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Presentation of Quiz #47

A patient is a 6 month-old male, living within the United States, with multiple medical problems who was admitted to the hospital with the complaint of irregular recurrent fever of 3 months duration. He had received several blood transfusions over a period of several months, primarily for a low hemoglobin. He became feverish with a temperature of 102 - 104 F, which did not respond to antimicrobials. His fever appeared to peak about every four days. Just prior to admission, the fever began to occur daily. On examination of both thick and thin blood films prepared from blood collected in EDTA tube (purple top), the following images were seen. Please comment on the identification of the organisms seen.

Both the thick and thin blood films were stained using a blood stain.

After the appropriate diagnosis was made, additional blood was drawn with the following images seen in the thick and thin blood films. Please comment on the objects seen below.

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Answer and Discussion of Quiz #47

The images presented after the first blood specimen was drawn represent Plasmodium malariae developing schizonts in the thick blood film (left) and a mature schizont (containing merozoites) in the thin blood film (right). Note the small size of the infected RBC (typical of P. malariae). The number of merozoites in the mature schizont is always a clue to the species identification; in this case there appear to be about 8 merozoites.  MALARIA (FIVE) SPECIES; MALARIA (FIVE) SPECIES IMAGES

After the second blood draw, the images represent developing trophozoites, which are spread across the infected RBC as "band" forms (again P. malariae). This configuration is not always seen, but is very suggestive of P. malariae.

Key characteristics of P. malariae include the following:

  1. 72-hour cycle
  2. Tends to infect old cells
  3. Small to normal sized RBCs
  4. No Schüffner's dots present; small dots (Ziemann's dots) may be present, but they are not considered true stippling.
  5. Thick ring, and heavy chromatin dot
  6. "Band" form trophozoites are often present.
  7. Mature schizont contains about 8 merozoites, often arranged around the remaining clump of malarial pigment. This configuration of the merozoites is often called the "daisy" form.

Comments on the Patient:

Since this patient had received several blood transfusions, it is logical to assume one of the transfusions was the source of the infection. Individuals can harbor P. malariae in the blood for many years at very low levels of parasitemia; these individuals are asymptomatic. Often, even with a complete blood donor history, the possibility of malaria infection with this organism is not suspected. Individuals have been known to harbor this parasite up to 42 years. In spite of severe splenomegaly and splenectomy, after therapy with chloroquine, the patient was considered cured and remained asymptomatic.

Comments on Diagnostic Methods:

It is very important to realize that a single set of thick and thin blood films can be negative, although the patient may be positive. In this case, both thick and thin blood films were positive. A second draw was taken to examine the thick and thin blood films for additional stages and/or evidence of a mixed infection. Venipunctures were performed for both blood draws, with the recommended EDTA anticoagulant in the lavender (purple) top tube. It is important that the slides be prepared as quickly as possible after the blood draw, in order to prevent organism distortion and possible loss that can occur if the blood is allowed to stand for a period of hours prior to slide preparation. Remember, every request for malaria blood films should always be considered a STAT request and the laboratory coverage should be 24 hours/day, 7 days/week.  STAT TESTING

Examination of the thin blood film is relatively simple when the parasitemia is high, as in this slide. However, a returning traveler with his or her first malaria infection may experience the typical clinical symptoms of high fever, chills, myalgia, and headache with a much lower parasitemia. Also, these patients may present to the emergency room with vague symptoms that do not represent the typical textbook description; they may have malaise, a steady low-grade fever, and may even have diarrhea. These low levels of parasitemia are often impossible to detect using thin blood film examination only. For this reason, the key to successful detection of malaria parasites in the peripheral blood is the examination of thick and thin blood films from every patient suspected of having malaria (or any patient from whom blood is submitted to the laboratory for blood film examination).  MALARIA PARASITEMIA METHOD; MALARIA PARASITEMIA INTERPRETATION

Thick films allow a larger amount of blood to be examined, which increases the possibility of detecting light infections. Species identification from the thick film examination, particularly in the case of malaria, may be difficult for those with little experience examining thick blood films. The morphological characteristics of blood parasites are best seen in thin films, particularly the relationship between the size of the infected RBC and those that are uninfected. However, in cases with a low parasitemia, the identification to the species level may have to be accomplished by thick film examination.

The accurate examination of thick and thin blood films and identification of parasites depends on the use of absolutely clean, grease-free slides for preparation of all blood films. Old (unscratched) slides should be cleaned first in detergent and then with 70% ethyl alcohol; new slides should also be cleaned with alcohol before use.

Blood films are usually prepared when the patient is admitted; in instances in which malaria is a possible diagnosis, after the first set of negative smears, samples should be taken at intervals of 6 to 8 h for at least 3 successive days, particularly if P. falciparumhas not been excluded as a diagnosis.


  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Garcia, L.S. (ed.). 2010. Clinical Microbiology Procedures Handbook, 3rd Ed., vol. 1, 2, and 3. ASM Press, Washington, D.C.
  3. Isenberg, H. D. (ed.). 2004. Clinical Microbiology Procedures Handbook, 2nd Ed, vol. 1, 2 and 3. ASM Press, Washington, D.C.
  4. Isenberg, H. D. (ed.). 1995. Essential Procedures for Clinical Microbiology, ASM Press, Washington, D.C.
  5. National Committee for Clinical Laboratory Standards. 2000. Laboratory Diagnosis of Blood-borne Parasitic Diseases. Approved Guideline, M15-A. National Committee for Clinical Laboratory Standards, Villanova, Pa.
  6. Wilcox, A., 1960. Manual for the Microscopical Diagnosis of Malaria in Man. U.S. Department of Health, Education, and Welfare, Washington, D.C.