Babesiosis is a parastic infection by a particular protozoa (Babesia) which is transmitted through tick bites. The disease produces symptoms similar to malaria. Babesia infection can range in severity from asymptomatic to life threatening. The infection is both treatable and preventable. Human babesiosis is an uncommon but emerging disease in the Northeastern and Midwestern United States and parts of Europe, and sporadic throughout the rest of the world. It occurs in warm months.


  • High fever
  • Abnormality of temperature regulation
  • Migraine
  • Diaphoresis
  • Fatigue
  • Myalgia
  • Chills
  • Gastrointestinal upset
  • Rash
  • Jaundice
  • Asymptomatic
  • Fever
  • Malaise
  • Muscle pain
  • Nausea
  • Vomiting
  • Abdominal pain
  • Anemia due to destruction of red blood cells
  • Low blood platelet level
  • Reduced white blood cell count
  • Kidney failure
  • Headache
  • Anorexia
  • Nonproductive cough (mucus is not coughed up)
  • Arthralgias (noninflammatory joint pain, unlike arthritis, which is inflammatory)
  • Sore throat
  • Pink eye
  • Photophobia
  • Weight loss
  • Emotional lability
  • Depression
  • Hyperesthesia (more sensitive to stimuli)
  • Enlarged spleen
  • Pharyngeal erythema
  • Enlarged liver
  • Jaundice (yellowing of the skin and of the sclera)
  • Retinopathy with splinter hemorrhages
  • Retinal infarcts
  • Neutropenia


Babesiosis is caused by microscopic parasites that infect red blood cells and are spread by certain ticks. Most human babesial infections are caused by B. microti (found only in the United States) or by B. divergens and B. bovis (found only in Europe).


To help prevent babesiosis, you should avoid wooded areas, tall grass, and brush where there may be ticks, particularly from May through September when ticks are most active. If you do walk or hike in these areas, be sure to

  • Wear light-colored clothing.
  • Tuck your pants legs into your socks so ticks can’t get inside your pants.
  • Wear a long-sleeved shirt and tuck it inside your pants.
  • Apply an insecticide containing permethrin to your clothes. Note, permethrin should be applied only to clothes (e.g., pants bottoms, socks, shirt sleeves). The effects will last several days.
  • Apply insect repellent containing DEET to your skin. Because DEET lasts only a few hours, you may need to reapply it.
  • Look for ticks on your body, including in your scalp, after returning from a walk or hike.
  • Check children and pets for ticks.

Generally, an infected tick has to be on your body for at least 24 hours before it passes on the parasite to you via a bite.


Accurate assessment helps identify infectious diseases and prevents avoidable complications. Complete assessment consists of patient history, physical examination, and laboratory data. The history should include the patient's sex, age, address, occupation, and place of work; known exposure to illness and recent medications, including antibiotics; and date of disease onset. Signs and symptoms, including their duration and whether they occurred suddenly or gradually, should be included in the history as well as precipitating factors, relief measures, and weight loss or gain.

Detailed information about recent hospitalization; blood transfusions; blood donation denial by the Red Cross or other agencies; recent travel or camping trips; exposure to animals; and vaccinations. (See Immunization schedule.) If applicable, ask about possible exposure to sexually transmitted diseases or about drug abuse. Also, try to determine the patient's resistance to infectious disease.

Ask about usual dietary patterns, unusual fatigue, and any conditions, such as neoplastic disease or alcoholism, that may predispose him to infection. Notice if the patient is listless or uneasy, lacks concentration, or has any obvious abnormality of mood or affect.

In suspected infection, a physical examination must assess the skin, mucous membranes, liver, spleen, and lymph nodes. Check for and make note of the location and type of drainage from any skin lesions. Record skin color, temperature, and turgor; ask if the patient has pruritus. Take his temperature, using the same route consistently, and watch for a fever, which is the best indicator of many infections. (Keep in mind that some patients, such as those who are immunocompromised, are unable to spike a fever.) Note and record the pattern of temperature change and the effect of antipyretics. Be aware that certain analgesics may contain antipyretics. With a high fever, especially in children, watch for seizures. Check the pulse rate. Infection commonly increases the pulse rate, but some infections, notably typhoid fever and psittacosis, may decrease it. Also observe for increased respiratory rate or a change in mental status.

In severe infection or when complications are possible, watch for hypotension, hematuria, oliguria, hepatomegaly, jaundice, bleeding from gums or into joints, and an altered level of consciousness. Obtain laboratory studies and appropriate cultures as ordered.


Many people who are infected with Babesia microti feel fine and do not have any symptoms. Some people develop flu-like symptoms. Because Babesia parasites infect red blood cells, babesiosis can cause hemolytic anemia (from the destruction of red blood cells).

Babesiosis can be a severe, life-threatening disease, particularly in people who:
  • do not have a spleen;
  • have a weak immune system for other reasons (such as cancer, lymphoma, or AIDS);
  • have other serious health conditions (such as liver or kidney disease); or
  • are elderly.


If you have babesiosis, your healthcare provider will treat it with an antibiotic combined with an anti-parasite medicine. Even with treatment, you may continue to have the disease for as long as 2 months.

People with severe cases of the disease may need an exchange transfusion. This procedure involves gradually withdrawing a person’s blood while replacing it with fresh donor blood or plasma.


  • NIH