Presentation of Quiz #38

A patient is a 43 year-old male from Maine who has just returned from a trip to Africa. On his return, he was involved in a bicycle accident, and subsequently, required blood transfusions during treatment for internal injuries. Several weeks post-transfusion, he began complaining of fever, headache, and general malaise. The first blood specimens examined using automated instrumentation revealed nothing significant. He continued to have high fevers and severe headaches, and eventually several additional blood specimens were submitted to the microbiology laboratory for examination as thick and thin blood films. The following images were seen – please comment on the possible diagnosis.

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Answer and Discussion of Quiz #38

The images presented in Diagnostic Quiz #38 are the following:

Comments on the Patient:

The fact that the man lived in the northeast and had received a blood transfusion might suggest infection with Babesia spp. The bicycle accident and subsequent blood transfusions were certainly factors in the patient’s overall health status. However, the patient’s symptoms were caused by an infection with Plasmodium falciparum, an infection that he had acquired in Africa. Although the patient had taken prophylaxis for malaria, he had not taken the medication on a regular basis and did not continue to take the medication after returning to the United States. Because he had never had any contact with malaria before (immunologically naive), he began to have symptoms with a very low parasitemia (<0.01%) that was undetectable using automated instrumentation. By the time his symptoms became more severe (about two weeks), he had gametocytes in the peripheral blood, as well as numerous rings. By the time P. falciparum malaria was diagnosed, the man was severely ill.

Comments on P. falciparum Malaria:

P. falciparum tends to invade all ages of RBCs, and the proportion of infected cells may exceed 50%. Schizogony occurs in the internal organs (spleen, liver, bone marrow, etc.) rather than in the circulating blood. Ischemia caused by the plugging of vessels within these organs by masses of parasitized RBCs will produce various symptoms, depending on the organ involved. It has been suggested that a decrease in the ability of the RBCs to change shape when passing through capillaries or the splenic filter may lead to the plugging of the vessels.

Onset of a P. falciparum malaria attack occurs from 8 to 12 days after infection and is preceded by 3 to 4 days of vague symptoms such as aches, pains, headache, fatigue, anorexia, or nausea. The onset is characterized by fever, a more severe headache, and nausea and vomiting, with occasional severe epigastric pain. There may be only a feeling of chilliness at the onset of fever. Periodicity of the cycle will not be established during the early stages, and the presumptive diagnosis may be totally unrelated to a possible malaria infection. If the fever does develop a synchronous cycle, it is usually a cycle of somewhat less than 48 h. True relapses from the liver do not occur, and after a year, recrudescences are rare.

Severe or fatal complications of P. falciparum malaria can occur at any time during the infection and are related to the plugging of vessels in the internal organs, the symptoms depending on the organ(s) involved. The severity of the complications in a malaria infection may not correlate with the parasitemia seen in the peripheral blood, particularly in P. falciparum infections.

Disseminated intravascular coagulation is a rare complication of malaria associated with high parasite burden, pulmonary edema, rapidly developing anemia, and cerebral and renal complications. Vascular endothelial damage from endotoxins and bound parasitized blood cells may lead to clot formation in small vessels. Cerebral malaria is most often seen in P. falciparum malaria, although it can occur in the other types as well. If the onset is gradual, the patient may become disoriented or violent or may develop severe headaches and pass into coma. Some patients, even those who exhibit no prior symptoms, may suddenly become comatose. Physical signs of central nervous system involvement are quite variable, and there is no real correlation between the severity of the symptoms and the peripheral blood parasitemia.

Although malaria is no longer endemic within the United States, this infection is considered to be life threatening, and laboratory requests for blood smear examination and organism identification should be treated as “STAT” requests. Malaria is usually associated with patients having a history of travel within an area where malaria is endemic, although other routes of infection are well documented. During 2002 (most recent data available), >45% of the malaria cases reported in the United States were caused by P. falciparum, the most pathogenic of the four species infecting humans.

Frequently, for a number of different reasons, organism recovery and subsequent identification may be more difficult than the textbooks imply. It is very important that this fact be recognized, particularly when one is dealing with a possibly fatal infection with P. falciparum. 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:

Often the diagnosis of malaria is considered, and a single blood specimen is submitted to the laboratory for examination; however, single films or specimens cannot be relied upon to exclude the diagnosis, especially when partial prophylactic medication or therapy is used. Partial use of antimalarial agents may be responsible for reducing the numbers of organisms within the peripheral blood, thus leading to a blood smear that contains few organisms, which then reflects a low parasitemia when in fact serious disease is present. Patients with a relapse case or an early primary case may also have few organisms in the blood smear.

Comments on Diagnosis:

It is recommended that both thick and thin blood films be prepared upon admission of the patient, and at least 200 to 300 oil immersion fields should be examined on the thin film before a negative report is issued. Since one set of negative films will not rule out malaria, additional blood specimens should be examined over a 36-h time frame. Although Giemsa stain is recommended for all parasitic blood work, the organisms can also be seen with use of other blood stains such as Wright’s stain and the rapid blood stains. Blood collected with use of EDTA anticoagulant is acceptable; however, if the blood remains in the tube for any length of time, true stippling may not be visible within the infected RBCs (P. vivax, as an example). Also, when using anticoagulants, it is important to remember that the proper ratio between blood and anticoagulant is necessary for good organism morphology. If the blood stands for >2 hrs prior to blood film preparation, organism distortion is very likely, with the morphology beginning to mimic that seen with P. malariae. If the blood stands >6 hrs prior to blood film preparation, organisms will disintegrate.

Malaria is one of the few parasitic infections considered to be immediately life threatening, and a patient with the diagnosis of P. falciparum malaria should be considered a medical emergency because the disease can be rapidly fatal. Any laboratory providing the expertise to identify malarial parasites should do so on a 24-h basis, 7 days/week.

Plasmodium falciparum (malignant tertian malaria)

NOTE: Without the appliqué form, Schüffner’s dots, multiple rings/cell, and other developing stages, differentiation among the species can be very difficult. It is obvious that the early rings of all four species can mimic one another very easily. Remember: One set of negative blood films cannot rule out a malaria infection, and this information must be conveyed to the physician.

Comments on Reporting Parasitemia:

It is important to report the level of parasitemia when blood films are reviewed and found to be positive for malaria parasites. Because of the potential for drug resistance in some of the Plasmodium species, particularly P. falciparum, it is important that every positive smear be assessed and the parasitemia reported using the exact, same method on followup specimens as on the initial specimen. This allows the parasitemia to be followed after therapy has been initiated. In cases where the patient is hospitalized, monitoring should be performed at 24, 48, and 72 hours after initiating therapy. Generally, the parasitemia will drop very quickly within the first 24 hours; however, in cases of drug resistance, the level may appear to drop, then begin to rise again or the level may not decrease, but actually increase over time. 

Malaria Parasitemia Method

Malaria Parasitemia Interpretation

MALARIA (FIVE) SPECIES

MALARIA (FIVE) SPECIES IMAGES

Specific methods and additional information can be found in the first reference.

Additional Reading: