About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

CPT Codes

Quizzes, General

Quizzes, Histology

Quizzes, Blood

Review Tests


Information Tables

Organism Index (A-Z)

Back To Home Page ->

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.

Scroll Down for Answer and Discussion





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.


Each Quiz has a two section format: the first section will present the Quiz topic and the second section will provide a discussion of the answer and/or various options in response to the Quiz situation presented to the user. In some situations, there may be more than one correct response.

The content within this site is made possible through the extensive contribution of Lynne S. Garcia, M.S., MT(ASCP), CLS(NCA), BLM(AAB), F(AAM), Director, Consultantation and Training Services (Diagnostic Medical Parasitology and Health Care Administration). For additional information, she can be contacted at LynneGarcia2@verizon.net.

Reference: Garcia, L.S. 2015. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.

Quiz 1 Quiz 2 Quiz 3
Quiz 4 Quiz 5 Quiz 6
Quiz 7 Quiz 8 Quiz 9
Quiz 10 Quiz 11 Quiz 12
Quiz 13 Quiz 14 Quiz 15
Quiz 16 Quiz 17 Quiz 18
Quiz 19 Quiz 20 Quiz 21
Quiz 22 Quiz 23 Quiz 24
Quiz 25 Quiz 26 Quiz 27
Quiz 28 Quiz 29 Quiz 30
Quiz 31 Quiz 32 Quiz 33
Quiz 34 Quiz 35 Quiz 36
Quiz 37 Quiz 38 Quiz 39
Quiz 40 Quiz 41 Quiz 42
Quiz 43 Quiz 44 Quiz 45
Quiz 46 Quiz 47 Quiz 48
Quiz 49 Quiz 50 Quiz 51
Quiz 52 Quiz 53 Quiz 54
Quiz 55 Quiz 56 Quiz 57
Quiz 58 Quiz 59 Quiz 60
Quiz 61 Quiz 62 Quiz 63
Quiz 64 Quiz 65 Quiz 66
Quiz 67 Quiz 68 Quiz 69
Quiz 70 Quiz 71 Quiz 72
Quiz 73 Quiz 74 Quiz 75
Quiz 76 Quiz 77 Quiz 78
Quiz 79 Quiz 80 Quiz 81
Quiz 82 Quiz 83 Quiz 84
Quiz 85 Quiz 86 Quiz 87
Quiz 88 Quiz 89