Prevalence and seroprevalence of Plasmodium infection in Myanmar reveals highly heterogeneous transmission and a large hidden reservoir of infection

Abstract

Malaria incidence in Myanmar has significantly reduced over recent years, however, completeness and timeliness of incidence data remain a challenge. The first ever nationwide malaria infection and seroprevalence survey was conducted in Myanmar in 2015 to better understand malaria epidemiology and highlight gaps in Annual Parasite Index (API) data. The survey was a cross-sectional two-stage stratified cluster-randomised household survey conducted from July-October 2015. Blood samples were collected from household members for ultra-sensitive PCR and serology testing for P. falciparum and P. vivax. Data was gathered on demography and a priori risk factors of participants. Data was analysed nationally and within each of four domains defined by API data. Prevalence and seroprevalence of malaria were 0.74% and 16.01% nationwide, respectively. Prevalent infection was primarily asymptomatic P. vivax, while P. falciparum was predominant in serology. There was large heterogeneity between villages and by domain. At the township level, API showed moderate correlation with P. falciparum seroprevalence. Risk factors for infection included socioeconomic status, domain, and household ownership of nets. Three K13 P. falciparum mutants were found in highly prevalent villages. There results highlight high heterogeneity of both P. falciparum and P. vivax transmission between villages, accentuated by a large hidden reservoir of asymptomatic P. vivax infection not captured by incidence data, and representing challenges for malaria elimination. Village-level surveillance and stratification to guide interventions to suit local context and targeting of transmission foci with evidence of drug resistance would aid elimination efforts.

Fig 1. Map of Myanmar showing location of the four sampling domains.

Domain 1: API>5; Domain 2: API 1–5; Domain 3: API<1; Domain 4: non-state areas.

Fig 2

usPCR prevalence (top) and seroprevalence (bottom) of P. falciparum, P. vivax and mixed infection in Myanmar nationwide and within each of four domains. Mixed infection not included in separate P. falciparum/P. vivax prevalence figures.

Fig 3. Normalised age-stratified antibody responses to P. falciparum antigens A] PfAMA, B] PfMSP-1, and P. vivax antigens C] PvAMA, D] PvMSP-1.

Horizontal red lines represent antigen-specific cut-off valus.

Fig 4

Maps showing prevalence (left column) and seroprevalence (right column) of P. falciparum (top row) and P. vivax (bottom row) in each sampled cluster. Each dot represents one cluster (one village) coloured according to level of prevalence or seroprevalence. Black dots indicate clusters where no positive PCR or serology cases were identified.

Fig 5. Forest plots showing Adjusted Odds Ratios (AOR) for risk factors related to being positive by usPCR or by serology across the whole study sample (n = 13,716 for PCR and 11,653 for serology).

A] Prevalence of P. falciparum, B] PCR prevalence of P. vivax, C] Seroprevalence of P. falciparum, D] Seroprevalence of P. vivax. Factors shown are those that remained significant in multivariate logistic regression analyses (plus sex and age group).

Fig 6

Association of prevalence and seroprevalence with incidence data, aggregated by township and split by P. falciparum (top) and P. vivax (bottom).