# Pediatric Mixed Plasmodium vivax–P. falciparum Infection with Disparate Parasitemias: Diagnostic and Surveillance Challenges

## TL;DR

A child with mixed malaria infections had very different parasite levels, highlighting the need for better diagnostic methods to avoid missed cases.

## Contribution

Demonstrates the importance of integrated diagnostic approaches to detect low-density P. falciparum in mixed infections with high P. vivax parasitemia.

## Key findings

- Mixed P. vivax–P. falciparum infection detected with 5500 parasites/µL P. vivax and 562 parasites/µL P. falciparum.
- Low-density P. falciparum was confirmed using combined microscopy and rapid diagnostic tests.
- Integrated diagnostics enabled appropriate treatment and highlighted limitations in conventional methods.

## Abstract

What are the main findings?
Mixed P. vivax–P. falciparum infection with marked parasitemia disparity (5500 parasites/µL P. vivax vs. 562 parasites/µL P. falciparum) detected using complementary microscopy and rapid diagnostic testing.Low-density P. falciparum coinfection confirmed through integrated diagnostic approach despite predominant P. vivax parasitemia, enabling species-appropriate antimalarial therapy.

Mixed P. vivax–P. falciparum infection with marked parasitemia disparity (5500 parasites/µL P. vivax vs. 562 parasites/µL P. falciparum) detected using complementary microscopy and rapid diagnostic testing.

Low-density P. falciparum coinfection confirmed through integrated diagnostic approach despite predominant P. vivax parasitemia, enabling species-appropriate antimalarial therapy.

What are the implications of the main findings?
Coinfections with markedly disparate parasitemias can be missed by conventional diagnostic methods, posing a risk of delayed or incomplete treatment.Comprehensive parasitological evaluation combining microscopy and rapid testing for pan-Plasmodium antigens and HRP2 is recommended in endemic areas to optimize outcomes and prevent severe malaria.

Coinfections with markedly disparate parasitemias can be missed by conventional diagnostic methods, posing a risk of delayed or incomplete treatment.

Comprehensive parasitological evaluation combining microscopy and rapid testing for pan-Plasmodium antigens and HRP2 is recommended in endemic areas to optimize outcomes and prevent severe malaria.

Background and Clinical Significance: Malaria remains a significant public health issue in Latin America, where Plasmodium vivax predominates but P. falciparum continues to circulate. Mixed-species infections are uncommon and can pose diagnostic challenges, particularly when parasite densities differ markedly, increasing the risk of underdetecting P. falciparum with conventional methods. Case report: We report a 9-year-old boy from an endemic area with a six-day febrile syndrome. Thick smear and peripheral blood film microscopy, complemented by rapid diagnostic tests for pan-Plasmodium and HRP2 antigens, confirmed a mixed infection with P. vivax (5500 parasites/µL) and P. falciparum (562 parasites/µL). The patient was hemodynamically stable, without severe malaria criteria, and laboratory values were within normal limits. Following confirmation of normal glucose-6-phosphate dehydrogenase activity, treatment with artemether–lumefantrine was initiated, followed by primaquine for hypnozoite eradication. Clinical evolution was favorable, with progressive defervescence, treatment tolerance, and documented parasite clearance. Conclusions: This case illustrates the risk of underestimating P. falciparum in mixed infections with disparate parasitemias and highlights the value of integrated diagnostic approaches in resource-limited endemic settings. It also underscores surveillance limitations that can misclassify mixed infections, potentially affecting epidemiological estimates and treatment strategies. Timely recognition and comprehensive diagnostic evaluation are essential to ensure appropriate antimalarial therapy, prevent complications, and inform public health interventions in regions where both species coexist.