Los Angeles County West Vector & Vector-Borne Disease Control District
is an infection caused by the malaria-like protozoan, Babesia microti
(Babesia in blood, see photo to right). Since the late1980s, 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.
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
||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
What is the treatment for babesiosis?
A combination of anti-parasite medicines can be effective in treating
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
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.