An active and targeted survey reveals asymptomatic malaria infections among high-risk populations in Mondulkiri, Cambodia

Abstract

Background Malaria is a mosquito-borne disease that is one of the most serious public health issues globally and a leading cause of mortality in many developing countries worldwide. Knowing the prevalence of both symptomatic and asymptomatic malaria on a subnational scale allows for the estimation of the burden of parasitaemia present in the transmission system, enabling targeting and tailoring of resources towards greater impact and better use of available capacity. This study aimed to determine the PCR-based point prevalence of malaria infection, by parasite species, among three high-risk populations in Mondulkiri province, Cambodia: forest rangers, forest dwellers, and forest goers. Methods A cross-sectional survey was performed during the transmission season in November and December 2021. Blood samples collected on filter paper from participants (n = 1301) from all target groups were screened for Plasmodium spp using PCR. Results Malaria prevalence among all study participants was 6.7% for any Plasmodium species. Malaria prevalence in the forest ranger group was 8.1%, was 6.8% in forest goers, and 6.4% in forest dwellers; all infections were asymptomatic. Plasmodium vivax was detected in all participant groups, while the few Plasmodium falciparum infections were found in goers and dwellers. 81% of all infections were due to P. vivax, 9% were due to P. falciparum, 3% due to Plasmodium cynomolgi, and the rest (7%) remained undefined. Gender was associated with malaria infection prevalence, with male participants having higher odds of malaria infection than female participants (OR = 1.69, 95% CI 1.08–2.64). Passively collected malaria incidence data from the Cambodian government were also investigated. Health facility-reported malaria cases, based on rapid diagnostic tests, for the period Jan-Dec 2021 were 521 Plasmodium vivax (0.89% prevalence), 34 P. falciparum (0.06%) and four P. falciparum + mixed (0.01%)—a total of 559 cases (0.95%) for all of Mondulkiri. Conclusion This reservoir of asymptomatic parasitaemia may be perpetuating low levels of transmission, and thus, new strategies are required to realize the goal of eliminating malaria in Cambodia by 2025.

A systematic review of the factors associated with malaria infection among forest rangers

“…A cross-sectional study in Cambodia revealed that females have a lower risk of contracting malaria than males (aOR = 0.61; 95% CI: 0.38–0.97, p = 0.04) [ 16 ]. Nonetheless, a study conducted in Kalimantan indicated no significant links between gender and malaria infection [ 17 ].…”

“…The report also revealed that individuals under 25 years old were more likely to be infected with malaria than their older counterparts (aOR = 2.526; 95% CI: 0.804–7939) [ 17 ]. Another study documented no remarkable association between age and malaria infection [ 16 ]. Ethnicity was also not a considerable factor in contracting malaria [ 16 , 17 ].…”

“…Another study documented no remarkable association between age and malaria infection [ 16 ]. Ethnicity was also not a considerable factor in contracting malaria [ 16 , 17 ].…”

“…Some participants also reported spending a few days to a week in forests once or twice a month [ 9 ]. Nonetheless, among the 1301 respondents in the study, the frequency of travelling outside the village and working in the forest recorded no significant association with malaria infection [ 16 ].…”

“…Age was not significantly associated with malaria infection [ 16 ]. Nonetheless, other study indicated that individuals aged under 25 had increased chances of being infected with malaria [ 17 ].…”