Vector composition, abundance, biting patterns and malaria transmission intensity in Madang, Papua New Guinea: assessment after 7 years of an LLIN-based malaria control programme.

BACKGROUND: 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. 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. METHODS: All-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. RESULTS: Five 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. CONCLUSION: The 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.

Species abundance, composition, and nocturnal activity of female Anopheles (Diptera: Culicidae) in malaria-endemic villages of Papua New Guinea: assessment with barrier screen sampling.

BACKGROUND: Community composition of Anopheles mosquitoes, and their host-seeking and peridomestic behaviour, are important factors affecting malaria transmission. In this study, barrier screen sampling was used to investigate species composition, abundance, and nocturnal activity of Anopheles populations in villages of Papua New Guinea. METHODS: Mosquitoes were sampled from 6 pm to 6 am in five villages from 2012 to 2016. The barrier screens were positioned between the village houses and the perimeter of villages where cultivated and wild vegetation ("the bush") grew thickly. Female Anopheles that rested on either village or bush side of the barrier screens, as they commuted into and out of the villages, were captured. Similarity in species composition among villages was assessed. Mosquitoes captured on village and bush sides of the barrier screens were sorted by feeding status and by hour of collection, and their numbers were compared using negative binomial generalized linear models. RESULTS: Females of seven Anopheles species were present in the sample. Species richness ranged from four to six species per village, but relative abundance was highly uneven within and between villages, and community composition was similar for two pairs of villages and highly dissimilar in a fifth. For most Anopheles populations, more unfed than blood-fed mosquitoes were collected from the barrier screens. More blood-fed mosquitoes were found on the side of the barrier screens facing the village and relatively more unfed ones on the bush side, suggesting commuting behaviour of unfed host-seeking females into the villages from nearby bush and commuting of blood-fed females away from villages towards the bush. For most populations, the majority of host-seeking mosquitoes arrived in the village before midnight when people were active and unprotected from the mosquitoes by bed nets. CONCLUSION: The uneven distribution of Anopheles species among villages, with each site dominated by different species, even among nearby villages, emphasizes the importance of vector heterogeneity in local malaria transmission and control. Yet, for most species, nocturnal activity patterns of village entry and host seeking predominantly occurred before midnight indicating common behaviours across species and populations relative to human risk of exposure to Anopheles bites.

Use of anthropophilic culicid-based xenosurveillance as a proxy for Plasmodium vivax malaria burden and transmission hotspots identification.

Vector-borne diseases account for more than 17% of all infectious diseases, causing more than one million deaths annually. Malaria remains one of the most important public health problems worldwide. These vectors are bloodsucking insects, which can transmit disease-producing microorganisms during a blood meal. The contact of culicids with human populations living in malaria-endemic areas suggests that the identification of Plasmodium genetic material in the blood present in the gut of these mosquitoes may be possible. The process of assessing the blood meal for the presence of pathogens is termed 'xenosurveillance'. In view of this, the present work investigated the relationship between the frequency with which Plasmodium DNA is found in culicids and the frequency with which individuals are found to be carrying malaria parasites. A cross-sectional study was performed in a peri-urban area of Manaus, in the Western Brazilian Amazon, by simultaneously collecting human blood samples and trapping culicids from households. A total of 875 individuals were included in the study and a total of 13,374mosquito specimens were captured. Malaria prevalence in the study area was 7.7%. The frequency of households with at least one culicid specimen carrying Plasmodium DNA was 6.4%. Plasmodium infection incidence was significantly related to whether any Plasmodium positive blood-fed culicid was found in the same household [IRR 3.49 (CI95% 1.38-8.84); p = 0.008] and for indoor-collected culicids [IRR 4.07 (CI95%1.25-13.24); p = 0.020]. Furthermore, the number of infected people in the house at the time of mosquito collection was related to whether there were any positive blood-fed culicid mosquitoes in that household for collection methods combined [IRR 4.48 (CI95%2.22-9.05); p<0.001] or only for indoor-collected culicids [IRR 4.88 (CI95%2.01-11.82); p<0.001]. Our results suggest that xenosurveillance can be used in endemic tropical regions in order to estimate the malaria burden and identify transmission foci in areas where Plasmodium vivax is predominant.

A comparative study of a flow-cytometry-based assessment of in vitro Plasmodium falciparum drug sensitivity.

BACKGROUND: Recently developed Sybr Green-based in vitro Plasmodium falciparum drug sensitivity assays provide an attractive alternative to current manual and automated methods. The present study evaluated flow cytometry measurement of DNA staining with Sybr Green in comparison with the P. falciparum lactate dehydrogenase assay, the tritiated hypoxanthine incorporation assay, a previously described Sybr Green based plate reader assay and light microscopy. METHODS: All assays were set up in standardized format in 96-well plates. The 50% inhibitory concentrations (IC50) of chloroquine, mefloquine and dihydroartemisinin against the laboratory adapted P. falciparum strains 3D7, E8B, W2mef and Dd2 were determined using each method. RESULTS: The resolution achieved by flow cytometry allowed quantification of the increase in individual cell DNA content after an incubation period of only 24 h. Regression, and Bland and Altman analyses showed that the IC50 values determined using the flow cytometry assay after 24 h agreed well with those obtained using the hypoxanthine incorporation assay, the P. falciparum lactate dehydrogenase assay, the Sybr Green plate reader assay and light microscopy. However the values obtained with the flow cytometry assay after 48 h of incubation differed significantly from those obtained with the hypoxanthine incorporation assay, and the P. falciparum lactate dehydrogenase assay at low IC50 values, but agreed well with the Sybr Green plate reader assay and light microscopy. CONCLUSIONS: Although flow cytometric equipment is expensive, the necessary reagents are inexpensive, the procedure is simple and rapid, and the cell volume required is minimal. This should allow field studies using fingerprick sample volumes.