A-Z Index × Submit A-Z Index × Submit A-Z Index Search Dropdown × Submit Facebook Twitter LinkedIn Syndicate Emerging Infectious Disease journal ISSN: 1080-6059 Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
A large malaria outbreak caused by Plasmodium malariae parasites occurred in Khanh Hoa Province, Vietnam, in 2023. Since then, P. malariae parasites have persisted in the region alongside P. falciparum and P. vivax species, changing malaria patterns. Those findings reinforce the need for strengthened surveillance in the region.
Malaria, a mosquitoborne disease caused by Plasmodium species parasites, poses a global health burden. Malaria incidence and mortality rates have markedly decreased in Vietnam over the past few decades ( 1 ); however, the Central Highlands region is a malaria hotspot, accounting for >90% of malaria cases in the country. P. falciparum and P. vivax are the major parasite species responsible for malaria in the region ( 2 , 3 ), whereas P. malariae cases historically have been rare. However, a large P. malariae outbreak occurred in Khanh Hoa Province, Vietnam, in 2023 ( 4 ), and the epidemic has persisted, further complicating malaria patterns and control efforts in the province. We investigated the epidemiologic characteristics of malaria cases and Plasmodium species in Khanh Hoa Province, Vietnam, during January 2023–December 2025, to characterize the epidemic in the province.
We retrieved epidemiologic data on malaria cases from the Electronic Case-based Disease Surveillance—Malaria and Mosquito-borne Diseases Reporting System, a national electronic reporting system in Vietnam. We performed statistical analyses by using negative binomial regression followed by Tukey-adjusted pairwise comparisons. We calculated incidence rate ratios (IRRs) and 95% CIs and considered p<0.05 statistically significant.
Figure 1 . Malaria incidences from a study of emergence of Plasmodium malariae and co-endemicity of 3 Plasmodium species parasites, Khanh Hoa Province, Vietnam, 2023–2025. A) Monthly incidences by ...
During the 3 years studied, we identified a total of 493 symptomatic malaria cases in the province that were confirmed by standard microscopic examination and molecular methods targeting parasite 18S rRNA ( 5 ). Before 2023, the region had few reported malaria cases annually, just 3 in 2021 and 12 in 2022. However, cases increased sharply in 2023 and peaked in July 2023, when P. malariae emerged, gradually declining thereafter ( Figure 1 , panel A).
Annual malaria cases exhibited typical summer peaks and totaled 209 in 2023, 199 in 2024, and 85 in 2025. During those years, most malaria cases were caused by P. malariae (44.8%; n = 221) and P. falciparum (36.9%; n = 182), whereas P. vivax (17.9%; n = 88) and mixed species (0.4%; n = 2) infections occurred less frequently. Three Plasmodium species were co-endemic in 2023 and 2024, but only P. malariae and P. falciparum were prevalent in 2025. Of the 8 districts and cities in Khanh Hoa Province, Khanh Vinh district had the most (93.1%; n = 459) cumulative malaria cases, whereas the other areas had <15 cases each, fluctuating from 0 in Cam Ranh to 14 in Dien Khanh ( Figure 1 , panel B). P. malariae is reportedly common in mixed co-infections with other species, particularly P. falciparum ( 6 ). However, molecular methods confirmed that all P.…