Abstract
BackgroundA malaria control programme based on distribution of long-lasting insecticidal bed nets (LLINs) and artemisinin combination therapy began in Papua New Guinea in 2009. After implementation of the programme, substantial reductions in vector abundance and malaria transmission intensity occurred. The research reported here investigated whether these reductions remained after seven years of sustained effort.MethodsAll-night (18:00 to 06:00) mosquito collections were conducted using human landing catches and barrier screen methods in four villages of Madang Province between September 2016 and March 2017. Anopheles species identification and sporozoite infection with Plasmodium vivax and Plasmodium falciparum were determined with molecular methods. Vector composition was expressed as the relative proportion of different species in villages, and vector abundance was quantified as the number of mosquitoes per barrier screen-night and per person-night. Transmission intensity was quantified as the number of sporozoite-infective vector bites per person-night.ResultsFive Anopheles species were present, but vector composition varied greatly among villages. Anopheles koliensis, a strongly anthropophilic species was the most prevalent in Bulal, Matukar and Wasab villages, constituting 63.7–73.8% of all Anopheles, but in Megiar Anopheles farauti was the most prevalent species (97.6%). Vector abundance varied among villages (ranging from 2.8 to 72.3 Anopheles per screen-night and 2.2–31.1 Anopheles per person-night), and spatially within villages. Malaria transmission intensity varied among the villages, with values ranging from 0.03 to 0.5 infective Anopheles bites per person-night. Most (54.1–75.1%) of the Anopheles bites occurred outdoors, with a substantial proportion (25.5–50.8%) occurring before 22:00.ConclusionThe estimates of vector abundance and transmission intensity in the current study were comparable to or higher than estimates in the same villages in 2010–2012, indicating impeded programme effectiveness. Outdoor and early biting behaviours of vectors are some of the likely explanatory factors. Heterogeneity in vector composition, abundance and distribution among and within villages challenge malaria control programmes and must be considered when planning them.
Highlights
A malaria control programme based on distribution of long-lasting insecticidal bed nets (LLINs) and artemisinin combination therapy began in Papua New Guinea in 2009
A considerable proportion (25.5–50.8%) of the vectors in all the villages encountered human hosts in the evening. These results show that a high proportion of vectors evaded LLINs by encountering humans outdoors and in the evening and may be contributing to high vector abundance and malaria transmission in these villages
The results of this study indicate that vector abundance and malaria transmission in the coastal areas is Madang and likely in other parts of Papua New Guinea (PNG) as well may have increased in recent years after a period of decline after the roll-out of the LLIN campaign in 2009
Summary
A malaria control programme based on distribution of long-lasting insecticidal bed nets (LLINs) and artemisinin combination therapy began in Papua New Guinea in 2009. Of the 13 closely related species comprising this group, Anopheles farauti sensu stricto (s.s.), An. koliensis and An. punctulatus s.s. are the primary vectors [5,6,7,8,9,10,11,12]. Two species outside this group, An. bancroftii and An. longirostris, are often found in sympatry with members of the punctulatus group. An. punctulatus s.s. tends to be more abundant than An. koliensis in hilly areas whereas in lowland areas An. koliensis tends to be more abundant An. punctulatus s.s. [15]
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