What is babesiosis? Cases of this tickborne disease more than double in Northeast.

Cases of a tickborne disease called babesiosis increased significantly from 2011 to 2019 in a cluster of Northeastern states, the Centers for Disease Control and Prevention reported Friday.

The CDC said the largest increase in cases were found in Vermont, Maine, New Hampshire and Connecticut. The disease also is endemic in six other states, including in the upper Midwest: Massachusetts, Minnesota, New Jersey, New York, Rhode Island and Wisconsin.

The study authors said doctors and public health officials should be aware of babesiosis and inform people in at-risk states on ways to prevent the tickborne disease. The study describes itself as the first comprehensive assessment of state trends over several years.

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Here's what to know about babesiosis, symptoms, treatment and how to protect yourself.

What is babesiosis?

Babesiosis is a tickborne disease with cases reported mostly in the Northeast and upper Midwest. Most cases are caused by Babesia microti, which is transmitted from bites of blacklegged ticks, also known as deer ticks. Deer ticks also transmit Lyme disease as well as two other lesser-known bacterial diseases, anaplasmosis and ehrlichiosis.

Cases also can occur through blood transfusions, organ transplants or childbirth when a mother is infected.

The Food and Drug Administration has recommended screening blood donations in Washington, D.C., and the following states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia and Wisconsin. 

Why are cases of babesiosis increasing?

Even though the study showed the number of cases doubled in the states that were studied, experts say the increase might be partly explained by better testing for tickborne diseases, which increased 25% from 2011 to 2019.

More than 16,000 cases of babesiosis were detected in 10 states that were included in the CDC study. Those states accounted for over 98% of all babesiosis cases. 

"There's been kind of revolution in diagnostic testing that's made it easier" to test for babesiosis and other tickborne diseases, said Dr. Amesh Adalja, an infectious disease expert and senior scholar at Johns Hopkins Center for Health Security. 

But the CDC study warned not all cases are likely captured. For example, babesiosis is not a reportable disease in Pennsylvania even though cases have been found there. Others might not get tested because they don't have symptoms. Cases are reported in states were the patient lives, but that might not be the state where the infection occurred.

What are the symptoms of babesiosis?

People infected might develop fever, chills, headache or muscle and joint pain. Others with more severe cases can develop kidney failure, breathing difficulty or thrombocytopenia, which causes a low blood platelet count. Some people have no symptoms. In others with compromised immune systems, infections can be fatal.

How is babesiosis treated?

Babesiosis can be treated using antibiotics such as azithromycin and atovaquone. 

People with a compromised immune system or those without a spleen can be at risk for more severe cases, even death, Adalja said. 

How to protect yourself against ticks and babesiosis

If you live in a state or region where ticks are widespread, you should regularly check your body for ticks after going outside. You should wear long sleeves and pants and apply tick repellant before going outdoors. Also, avoid areas such as long grass, shrubs, small trees or other underbrush. 

How to pronounce babesiosis

Babesiosis is pronounced ba-bee-zee-oh-ses, according to Merriam-Webster. 

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