Babesiosis: The Tick Disease That Acts Like Malaria

Most Mainers have made their peace with Lyme disease. We check for ticks after a hike up Bradbury Mountain, we know to watch for a bullseye rash, and we have a vague sense that the woods come with strings attached. Far fewer people have heard of babesiosis, even though the same tick that gives you Lyme can hand you this one in the same bite. And in 2024, Maine recorded more cases of it than ever before.

A malaria-like illness, in the Maine woods

Babesiosis is an infection of the red blood cells. The culprit is a microscopic parasite, most often Babesia microti in the United States, according to the CDC. If that setup sounds familiar, it should. The malaria parasite, Plasmodium, does much the same thing, invading and destroying red blood cells. Both are protozoa, and under a microscope they can look enough alike that a lab has to tell them apart carefully. That is why doctors and the NIH StatPearls reference both describe babesiosis as a malaria-like illness.

The comparison is not just academic. Because the parasite chews through red blood cells faster than the body can rebuild them, babesiosis can cause hemolytic anemia. The CDC’s clinical guidance lists that anemia, alongside vague flu-like symptoms, as a hallmark of the infection. Maine does not have malaria. It does, increasingly, have a homegrown cousin.

One tick, more than one disease

The carrier is the blacklegged tick, better known here as the deer tick (Ixodes scapularis). It is the same species that spreads Lyme, which is the inconvenient heart of the problem. The CDC notes that people usually get babesiosis from a deer tick bite, though it can also pass through a contaminated blood transfusion or from a mother to her baby during pregnancy or birth.

Timing matters. A deer tick nymph generally needs to stay attached and feeding for more than 36 to 48 hours before it passes the babesiosis parasite along, per CDC prevention guidance. That window is the whole reason a tick check after a day outdoors is worth the trouble. Find the tick on the same evening and you have likely beaten the clock.

Because a single tick can carry several pathogens at once, one bite can deliver more than one infection. Researchers studying blacklegged ticks found that co-infection with the babesiosis parasite and the Lyme bacterium happened more often than chance alone would predict, a pattern they traced to the small mammals, like mice, that both pathogens use as reservoir hosts. If you want the fuller picture on the tick itself and the rest of what it carries, our complete guide to ticks and Lyme in Maine and New Hampshire covers the ground.

Why so many cases slip by unnoticed

Here is the tricky part. Many people who carry Babesia never feel sick at all. The CDC says a large share of infected people have no symptoms whatsoever. The ones who do get ill tend to come down with something that looks like a bad summer flu: fever, chills, sweats, headache, body aches, loss of appetite, nausea, fatigue. Nothing on that list points a flashing arrow at a tick.

So picture a humid July week. You felt run down for a few days, blamed it on the heat or a long weekend, and moved on. That is exactly how a real infection can hide in plain sight, and it is part of why surveillance numbers almost certainly undercount what is actually circulating.

Who needs to take it seriously

For a healthy adult, babesiosis is often mild or silent. The risk changes sharply for certain groups. The CDC flags people without a working spleen, anyone over 50, and those with a weakened immune system from cancer, lymphoma, or HIV, along with people who have serious liver or kidney disease. In those cases the infection can turn severe, with complications the CDC’s clinical guidance describes ranging from dangerously low platelet counts to organ failure, and in the worst outcomes it can be fatal.

None of that is meant to frighten the average reader. It is meant to sort the response. A young hiker shrugging off a mild fever is a different situation than an older neighbor without a spleen running the same temperature. The second one should not wait it out.

Why Maine became a hot spot

The numbers tell the story plainly. A CDC report tracking babesiosis from 2011 to 2019 found cases climbing across the Northeast, enough that the agency now considers Maine, New Hampshire, and Vermont endemic for the disease. Over that window, Maine’s reported cases rose from 9 to 138, which the CDC scored as a 1,422% increase in rate. New Hampshire’s rate climbed 372%. Vermont’s rose 1,602%.

Then came 2024. Maine logged a record-high number of babesiosis cases, with reporting placing the total above 300 (roughly 309 to 310, up from 194 in 2023), as Maine Public reported the disease broke state records alongside other tick-borne illnesses. Local surveillance puts a finer point on it. The University of Maine Cooperative Extension Tick Lab, which processed 4,776 tick submissions from 398 towns across all 16 counties in 2024, found that 12% of the deer ticks people sent in carried the babesiosis parasite. For comparison, 41.5% carried the Lyme bacterium. One in eight is not a fluke. If you want a sense of the other infection riding along on these same ticks, see our piece on anaplasmosis in New England.

