Babesiosis: What To Know About The Tick-Borne Disease

Parasites are organisms that live in — and feed off of — another organism. Khan Academy explains that the relationship between two organisms can only be considered parasitic if one is gaining something (i.e., the parasite) at the expense of the other (i.e., the host). Otherwise, it is a commensal relationship if one is gaining something but the other is not getting affected by any means; and it is a mutualistic relationship if both parties are benefiting from each other.

Some parasites are completely dependent on the host to survive, while others are only partially reliant. Although most people imagine parasites as tiny little worms, the Centers for Disease Control and Prevention (CDC) explains that parasitic infections in humans can actually be caused by three main types of parasites: helminths, protozoa, and ectoparasites. Helminths are parasitic worms that are often large enough to see with the naked eye. They include flukes, flatworms, and roundworms. On the other hand, protozoa are microorganisms made up of only one cell, which make them too small to be seen without using a microscope. Common examples of diseases caused by protozoa include amebiasis, giardiasis, leishmaniasis, and cryptosporidiosis. Lastly, ectoparasites are a group of arachnids and insects that latch onto the skin and cause disease. These include fleas, lice, mites, and ticks.

Per a 2017 article in the Journal of Clinical Microbiology, babesiosis has been present in the United States as early as 1968, but epidemiologic data shows that the number of cases has been steadily rising over the past few years. Previously known as the Nantucket fever (following the emergence of several cases in Nantucket Island, Massachusetts in the 1970s), babesiosis has since spread to other parts of the United States, particularly in the Northeast and upper Midwest.

Early in 2023, the CDC published a report indicating that aside from the seven states where babesiosis has already long been established as endemic (i.e., Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin), three additional states (i.e., Maine, New Hampshire, and Vermont) have reported a significantly increased number of cases between 2011 to 2019, prompting the CDC to declare babesiosis as endemic in these three states as well. Alarmingly, the total number of babesiosis cases reported in the United States almost doubled from 2011 to 2019. 

Additionally, among the total number of cases reported during the same period, more than 98% of them were from the 10 endemic states, with the top three states with the highest documented cases being New York, Massachusetts, and Connecticut. While it is still unclear exactly why this is happening, the rising number of cases should not be ignored. Thus, it's beneficial to learn about this relatively rare but potentially fatal parasitic infection.

According to the CDC, the primary mechanism of Babesia infection in humans is through a tick bite. In rare instances, babesiosis can be transmitted via blood transfusions, organ transplants, and from an infected mother to their baby through the placenta. Because these latter three modes of transmission do not involve ticks, it can occur throughout the year and in places where babesiosis is not endemic.

Because of a continuous rise in cases of transfusion-related babesiosis, the U.S. Food and Drug Administration (FDA) released a report in 2019, recommending that blood donations coming from Maryland, Virginia, Maine, Massachusetts, Delaware, Minnesota, New Hampshire, Vermont, New York, Connecticut, New Jersey, Pennsylvania, Wisconsin, Rhode Island, and Washington be screened year-round for babesiosis. As for blood donation centers in other states, the FDA recommended that they change their questionnaire to include if they have ever been diagnosed with babesiosis, or had a previous donor screening that indicated they were positive for Babesia.

There are only a few documented cases of transplacental transmission of Babesia (and consequently, congenital babesiosis in the newborn). Reports show that the mothers were either asymptomatic or only had flu-like symptoms during pregnancy. The newborns presented with various signs and symptoms of babesiosis, including hemolytic anemia, low platelet count, jaundice, splenomegaly, and increased bilirubin. They responded well to antimicrobial therapy, with some infants requiring blood transfusions.

The signs and symptoms of babesiosis are nonspecific, and can be mistaken as something else. However, the suspicion usually becomes high when a person is experiencing the possible clinical manifestations of babesiosis (e.g., fever, flu-like symptoms) and they are living in, or have recently been to, places where the disease is known to be endemic.

If your doctor is suspecting that you may have babesiosis, they will most likely order a simple blood test. Laboratory analysis of your blood may reveal a decreased number of red blood cells, white blood cells, and platelets. You may also have increased lactate dehydrogenase and bilirubin levels, as well as an elevated erythrocyte sedimentation rate (via Columbia University).

All of these results do not necessarily point to a diagnosis of babesiosis, so another test called a peripheral blood smear (PBS) is also often done. People with babesiosis may have visible parasites in the shape of a ring or Maltese cross inside their red blood cells. While this is a very unusual finding, it can also sometimes be seen in people with malaria. Additionally, babesiosis commonly causes destruction of red blood cells, which makes it difficult to visualize the parasites with just one sample. If your blood smears are normal but your doctor is highly suspicious of babesiosis, they may order a polymerase chain reaction (PCR) test to look for the presence of Babesia DNA or an antibody test to see if you have (or had) been infected with Babesia (per Osmosis).

Severe, untreated babesiosis can cause a wide range of effects throughout the body. Because Babesia directly invades and destroys red blood cells, it can lead to a condition called hemolytic anemia, where the amount of red blood cells being destroyed outcompetes the body's ability to produce and replace them. Possible signs and symptoms of hemolytic anemia include weakness, dizziness, fever, pale skin, jaundice, heart murmurs, and an enlarged liver and/or spleen. Consequently, an enlarged spleen can rupture, resulting in a medical emergency with additional symptoms of upper left abdominal pain and tenderness, left shoulder pain, and lightheadedness. Splenic rupture can cause significant and fatal bleeding if it is not addressed immediately.

Per Cleveland Clinic, other possible complications of babesiosis include fluid buildup in the lungs (i.e., pulmonary edema), disseminated intravascular coagulation (DIC), and organ failure. Pulmonary edema can initially present as difficulty breathing, but it may eventually result in heart failure or respiratory failure. DIC is a condition where the body's clotting system becomes overactive. Paradoxically, platelets get consumed, which ultimately leads to uncontrollable bleeding. In people who are at high risk of infection (especially those without a functioning spleen), multiorgan failure is common, especially involving the kidneys and liver (via StatPearls). These complications can result in death if not managed closely in the hospital. Unfortunately, while most people are expected to fully recover from a Babesia infection, it is estimated that death occurs in around 10% of people who are hospitalized for babesiosis.

Lyme disease is a bacterial infection caused by Borrelia burgdorferi, and is transmitted through a bite from an infected tick, the same kind of tick that can transmit babesiosis. Studies show that ticks can become co-infected with more than one pathogen, including those that cause babesiosis and Lyme disease (via the National Institute of Allergy and Infectious Diseases). Research on mice also revealed that those who were bitten by co-infected ticks (with at least one infection coming from Borrelia) developed a more severe form of Lyme disease compared to those who were bitten by ticks with only one infection. As cases of tick-borne illnesses have been increasing (per NBC News), we should be aware of the possibility of getting infected by more than one pathogen at the same time.

Lyme disease can be categorized into three stages. The first stage begins days to weeks following a tick bite. A unique "bulls-eye" rash appears, accompanied by nonspecific symptoms like fatigue, muscle aches, appetite loss, and fever. Weeks to months afterward, the infection spreads to other body areas, initiating the second stage. More "bulls-eye" rashes may appear, and you may experience migrating body pain, headaches, neck stiffness, numbness and tingling, shortness of breath, and palpitations. Months to years later, you may start to experience nerve, sleep, and mood problems, which usually means that you have progressed to the third stage (per Harvard). Although it is associated with several signs and symptoms, Lyme disease is curable with proper treatment and is rarely ever fatal (via Cleveland Clinic).