Babesiosis 

Babesiosis is a tick-borne disease caused by Babesia parasites, which infect and destroy red blood cells and cause symptoms similar to malaria. It is the third most common tick-borne illness in the United States, behind Lyme disease and anaplasmosis.¹ It is primarily transmitted through black-legged ticks, also known as deer ticks. These are the same ticks that transmit Lyme disease as well as other tick-borne infections. While babesiosis can be contracted by itself, it is possible to have both babesiosis and Lyme disease at the same time, which is known as a co-infection. They share similar symptoms such as fever, headache, and fatigue, but require different treatments. The best way to prevent babesiosis is to use tick repellents, wear protective clothing, and perform thorough tick checks after spending time in tick-prone areas.   

Some cases of babesiosis present asymptomatically, which means there may not be any symptoms present. Symptomatic cases usually start with flu-like symptoms, such as:

• High fever
• Fatigue
• Sweating
• Chills
• Muscle and joint pain
• Headaches
• Low appetite

Unlike Lyme disease, babesiosis does not cause a characteristic rash. And while anyone can contract babesiosis, it can be a life-threatening disease for people without a spleen or weakened immune systems (e.g., people with HIV/AIDS, cancer, and people taking immuno-suppressant drugs).² The following more severe symptoms require hospitalization:

• Severe hemolytic anemia (when red blood cells are destroyed faster than they are made which can lead to dark urine and jaundice, the yellowing of the skin and eyes)
• Heart failure
• Difficulty breathing
• Renal failure 

Although extremely rare, neurological symptoms have been documented in two case reports.

If you suspect you have been bitten by a tick, even if you are not sure, let your healthcare provider know this as you report your symptoms. Inform them about areas you may have visited where ticks are active (hiking, at parks, in the backyard, etc.). If you have received a blood transfusion within the last 6 months, report this as well, since babesiosis can also be transmitted through infected blood, though this is more rare. 

Your healthcare provider can perform a blood smear test to detect the presence of the Babesia parasite in your red blood cells under a microscope. This method offers a quick and inexpensive way to make a diagnosis. Alternatively, your healthcare provider can order a PCR (polymerase chain reaction) blood test, which is more sensitive.

There are also lab tests available that can identify antibodies against Babesia in your blood. However, these tests cannot distinguish between past or current infections, so confirmation of an active infection with a blood smear or PCR is necessary. Testing should also exclude other potential pathogens.³

Typically, babesiosis treatment includes a course of antibiotics and antimalarial drugs. The recommended antimicrobial treatment for patients with babesiosis is a combination of atovaquone and azithromycin, with clindamycin and quinine as an alternative option.³ Sometimes, a patient can relapse even after the initial treatment, which will require them to undergo further treatment. Researchers, including those funded by GLA, are exploring more effective treatment options to prevent these relapses.

How is Babesiosis Spread?

The majority of Babesia infections in humans are acquired through the bite of the black-legged tick (Ixodes scapularis), which also carries and spreads the Lyme disease bacteria and other pathogens. These ticks will feed on animals (white-footed mouse, shrews, chipmunks, deer, etc.), after which they can pass the infection on to humans. Babesia parasites do not spread from person to person. 

A rare cause of infection can be through a blood transfusion. If a blood donor has babesiosis but has been asymptomatic, it is possible for their blood donation to be contaminated with Babesia parasites. The Red Cross now screens all blood donations for Babesia, though that was not always the case. Another rare way that the Babesia parasite can spread is through maternal-fetal transmission. If a pregnant person has babesiosis, it is possible for the baby to become infected during pregnancy or during birth.² 

Where is Babesiosis Most Common?

There are eight known Babesia species that can cause infection in humans. Babesiosis is endemic in the United States where approximately 2,000 cases are reported annually.¹ The majority of cases are caused by Babesia microti and spread by the black-legged tick (Ixodes scapularis) in the Northeast, Mid-Atlantic, and Upper-Midwestern states. Babesia duncani is another species found to cause disease along the West Coast of the United States but is spread by the winter tick (Dermacentor albipictus).⁴ Babesia duncani can cause more severe disease and a GLA-funded investigator has been conducting research to understand why.    

Babesiosis is also endemic in China and caused by Babesia venatorum and Babesia crassa-like parasites through bites of different Ixodes ticks. Babesia divergens predominantly causes disease in Europe and can be found sporadically around the world.⁵  Babesiosis is most often reported during the months when ticks are most active: spring, summer, and fall. Transfusion-related cases can occur anywhere or anytime if infected blood donations are used.

Incubation Period

Typically, the incubation period (the time between the bite and emergence of symptoms) is between 1 and 4 weeks. Those who contract babesiosis through a blood transfusion may have a 1 to 9-week incubation period.

Being tick aware is the best way to prevent babesiosis. This means using bug sprays that repel ticks and wearing clothes that cover exposed skin (like tucking your pants into your socks) if you plan to be out in the woods or wilderness. Always do a tick-check after time outdoors, and make sure someone else checks the areas you can’t see (like your back and scalp). If you find a tick, safely remove it and save it in a plastic bag for testing. It usually takes 36-48 hours for a tick to transmit the Babesia parasite, so the sooner you can remove a tick, the better. There is currently no vaccine for babesiosis.²

Because one black-legged tick can carry both the Lyme disease bacteria and Babesia parasite at the same time (not to mention other pathogens such as Powassan virus, Anaplasma bacteria, and Borrelia miyamotoi), a person bitten by that tick can contract one or both diseases simultaneously, presenting a challenge for diagnosis and treatment.⁶ When a person contracts more than one tick-borne disease at the same, this is called a co-infection.

Hungarian pathologist Victor Babes was the first to identify the microorganism in 1888 when studying cattle illnesses, and this is how babesiosis got its name. The first documented human cases of babesiosis emerged in Croatia and Nantucket Island in the mid-1900s. Researchers at the time began calling it “Nantucket fever”, although its reach was clearly wider than the small Massachusetts island.⁵

If you or a loved one has been struggling with babesiosis or Lyme disease, reach out to us today at the Global Lyme Alliance. We can connect you to support, resources, and experts in the tick-borne pathogen field who can help you through the challenges of a diagnosis. And if you can, we urge you to donate to the Global Lyme Alliance cause to fund research to find effective cures for Lyme disease, babesiosis, and other tick-borne diseases.

Content last reviewed August 2024