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, underscoring the potential of the mine company to enhance malaria control in Lihir. Measures focusing on at-risk groups, including vector-control and transmission interruption methods, could be used to reduce malaria burden, especially outside the MIZ.

AUTHOR SUMMARY

The Lihir Islands of Papua New Guinea host a mining operation on Aniolam, the main island, which implements specific vector control strategies in the mine-impacted zone (MIZ); whereas the remaining areas rely solely on distribution of long-lasting insecticidal-treated nets (LLIN). Our study compared transmission dynamics in the different geographic areas and demonstrated lower malaria incidence, prevalence, Anopheles density and biting intensities in the MIZ. Living outside the MIZ on Aniolam and on Malie Island was associated with a higher risk of infection, with transmission metrics rarely seen outside high burden countries in sub-Saharan Africa. Besides the geographic area, other risk factors for infection included younger age, cohabiting with infected individuals, and living in traditional housing; while the use of LLINs was not associated with a reduction of infection risk.

Our results highlight the need for tailored strategies based on local transmission patterns and could be beneficial for ongoing initiatives aimed at malaria control and elimination. In Lihir, there is an opportunity to invest and improve the collaboration between the mine company and public health authorities. Such a public-private partnership could enhance control efforts, including expansion of diagnostics and treatments, the vector control program and community education beyond the MIZ.