicately balanced ecosystem into chaos, creating earlier blooms and causing atypical animal behavior and a phenomonon called "ecological mismatch."

"Plants are really sensitive to temperature, humidity and rainfall," Megan O'Connell, a research associate with the Botanical Research Institute of Texas, told AccuWeather. "They're sensitive to photo periods; so the sun and things like that. They're responding to these kinds of triggers in the environment, these cues that the climate is giving them, and they respond to that."

Early blooms and growths also have an obvious impact on animals and insects that rely on those plants for food. In some cases, animals might forage elsewhere, changing browsing patterns.

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.

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.