Human and entomological determinants of malaria transmission in the Lihir Islands of Papua New Guinea: A cross-sectional study.

Background: The Lihir Islands of Papua New Guinea, located in an area with high burden of malaria and hosting a large mining operation, offer a unique opportunity to study transmission. There, we investigated human and vector factors influencing malaria transmission.

Methods: In 2019, a cross-sectional study was conducted on 2,914 individuals assessing malaria prevalence through rapid diagnostic tests (RDT), microscopy, and quantitative PCR (qPCR). A logistic regression analysis identified infection-associated factors. Anopheles species distribution, biting behaviours, and sporozoite carriage were assessed through human landing catches and larval surveys.

Results: Overall malaria prevalence (any species) was 3.6% by RDT, 4.5% by microscopy, and 15.0% by qPCR. P. vivax accounted for 37.1% of infections, P. falciparum for 34.6%, P. malariae for 3.0%, P. ovale 0.2%, and mixed infections for 24.5%. Prevalence (qPCR) varied across geographic areas, from 8.5% in the mine-impacted zone (MIZ) to 27.0% in the non-MIZ. Other factors independently associated with infection risk included cohabiting with an infected individual (aOR = 1.94, 95%CI: 1.56-2.42), and residing in traditional housing (aOR = 1.65, 95%CI: 1.21-2.25). Children had double the infection risk compared to adults, and the use of long-lasting insecticidal-treated nets did not decrease risk of infection. An. punctulatus was the major vector in one of the four geographical areas; while An. farauti was predominant in the rest of them, both with an early biting behaviour but with different biting intensities by geographical area. Entomological inoculation rates ranged from 26.9 (95%CI: 12.3-45.2) infective bites per person-year in the MIZ to 441.3 (95%CI: 315.7-572.1) in the non-MIZ.

Conclusions: Malaria transmission and infection was lower in the MIZ compared to other areas. Measures focusing on at-risk groups, including vector-control and transmission interruption methods, could be taken into account by the mine and the healthcare authorities to reduce malaria burden outside the MIZ.