What Is Babesiosis?

Medically Reviewed by Minesh Khatri, MD on November 27, 2022
Written by Kelli Miller
3 min read

Babesiosis is a rare and life-threatening infection of the red blood cells that's usually spread by ticks. It's caused by tiny parasites called Babesia. The kind that most often affects humans is called Babesia microti. They enter your bloodstream when you're bitten by an infected deer tick.

Other ways babesiosis can spread include:

  • Contaminated blood transfusions
  • A pregnant, infected mother passing it to their baby in the womb or during birth

Babesiosis usually happens in the warmer months. Ticks carrying the parasite have been found in:

  • Block Island, R.I.
  • Fire Island, Shelter Island, and eastern Long Island, N.Y.
  • Martha's Vineyard, Mass.
  • Nantucket, Mass.
  • Coastal areas of New Jersey

People have gotten this infection in other states, too, including:

  • California
  • Connecticut
  • Delaware
  • Maine
  • Minnesota
  • Wisconsin

It's also been seen in Europe.

Signs of babesiosis start 1 to 8 weeks after you come in contact with the parasite that causes the disease. Sometimes you won't notice any symptoms. If you do, they might include:

You also can get a condition called hemolytic anemia in which your red blood cells die faster than your body can make new ones. Symptoms of this can include:

Symptoms can be worse if you're elderly, no longer have your spleen, or have a health condition or take medications that weaken your immune system.

If you notice any of these symptoms, see your doctor and be sure to tell them if you've traveled recently. Ticks can be the size of a poppy seed, so you may not know if you've been bitten by one.

Your doctor will order blood tests to check for signs of infection. This includes looking for Babesia in the blood under a microscope. They may also want to do other blood tests to rule out conditions with similar symptoms, such as anaplasmosis or Lyme disease, which is also caused by ticks. It's possible to have Lyme disease at the same time as babesiosis.

If you don't have any symptoms, you probably won't need treatment. If you do, your doctor may prescribe  a drug called atovaquone that kills microorganisms along with the antibiotic  azithromycin.  Another combination they may recommend is quinine with the antibiotic clindamycin.

The ticks that cause babesiosis typically have to stay on your body for 36 to 48 hours to cause an infection. Here are some ways to prevent one:
 
  • Stay away from overgrown grasses and leaf piles, where ticks are likely to be.
  • Wear long pants tucked into your socks and a long-sleeve shirt when you're near where ticks thrive.
  • Wear light-colored clothes so you can easily spot ticks.
  • Use bug repellant that has DEET in it on your skin and clothing.
  • Before going indoors, check your clothing and pets for ticks.
  • Once inside, check your entire body for ticks using a full-length or hand-held mirror.
  • Remove any ticks with pointed tweezers.