Nightly Biting Cycles of Anopheles Species in Rural Northwestern Burkina Faso

Abstract

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.

Fig. 1.

Study villages in the Kossi region in Northwestern Burkina Faso in which human landing catches were performed.

Fig. 2.

Sampling scheme within a study village (Cissé). Each study village featured three zones with three sample points each. Each sample location consisted of one outdoor (blue) and one indoor (red) capture post. Satellite image: Google Maps/ Digital Globe September 2012.

Fig. 3.

Nightly outdoor (blue) and indoor (red) biting cycles of Anopheles species within the survey region for the period August to November 2012. Bars show the average HBRs per person per hour and 95 % confidence intervals. Values are averaged over the six study villages.

Fig. 4.

Monthly variation in HBRs per person per hour of An. gambiae s.l. from August to November 2012. Month fixed effects in our negative binomial regression are significantly different from zero (P value < 0.01) and a Likelihood Ratio test rejects the hypothesis that all month fixed effects equal zero (χ² = 69.63; P value < 0.01).

Fig. 5.

Weekly HBRs of female Anopheles s.l. outdoors (blue) and indoors (red), August through November 2012. Averages of HBRs per person per hour were calculated by week. The dotted line indicates averaged cumulated weekly precipitations for the study region. Precipitation data was obtained from NASA’s Tropical Rainfall Measuring Mission (TRMM/Giovanni).