Ellen Stromdahl was at a garden party in coastal Virginia in June 2023 when her friend Albert Duncan stood up from where he was sitting and abruptly fainted. Duncan is an outdoorsman in his mid-80s — still active and healthy for his age. Stromdahl, an entomologist who works for the United States Army Public Health Center, the Army’s public health arm, rushed to his side. As Duncan came to, she noticed that his tanned skin was tinged with yellow. “This man looks jaundiced,” she thought to herself.
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Over the following week, Duncan frequently visited the emergency room. Despite numerous blood tests, his physicians could not pinpoint any typical ailments for someone his age, such as heart disease, diabetes, or pneumonia. Eventually, at Stromdahl’s suggestion, Duncan’s wife, Nancy, requested that they check for babesiosis, a rare parasitic condition similar to malaria transmitted through black-legged ticks. The diagnostic results were positive for both babesiosis and Lyme disease, which is much more prevalent and also spread by these ticks.
If Duncan’s doctors had identified the infections earlier, they might have eliminated them using a mix of oral antibiotics and antiparasitic drugs. However, since Duncan was several weeks deep into his sickness, he required an exchange transfusion. This process involved removing all of his contaminated blood and replacing it with clean donated blood. Roughly two weeks following the garden party, he made a full recovery.
Babesiosis is uncommon; according to the Centers for Disease Control and Prevention,
approximately 2,000 instances occur annually in the United States
However, what made Duncan’s situation particularly uncommon was that he contracted babesiosis in Virginia, a state which reported only 17 locally acquired cases of the disease from 2016 to 2023.
This made Stromdahl question whether babesiosis might be increasing in frequency in Virginia and nearby regions. Over the next two years, she collaborated with a group of 21 tick experts from various parts of the eastern United States and South Africa to evaluate how widespread Babesia microti—the parasite responsible for causing babesiosis—is among both ticks and people in these areas between 2009 and 2024.
The
results of the study
, published in April in the Journal of Medical Entomology, reveal that the Babesia parasite is rapidly expanding through the mid-Atlantic. This shift, which has coincided with changing weather patterns, could pose a serious threat to people in communities where the disease has long been considered rare.
“Wherever we found positive ticks, there were cases,” Stromdahl said. “They’re small numbers, but that’s why we want to give the early warning before more people get sick.”
A quarter of Babesia infections occur without noticeable symptoms. However, individuals who do exhibit signs—particularly elderly persons and those with weakened immune systems—may experience severe manifestations such as fever, chills, anemia, exhaustion, and yellowing of the skin. If left untreated, these parasitic organisms, known for attacking and destroying red blood cells, can result in organ dysfunction and even fatalities.
Babesiosis generally occurs in the northeastern region and parts of the upper Midwest. From 2015 through 2022, the number of reported cases in the states where this illness frequently surfaces—Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin—has been tracked.
increases by 9 percent annually
, a phenomenon that researchers largely link to warmer temperatures due to climate change. These conditions provide black-legged ticks with increased chances to bite humans over longer periods each year and allow them to expand their habitats into new areas.
The climatic conditions in the southern mid-Atlantic have consistently been hospitable for ticks; however, winters with above-average warmth that have occurred recently have further exacerbated this issue.
occurring with grim regularity
In recent years, certain areas within the region have become perpetual breeding grounds for ticks as well as small mammals such as mice, chipmunks, and shrews—these creatures being carriers of Lyme bacteria and the Babesia parasite in their bloodstream. Unusually high yearly precipitation levels, which permeate the soil and increase regional moisture content, further contribute to tick population growth. The winters from 2023 through 2024 were notably mild over large parts of the Mid-Atlantic area,
4 to 6 degrees Fahrenheit above average temperature
, with numerous states experiencing some of their wettest December and January periods on record.
Stromdahl has spent many years researching tick movements and the diseases they transmit. Over this time, she has witnessed various phenomena, such as the expansion of tick populations further north.
Lone Star tick
, which can cause a lifelong, occasionally fatal reaction to red meat. However, even she was surprised at the extent of the Babesia parasite’s dissemination.
She and her collaborators gathered 1,310 ticks from Virginia, Maryland, and Delaware, discovering the presence of the B. microti parasite in each of these locations. This finding suggests that there could be an increased risk of human infections throughout the southern part of the mid-Atlantic region. Prior to this study, none of these states had reported detecting the parasite in local tick populations.
A significant number of the ticks examined by the researchers were found to harbor the bacterium responsible for causing Lyme disease. The relationship between Lyme disease and babesiosis continues to be explored actively by experts. Researchers believe that ticks carrying one illness may have a higher likelihood of being carriers of the other as well, although the exact reasons remain unclear. However, what is known is that individuals who contract Lyme disease often go on to develop cases of babesiosis.
Prior research on illnesses transmitted by ticks
discovered that regions experiencing an increase in Lyme disease cases between the 1980s and early 2000s reported higher instances of babesiosis approximately one to two decades afterward.
“The findings in the Stromdahl paper are consistent with what we’ve seen in the Northeast: Babesia infection seems to spread where Lyme infection is already present,” said Shannon LaDeau, a disease ecologist at the Cary Institute of Ecosystem Studies who was not involved in the study.
The researchers looked into areas with high concentrations of human cases of babesiosis. Two concerning regions emerged as significant clusters: the five counties encircling and including Baltimore City, and the Delmarva Peninsula—a 180-mile long coastal region covering sections of Delaware, Maryland, and Virginia. Over half of Maryland’s reported cases originated near Baltimore, whereas approximately 38% of total confirmed instances across Virginia, Maryland, West Virginia, and Washington D.C., stemmed from the Delmarva Peninsula.
Experts think that the number of reported babesiosis cases is much lower than reality because many physicians aren’t aware enough about this condition. Stromdahl along with her team aims to motivate health departments in the mid-Atlantic area to acknowledge that babesiosis is becoming an increasing issue. They encourage these departments to monitor ticks for infections and alert the public accordingly. By making local doctors knowledgeable about testing for babesiosis, serious instances similar to Duncan’s case could potentially be prevented.
“Jurisdictions in the southern mid-Atlantic region should expect babesiosis cases,” the authors warn. “Tick range expansion is occurring at such a precipitous rate that public health guidance regarding tick-borne disease prevention and treatment can be rapidly rendered obsolete.”
Climate change is not the sole environmental factor contributing to the increasing density and spread of tick populations.
Efforts over the past few decades to reforest
barren areas have encouraged herds of white-tailed deer, animals that pick up ticks and carry them miles before the arachnids drop off into the leaf litter, to
proliferate
.
Declining rates
of recreational and subsistence hunting are adding to deer overpopulations. At the same time, an
continuous growth of urban sprawl
into forested zones is putting more people in contact with ticks and the diseases they carry.
“The most important take-home is that tick-borne disease is a growing risk,” LaDeau said. The big question as tick populations increase, she added, is to figure out where and when infected ticks overlap with people. “There is still a huge need for data to understand how often these infected ticks come into contact with humans.”
This article originally appeared in
Grist
at
https://grist.org/health/babesiosis-mid-atlantic-delaware-maryland-virginia-tick-borne-disease-lyme-research/
.
Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and a just future. Learn more at
Grist.org
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