Babesiosis

How babesiosis spreads

Babesia parasites live in mice and are passed to ticks when they feed. Blacklegged ticks (Ixodes scapularis), especially the tiny nymph stage the size of a poppy seed, then infect people. Most people do not remember the bite. The same tick can carry Lyme disease and anaplasmosis, so co-infections occur.

Babesiosis can also spread through blood transfusions from donors without symptoms; US blood centers in affected states now screen donations. Rarely it passes from mother to baby during pregnancy.

Symptoms

Symptoms appear 1 to 4 weeks after a tick bite, or up to several months after a transfusion.

• gradual onset of tiredness and loss of appetite
• fever, often with sweats and chills
• muscle and joint aches, headache
• nausea
• dark urine from breakdown of red blood cells
• jaundice in more severe cases
• an enlarged spleen or liver

Unlike Lyme disease, babesiosis does not cause a rash. A rash suggests Lyme co-infection.

Severe babesiosis

Severe disease is more likely with:

• no spleen (asplenia), which normally clears infected red cells
• age over 50
• weakened immunity: cancer, HIV, organ transplant, rituximab and other immune-suppressing medicines
• other chronic illness

Complications include severe hemolytic anemia, low platelets, kidney failure, breathing failure, heart failure, a ruptured spleen and death. Mortality in hospitalized patients is a few percent and higher in the immunocompromised.

Diagnosis

• Blood smear: a microscope examination of a thin blood smear shows parasites inside red cells, sometimes in a characteristic "Maltese cross" shape. It also estimates the percentage of infected cells (parasitemia).
• PCR blood test: detects Babesia DNA; more sensitive than a smear, especially early.
• Antibody tests: support the diagnosis but cannot distinguish current from past infection.
• Other blood tests: blood count (anemia, low platelets), signs of red cell breakdown (high LDH and bilirubin, low haptoglobin), and kidney and liver function.
• Tests for co-infections: Lyme disease and anaplasmosis.

Treatment

• Mild to moderate illness: atovaquone plus azithromycin for 7 to 10 days.
• Severe illness: hospital care with intravenous azithromycin plus oral atovaquone, or clindamycin plus quinine. Red blood cell exchange transfusion may be used for very high parasite levels or organ failure.
• Immunocompromised people: longer treatment, often 6 weeks or more, until blood tests are negative for at least 2 weeks.

People without symptoms who have parasites detected incidentally are usually not treated unless the parasites persist for more than 3 months.

Outlook

Most healthy people recover fully. Fatigue may persist for weeks to months. Without treatment, parasites can remain in the blood for months in people without symptoms. Relapses are more common in those with weak immune systems.

Prevention

There is no vaccine. Preventing tick bites is the best protection:

• Use an EPA-registered repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on skin, and permethrin on clothing and gear.
• Wear long sleeves and pants, tucked into socks, in wooded or grassy areas.
• Stay in the center of trails.
• Check your whole body, children and pets for ticks after being outdoors, and shower within 2 hours.
• Remove ticks promptly with fine-tipped tweezers, pulling straight up.
• People without a spleen should take extra care in tick areas during spring and summer.

Frequently asked questions

What are the symptoms of babesiosis?

Many people have no symptoms. Others develop a flu-like illness with fever, chills, sweats, fatigue, muscle aches, headache, nausea and dark urine, 1 to 4 weeks after a tick bite. Severe illness with jaundice, anemia and organ failure can occur in high-risk people.

How do you get babesiosis?

Most people get it from the bite of an infected blacklegged (deer) tick in the northeastern or upper midwestern US. Less often, it is spread through a blood transfusion from an infected donor or from mother to baby during pregnancy.

Is babesiosis the same as Lyme disease?

No. They are different infections spread by the same tick, and people can have both. Babesiosis is caused by a parasite that infects red blood cells, while Lyme disease is caused by bacteria. They need different treatments.

Can babesiosis be cured?

Yes. Most people are cured with atovaquone and azithromycin for 7 to 10 days. People with severe disease or weakened immune systems may need hospital treatment and longer courses, but most still recover.