Changes in malaria burden and transmission in sentinel sites after the roll-out of long-lasting insecticidal nets in Papua New Guinea

Abstract

BackgroundPapua New Guinea exhibits a complex malaria epidemiology due to diversity in malaria parasites, mosquito vectors, human hosts, and their natural environment. Heterogeneities in transmission and burden of malaria at various scales are likely to affect the success of malaria control interventions, and vice-versa. This manuscript assesses changes in malaria prevalence, incidence and transmission in sentinel sites following the first national distribution of long-lasting insecticidal nets (LLINs).MethodsBefore and after the distribution of LLINs, data collection in six purposively selected sentinel sites included clinical surveillance in the local health facility, household surveys and entomological surveys. Not all activities were carried out in all sites. Mosquitoes were collected by human landing catches. Diagnosis of malaria infection in humans was done by rapid diagnostic test, light microscopy and PCR for species confirmation.ResultsFollowing the roll-out of LLINs, the average monthly malaria incidence rate dropped from 13/1,000 population to 2/1,000 (incidence rate ratio = 0.12; 95 % CI: 0.09–0.17; P < 0.001). The average population prevalence of malaria decreased from 15.7 % pre-LLIN to 4.8 % post-LLIN (adjusted odds ratio = 0.26; 95 % CI: 0.20–0.33; P < 0.001). In general, reductions in incidence and prevalence were more pronounced in infections with P. falciparum than with P. vivax. Additional morbidity indicators (anaemia, splenomegaly, self-reported fever) showed a decreasing trend in most sites. Mean Anopheles man biting rates decreased from 83 bites/person/night pre-LLIN to 31 post-LLIN (P = 0.008). Anopheles species composition differed between sites but everywhere diversity was lower post-LLIN. In two sites, post-LLIN P. vivax infections in anophelines had decreased but P. falciparum infections had increased despite the opposite observation in humans.ConclusionsLLIN distribution had distinct effects on P. falciparum and P. vivax. Higher resilience of P. vivax may be attributed to relapses from hypnozoites and other biological characteristics favouring the transmission of P. vivax. The effect on vector species composition varied by location which is likely to impact on the effectiveness of LLINs. In-depth and longer-term epidemiological and entomological investigations are required to understand when and where residual transmission occurs and whether observed changes are sustained.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1635-x) contains supplementary material, which is available to authorized users.

Higher Complexity of Infection and Genetic Diversity of Plasmodium vivax Than Plasmodium falciparum Across All Malaria Transmission Zones of Papua New Guinea

“…12 Genetic diversity was high for both P. vivax and P. falciparum throughout PNG. Diversity of the P. vivax markers PvMS16 and Pvmsp1F3 was similar to diversity reported from other endemic settings 42,75,77,78 and similar to previous reports from the north coast of PNG. 42,44,79 Despite high variability in complexity of infection, P. falciparum genetic diversity based on the Pfmsp2 marker was also similar among different geographic areas.…”

“…51,76 A study from Indonesia showed a positive correlation between the rate of polyclonal infections and annual parasite incidence indicating that polyclonality might provide a complementary gauge of local transmission intensity. 33 In the case of P. falciparum in PNG, this measure correlates well with prevalence, however in this and other studies, 77,78 P. vivax infections had a high proportion of multiple clones even in areas with decreasing transmission, so polyclonality may be less effective for determining the transmission of the latter species.…”

Mosquito behaviour change after distribution of bednets results in decreased protection against malaria exposure

“…The methods used in this household survey have already been described [19]. Briefly, a finger prick blood sample was taken from consenting individuals aged >5 months old from 30–35 randomly selected households in each village.…”

Increasingly inbred and fragmented populations ofPlasmodium vivaxwith declining transmission

“…Historically, the Southwest Pacific region, in particular PNG and Solomon Islands, has endured some of the highest P. vivax transmission anywhere in the world (Gething et al 2012;Gething et al 2011;Organisation 2013). This region has a natural, gradual decline in malaria endemicity from west to east with high transmission in PNG, moderate-to-high in Solomon Islands and low transmission in Vanuatu (Gething et al 2012) that has been accentuated by recent control efforts (Hetzel et al 2016;Koepfli et al 2015a;. Our previously published population genetic data from PNG and Solomon Islands , combined with new samples from ongoing studies within Solomon Islands and Vanuatu, presents a unique opportunity to understand the population genetics of P. vivax in context with declining transmission.…”