What Is Babesia? Symptoms, Treatment And Prevention.


What Is Babesia


Babesia is a tiny parasite that infects your red blood cells. Infection with Babesia is called babesiosis. The parasitic infection is usually transmitted by a tick bite.

Babesiosis often occurs at the same time as Lyme disease. The tick that carries the Lyme bacteria can also be infected with the Babesia parasite.

Babesiosis infections in humans used to be rare, but the number of cases is increasing. Most reported infections are in the northeastern states and the upper Midwest.

Babesia are malaria-like protozoans that parasitize and reproduce within mammalian red blood cells. They have a complex life cycle involving several different stages and physical forms and are maintained in nature primarily via exchange between Ixodes ticks and various mammals. The first Babesia species was discovered in 1888 by Victor Babes, a Hungarian pathologist in whose honor the organisms were subsequently named. Over 100 distinct species have since been identified within the Babesia genus, though only a few of these are currently known to be human pathogens.

Babesiosis has long been recognized as a disease of cattle and other domesticated animals, but the first human case was not described until 1957, when a young Croatian farmer contracted the illness and died some days later of renal insufficiency. In the late 1960s, the first North American cases appeared on Nantucket Island, and the disease is now recognized as an emerging and occasionally serious zoonosis in the United States.

What Is Babesia

Babesiosis has been reported in North and South America, Europe, and southern and eastern Asia. In the United States, the primary agent of human babesiosis is Babesia microti, which is transmitted by the bite of Ixodes scapularis, the same tick species that vectors Lyme disease. Cases of babesiosis caused by B. microti occur in southern New England and the northern Midwest. Additional cases of babesiosis caused by other species of Babesia occur primarily in the western U.S.; cases from Missouri and Kentucky have also been reported.

Clinically, babesiosis appears to have a wide spectrum of disease severity. Most patients experience a viral-like illness that can last weeks to months but which usually resolves fully. A significant minority of patients are entirely asymptomatic. In patients with a complicating condition, however – such as underlying immunosuppression – the disease course can be severe and potentially fatal. Some species of Babesia, such as B. divergens, appear to be more virulent than others.

Although primarily transmitted by tick bite, babesiosis can also be acquired via blood transfusion and maternal-fetal transmission.

What is Babesiosis?

Babesiosis is caused by a protozoa that infects red blood cells (erythrocytes). Although several different species of Babesia infect humans, B. microtiis the most common cause of infection in the United States. B. microti is transmitted by I. scapularisticks, the same ticks that transmit Lyme disease. B. microti infections occurs in parts of New England, New York State, New Jersey, Minnesota, and Wisconsin; however, it occurs in a only limited portion of the geographic areas where Lyme disease is endemic, and the number of reported cases of babesiosis is less than that of Lyme disease. High-incidence areas include coastal southern New England and the chain of islands off the coast that include Martha’s Vineyard and Nantucket Island, MA; Block Island, RI; and eastern Long Island and Shelter Island, NY.

Other species of Babesia have been found to cause disease in California,Washington State (WA-1), and Missouri (MO-1). Sporadic cases of babesiosis have also been reported in Europe (Babesia divergens and B. microti), Africa, Asia, and South America.

The clinical features of babesiosis are similar to those of malaria and range in severity from asymptomatic to rapidly fatal. Most patients experience a viral infection–like illness with fever, chills, sweats, myalgia, arthralgia, anorexia, nausea, vomiting, or fatigue. On physical examination, fever, splenomegaly, hepatomegaly, or jaundice may be observed. Laboratory findings may include hemolytic anemia with an elevated reticulocyte count, thrombocytopenia, proteinuria, and elevated levels of liver enzymes, blood urea nitrogen, and creatinine. Complications of babesiosis include acute respiratory failure, disseminated intravascular coagulation, congestive heart failure, coma, and renal failure. Immunocompromised patients, such as those who lack a spleen, have a malignancy or HIV infection, or who exceed 50 years of age, are at increased risk of severe babesiosis. Approximately one-quarter of infected adults and one-half of children experience asymptomatic infection or such mild viral–like illness that the infection is only incidentally diagnosed by laboratory testing. In both untreated and treated patients, parasitemia may occasionally persist, resulting either in subsequent recrudescence weeks or months later (primarily in immunocompromised hosts) or, rarely, in transmission of the pathogen to others through blood transfusion.

