Is biological larviciding against malaria a starting point for integrated multi-disease control? Observations from a cluster randomized trial in rural Burkina Faso.

OBJECTIVES: To evaluate the impact of anti-malaria biological larviciding with Bacillus thuringiensis israelensis on non-primary target mosquito species in a rural African setting. METHODS: A total of 127 villages were distributed in three study arms, each with different larviciding options in public spaces: i) no treatment, ii) full or iii) guided intervention. Geographically close villages were grouped in clusters to avoid contamination between treated and untreated villages. Adult mosquitoes were captured in light traps inside and outside houses during the rainy seasons of a baseline and an intervention year. After enumeration, a negative binomial regression was used to determine the reductions achieved in the different mosquito species through larviciding. RESULTS: Malaria larviciding interventions showed only limited or no impact against Culex mosquitoes; by contrast, reductions of up to 34% were achieved against Aedes when all detected breeding sites were treated. Culex mosquitoes were captured in high abundance in semi-urban settings while more Aedes were found in rural villages. CONCLUSIONS: Future malaria larviciding programs should consider expanding onto the breeding habitats of other disease vectors, such as Aedes and Culex and evaluate their potential impact. Since the major cost components of such interventions are labor and transport, other disease vectors could be targeted at little additional cost.

Nightly Biting Cycles of Anopheles Species in Rural Northwestern Burkina Faso.

The biting behavior of anophelines is an important determinant of malaria transmission. Understanding the local vector host-seeking behavior, its outdoor/ indoor biting preference, and nocturnal biting periods is essential for effectively applying and improving vector control methods, such as Long Lasting Insecticidal Nets (LLINs) and personal protective measures. To better understand the biting and host-seeking patterns of Anopheles mosquitoes in Northwestern Burkina Faso, we performed biweekly Human Landing Catches (HLC) in six villages during the period of highest mosquito abundance and malaria transmission. We applied a negative binomial regression framework to statistically analyze the host-seeking activities of Anopheles species and test for differences across hours, months, and villages, as well as for differences between indoor and outdoor capture points. Anopheles gambiae s.l. was identified as the main malaria vector in this region, representing about 90% of the total anopheline population. Biting activity was significantly different across hours and showed a peaked plateau between 2000 and 0200 hours. Differences in the pattern of biting cycles were observed between the early and late rainy season. This study shows that anopheline biting activity in Northwest Burkina Faso is high throughout the night, at indoor and outdoor posts alike. Consequently, bed nets alone may not provide sufficient protection against early biting anophelines and should be complemented with additional strategies such as indoor residual spraying (IRS) and larval source management (LSM) to meet the WHO's ambitious goals that are reflected in the global technical malaria strategy for 2030.

High olfactory sensitivity for dimethyl sulphide in harbour seals.

Productive areas are patchily distributed at sea and represent important feeding grounds for many marine organisms. Although pinnipeds are known to travel on direct routes and return regularly to particular feeding sites, the environmental information seals use to perform this navigation is as yet unknown. As atmospheric dimethyl sulphide (DMS) has been demonstrated to be a reliable indicator for profitable foraging areas, we tested seals for their ability to smell DMS at concentrations typical for the marine environment. Using a go/no-go response paradigm we determined the DMS detection threshold in two harbour seals (Phoca vitulina vitulina). DMS stimuli from 8.05 x 108 to 8 pmol (DMS)m(-3)(air) were tested against a control stimulus using a custom-made olfactometer. DMS-thresholds determined for both seals (20 and 13 pmol m(-3)) indicate that seals can detect ambient concentrations associated with high primary productivity, e.g. in the North Atlantic. Thus, seals possess an extraordinarily high olfactory sensitivity for DMS, which could provide a sensory basis for identifying or orienting to profitable foraging grounds.