When worlds collide: where and when anophelines and humans interact

Abstract

Malaria is a disease spread by mosquitoes and kills almost half a million people each year. While substantial gains have been made in combatting the disease, progress has stalled partly because of changes in mosquito behaviour, resistance to the insecticides in vector-control measures, drug resistance in the parasites, inadequate financing, a lack of political support as well as a host of other factors. These vector control measures have been successful since the 1990s in reducing malaria-related mortality; however, their efficacy is now waning. New tools are needed to complement the current vector control measures and combat outdoor biting; however, to develop and roll out new tools the behaviour of mosquitoes and humans needs to be better understood. Malaria is an endemic problem in the Solomon Islands and is primarily transmitted by Anopheles farauti. This study examined the behaviour of An. farauti mosquitoes and humans in the Solomon Island and Austrialia in four distinct components. The first component optimized the barrier screen method for mosquito collections. The second component used these optimized barrier screens to collect and record mosquito distributions in Solomon Island villages. The third component used movement diaries to record human behaviour in Solomon Island villagers. The fourth component explored serological techniques to measure mosquito-human interactions. The characteristics of barrier screens (colour, weight and design) and frequency of inspection were found to be important determinants affecting the collection efficiency. The results for optimising barrier screens indicated that black coloured, medium weighted shade cloth maximized An. farauti collection numbers including the first ever-recorded distributions of sugar-fed and male An. farauti. Anopheles farauti activity including biting in Solomon Islands villages peaked during 7-8pm. During this period of peak biting the majority of people were outdoors in the peri-domestic area, predominantly on the veranda or in adjacent kitchen buildings. Therefore, greatest interactions between the human and the malaria vector populations and therefore the most likely area of malaria transmission is in the early evening in this peri-domestic space. To better evaluate the risk associated with humans being bitten by An. farauti the serological response of humans to a mosquito salivary gland antigen was investigated in the Solomon Islands. While of insufficient sensitivity to guide programs when using the gSG6 antigen, this approach holds great promise and might be improved by using antigens from An. farauti in the assay. The peri-domestic space is identified as the area of greatest risk but also of greatest potential for vector control. The implications of this study indicate that the current vector control measure (insecticide treated nets) are not being used during the peak biting period. Focusing mosquito control on the peridomestic spaces in villages is needs as this is where the highest transmission potential exists. New tools targeting this area are needed to minimize interactions between the mosquito and human populations.