Los Angeles County West Vector & Vector-Borne Disease Control District


   Babesiosis is an infection caused by the malaria-like protozoan, Babesia microti (Babesia in blood, see photo to right).  Since the late1980’s, the disease has spread from the islands off the New England coast to the mainland.  Like malaria, the protozoan inhabits red blood cells and can result in anemia-causing fatigue and poor exercise tolerance. The infection can be asymptomatic to mild in the young. It can be severe and even life-threatening in patients without spleens, immune-compromised patients, and older patients with pre-existing medical conditions. Antibiotics are effective in treating the infection and fewer complications occur with earlier treatment.

Where is babesiosis found?

    Babesiosis occurs mainly in coastal areas in the northeastern United States, especially the offshore islands of New York and Massachusetts. Cases have also been reported in Wisconsin, California, Georgia, and in some European countries.

How does babesiosis spread?  

Babesiosis is most commonly spread to people by the bite of a tick infected with the Babesia parasite. Female deer tick Babesiosis is spread by deer ticks, which are carried mainly by deer, meadow voles, and mice. Deer ticks also spread Lyme disease. People can be infected with both babesiosis and Lyme disease at the same time. People can also get babesiosis from a contaminated blood transfusion.

What are the signs and symptoms of babesiosis?

    The parasite attacks the red blood cells. Symptoms, if any, begin with tiredness, loss of appetite, and a general ill feeling. As the infection progresses, these symptoms are followed by fever, drenching sweats, muscle aches, and headache. The symptoms can last from several days to several months.

How soon after exposure do symptoms appear?

    It can take from 1 to 12 months for the first symptoms to appear, but less time for persons with weakened immune systems.

How is babesiosis diagnosed?

    Laboratory diagnosis is based on identifying the parasite in red blood cells.

Who is at risk for babesiosis?

    Anyone can get babesiosis, but some people are at increased risk for severe disease:

Elderly persons
Persons with weakened immune systems
Persons whose spleens have been removed

What complications can result from babesiosis?

    Complications include very low blood pressure, liver problems, severe hemolytic anemia (a breakdown of red blood cells), and kidney failure. Complications and death are most common in persons whose spleens have been removed. Other people usually have a milder illness and often get better on their own.

What is the treatment for babesiosis?

    A combination of anti-parasite medicines can be effective in treating babesiosis.

How common is babesiosis?

    It is not known how common babesiosis is in the United States. Most people have no symptoms, and those who do are usually older persons and people who are already sick with other conditions. Most cases occur during spring, summer, and fall.

Is babesiosis an emerging infectious disease?

    Yes. The first case was reported from Nantucket Island, Massachusetts, in 1969. Since then, babesiosis has emerged as a health threat in the United States, with increasing reports of babesiosis symptoms and some deaths in areas where the risk of infection was not previously recognized.

How Can Tick Borne Illnesses be Prevented?



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