The epidemiology of Plasmodium falciparum and Plasmodium vivax in East Sepik Province, Papua New Guinea, pre- and post-implementation of national malaria control efforts

Abstract

Background: In the past decade, national malaria control efforts in Papua New Guinea (PNG) have received renewed support, facilitating nationwide distribution of free long-lasting insecticidal nets (LLINs), as well as improvements in access to parasite-confirmed diagnosis and effective artemisinin-combination therapy in 2011-2012.

Methods: To study the effects of these intensified control efforts on the epidemiology and transmission of Plasmodium falciparum and Plasmodium vivax infections and investigate risk factors at the individual and household level, two cross-sectional surveys were conducted in the East Sepik Province of PNG; one in 2005, before the scale-up of national campaigns and one in late 2012-early 2013, after 2 rounds of LLIN distribution (2008 and 2011-2012). Differences between studies were investigated using Chi square (χ²), Fischer's exact tests and Student's t-test. Multivariable logistic regression models were built to investigate factors associated with infection at the individual and household level.

Results: The prevalence of P. falciparum and P. vivax in surveyed communities decreased from 55% (2005) to 9% (2013) and 36% to 6%, respectively. The mean multiplicity of infection (MOI) decreased from 1.8 to 1.6 for P. falciparum (p = 0.08) and from 2.2 to 1.4 for P. vivax (p < 0.001). Alongside these reductions, a shift towards a more uniform distribution of infections and illness across age groups was observed but there was greater heterogeneity across the study area and within the study villages. Microscopy positive infections and clinical cases in the household were associated with high rate infection households (> 50% of household members with Plasmodium infection).

Conclusion: After the scale-up of malaria control interventions in PNG between 2008 and 2012, there was a substantial reduction in P. falciparum and P. vivax infection rates in the studies villages in East Sepik Province. Understanding the extent of local heterogeneity in malaria transmission and the driving factors is critical to identify and implement targeted control strategies to ensure the ongoing success of malaria control in PNG and inform the development of tools required to achieve elimination. In household-based interventions, diagnostics with a sensitivity similar to (expert) microscopy could be used to identify and target high rate households.

Keywords: Epidemiology; LLINs; Malaria; Malaria control; Plasmodium falciparum; Plasmodium vivax; Spatial heterogeneity.

Fig. 1

Age distributions of malaria prevalence. Top 4 panels: P. falciparum or P. vivax prevalence by LDR-FMA or qPCR, prevalence by light microscopy and proportion symptomatic P. falciparum or P. vivax infections. Bottom panels: prevalence of P. malariae and P. ovale. Error bars represent 95% confidence intervals. Left 2005 survey, right 2012/13 survey

Fig. 2

Map of study area with village-specific malaria prevalence in 2005 and 2013. Red bars indicate P. falciparum prevalence and blue bars P. vivax prevalence. Villages with a blue symbol (pentagon) were included in both surveys, villages with a green symbol were included in the 2005 survey only and villages with a purple symbol were included in the 2012–2013 survey only

Fig. 3

Proportion of single and multiple clone P. falciparum and P. vivax infections. aP. falciparum infection by age group and catchment area; bP. vivax infection by age group and catchment area; Left 2005, right 2012/13. Red/grey: P. falciparum, Blue/grey: P. vivax. MOI multiplicity of infection