A longer season, courtesy of milder winters

Part of what is driving the rise is the calendar. Researchers studying 1,130 confirmed babesiosis cases across three Boston-area hospitals from 1993 to 2024 found the active season for Babesia microti stretched dramatically over those decades. The mean active season grew from 2.2 months before the year 2000 to 9.2 months after 2015. They link the shift to warming winters, noting that New England warmed nearly 1.83 degrees Celsius across the last century, with winter minimum temperatures climbing even faster.

For anyone who has noticed ticks turning up in November, or on a freakishly warm February afternoon, that finding will not be a surprise. A tick season that used to be a summer problem now bleeds into the shoulder months on both ends.

Diagnosis and the co-infection catch

Babesiosis is confirmed by looking at a blood smear under a microscope, where the parasite can be seen inside red blood cells. The catch, according to the CDC’s clinical guidance, is that diagnosis takes what doctors call a high index of suspicion. The symptoms are so generic that the parasite gets missed unless a provider specifically asks the lab for a manual, non-automated review of the smear. An automated machine can skate right past it.

This is where the co-infection problem bites twice. Someone treated for Lyme who is not improving may also be carrying babesiosis that no one thought to look for, because the two travel together. Knowing how to tell the deer tick from its less worrisome relatives helps you give a provider the right context, which is exactly what our guide to identifying deer, dog, and lone star ticks is for.

Prevention is still the best medicine

The good news is that the defenses against babesiosis are the same boring, effective habits that fend off Lyme. Cover up in tick country. Do a thorough check at the end of the day, especially the warm, hidden spots ticks favor. And remember that 36-to-48-hour window: prompt removal genuinely lowers your risk, because a tick that has not fed long enough has not passed the parasite along.

If you develop an unexplained fever, chills, or that wrung-out flu feeling within a few weeks of being in the woods, mention the tick exposure to your provider directly. That single sentence can be the difference between a smear that gets ordered and one that does not, particularly for anyone in a higher-risk group. Maine’s record year is a reason to pay attention, not to panic. The parasite has been here a while. We are just finally counting it.

Sources

• Centers for Disease Control and Prevention. About Babesiosis. CDC. 2024. https://www.cdc.gov/babesiosis/about/index.html
• Centers for Disease Control and Prevention. Clinical Overview of Babesiosis. CDC. 2024. https://www.cdc.gov/babesiosis/hcp/clinical-overview/index.html
• Centers for Disease Control and Prevention. Preventing Babesiosis. CDC. 2024. https://www.cdc.gov/babesiosis/prevention/index.html
• Centers for Disease Control and Prevention. Trends in Reported Babesiosis Cases, United States, 2011-2019. CDC MMWR. 2023. https://www.cdc.gov/mmwr/volumes/72/wr/mm7211a1.htm
• NIH / NCBI Bookshelf. Babesiosis, StatPearls. NIH / NCBI. 2024. https://www.ncbi.nlm.nih.gov/books/NBK430715/
• Diuk-Wasser MA, et al. Co-Infection of Blacklegged Ticks with Babesia microti and Borrelia burgdorferi Is Higher than Expected and Acquired from Small Mammal Hosts. PubMed Central (PLoS ONE). 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC4062422/
• Increasing Length of the Babesia Season in New England in the Climate Change Era. PubMed Central. 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12343110/
• University of Maine Cooperative Extension. 2024 Surveillance Report from UMaine Extension Tick Lab Highlights Tick-Borne Disease Risk. UMaine Extension. 2025. https://extension.umaine.edu/2025/04/17/2024-surveillance-report-tick-lab-highlights/
• Central Maine. Where in Maine Are You Most Likely to Get a Dangerous Tick Bite? Central Maine. 2025. https://www.centralmaine.com/2025/06/23/where-in-maine-are-you-most-likely-to-get-a-dangerous-tick-bite/
• Piscataquis Observer. Maine Broke Tick-Borne Disease Record in 2024. Piscataquis Observer. 2025. https://observer-me.com/2025/01/06/news/maine-broke-tick-borne-disease-record-in-2024/
• Maine Public. Maine Reported Record-High Number of Tickborne Disease Cases Last Year. Maine Public. 2025. https://www.mainepublic.org/health/2025-01-03/maine-reported-record-high-number-of-tickborne-disease-cases-last-year
• CIDRAP, University of Minnesota. Babesiosis Spread Linked to Changing Climate in New England. CIDRAP. 2025. https://www.cidrap.umn.edu/tick-borne-disease/babesiosis-spread-linked-changing-climate-new-england

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health decisions.