How to Diagnose Babesiosis

Babesiosis is an infection of any member of the Babesia genus. Babesia microti is the most common cause in the United States. These are protozoans similar to malaria and can be found throughout the world. They are parasites of red blood cells and primarily infect animals with humans as accidental hosts. Babesiosis in humans is limited to specific geographic areas and usually only serious in people with compromised immune systems.

Difficulty: Challenging

Instructions

1. Check for recent tick bites. The black-legged deer tick (Ixodes scapularis) is the primary vector for babesiosis in the United States. However, the nymph of this species is only 2 mm in diameter even when fully engorged, so it frequently goes unnoticed. Also, the incubation period is one to three weeks and may be as long as nine weeks, so many people may not remember being bitten.

2. Expect the onset of babesiosis to be gradual with nonspecific symptoms. These include anorexia, dark urine, fatigue, fever, headaches, muscle and joint aches, nausea and vomiting.

3. Perform blood chemistries. Babesiosis usually produces decreased levels of serum haptoglobin, hemolytic anemia and elevated reticulocyte counts. The percentage of parasitized blood cells is usually in the 1 to 10 percent range.

4. Identify Babesia in blood smears. These samples are Giemsa or Wright stained and examined microscopically. Babesia species are similar to those of Plasmodium and may be distinguished by Babesia's lack of brownish pigment and the lack of synchronous stages. Plasmodium has gametocytes and schizonts.

5. Make a serologic diagnosis of babesiosis with an indirect immunofluorescent antibody (IFA) assay. A positive result is a titer of 1:256 or greater.

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