Temporal Dynamics of Subclinical Malaria in Different Transmission Zones of Myanmar

Abstract

Countries in the Greater Mekong Subregion have committed to eliminate Plasmodium falciparum malaria by 2025. Subclinical malaria infections that can be detected by highly sensitive polymerase chain reaction (PCR) testing in asymptomatic individuals represent a potential impediment to this goal, although the extent to which these low-density infections contribute to transmission is unclear. To understand the temporal dynamics of subclinical malaria in this setting, a cohort of 2,705 participants from three epidemiologically distinct regions of Myanmar was screened for subclinical P. falciparum and P. vivax infection using ultrasensitive PCR (usPCR). Standard rapid diagnostic tests (RDTs) for P. falciparum were also performed. Individuals who tested positive for malaria by usPCR were followed for up to 12 weeks. Regression analysis was performed to estimate whether the baseline prevalence of infection and the count of repeated positive tests were associated with demographic, behavioral, and clinical factors. At enrollment, the prevalence of subclinical malaria infection measured by usPCR was 7.7% (1.5% P. falciparum monoinfection, 0.3% mixed P. falciparum and P. vivax, and 6.0% P. vivax monoinfection), while P. falciparum prevalence measured by RDT was just 0.2%. Prevalence varied by geography and was higher among older people and in those with outdoor exposure and travel. No difference was observed in either the prevalence or count of subclinical infection by time of year, indicating that even in low-endemicity areas, a reservoir of subclinical infection persists year-round. If low-density infections are shown to represent a significant source of transmission, identification of high-risk groups and locations may aid elimination efforts.

Serological surveillance on potential Plasmodium vivax exposure risk in a post-elimination setting

“…Population movement from transmission area to non-malaria-endemic areas can result in imported infections or corresponding increasing seroprevalence in these migrant population. Secondly, although ultrasensitive detection methods could detect subclinical malaria infections with low parasitemia, hidden indigenous transmission and asymptomatic infections might be existing ( Egger et al., 2022 ), which would be identified as seropositive using serological test. Third, as the unique biological characteristics of P. vivax with residual dormant stages in the liver and periodic relapses ( Adams and Mueller, 2017 ), population with historical P. vivax infection might lead to relapse and seropositivity over a prolonged period.…”