High Seasonal Variation in Entomologic Inoculation Rates in Eritrea, a Semi-Arid Region of Unstable Malaria in Africa

Abstract

Abstract. Entomologic studies were conducted in eight villages to investigate the patterns of malaria transmission in different ecologic zones in Eritrea. Mosquito collections were conducted for 24 months between September 1999 and January 2002. The biting rates of Anopheles arabiensis were highly seasonal, with activity concentrated in the wet season between June and October in the highlands and western lowlands, and between December and March in the coastal region. The biting rates in the western lowlands were twice as high as in the western escarpment and 20 times higher than in the coastal region. Sporozoite rates were not significantly different among villages. The risk of infection ranged from zero on the coast to 70.6 infective bites per year in the western lowlands. The number of days it would take for an individual to receive an infective bite from an infected An. arabiensis was variable among villages (range ‫ס‬ 2.8-203.1 days). The data revealed the presence of only one main malaria transmission period between July and October for the highlands and western lowlands. Peak inoculation rates were recorded in August and September (range ‫ס‬ 0.29-43.6 infective bits/person/month) at all sites over the two-year period. The annual entomologic inoculation rates (EIRs) varied greatly depending on year. The EIR profiles indicated that the risk of exposure to infected mosquitoes is highly heterogeneous and seasonal, with high inoculation rates during the rainy season, and with little or no transmission during the dry season. This study demonstrates the need to generate spatial and temporal data on transmission intensity on smaller scales to guide targeted control of malaria operations in semi-arid regions. Furthermore, EIR estimates derived in the present study provide a means of quantifying levels of exposure to infected mosquitoes in different regions of the country and could be important for evaluating the efficacy of vector control measures, since Eritrea has made significant steps in reducing the burden of malaria based on the Roll Back Malaria initiative of the World Health Organization.

Seasonality, Blood Feeding Behavior, and Transmission of Plasmodium Falciparum by Anopheles Arabiensis After an Extended Drought in Southern Zambia

“…arabiensis between two villages located in the same ecological zone in Eritrea. 37 Additionally, