Babesiosis is an infection of the blood which is caused by a parasite known as Babesia. It is found in the United States in people who have been bitten by an infected black-legged tick, or ‘deer tick,’ as they are also known. The ticks that are most likely to spread it are very small, young ones. This means that a lot of people who are bitten don’t realize that it has happened until the infection starts to show symptoms. The parasite attacks red blood cells and eventually can cause them to burst. There have been some very rare cases of people who have received a blood transfusion of infected blood catching the disease.
For most people, the infection causes non-specific symptoms that are mistaken for the flu. Sufferers may experience fever, chills, fatigue, headaches, and sweats. In some cases, the symptoms can become life-threatening. The condition attacks red blood cells, which can lead to hemolytic anemia. This can be a serious condition in the elderly, those with weakened immune systems, and those who have kidney disease or who do not have a spleen. In healthy individuals, the spleen helps to clear infected blood cells, helping to stop the progress of the infection.
In total, there are more than 100 species of Babesia, but only a small portion of those can infect human beings. The most common cause of infection in the United States is Babesia microti. The CDC received notice of 1,994 cases of Babesiosis in 2017, with most of those cases being in the Mid-Atlantic, Northeast, and Upper Midwest. These are the areas where the condition is endemic.
There have been some cases in the West Coast areas, but these are caused by Babesia duncani. Other species of Babesia are commonly found in Asia and Europe. Different species may cause slightly different symptoms, but in areas where malaria exists, it is hard to determine whether an infection targeting blood cells was caused by Plasmodium (the species that causes malaria) or by a Babesia parasite.
Borrelia burgdorferi (a bacteria which causes Lyme disease) is transmitted by the same species of tick as Babesia, so the two conditions are comorbid. Around 20% of people who have Babesiosis also suffer from Lyme disease. When someone develops both conditions, the symptoms tend to be longer-lasting and more severe than in someone who has just one of the conditions.
The condition does not tend to spread from human to human, but it can spread from rodents such as the white-footed mouse to humans.
Symptoms of Babesiosis
One of the challenging things about this condition is that the symptoms can vary massively. Some people are asymptomatic. If symptoms do occur, it may not be until months or weeks after the person has become infected. In some cases, a person feels as if they have made a recovery after their initial symptoms and experiences a relapse months later. This is particularly common in people who have a weaker immune system.
Common symptoms of Babesiosis include:
- Chills, fever or sweats
- Aching muscles
- Joint pain
- Low appetite
If left untreated, these symptoms can last for months.
The condition affects the red blood cells, which are the cells that transport oxygen around the body. If enough cells are affected, then a person may develop hemolytic anemia, which is a condition where red blood cells are destroyed more rapidly than new cells are made. This can be debilitating at best and can become a very serious condition.
Symptoms of hemolytic anemia include:
- Pale skin
- Darker than normal urine
- Enlargement of the liver and spleen
If left untreated, Babesiosis can cause life-threatening complications. This is particularly of concern for people who:
- Have no spleen
- Are suffering from a weakened immune system
- Have kidney or liver problems
- Are over the age of 50
In the United States, fewer than ten percent of people who are diagnosed with Babesiosis suffer from fatal complications. Most fatalities were associated with the elderly or people who do not have a spleen.
Complications can include:
- Low blood pressure and shock
- Hemolytic anemia
- Thrombocytopenia (low platelet count)
- Congestive heart failure
- Blood clots or bleeding from disseminated intravascular coagulation
- Kidney failure
Testing for Babesiosis
Diagnostic testing for Babesiosis helps to identify cases early or rule out the possibility of someone having the condition. Where necessary, additional tests can be used to detect organ dysfunction or other complications.
It can be hard to diagnose Babesiosis because there are no specific symptoms that are clearly linked to it, and some sufferers have no symptoms at all. However, the condition should be considered as a possibility in people complaining of lasting flu-like symptoms in regions where the parasite is endemic.
Diagnosis of Babesiosis
One of the most common tests is the peripheral blood smear. This is done if a complete blood count shows abnormal results. The blood sample is examined under a microscope to look for parasites, which are often visible inside a blood cell. Whether or not a blood smear will correctly identify Babesiosis depends on the degree of infection. In some cases, multiple smears would need to be examined for a laboratory technician to see parasites in a cell. Special training is needed to ensure that the parasite is identified. The presence of Babesia parasites in a blood cell is confirmation of infection; however, it can be difficult to tell the parasites apart from other parasites.
If a blood smear is negative, this does not completely rule out a Babesia infection. Depending on the severity of the symptoms and the results of other tests, results may need to be confirmed through additional testing.
Antibody testing using the indirect fluorescent antibody test is another good option. This blood test will look for antibodies that are produced following infection with the parasite. If blood smear test results are not conclusive, then this test is a good option since it is more sensitive. Antibody levels rise in the two to four week period after infection and then wane after 6 to 12 months.
Someone who has a negative result for B. microti antibodies has most likely never had Babesiosis. The test correctly detects antibodies in 88 to 96% of cases. False negatives are possible but less likely than with blood smears.
One challenge with the test is that it only detects B. microti antibodies. Other Babesia species can also cause the condition. Someone on the West coast may not have B. microti antibodies but could have B. duncani antibodies and have caught the infection from that species.
High immunoglobulin M antibodies to Babesia species indicate that there is a current infection. In contrast, a lower level of antibodies (but still some) suggests that the person has been infected in the past. Elevated immunoglobin G antibody levels are also suggestive of past infection.
Molecular testing using Polymerase Chain Reaction tests can identify B. microti infection. Positive results mean that the parasite was detected. Negative results mean that there was not a high level of B. microti in the blood, but it is possible that there may have been some present, just not enough for the test to detect.
Complete blood count tests can identify if someone has low red blood cell counts, reduced hemoglobin, or hematocrit. Tests can also detect decreased platelet numbers or a lower white blood cell count.
Comprehensive metabolic panel tests can identify elevated creatine levels, blood urea nitrogen levels, increased liver enzymes, or increased lactate dehydrogenase. These are all things that are consistent with someone who has Babesiosis but does not necessarily mean that a person has the condition.
Urinalysis on a person with Babesiosis may show as being positive for blood or protein in the urine.