The rising proportion of Plasmodium ovale spp. in imported malaria in Anhui Province, China: A retrospective propensity score-matched case-control study

Abstract

No autochthonous malaria cases have been reported in Anhui Province, China, since 2014. However, imported malaria remains a significant public health concern. Moreover, the proportion of reported imported malaria cases attributed to Plasmodium ovale spp. (P. ovale spp.) has risen to unexpectedly high levels. The factors contributing to this increase and its potential impact on the healthcare system remain unknown. A retrospective case-control study utilizing surveillance data from 2012 to 2023 was conducted to explore these issues. By comparing individuals infected with P. ovale spp. to those with P. falciparum and employing propensity score matching, the research assessed epidemiological and clinical data. Results indicated that the proportion of cases from P. ovale spp. increased significantly (χ² = 9.388, P = 0.002), reaching 50.00 % in 2021. Differences between groups were noted in previous infection history (χ² = 8.358, P = 0.004), overseas stay duration (χ² = 7.856, P = 0.049), and onset timing (W = 2991.000, P < 0.001). P. ovale spp. cases had longer intervals from symptom onset to first medical visit and diagnosis than P. falciparum cases. Initial diagnosis and species identification were less accurate for P. ovale spp. (62.99 % and 30.52 %) compared to P. falciparum (74.03 % and 93.51 %). The increase in infections can be attributed to repeated exposure, which heightens the risk of contracting P. ovale spp. during extended stays in endemic regions, as well as to insufficient treatment of hepatic hypnozoites. It underscores the need for Anhui Province's healthcare facilities to enhance their diagnostic and treatment capacities for P. ovale spp., particularly through more sensitive detection techniques.