Infectivity of Symptomatic Malaria Patients to Anopheles farauti Colony Mosquitoes in Papua New Guinea

Plasmodium transmission from humans to mosquitoes is an understudied bottleneck in the transmission of malaria. Direct membrane feeding assays (DMFA) allow detailed malaria transmission studies from humans to mosquitoes. Especially for Plasmodium vivax, which cannot be cultured long-term under laboratory conditions, implementation of DMFAs requires proximity to P. vivax endemic areas. In this study, we investigated the infectivity of symptomatic Plasmodium infections to Anopheles farauti colony mosquitoes in Papua New Guinea (PNG). A total of 182 DMFAs were performed with venous blood collected from rapid diagnostic test (RDT) positive symptomatic malaria patients and subsequently analysed by light microscopy and quantitative real time polymerase chain reaction (qPCR). DMFAs resulted in mosquito infections in 20.9% (38/182) of cases. By light microscopy and qPCR, 10 – 11% of P. falciparum and 32 – 44% of P. vivax positive individuals infected An. farauti. Fifty-eight percent of P. vivax and 15% of P. falciparum gametocytaemic infections infected An farauti.

Optimization of the feeding rate of Anopheles farauti s.s. colony mosquitoes in direct membrane feeding assays

Background Direct membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes. Mosquito feeding rates in these artificial systems require optimization, as there are a number of factors that potentially influence the feeding rates and there are no standardized methods that apply to all anopheline species. Methods A range of parameters prior to and during direct membrane feeding (DMF) were evaluated for their impact on Anopheles farauti sensu stricto feeding rates, including the starving conditions and duration of starving prior to feeding, membrane type, DMF exposure time, mosquito age, feeding in the light versus the dark, blood volume, mosquito density and temperature of water bath. Results The average successful DMFA feeding rate for An. farauti s.s. colony mosquitoes increased from 50 to 85% when assay parameters were varied. Overnight starvation and Baudruche membrane yielded the highest feeding rates but rates were also affected by blood volume in the feeder and the mosquito density in the feeding cups. Availability of water during the pre-feed starvation period did not significantly impact feeding rates, nor did the exposure duration to blood in membrane feeders, the age of mosquitoes (3, 5 and 7 days post-emergence), feeding in the light versus the dark, or the temperature (34 °C, 38 °C, 42 °C and 46 °C) of the water bath. Conclusion Optimal feeding conditions in An. farauti s.s. DMFA were to offer 50 female mosquitoes in a cup (with a total surface area of ~ 340 cm2 with 1 mosquito/6.8 cm2) that were starved overnight 350–500 µL of blood (collected in heparin-coated Vacutainer tubes) per feeder in feeders with a surface area ~ 5 cm2 (with a maximum capacity of 1.5 mL of blood) via a Baudruche membrane, for at least 10–20 min. Graphical Abstract

Optimization of the Feeding rate of Anopheles Farauti Colony Mosquitoes in Direct Membrane Feeding Assays

Background: Direct membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes. Mosquito feeding rates in these artificial systems require optimization as there are a number of factors that potentially influence the feeding rates and there are no standardized methods that apply to all Anopheline species.Methods: A range of parameters prior to and during direct membrane feeding (DMF) were evaluated for their impact on Anopheles farauti feeding rates; including the starving conditions and duration of starving prior to feeding, membrane type, DMF exposure time, mosquito age, illumination level, blood volume, mosquito density and temperature of water bath. Results: The average successful DMFA feeding rate for An. farauti colony mosquitoes increased from 50 % to 85 % when assay parameters were varied. Overnight starvation and Baudruche membrane yielded the highest feeding rates but rates were also affected by blood volume in the feeder and the mosquito density in the feeding cups. Availability of water during the pre-feed starvation period did not significantly impact feeding rates, nor did the exposure duration to blood in membrane feeders nor, the age of mosquitoes (3, 5 and 7 days post-emergence), illumination during feeding or the temperature (34 °C, 38 °C, 42 °C and 46 °C) of the water bath.Conclusion: Optimal feeding conditions in An. farauti DMFA were to offer 50 female mosquitoes in a cup (with a total surface area of ~340 cm2 with 1 mosquito / 6.8 cm2) that were starved overnight 350-500 µL of blood (collected in heparin coated vacutainers) per feeder in feeders with a surface area ~5 cm2 (with a maximum capacity of 1.5 mL of blood) via a Baudruche membrane, for at least 10-20 min.