The diagnosis of babesiosis is based on epidemiologic, clinical, and laboratory information. Babesiosis only occurs in patients who live in or travel to areas of endemicity or who have received a blood transfusion containing the parasite within the previous 9 weeks. Because the clinical findings are nonspecific, laboratory studies are necessary to confirm the diagnosis. Specific diagnosis of babesiosis is made by microscopic identification of the organism on Giemsa stains of thin blood smears. On thick blood smears, the organisms appear as simple chromatin dots that might be mistaken for stain precipitate or iron inclusion bodies. Consequently, this method should only be performed by someone with extensive experience in interpreting thick smears. Multiple blood smears should be examined, because only a few erythrocytes may be infected in the early stage of the illness when most people seek medical attention. Because Babesia species may be confused with malarial parasites on blood smear, confirmation of the diagnosis and identification of the specific babesial pathogen may require additional laboratory testing. Also, it is important to have other supportive laboratory results if only a few ring-like structures are observed by microscopy. Both IgG and IgM antibodies to Babesia can be detected by indirect fluorescent antibody assay. Virtually all infected patients will have detectable antibodies in an acute-phase serum sample or a convalescent-phase sample obtained 4–6 weeks later. PCR detection of Babesia DNA in blood has been shown to be slightly more sensitive than microscopic detection of parasites on blood smear.

In summary, the diagnosis of babesiosis is most reliably made in patients who have lived in or traveled to an area where babesiosis is endemic, experience viral infection–like symptoms, and have identifiable parasites on blood smear and anti-babesial antibody in serum. The diagnosis of active babesial infection based on seropositivity alone is suspect. PCR is a useful laboratory adjunct, but as with smear and antibody testing, it should only be performed in laboratories that are experienced in such testing and meet the highest laboratory performance standards.

Symptoms and complications

The severity of the symptoms of babesiosis can vary. You may have no symptoms at all, or you may have slight flu-like symptoms. Some cases can cause serious, life-threatening complications.

A Babesia infection most often starts with a high fever and chills. Common symptoms include:

  • fatigue
  • severe headache
  • muscle aches
  • joint pain
  • abdominal pain
  • nausea
  • skin bruising
  • yellowing of your skin and eyes
  • mood changes

As the infection progresses, you may develop chest or hip pain, shortness of breath, and drenching sweats.

It’s possible to be infected with Babesia and not have any symptoms. A relapsing high fever is sometimes a sign of undiagnosed babesiosis.

Complications can include:

  • very low blood pressure
  • liver problems
  • breakdown of red blood cells, known as hemolytic anemia
  • kidney failure

In young, healthy adults, the infection usually isn’t severe. But the illness can quickly become serious, and can even cause death. Babesiosis could be life-threatening in people who:

  • Are elderly.
  • Have had their spleen removed.
  • Have liver or kidney disease.
  • Have weak immune systems (due to conditions such as HIV/AIDSor cancer).


People get babesiosis when an infected tick bites them. The Babesia parasite is usually spread when the tick is in its nymph stage. At that stage, the tick is the size of a poppy seed. It can be hard to detect a tick this small.

Ticks live in areas with a lot of plant life, such as wooded areas or fields. They sit near the top of grassy plants and low bushes. They wait there for people or animals to brush up against them. Ticks can crawl on your clothes or body for several hours before attaching to the skin.

Ticks can attach to any part of your body. They are usually found in hard-to-see areas, including the armpits, groin, or scalp. An infected tick needs to be attached to your skin for 36 to 48 hours before it passes the parasite on to you.

People who spend time in outdoor areas where ticks are common are at higher risk of getting tick-borne diseases.

Though rare, it is possible to get babesiosis through a blood transfusion. It is also possible for an infected mother to pass the parasite to her baby. This can happen during pregnancy or delivery. This is also rare.

Babesiosis is caused by infection with a malaria-like parasite of the species Babesia. The Babesia parasite can also be called Nuttalia.

The parasite grows and reproduces inside the red blood cells of the infected person or animal, often causing intense pain.

There are more than 100 species of the Babesia parasite. In the United States, Babesia microtiis the most common strain to infect humans, according to the Centers for Disease Control and Prevention (CDC). Other strains can infect:

  • cattle
  • horses
  • sheep
  • pigs
  • goats
  • dogs


The fact that the early symptoms of babesiosis are largely non-specific makes diagnosis difficult. Nevertheless, physicians encountering a patient from an endemic area who presents with fever and a viral-like illness, especially in the summer months, should be alert to the possibility that babesiosis may be responsible for the patient’s symptoms.

While the physical exam is usually unremarkable, conventional blood tests can produce a pattern that suggests the diagnosis. Because the Babesia organisms cause lysis of red blood cells, patients will frequently develop hemolytic anemia, as well as lymphopenia and thrombocytopenia. Elevated serum lactate dehydrogenase levels are also common, and hyperbilirubinemia and an elevated erythrocyte sedimentation rate may also be present.

If babesiosis is suspected, microscopic examination of blood smears should be pursued. Giemsa or Wright stains are typically used. In early illness, the infection rate of erythrocytes can be less than 1%, so multiple smears over  a period of days may be needed to confirm the diagnosis. Babesial DNA can also be detected by polymerase chain reaction (PCR) in cases where smears are negative but the diagnosis is still suspected.

Immunofluorescence (IFA) of IgM and IgG antibodies is sometimes employed to confirm a babesiosis diagnosis. However, antibodies to Babesia organisms can remain high for months or years after clinical resolution of illness, so the test is not a reliable indicator of active infection.

Can babesiosis be prevented or avoided?

The best way to prevent babesiosis and other tick-borne diseases is to avoid being bitten by ticks. When you are outdoors, follow these guidelines:

  • Avoid areas that are wooded, brushy, or have tall grass.
  • Walk in the center of trails.
  • Use an insect repellent with at least 20% DEET. It can be put on clothing or sparingly on the skin. Don’t apply it to children’s faces or hands.
  • Treat clothing, tents, or other gear with repellents containing 0.5% permethrin.
  • Wear light-colored clothing. This makes it easier to see and remove ticks from your clothes.
  • Wear a long-sleeved shirt and long pants. Tuck your pant legs into your socks or boots for added protection.

After you get home, check everything and everyone for ticks.

  • Bathe or shower as soon as you can to wash off any ticks that have not attached to you.
  • Check your entire body for ticks. Use a mirror for places you can’t see. Check your children and your pets. Common tick locations include the back of the knees, groin area, underarms, ears, scalp, and the back of the neck.
  • Check any gear you used, including coats, backpacks, or tents.
  • Tumble dry clothes or blankets on high heat in the dryer for 10 to 15 minutes. This should kill any ticks. If clothes are dirty, wash them in hot water and dry on high heat for 60 minutes.

During the months of May through September, stay away from places where ticks are common. This is especially important if you have:

  • Had your spleen removed.
  • Had an organ transplant or are taking immunosuppressant medicines (which weaken or suppress the immune system).
  • An HIV infection or AIDS.
  • Any other chronic condition that affects your immune system.

Babesiosis Treatment

What do I do if I find a tick on my skin?

Don’t panic. Use fine-tipped tweezers to grab the tick as close to the skin’s surface as possible. Pull up with steady, even pressure. Be careful not to squeeze or twist the tick body. Sometimes parts of the tick remain in the skin. You can leave them alone or carefully remove them the same way you would a splinter. Do not use heat (such as a lit match), petroleum jelly, or other methods to try to make the tick “back out” on its own. These methods are not effective.

