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

BACKGROUND: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Long-lasting insecticidal nets remain efficacious after five years of use in Papua New Guinea.

Long-lasting insecticide-treated nets (LLINs) have been distributed throughout Papua New Guinea since 2004 as part of the country's malaria control program. This study aimed to evaluate the efficacy of these used bednets over time and with respect to the various household factors related to their use in order to enable the National Department of Health to maximize on the benefits of LLINs. In 2008 and early 2009, used LLINs (0-9 years old) were collected in various villages in Papua New Guinea as part of the Global Fund to Fight AIDS, Tuberculosis and Malaria (GFATM)-supported National Malaria Control Program and data were collected on net usage. A subset of the nets were tested for residual insecticide content. Net efficacy was measured by the rate of knockdown of Anopheles farauti s.s. following exposure to LLINs using the World Health Organization cone bioassay. Optimal effectiveness (> 95% knockdown 1 hour post exposure) was observed in 92% of the LLINs. A slight reduction in efficacy was observed after two years of household use and there was a significant relationship between the number of years in use and percent knockdown (p < 0.001) as well as deltamethrin concentration (p < 0.001). Washing of nets was not associated with a reduction in deltamethrin concentration, but drying them in the sun was (p = 0.008). The physical conditions of these nets also degraded over time with a significant increase in the number of large holes after 5 years (p = 0.02). These findings are in support of the current recommendation to replace LLINs after five years of use, and demonstrate that proper net care can extend the length of efficacy.

Ownership and usage of mosquito nets after four years of large-scale free distribution in Papua New Guinea.

BACKGROUND: Papua New Guinea (PNG) is a highly malaria endemic country in the South-West Pacific with a population of approximately 6.6 million (2009). In 2004, the country intensified its malaria control activities with support from the Global Fund. With the aim of achieving 80% ownership and usage, a country-wide campaign distributed two million free long-lasting insecticide-treated nets (LLINs). METHODS: In order to evaluate outcomes of the campaign against programme targets, a country-wide household survey based on stratified multi-stage random sampling was carried out in 17 of the 20 provinces after the campaign in 2008/09. In addition, a before-after assessment was carried out in six purposively selected sentinel sites. A structured questionnaire was administered to the heads of sampled households to elicit net ownership and usage information. RESULTS: After the campaign, 64.6% of households owned a LLIN, 80.1% any type of mosquito net. Overall usage by household members amounted to 32.5% for LLINs and 44.3% for nets in general. Amongst children under five years, 39.5% used a LLIN and 51.8% any type of net, whereas 41.3% of pregnant women used a LLIN and 56.1% any net. Accessibility of villages was the key determinant of net ownership, while usage was mainly determined by ownership. Most (99.5%) of the household members who did not sleep under a net did not have access to a (unused) net in their household. In the sentinel sites, LLIN ownership increased from 9.4% to 88.7%, ownership of any net from 52.7% to 94.1%. Usage of LLINs increased from 5.5% to 55.1%, usage of any net from 37.3% to 66.7%. Among children under five years, usage of LLINs and of nets in general increased from 8.2% to 67.0% and from 44.6% to 76.1%, respectively (all p ≤ 0.001). CONCLUSIONS: While a single round of free distribution of LLINs significantly increased net ownership, an insufficient number of nets coupled with a heterogeneous distribution led to overall low usage rates. Programme targets were missed mainly as a result of the distribution mechanism itself and operational constraints in this very challenging setting.