An unusual presentation of Plasmodium spp. in peripheral blood smear

Abstract

A 7-year-old boy presented to the paediatric out-patient department with complaints of abdominal pain and fever for the past 6–7 days. On clinical examination, the child was febrile, with no evidence of hepatosplenomegaly. He was admitted for further evaluation and management and was started on intravenous ceftriaxone, paracetamol, pantoprazole, and Ringer lactate. Baseline laboratory investigations revealed normocytic, normochromic red blood cells with leukocytosis and a left shift, along with the presence of a few activated lymphocytes. The total leukocyte count was 16.3 × 10³/µL. Haemoglobin level was 9.2 g/dL, and the platelet count was markedly reduced at 35,000/µL. Inflammatory markers were significantly elevated, with a C-reactive protein (CRP) level of 144.8 mg/L. Liver function tests were within normal limits. Peripheral blood smear examination was performed in view of thrombocytopenia and persistent fever, which revealed unusual microscopic findings. These findings and their clinical significance are discussed below.

QUESTION

A 7-year-old boy presented to the pediatric outpatient department with a complaint of pain in the abdomen and fever for 6–7 days. On examination, he was febrile, temperature 99.9°F, heart rate at 98/min, respiratory rate − 24/min, and SpO₂ was 98%. Liver and spleen were not palpable. The patient was admitted and started on injection ceftriaxone, injection paracetamol, injection pantoprazole, and intravenous ringer lactate. Further investigations were done, his blood examination showed normocytic, normochromic red blood cells, and leukocytosis with shift to the left along with a few activated lymphocytes. White blood cell count was 16.3 × 10³/µl, hemoglobin was 9.2 g%, platelet count was low (35,000/µl) with raised C-reactive protein, 144.8 mg/l, and liver function test within normal range. Immunoglobulin M antibody (Salmonella Typhi) rapid test and Widal were also found negative. A peripheral blood smear was made and stained with Giemsa stain. The image of the microscopic finding is given below. Figures 1 and 2 illustrates the image of the parasite in Peripheral Blood Smear. Identify the structure.

Figure 1.

Peripheral Blood smear with a single crescent-shaped structure in the center

Figure 2.

Peripheral blood smear with multiple crescent-shaped structures

ANSWER TO PHOTO CHALLENGE

After thorough examination of the peripheral blood smear, the observed structures were identified as the ookinete stage of Plasmodium vivax, which can be clearly differentiated from the gametocyte stage of Plasmodium falciparum. P. falciparum gametocytes are characteristically banana-shaped (both microgametocytes and macrogametocytes) and are found in human peripheral blood, whereas P. vivax ookinetes are described as vermiform, elongated forms with pointed ends and are normally found in the midgut of mosquitoes.[1,2] Gametocytes are nonmotile and represent the infectious stage for mosquitoes, while ookinetes are motile forms that subsequently develop into oocysts within the mosquito.

Further examination of the peripheral smear revealed schizonts and gametocytes of P. vivax, with a parasitemia load of 0.12%. The presence of sickle-shaped forms raised suspicion of a possible co-infection with P. falciparum. However, the rapid diagnostic test (Standard Q by SD Biosensor) and polymerase chain reaction were positive only for P. vivax, and no other peripheral smear findings suggestive of P. falciparum were observed.

On further enquiry, it was noted that the blood sample had been collected 1 day earlier and the peripheral blood smear was prepared only the following morning, due to a delay in transport of the sample from the ward to the parasitology laboratory. Delayed sample transportation and delayed preparation of peripheral blood smears can lead to in vitro development of ookinetes within the blood sample itself. Laboratory temperature plays a crucial role in this process.[3,4] The ookinete stage is normally seen in mosquitoes; it is a motile, elongated, worm-like, or crescent-shaped form with an apical complex, formed from nonmotile rounded zygotes in the mosquito midgut.[5] In the present case, the laboratory temperature was maintained between 25°C and 30°C, which may have facilitated this transformation.

This case highlights the morphological alterations that can occur within a vacutainer or sample vial and demonstrates how delays between sample collection, transport, and processing can lead to unusual or misleading findings. Therefore, prompt transport of blood samples and immediate preparation of peripheral blood smears are essential in suspected cases of malaria to prevent misinterpretation and diagnostic confusion.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.