Diagnosing P. simium zoonotic malaria infection in the Rio de Janeiro Atlantic forest, Brazil.

Malaria remains a pressing health challenge in Brazil, primarily due to Plasmodium vivax. Most cases occur in the Amazon; however, outbreaks in the Atlantic Forest involving P. simium, a non-human primate parasite closely related to P. vivax, have posed challenges for control efforts. This study aimed to differentiate P. vivax infections from those of P. simium acquired within the Atlantic Forest. Ninety-nine samples initially identified as P. vivax-positive, comprising 95 from humans and four from non-human primates, were analyzed. The results using a refined molecular tool revealed that 93% of human samples from the Atlantic Forest were P. simium, corroborating the substantial rate of zoonotic transmission in this region. The remaining samples from the Amazon and nearby countries were confirmed as P. vivax, including five Atlantic Forest cases linked to travel to endemic areas, suggesting imported or relapsed cases. The study emphasizes the importance of molecular tools in accurately distinguishing malaria parasite species, especially in identifying the origins of the parasites infecting humans. This understanding is crucial for grasping malaria transmission dynamics, ensuring accurate epidemiological surveillance, and preventing zoonotic transmission. It also supports targeted control strategies and effective public health interventions.