First report of severe Plasmodium vivax malaria with sub-microscopic co-infection of Plasmodium vivax and Plasmodium falciparum and their clinicodemographic correlates: a study from hyperendemic areas of Tripura

Malaria remains a major public health problem in Northeast India, particularly among the tribal population of Tripura, with increasing Plasmodium vivax ( Pv ) cases alongside predominant Plasmodium falciparum ( Pf ). This study assessed the demographic, clinical, haematological, and biochemical characteristics of severe malaria in hyperendemic areas of Tripura. A prospective hospital- and community-based study was conducted in three districts of Tripura from April 2023 to December 2024. Febrile individuals were screened through door-to-door village visits and primary health centres. Malaria was diagnosed using rapid diagnostic test, microscopy, and polymerase chain reaction, while severe malaria was classified according to World Health Organisation criteria. Among 1205 febrile tribal individuals screened, 465 malaria cases were identified. PCR detected the highest number of infections (422), including Pf (174), Pv (213), and mixed infections (35). Both RDT and microscopy showed high specificity (> 97%) but moderate sensitivity compared to PCR, missing many submicroscopic infections. Of 444 confirmed malaria cases (excluding 21 RDT positive but microscopy and PCR negative cases, which can be false positives due to persistence of antigens), 32 (7.2%) were severe, including Pf (17), Pv (11), and mixed infections (4). Severe malaria was associated with significantly lower haemoglobin, RBC count, haematocrit, platelet levels, and higher bilirubin. The high burden of submicroscopic malaria highlights limitations of conventional diagnostics. Pv emerged as an important cause of severe malaria in Northeast India, challenging its traditionally benign perception and emphasizing the need for integrated molecular surveillance and improved case management.