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What is babesiosis?
Babesiosis is a potentially
severe, and sometimes rapidly fatal, tick-borne illness caused
by a protozoan parasite that infects and destroys the red
blood cells. Babesia microti appears to be responsible for
the majority of cases of human babesiosis in the United States.
It is the most common species in the eastern and Midwestern
U. S. where most cases occur. Additional types of Babesia
that have been associated with human disease in limited areas
of the U.S., but that have not yet been designated as distinct
species, are currently known only as Babesia isolate type
WA1 parasites (detected on the West Coast) and Babesia isolate
type MO1 (detected in Missouri). Babesia divergens is the
most common species in Europe. Other Babesia species cause
illness in animals.
How does a person get babesiosis?
You can
get babesiosis if you are bitten by a tick that is infected
with B. microti, or less commonly, another Babesia species.
Protozoa in the tick’s saliva are transmitted to you
while the tick is feeding. An infected tick must be attached to you for at least several hours (usually 24-48)
in order for transmission to take place. Occasionally, cases
of babesiosis have also been acquired via blood transfusion
from apparently healthy (asymptomatic, lacking symptoms),
but nevertheless infected, individuals.
Do all ticks transmit babesiosis?
No. Only
certain species of ticks are capable of transmitting Babesia.
There are two vectors (transmitters) of babesia to humans
in the United States. Ixodes scapularis, the blacklegged
tick (also known as the “deer
tick”), is the primary vector for Babesia in the east
and Midwest, while Ixodes pacificus, the western blacklegged
tick, is a presumptive vector along the West Coast. Ixodes
ricinus, sometimes referred to as the sheep tick or European
castor bean tick, transmits B. divergens in Europe. Simultaneous
infections with both B. microti and Borrelia burgdorferi,
the agent of Lyme disease, have been documented in ticks,
and there is evidence that both organisms may be transmitted
during a single tick bite.
How do ticks acquire Babesia?
Ticks become
infected by feeding on an infected animal known as a reservoir
host. Reservoir hosts carry Babesia parasites in their bloodstream
for a prolonged period of time, thus causing ticks that feed
on them to become infected. Then, when the infected tick
feeds on its next host, parasites are passed on to that host
and the cycle of infection continues. Rodents, especially
the white-footed mouse (Peromyscus leucopus), are the reservoir
hosts for B. microti, while in Europe, cattle serve as the
reservoir hosts for B. divergens.
How prevalent is babesiosis?
Within the
United States, human babesiosis does not appear to be geographically
widespread. It is difficult to assess the true prevalence
of the disease because it has not been designated as a nationally
reportable illness to the Centers for Disease Control and
Prevention (CDC). Also, it is suspected that many cases go
undiagnosed because of the lack of symptoms in many individuals.
Since the first cases were recognized in California in 1966
(unknown Babesia species) and Massachusetts (Nantucket) in
1969 (Babesia microti), several hundred cases have been documented.
The majority of these cases have occurred in southern New
England, especially on the coastal islands of Massachusetts
(Nantucket, Martha’s
Vineyard), Rhode Island (Block Island), and New York (Shelter
Island, Long Island). Cases have also been reported in California,
Connecticut, Missouri, New Jersey, Washington, and Wisconsin.
What are the symptoms of babesiosis?
Based on serologic (blood) studies, most infections appear
to be asymptomatic. Manifestations of symptomatic disease
include fever, headache, chills, sweating, muscle aches
(myalgias), fatigue, nausea, vomiting, enlarged spleen
and liver (sometimes resulting in jaundice), and hemolytic
anemia (anemia due to the destruction of red blood cells).
Symptoms usually occur 1 to 4 weeks following an infective
tick bite, and can last for several days, weeks, or months.
The disease is more severe, and sometimes fatal, in patients
who are immunosuppressed (have a weakened immune system),
lack a healthy spleen, or who are elderly. In some cases,
parasites may continue to circulate in the blood of asymptomatic
individuals for several months or even years, making transmission
of babesiosis by blood transfusion a concern. Because there
have been documented cases of transfusion-acquired babesiosis,
the American Red Cross does not accept blood donations
from anyone who has ever had babesiosis, even if they have
been treated with appropriate antibiotics. Co-infection
with Lyme disease has been documented in some patients.
Co-infection may complicate diagnosis and treatment, and
may result in more severe illness in the individual.
To read the rest of this great brochure from the U.S. Army
Center for Health Promotion and Preventive Medicine, Entomological
Sciences Program, (including treatment information and prevention
tips), please click here: http://chppm-www.apgea.army.mil/ento/FACTS/Babesiosis-JusttheFactsJanuary2006.pdf
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