Nationwide insecticide resistance status and biting behaviour of malaria vector species in the Democratic Republic of Congo

Abstract

Background: Globally, the Democratic Republic of Congo (DRC) accounted for 9% of malaria cases and 10% of malaria deaths in 2015. As part of control efforts, more than 40 million long-lasting insecticidal nets (LLINs) were distributed between 2008 and 2013, resulting in 70% of households owning one or more LLINs in 2014. To optimize vector control efforts, it is critical to monitor vector behaviour and insecticide resistance trends. Entomological data was collected from eight sentinel sites throughout DRC between 2013 and 2016 in Kingasani, Mikalayi, Lodja, Kabondo, Katana, Kapolowe, Tshikaji and Kalemie. Mosquito species present, relative densities and biting times were monitored using human landing catches (HLC) conducted in eight houses, three times per year. HLC was conducted monthly in Lodja and Kapolowe during 2016 to assess seasonal dynamics. Laboratory data included resistance mechanism frequency and sporozoite rates. Insecticide susceptibility testing was conducted with commonly used insecticides including deltamethrin and permethrin. Synergist bioassays were conducted with PBO to determine the role of oxidases in permethrin resistance.

Results: In Lodja, monthly Anopheles gambiae s.l. biting rates were consistently high at > 10 bites/person/night indoors and outdoors. In Kapolowe, An. gambiae s.l. dominated during the rainy season, and Anopheles funestus s.l. during the dry season. In all sites, An. gambiae and An. funestus biting occurred mostly late at night. In Kapolowe, significant biting of both species started around 19:00, typically before householders use nets. Sporozoite rates were high, with a mean of 4.3% (95% CI 3.4-5.2) for An. gambiae and 3.3% (95% CI 1.3-5.3) for An. funestus. Anopheles gambiae were resistant to permethrin in six out of seven sites in 2016. In three sites, susceptibility to deltamethrin was observed despite high frequency permethrin resistance, indicating the presence of pyrethroid-specific resistance mechanisms. Pre-exposure to PBO increased absolute permethrin-associated mortality by 24%, indicating that resistance was partly due to metabolic mechanisms. The kdr-1014F mutation in An. gambiae was present at high frequency (> 70%) in three sites (Kabondo, Kingasani and Tshikaji), and lower frequency (< 20%) in two sites (Lodja and Kapolowe).

Conclusion: The finding of widespread resistance to permethrin in DRC is concerning and alternative insecticides should be evaluated.

Fig. 1

Map of Democratic Republic of the Congo indicating ecological classification and the location of eight sentinel sites for entomological monitoring

Fig. 2

Frequency of the Vgsc-1014F mutation in Anopheles gambiae s.l. was at high frequency in Kabondo, Tshikaji and Kingasani but mostly wild type in Lodja. A sub-sample of An. gambiae s.l. were analysed following WHO susceptibility tests in 2014

Fig. 3

Molecular species identification using SINE 200 PCR showed mixed An. gambiae and An. coluzzii populations in Lodja but predominantly An. gambiae elsewhere. A sub-sample of mosquito samples were analysed collected in 2015 by HLC

Fig. 4

Year-round high An. gambiae biting rates in Lodja (Sankuru) compared with seasonal peaks of An. gambiae biting during the rainy season and An. funestus during the dry season in Kapolowe (Haut Katanga). Monthly biting rate in 2016 from HLC collections (8 houses/month) from the following locations: a indoors, Lodja (Sankuru). b Outdoors, Lodja (Sankuru). c Indoors, Kapolowe (Haut Katanga). d Outdoors, Kapolowe (Haut Katanga)

Fig. 5

Monthly rainfall > 100 mm for 10 months (Aug–May) and warm monthly mean temperature (24–25.5 °C) in Lodja (Sankuru) provided year-round favourable conditions for An. gambiae s.l. Mean monthly rainfall and temperature between 1991 and 2015 for Lodja (Sankuru). The dataset was produced by the Climatic Research Unit (CRU) of University of East Anglia (UEA), UK

Fig. 6

The rainy season lasted 5 months with > 100 mm rainfall (Nov–Mar) in Kapolowe (Haut Katanga) with more seasonal variation in temperature (18–25 °C) than Lodja. Mean monthly rainfall and temperature between 1991 and 2015 for Kapolowe (Haut Katanga). The dataset was produced by the Climatic Research Unit (CRU) of University of East Anglia (UEA), UK

Fig. 7

Biting times of An. gambiae s.l. in six sentinel sites across DRC. a Kabondo, Tshopo province (2015–16), n = 1671 indoors, 1075 outdoors. b Kingasani, Kinshasa (2015–16), n = 356 indoors, 455 outdoors. c Lodja, Sankuru province (2016), n = 1870 indoors, 2878 outdoors. d Kapolowe, Haut Katanga province (2016), n = 1219 indoors, 1483 outdoors. e Katana, Sud Kivu province (2015–16), n = 58 indoors, 54 outdoors. f Kalemie, Tanganyika province (2015–16), n = 187 indoors, 127 outdoors. *R² values are presented to demonstrate the goodness of fit of the data points to the regression curve

Fig. 8

Biting times of An. funestus s.l. in three sentinel sites in DRC. a Mikalayi, Lulua province (2015–16), n = 493 indoors, 503 outdoors. b Lodja, Sankuru province (2016), n = 320 indoors, 200 outdoors. c Kapolowe, Haut Katanga province (2016), n = 1400 indoors, 1536 outdoors. *R² values are presented to demonstrate the goodness of fit of the data points to the regression curve