Wash the area where the tick was attached thoroughly with soap and water. Monitor how you’re feeling for the next month or two. Call your doctor if you develop flu-like symptoms. Be sure to tell your doctor that you were bitten by a tick and when it happened.

People who have healthy immune systems and only mild cases of babesiosis usually don’t need treatment. The body fights the infection on its own. People with more severe cases are treated with antibiotics. If you develop shortness of breath or other symptoms during treatment, tell your doctor right away. If you have a severe case of babesiosis or a weak immune system, you may need to go to a hospital.

Living with babesiosis

Many people infected with babesiosis don’t have any symptoms. They don’t even know they have it. Those who experience symptoms can be treated with antibiotics. They usually make a full and complete recovery.

People at risk of a more severe infection could experience complications. The most common is hemolytic anemia. This happens when the Babesia parasite destroys red blood cells faster than the body can make new ones. It can lead to jaundice (yellowing of the skin) and dark urine.

Other complications could include:

  • low or unstable blood pressure
  • low blood platelet count
  • blood clots and bleeding
  • vital organ malfunctions (such as liver, kidneys, or lungs).

How it’s transmitted

The most common way to contract Babesia is a bite from an infected tick.

Babesia microti parasites live in the gut of the black-legged or deer tick (Ixodes scapularis). The tick attaches to the body of white-footed mice and other small mammals, transmitting the parasite to the rodents’ blood. After the tick has eaten its meal of the animal’s blood, it falls off and waits to be picked up by another animal.

The white-tailed deer is a common carrier of the deer tick. The deer itself is not infected. After falling off the deer, the tick will typically rest on a blade of grass, a low branch, or leaf litter. If you brush up against it, it can attach to your shoe, sock, or other piece of clothing. The tick then climbs upward, seeking a patch of open skin.

You probably won’t feel the tick bite, and you may not even see it. That’s because most human infections are spread during spring and summer by ticks in the nymph stage. During this stage, the ticks are about the size and color of a poppy seed.

Besides a tick bite, this infection can also pass via contaminated blood transfusions or via transmission from an infected pregnant woman to her fetus.

Risk factors

People with no spleen or a weakened immune system are at greater risk. Babesiosis can be a life-threatening condition for these people. Older adults, especially those with other health problems, are also at higher risk.

The connection between babesiosis and Lyme disease

The same tick that carries the Babesia parasite can also carry the corkscrew-shaped bacteria responsible for Lyme disease.

Studies carried out in areas of southern New England, where Lyme disease is prevalent, found that 11 percent of people diagnosed with Lyme were also infected with Babesia. Researchers also found that the babesiosis often went undiagnosed.

According to the CDC, most cases of babesiosis occur in New England, New York, New Jersey, Wisconsin, and Minnesota. These are states where Lyme disease is also prevalent, though Lyme is also prevalent elsewhere.

The symptoms of babesiosis are similar to those of Lyme disease. Coinfection with Lyme and Babesia can cause the symptoms of both to be more severe.

How to reduce your risk

Avoiding contact with ticks is the best prevention against both babesiosis and Lyme disease. If you go into wooded and meadow areas where deer are present, take preventive measures:

  • Wear clothing treated with permethrin.
  • Spray repellent containing DEET on your shoes, socks, and exposed areas.
  • Wear long pants and long-sleeved shirts. Tuck your pant legs into your socks to keep ticks out.
  • Inspect your whole body after spending time outdoors. Have a friend look at your back and the backs of your legs, especially behind your knees.
  • Take a shower and use a long-handled brush on areas you can’t see.

A tick must attach to your skin before it can transmit the disease. Attaching usually takes some hours after the tick has contacted your skin or clothing. Even if the tick attaches, there is some time before it can transmit the parasite to you. You may have as long as 36 to 48 hours. This gives you time to look for the tick and remove it.

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