Photo: Jonathan Harford via Flickr

The mild winter in the U.S. suggests that it will be a busy year for ticks — just as more Americans are emerging from the COVID-19 pandemic.

Disease ecologists told Grist magazine that there is an uptick in people reporting ticks on their pets and themselves throughout the country, raising the risk there will be an increase in Lyme disease and other tick-borne related illnesses in 2021.

“All these people complaining of a horrendous year” with ticks, Rick Ostfeld, a disease ecologist at Cary Institute of Ecosystem Studies in Millbrook, N.Y., told Grist. “They’re actually right.”

Ostfeld has been studying black-legged ticks, also known as deer ticks, for more than 25 years and says one of the reasons this year is a busy tick season is related to oak trees. In 2019, oak trees dropped an unusually large amount of acorns across the Eastern seaboard, spawning a larger than average rodent population in the winter of 2019 and 2020. Rodents, which carry pathogens that cause diseases like Lyme, are a favorite food for baby ticks, also called nymphs. Ticks, which have up to a three-year life cycle, acquire the pathogens when they feed on rodents as nymphs. (See these graphics describing a tick life cycle.)

Ostfeld has been able to predict that when there are a lot of acorns, there will be an uptick in ticks and related diseases two years later. Blacklegged ticks are a primary carrier of Lyme disease, which can cause joint pain, weakness in the limbs and flulike symptoms.

Climate change also is playing a more significant role in the geographic expansion in tick populations as warmer winters can mean more ticks in more areas. The Carey Institute is currently conducting a five-year study with support from the U.S. Department of Defense’s Strategic Environmental Research and Development program to understand how climate change is impacting ticks populations and the spread of tick-borne diseases. Other dangerous tick-borne diseases include Ehrlichiosis, spotted fever rickettsiosis, babesiosis, tularemia and Powassan virus.

The Washington Post reported on May 29 that babesiosis cases are growing in frequency and geographic range among Medicare beneficiaries. The disease is caused by parasites that thrive in ticks and can cause death if it isn’t caught early.

The Centers for Disease Control Prevention says the total number of tick-borne diseases reported to the agency rose by 125 percent to 50,865 in 2019, from 22,527 in 2004. These figures, however, underestimate the prevalence of cases because most aren’t reported to the agency. In February 2021, the CDC estimated that the number of Americans with Lyme was closer to 467,000 based on an analysis of health insurance records.

In 2019, the CDC also began tracking tick populations, which the public can see in this map, to get a sense of where they might be at risk for a tick-borne disease. The map illustrates that ticks carrying Lyme were heavily concentrated in New England, the upper Midwest, parts of California and Washington state during 2020.

There currently is no vaccine offered for humans to prevent Lyme disease, but the University of Maryland is leading an effort to develop a vaccine. The road to a Lyme vaccine has been rocky. In 1998, the Food and Drug Administration approved LYMErix, a Lyme vaccine developed by SmithKline Beecham, which pulled it from the market one year later following too many reports of adverse reactions.

Here are more resources and recent reporting on this topic:

Check out my AHCJ tip sheet on covering ticks from 2019.

Tick-borne pathogen surveillance map: CDCl.

Tick-borne disease surveillance data summary: CDC.

Let’s do a tick check: New York Times, June 11. 2021.

Tick encounters are expected to be frequent this year. Here’s what you need to know: Washington Post, May 24, 2021.

Can a Tufts professor finally stop lyme disease? The story behind the failed Lyme disease vaccine, Boston magazine, May 11, 2021.

Effect of increased temperature on host selection by the Brown Dog tick: recent study on how climate change is making ticks more dangerous, American Society of Tropical Medicine and Hygiene, November 16, 2020

Nootkatonenow registered by EPA: CDC announcement of new tick and mosquito insecticide, August 10, 2020.

TickEncounter: this resource center hosted by the University of Rhode Island promotes tick-bite protection and tick-borne disease.

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