Human Babesiosis



Quick Facts on Babesiosis

·        Babesia microti and Babesia divergens are parasites transmitted by ticks

·        Human are accidental hosts of the babesia parasite

·        Babesia is a blood-borne disease, therefore many of its symptoms can mimic those of malaria

·        Infected persons can normally recover if they are treated with clindamycin and oral quinine

Text Box: ß Babesia microti
The picture on the left shows the blood smear of a person who is infected by the Babesia microti parasite.  The rings within the blood cells are the parasite.






Red blood cells infected with BabesiaQ:  What is Babesia?


A:  Human babesiosis, more commonly known as babesia is a rare, blood-borne disease which is transmitted by ticks and found in both North America and Europe.  Babesia is caused by the Babesia microti and Babesia divergens parasites, both of which are members of the protozoan kingdom.  The parasite will enter a human host when an ixodid tick, which is the definitive host of babesia, bites a human host and transfers the parasite while taking Text Box: The arrows in the above picture are pointing at the babesia parasite within the red blood cells.its blood meal.  An infected person, however, generally will not show signs of the disease for about 1-4 weeks.  After this incubation period has ended, a person will show non-specific disease signs and symptoms such as malaise, fever, headache and chills.  


Text Box: The top right pictures show the blood stain of a babesia infected individual; while the top left two pictures show the blood of a malaria infected individual.  Notice the similar ring stages in each smear.  The babesia infection can be differentiated from the malarial infection by the presence of a “Maltese Cross,” it appears as an X-like structure  in some of the blood cells.

To be babesia… or malaria???


The most intriguing aspect of babesia is its striking similarity to malaria.  Both are diseases caused by protozoan infections which manifest themselves in the human blood stream.  These two diseases also have similar clinical presentations; they both have similar symptoms such as fever, malaise, and occasional anemia.  Furthermore, they can also appear similar under a microscope; both have many stages in which they appear as rings with red blood cells.  These similarities make it difficult to know the prevalence and incidence of babesia in malaria endemic countries.  




Text Box: The above map on the right shows distribution of different species of ticks across the continental United States.  Ixodes dammini, located primarily along the East Coast, is the species of tick believed to pass babesia to humans.  The above map on the left shows the distribution of white-footed mice, a reservoir of babesia.  Note the overlap in the habitats of the vector and reservoir.





How serious of a problem is babesia?


          Although babesia can be fatal, most of the case fatalities have been in persons who were previously immunocompromised; the majority of the U.S. case fatalities have been in patients who were asplenic.  Those who do succumb to the disease generally die from renal failure.  Most patients can recover if they are diagnosed quickly and treated with the proper drugs. 

          While a babesia infection is undoubtedly unpleasant and potentially life threatening, it is not a major threat in Europe or North America.  America reports only 5-6 cases of babesia per year and about 95% of all victims recover from the infection.  Furthermore, proper precautions against tick bites can also protect people who spend extensive amounts of time in woodland areas.   



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The History of Babesia


Babesia was first described in Roman cattle in 1888, the species that infects cattle is Babesia bovis.  Babesia was first identified in humans in 1957 in the former Yugoslavia.  The first US case was reported in 1969 in Nantucket.  Since that time, there have been 300 reported cases of Babesia, mostly in the Northeastern states. 

Text Box: The map of Europe on the left depicts countries which are at risk for babesia infections.  The first recorded case occurred in the former Yugoslavia.








Comparison of United States and European Babeiosis




Reservoir Host




B. microti

United States


Ixodes dammini



B. divergens



Ixodes ricinus




Springtime in Paris?


The table on the above compares the main differences between cases of babesiosis in America and Europe.  Note that there is much higher morbidity in America but higher mortality in Europe




The Life and Death of Babesia


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Babesia Life Cycle

Life Cycle: The life cycle of the parasite fluctuates principally between the tick and mouse hosts. 

(1) Typically, the sporozoites are introduced into the tick through the bite of an infected animal, which can be a mouse or another kind of small mammal.  (2) The babesia then undergoes an asexual reproductive stage where it transforms into merozoites and trophozoites and eventually (3) gametocytes.  Because asexual reproduction can occur within white-footed mice, they are reservoirs for babesia. (5) The babesia parasite can then undergo sexual reproduction in the tick; therefore, the tick is also its definitive host.  (6) If the tick bites any unaffected animals, including humans, it can transfer the sporozoites to the new host and cause disease in humans. 




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Text Box: Upper Left: White-footed mouse, Peromyscus leucopus, is an animal reservoir of babesia.
Upper Right:  Photo of deer tick, the vector of babesia.  Ticks are typically 1-5mm in length.  
Lower Right: Scanning electron micrograph of deer tick.  The tick will generally stick the green protrusion into its prey to ingest its blood meal.










