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Presentation of Quiz #31

A 62 year old female, currently living in New Mexico, was admitted to the hospital with a three week history of fever, headache, and overall malaise. She experienced occasional chills, which appeared to coincide with the fevers. Her past medical history appeared to be unremarkable, with the exception of an emergency appendectomy about 20 years earlier.

Routine blood examinations for parasites revealed the following:

On the basis of this blood film, the patient was diagnosed with malaria. With this diagnosis, a more comprehensive history was taken in order to determine how and when she had acquired this Plasmodium spp. infection.

Based on the diagnosis of malaria, what other information would you like to have in order to better explain her illness within the context of her medical history? Take a few minutes and write down your questions. See if your questions matched any of those presented below.

Based on the questions she was asked, she responded: "NO":

  1. Any travel history outside of the United States (recent or within the last 20 years)?
  2. Any blood transfusions (medical history did not indicate any transplantation issues)?
  3. What about drug abuse (potential for shared needles)?

What additional questions would be appropriate to ask? Consider travel within the United States - what possible organisms could mimic Plasmodium spp.?

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Answer and Discussion of Quiz #31

Answers to Questions:

  1. Since the patient had no significant travel history outside of the United States, no history of blood transfusion or shared needle related to possible drug abuse, it is highly unlikely that this patient had malaria. The one question that wasn't asked relates to her place of residence, possibly by an airport, or does she work close to an airport. There is an unusual situation in which infected mosquitos may be transported from one country to another through baggage or the interior of airplanes. Once the plane lands, the mosquitos are free to disseminate throughout the new territory. Very rarely, someone who lives by or works at an airport might be bitten by an infected mosquito, thus transmitting a malaria infection within an area where malaria is not endemic. Continuous endemic malaria within the United States ended in the 1940's. This has been termed "airport" malaria. A patient with absolutely no relevant history pertaining to a malaria infection could still acquire the infection through proximity to an airport. Again, this is a rare situation, but it has been documented a number of times.

On further questioning, the woman had visited her niece who lived on Long Island for several weeks. Both had dogs, frequently requiring tick removal after running in the woods. Although she did not recall being bitten by ticks, there was considerable tick contact on a daily basis. Based on this additional information, it was likely that the correct diagnosis was babesiosis. The patient was treated and recovered with no recurrence of her illness.

Comments on the Patient: This case represents a situation where the clinical history was limited; many of the appropriate questions that should have been asked were not considered until the diagnosis of malaria failed to match the additional questions that were asked during some followup discussions with the patient.

Specific questions that need to be asked for this type of patient presentation:

When requests for malarial smears are received in the laboratory, some patient history information should be made available to the laboratorian. This information should include the following questions, particularly if the patient has a relevant travel history:

  1. Where has the patient been, and what was the date of return to the United States? Where do you live?
  2. Has malaria ever been diagnosed in the patient before? If so, what species was identified? (possibility of a relapse infection).
  3. What medication (prophylaxis or otherwise) has the patient received, and how often? When was the last dose taken?
  4. Has the patient ever received a blood transfusion? Is there a possibility of other needle transmission (drug abuse)?
  5. When was the blood specimen drawn, and was the patient symptomatic at the time? Is there any evidence of a fever periodicity?

If the patient does not have a relevant travel history, then additional questions must be addressed, particularly if the patient has a positive blood film with organisms that resemble Plasmodium spp.

  1. Does she have a history of travel to: Long Island, especially Montauk Point; Hawaii, Alaska, and Florida; Nantucket Island, Martha's Vineyard, and Shelter Island or nearby areas; California, Washington, Georgia?  What about travel to Europe? These are areas where human babesiosis has been acquired via tick bites.
  2. Has the patient been splenectomized? Based on her medical history, this was not the case. However, in splenectomized individuals, severe illness can occur, leading to death.

Comments on the Images: The Babesia ring forms mimic those of Plasmodium falciparum; thus the mistaken diagnosis of "malaria." It is important to review additional slides for some comparative differences and comments.


There are a number of rings in the image on the left, including the typical "Maltese" Cross formation with four ring forms. The image on the right is a repeat of the one above. Note the three small rings that are seen outside of the RBC; this is very unusual for a case of malaria, but can be seen in blood films in which Babesia spp. are present.


These three images show typical Plasmodium falciparum rings; note that they tend to be more consistent in shape than those seen in a case of babesiosis. In these images one can see multiple rings/cell, but often, only two rings/cell are seen. Also, note the "headphone" appearance of the rings; no rings are seen outside of the RBCs.


  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Rogers, W.O. 2011. Plasmodium and Babesia In: Versalovic, J., K.C. Carroll, Funke, G., J.H. Jorgensen, M.L. Landry, and D.W. Warnock (eds). Manual of Clinical Microbiology, 10th ed, vol 2, ASM Press, Washington, D.C.