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



Before 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.



Following 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.



LLIN 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.
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea. manuel.hetzel@unibas.ch.|Swiss Tropical and Public Health Institute, Basel, Switzerland. manuel.hetzel@unibas.ch.|University of Basel, Basel, Switzerland. manuel.hetzel@unibas.ch.
Manuel W
MW
Hetzel
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea.|Case Western Reserve University, Cleveland, OH, USA.|Present address: Liverpool School of Tropical Medicine, Liverpool, UK.
Lisa J
LJ
Reimer
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea.
Gibson
G
Gideon
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea.
Gussy
G
Koimbu
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea.|Population Health and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Vic, Australia.|Department of Medical Biology, University of Melbourne, Parkville, Vic, Australia.|Present address: European Public Health Microbiology (EUPHEM) training programme, European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.|Present address: Statens Serum Institut, Copenhagen, Denmark.
Céline
C
Barnadas
National Department of Health, Waigani, Papua New Guinea.
Leo
L
Makita
Papua New Guinea Institute of Medical Research, Goroka and Madang, Papua New Guinea.
Peter M
PM
Siba
Population Health and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Vic, Australia.|Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain.
Ivo
I
Mueller
D006801:Humans; D015994:Incidence; D057148:Insecticide-Treated Bednets; D007306:Insecticides / Q000494:pharmacology*; D008288:Malaria / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission*; D008297:Male; D009032:Mosquito Control / Q000379:methods; D010219:Papua New Guinea / Q000453:epidemiology; D015995:Prevalence; D018571:Sentinel Surveillance; D013997:Time Factors
D007306:Insecticides
Anopheles; Anopheles punctulatus; Insecticide treated nets; Malaria; Papua New Guinea