It’s a zoo through and through… the animal players



While Babesia microti itself is a protozoa, it can reside in a variety of different animal species.  The tick, Ixodes dammini is its vector and definitive host; the tick will pass the parasite sporozoites to mammals and sexual reproduction of babesia occurs in the tick.  The tick will frequently infect white-footed mice with babesia and the parasite will undergo asexual growth in its mammalian host.  Because the white-footed mouse can harbor the parasite, it is considered to be an animal reservoir for the infection.  Humans can also be a mammalian host to babesia; Babesia microti and Babesia divergens will undergo the same life cycle stages in humans (trophozoite and merozoite stages) as they do in white-footed mice.



Doctor, please… is it… babesia?


            After a person is bit by an infected flea, humans will generally experience a 1-4 week incubation period before they begin to show signs of the disease.  The length of the incubation period is related to the health status of the person; generally, healthier individuals experience a longer incubation period.  Once the incubation period has Text Box: Directly Above: Drawing of a classical Maltese cross.
To the Right:  The purple arrows show babesia in a ring stage in which it can be confused with malaria.  The blue arrows point to the tetrad formation of babesia.  
ended, infected individuals experience non-specific signs and symptoms such as fever, malaise, jaundice, a slightly enlarged spleen, headache, chills, sweating, and weakness.  Significantly, many of these symptoms mimic those of malaria.  The best way to distinguish between the symptoms of the two infections is that babesia does not have the periodic fever that characterizes malaria. 

          If a person is suspected to have babesia, they are generally diagnosed with a positive blood smear.  While babesia can be confused with malaria, the tell-tale sign of a babesia infection is the presence of tetrads, often referred to as a “Maltese Cross,” within the red blood cells.  The best chance of producing a positive stain is to draw blood while the patient is experiencing a fever or chills.  While malaria has myriad stages of development, none of them resemble the tetrad formation of babesia.  Other diagnostic tests include Giemsa stains, limited xenodiagnostics with hamsters and gerbils, IFA tests, and PCR techniques. 

          Babesia infections in America usually are not fatal, 95% of all victims recover.  If people are diagnosed in time, they are often prescribed clindamysin and oral quinine.  Chloroquine is also prescribed but it simply helps to relives the symptoms of the infection; the drug itself does not help to kill the parasite.  Despite its low fatality rate in America, the disease can kill persons who are immunocompromised by spreading to the kidneys and causing renal failure.  In Europe, the fatality rate is 50%, however, there is a much lower morbidity rate overall. 



Hit ‘em where it hurts – Epidemiology and Public Health Strategies

            Babesia is a rare disease in North America and Europe with a total of about 330 cases between the two continents over the last 50 years.  In malaria endemic parts of the world such as Africa and the Middle East, the incidence of babesia is unknown, since it is probably misdiagnosed as malaria, especially when doctors do Text Box: Left:  Not all tick bites will cause a rash
Right: The life cycle of the deer tick, note that it is most active during summer and fall.  
not have any technical equipment available to them.  Despite its low frequency, the number of cases of babesia can be further reduced by following simply public health strategies.  For instance, people should wear light covered clothing that covers their entire body upon entering a wooded area.  Light colored clothing makes spotting ticks much easier.  Furthermore, people can protect against ticks on their legs by tucking the cuffs of their pants into their socks.  Although this may not be fashionably desirable, it is better than a babesia infection.  Finally, ticks must have contact for 10 hours before they can pass enough sporozoites to cause an infection; therefore, immediate bathing and washing of clothes can protect against an infection.  These strategies are especially important because not all tick bites cause itching or a rash, hence, a person could be infected even if they don’t see any evidence of being bitten by a tick.  While ticks are active year round, they are most active during the late summer and early fall – these are the times when hikers and others venturing into woodland areas must take the highest precautions. 




Did you like this page?  Here’s some cool web links:

  1. e-Medicine,
  2. The Centers for Disease Control,


References (Many images and information were taken from the pages listed below)


  1. Centers for Disease Control, Babeiosis, 13 Dec 2002.  Centers for Disease Control.  10 May 2003 <http:/ /
  2. UC Davis Medical School, Conrad Lab, UC Davis.  11 May 2003 <>
  3. Medical Chemical Corporation, 8 Aug 2001.  Medical Chemistry Diagnostic Quizzes, 10 May 2003 <>
  4. Tulane University, 15 June 2001.  Tulane University Parasite Summary.  8 May 2003
  5. American Lyme Disease Foundation.  American Lyme Disease Foundation, Inc.  9 May 2003 <>
  6. Pacific Biomedical Center.  11 June 2002.  University of Hawaii 12 May 2003 <>
  7. ProLog.  1 June 2000.  Lyme and Tick Disease 12 May 2003 <>
  8. Davan, Inod.  eMedicine.  11 May 2003 <>