Infectivity of symptomatic malaria patients to Anopheles farauti colony mosquitoes in Papua New Guinea

Despite being a weak point in their life cycle, transmission of Plasmodium parasites from humans to mosquitoes is an understudied field of research. Direct membrane feeding assays (DMFA) are an important tool, allowing detailed mechanistic malaria transmission studies from humans to mosquitoes. Especially for Plasmodium vivax, which cannot be cultured long-term under laboratory conditions, implementation of DMFAs requires proximity to P. vivax endemic areas. In the present study, we investigated the infectivity of symptomatic Plasmodium infections to Anopheles farauti colony mosquitoes in Papua New Guinea (PNG), a country with one of the highest rates of Plasmodium vivax in the world. A total of 182 DMFAs were performed with venous blood collected from symptomatic malaria patients positive by rapid diagnostic test (RDT). DMFAs resulted in mosquito infection in 20.9% (38/182) of cases. The parasite species in the blood feeds were determined retrospectively by expert light microscopy and quantitative real-time qPCR. Based on light microscopy, 9.2% of P. falciparum and 42% of P. vivax human infections resulted in mosquito infections. Infections containing gametocytes detected by microscopy led to mosquito infections in 58.8% of P. vivax and 8.7% of P. falciparum infections. Based on qPCR, 10% of P. falciparum and 43.6% of P. vivax lead to a successful mosquito infection. Venous blood samples from symptomatic P. vivax patients were more infectious to An. farauti mosquitoes in DMFAs compared to P. falciparum infected patients. The capacity to perform DMFAs in a high-burden P. vivax setting creates a unique opportunity to address critical gaps in our understanding of P. vivax human-tomosquito transmission.

Defining the larval habitat: abiotic and biotic parameters associated with Anopheles farauti productivity

Background In the Solomon Island, the dominant malaria vector, Anopheles farauti, is highly anthropophagic and increasingly exophilic and early biting. While long-lasting insecticide-treated nets remain effective against An. farauti, supplemental vector control strategies will be needed to achieve malaria elimination. Presently, the only World Health Organization recommended supplemental vector control strategy is larval source management (LSM). Effective targeted larval source management requires understanding the associations between abiotic, chemical and biological parameters of larval habitats with the presence or density of vector larvae. Methods Potential and actual An. farauti larval habitats were characterized for presence and density of larvae and associated abiotic, chemical and biological parameters. Results A third of all sampled potential habitats harboured An. farauti larvae with 80% of An. farauti positive habitats being in three habitat classifications (swamps/lagoons, transient pools and man-made holes). Large swamps were the most abundant positive habitats surveyed (43% of all An. farauti positive habitats). Habitats with An. farauti larvae were significantly associated with abiotic (pH, nitrate, ammonia and phosphate concentrations and elevated temperature) and biotic (predators) parameters. Conclusion Large swamps and lagoons are the largest and most abundant An. farauti habitats in the Solomon Islands. Positive habitats were more frequently associated with the presence of predators (vertebrates and invertebrates) and higher water temperatures. Cohabitation with predators is indicative of a complex habitat ecosystem and raises questions about the potential of biological control as an effective control strategy. Increased presence of An. farauti with higher water temperature suggests a potential explanation for the coastal distribution of this species which is not found inland at elevated altitudes where temperatures would be cooler.

Unique fine scale village spatial-temporal distributions of Anopheles farauti differ by physiological state and sex

Background The ecology of many mosquitoes, including Anopheles farauti, the dominant malaria vector in the southwest Pacific including the Solomon Islands, remains inadequately understood. Studies to map fine scale vector distributions are biased when trapping techniques use lures that will influence the natural movements of mosquitoes by attracting them to traps. However, passive collection methods allow the detailed natural distributions of vector populations by sex and physiological states to be revealed. Methods The barrier screen, a passive mosquito collection method along with human landing catches were used to record An. farauti distributions over time and space in two Solomon Island villages from May 2016 to July 2017. Results Temporal and spatial distributions of over 15,000 mosquitoes, including males as well as unfed, host seeking, blood-fed, non-blood fed and gravid females were mapped. These spatial and temporal patterns varied by species, sex and physiological state. Sugar-fed An. farauti were mostly collected between 10–20 m away from houses with peak activity from 18:00 to 19:00 h. Male An. farauti were mostly collected greater than 20 m from houses with peak activity from 19:00 to 20:00 h. Conclusions Anopheles farauti subpopulations, as defined by physiological state and sex, are heterogeneously distributed in Solomon Island villages. Understanding the basis for these observed heterogeneities will lead to more accurate surveillance of mosquitoes and will enable spatial targeting of interventions for greater efficiency and effectiveness of vector control.

