What is Babesiosis? A rare tick-borne disease is on the rise in the Northeast

A rare tick-borne disease is on the rise in the northeastern United States, according to a new report from the Centers for Disease Control and Prevention.

Cases of babesiosis rose by 25% from 2011 to 2019, causing the CDC to add three states — Vermont, Maine and New Hampshire — to the list of those where the illness is considered endemic.

Here's what you need to know.

What is babesiosis, and how do I know if I have it?

Babesiosis is caused by the Babesia parasite — a type of protozoa that infects red blood cells — which can be carried by black-legged ticks (also known as deer ticks) in the northeastern and midwestern United States.

A bite from a tick carrying the parasite can send it into a person's bloodstream.

Some cases are completely asymptomatic, but others come with fever, muscle headaches, muscle pain, joint pain and other symptoms. A doctor can prescribe antimicrobial medications to help fight infection.

In the most extreme cases, babesiosis can be fatal, especially among those who are immunocompromised, the CDC says. The disease can also come with life-threatening complications, including low platelet counts, renal failure in the kidneys, or respiratory distress syndrome.

Although cases of babesiosis are on the rise, the disease is still relatively rare, with, states reported more than 1,800 cases of babesiosis per year to the CDC between 2011 and 2019. Compare that to the most common tick-borne affliction, Lyme disease: The CDC says it receives 30,000 Lyme case reports each year.

For both diseases, the actual number of cases is likely much higher, the CDC says, because data is reported on a state-by-state basis and procedures vary. Ten states, for example, don't require babesiosis to be reported at all.

Where is it spreading?

Among the states that do require reporting, eight saw significant increases in case numbers from 2011 to 2019, according to the CDC's first comprehensive national surveillance on babesiosis.

In three states — Vermont, Maine and New Hampshire — case numbers increased so much that the CDC says babesiosis should be considered endemic.

Increases also were noted in states where the disease already was endemic: Massachusetts, New Jersey, New York, Connecticut and Rhode Island.

The CDC did not give an explicit reason for the rise in babesiosis cases, but state programs that track cases of tick-borne illnesses have said that milder winters might be behind rising infection numbers, as they allow ticks to stay active year-round.

In the long-term, an expansion of babesiosis could impact the blood supply, says the CDC. The agency says that the parasite can be transmitted via a blood transfusion, and that those who contract the disease through contaminated blood have "significantly worse health outcomes."

The Food and Drug Administration already recommends screening for the parasite at blood donation centers in the 14 states with the most cases, as well as in Washington, D.C.

What can I do to prevent contracting babesiosis?

In general, the best way to avoid the Babesia parasite is to avoid black-legged ticks. Which is to say: Avoid tick encounters altogether.

Babesia is usually spread by young nymphs, which can be as small as a poppy seed.

Planning to head into the woods or brush in these warmer spring and summer months? Bobbi Pritt, a Mayo Clinic parasitologist, told NPR's Sheila Eldred some of her best tips for avoiding tick bites:

And if you do get bitten, stay calm. Not every tick is carrying harmful bacteria.

But it also doesn't hurt to check whether your tick has black legs. If so, Pratt recommends sticking it into your freezer so you can bring it to the doctor just in case any symptoms arise.

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