Microbe of the Week: Babesia microti

Photo Credit: Dr. George R. Healy 

CDC Public Health Image Library. 

Arrows and labels added by Maria Bergquist.

Microbe of the Week is written by undergraduate researcher, Maria Bergquist.

Microbe of the Week: Babesia microti

Welcome to microbe of the week, where we break down the different disease-causing microbes that lurk inside our tick vectors! This week’s microbe is Babesia microti which causes Babeosis in the United States.

What is Babesia microti?

Babesia microti is a microscopic parasite that infects red blood cells.  Babesiosis is caused primarily by Babesia microti in the US and Babesia divergens in Europe. Like the previous microbes discussed, Babesia is transmitted to humans via Ixodid ticks (deer ticks) most often in the nymph stage. Its life cycle requires passage back and forth between ticks and another host.

Babesia microti life cycle

To initiate the cycle, an infected Ixodid tick will feed on a host, which is typically the white-footed mouse. This feeding passes Babesia sporozoites (an infective, motile life stage of Babesia) into the host where the parasite undergoes budding (a form of asexual reproduction). There, the budded parasites differentiate into male and female gametes. At this stage the parasites move back into Ixodid ticks as the ticks feed on the infected mouse. Here the parasite gametes will fertilize in the tick gut then develop into the infective stage (the sporozoite) once more. 

A detailed infographic of the Babesia life cycle is available at:

http://www.antimicrobe.org/Lifecycle/b51lc.asp#:~:text=Life%20Cycle,undergo%20asexual%20reproduction%20(budding)%20.

Symptoms

The CDC reports that Babesiosis infections are frequently asymptomatic in otherwise healthy patients. Some people develop flu-like symptoms such as fever, chills, headache, and nausea.

Babesia parasites infect and destroy red blood cells which can lead to hemolytic anemia. Symptoms of this include jaundice (yellowing of skin and eyes) and dark urine.

Severe cases of Babesiosis are at a higher risk 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)
• Are elderly

More information on Babesiosis symptoms available at:

 https://www.cdc.gov/parasites/babesiosis/disease.html

Treatment

The CDC says most asymptomatic cases do not require treatment but recommend discussing treatment options with a medical professional. Medications are available for people at risk for or who are experiencing more complicated symptoms.

More information for Babesiosis treatment available at:

 https://www.cdc.gov/parasites/babesiosis/health_professionals

A Condensed History

• 1888 — First ever Babesia species found by Romanian Biologist Victor Babes, for which the genus was named. Disease thought to only be in animals, primarily cattle.
• 1893 — Babesia linked to tick vector.
• 1957 — First human case of Babesia found in a Croatian cattle farmer.
• 1969 — First US case of Babesia microti appears in Nantucket Island, Massachusetts.
• 2017 — Total US cases of Babesiosis reach 2,358 with over half of those cases located in New York and Massachusetts.