A tick is viewed atop a pencil eraser in the laboratory of researcher Erik Foster during a tour of the Center for Disease Control laboratory in Fort Collins, Colo., on April 4, 2024.

Few things are as unpleasant as finding a tick clinging to your skin after spending time outdoors. Not only is the parasite sucking your blood, but it might also be leaving behind bacteria, viruses, or parasites that can cause at least 15 different diseases, according to the U.S. Centers for Disease Control and Prevention (CDC). , , , and are just a few examples.

One disease, , is causing particular concern. It’s known colloquially as due to its expanding spread and clinical profile. Like malaria, the disease is caused by a parasite (carried by ticks instead of mosquitoes) that infects red blood cells. Similar to malaria, it can cause symptoms such as headache, fever, chills, nausea, vomiting, altered mental state, anemia, low blood pressure, respiratory distress, and more. 

A recent published in the journal revealed that more Americans are contracting babesiosis, often alongside other tick-related infections.

Paddy Ssentongo, an infectious disease fellow at Penn State Health Milton S. Hershey Medical Center, and his colleagues studied over 3,500 Americans with babesiosis from 2015 to 2022. Their initial finding highlighted the rapid increase of the disease in the U.S. population. During the seven-year study period, cases of babesiosis rose by an average of 9% annually—attributable, the researchers concluded, to a population boom, the main vector for babesiosis. The spread in the Northeast has been particularly dramatic: babesiosis increased by from 2011 to 2019, and during the same period, for example.

The ticks aren’t independently migrating to new habitats but are instead traveling on one of their primary hosts—the white-tailed deer, , attracted by warmer temperatures and reduced snowpack.

Geography isn’t the only issue. Ticks are also carrying more pathogens. While they may travel on deer, they acquire diseases from their hosts; if those hosts have Lyme disease, babesiosis, or other infectious agents, the parasite will pick them up and transmit them to a human it bites. This presents a significant problem, as the researchers discovered.

Among the study participants found to have babesiosis, 42% were also infected with one or more tick-borne diseases. Of those, 41% also had Lyme disease; 3.7% had ehrlichiosis; and 0.3% had anaplasmosis.

On the surface, this appears to be bad news. The wide-ranging symptoms of can be particularly dangerous for individuals with weakened immune systems or those who have undergone spleen removal during treatment for certain cancers, blood diseases, or cirrhosis of the liver. fever, chills, nausea, vomiting, diarrhea, and confusion can occur, and in later stages, it can lead to brain damage, uncontrolled bleeding, respiratory failure, and death. presents similar symptoms and potentially fatal complications, including respiratory failure and bleeding problems.

However, the researchers paradoxically found that having multiple infections at the same time might actually offer some protection. The risk of death from babesiosis was higher among those infected solely with the disease compared to those with coinfections.

“Having both babesiosis and Lyme disease seemed not to be associated with worse mortality,” Ssentongo said in a accompanying the release of the study. “It’s speculated that the concurrent presence of other tick-borne infections in the blood could alter the immune response by possibly ‘boosting’ it to effectively fight infections.”

This isn’t the only reason individuals with co-infections might fare better than those with babesiosis alone. The standard treatment for babesiosis involves a combination dose of the antibiotics azithromycin and atovaquone. The primary treatment for Lyme disease, anaplasmosis, and ehrlichiosis is a different antibiotic, doxycycline. People co-infected with one or more of these diseases along with babesiosis are more likely to be treated with doxycycline as well. This, according to Ssentongo, raises the question of whether doxycycline is effective against the babesia parasite—a question that requires further investigation.

Of course, the best way to manage any of these tick-borne diseases is to avoid contracting them in the first place. Wearing long-sleeved shirts and full-length pants, tucking pant cuffs into socks, , showering after coming inside, and conducting a full-body tick check are all proven infection prevention methods.