Pengaruh Faktor Klimatik Terhadap Kepadatan Nyamuk Anopheles farauti di Ekosistem Pantai dan Rawa Provinsi Papua

Infectious vectors are generally sensitive to environmental change, including climatic factor. Climate may affect the ability of vector in transmitting the disease. The purpose of this study was to determine the effect of climatic factors on density of Anopheles farauti Laveran in coastal and marsh ecosystems. The mosquito was collected by using human landing collection method. The climatic data recorded during the research were air suhue, wind velocity and humidity, while the rainfall rate data was obtained from the Provincial office of Meteorology and Geophysics Agency Suhue of Papua Province. The result showed that Anopheles farauti was constantly found during the study period as air suhue, humidity, rainfall and wind velocity fluctuated. This result suggest that during the data collection climatic factors did not significantly affect the presence and density of Anopheles farauti. Key words: climatic factor; mosquito density; coastal; swamp; Anopheles farauti.

Human exposure to Anopheles farauti bites in the Solomon Islands is not associated with IgG antibody response to the gSG6 salivary protein of Anopheles gambiae

Background Mosquito saliva elicits immune responses in humans following mosquito blood feeding. Detection of human antibodies recognizing the Anopheles gambiae salivary gland protein 6 (gSG6) or the gSG6-P1 peptide in residents of Africa, South America and Southeast Asia suggested the potential for these antibodies to serve as a universal marker to estimate human biting rates. Validating the utility of this approach requires concurrent comparisons of anopheline biting rates with antibodies to the gSG6 protein to determine the sensitivity and specificity of the assay for monitoring changes in vector populations. This study investigated whether seroprevalence of anti-gSG6 antibodies in humans reflected the relative exposure to Anopheles farauti bites in the Solomon Islands as estimated from sympatric human landing catches. Methods Human biting rates by An. farauti were estimated by landing catches at 10 sampling sites in each of 4 villages during the wet and dry seasons. Human serum samples from these same villages were also collected during the wet and dry seasons and analysed for antibody recognition of the gSG6 antigen by the Luminex xMAP© platform. Antibody titres and prevalence were compared to HLCs at the sampling sites nearest to participants’ residences for utility of anti-gSG6 antibodies to estimate human exposure to anopheline bites. Results In this study in the Solomon Islands only 11% of people had very high anti-gSG6 antibody titres, while other individuals did not recognize gSG6 despite nightly exposures of up to 190 bites by An. farauti. Despite clear spatial differences in the human biting rates within and among villages, associations between anti-gSG6 antibody titres and biting rates were not found. Conclusions Few studies to date have concurrently measured anopheline biting rates and the prevalence of human antibodies to gSG6. The lack of association between anti-gSG6 antibody titres and concurrently measured human biting rates suggests that the assay for human anti-gSG6 antibodies lacks sufficient sensitivity to be a biomarker of An. farauti exposure at an epidemiologically relevant scale. These findings imply that an improvement in the sensitivity of serology to monitor changes in anopheline biting exposure may require the use of saliva antigens from local anophelines, and this may be especially true for species more distantly related to the African malaria vector An. gambiae.

Keragaman Spesies Tersangka Vektor Filariasis Berdasarkan Tipe Habitat dan Ekosistem di Kabupaten Sarmi Provinsi Papua

Filariasis is one of the diseases that require a vector for the transmission process. Information on the determinants of filariasis transmission related to vectors is needed as a basis for control efforts. Further analysis of Vektora Research in 2015 was conducted in order to identify the diversity species of suspected filariasis vector and the environmental characteristics in Sarmi District of Papua Province. Data on mosquito catching, habitat type, and environment each ecosystem analyzed. Filariasis suspect vector species in Sarmi Regency Papua Province obtained were four genus with nine species. These vector/suspect filariasis vector were Anopheles farauti, An. koliensis, An. pediateniatus, An. punctulatus, An. tesselatus, An. subalbatus, Culex quinquefasciatus, Mansonia dives, and Ma. papuensis. Four specific habitat characteristics were found in the mosquito-data collecting sites: primary forest, secondary forest, shrubs, and grass/brown/grassland habitat. Anopheles farauti is a species found abundantly in all specific habitats. Based on the ecosystem, Cx. quinquefasciatus dominates the urban ecosystems of non-forest settlements and beaches near settlements, while An. farauti is found in forests settlements, remote forest settlements, non-remote forest settlements, distant coastal settlements, and beaches near settlements.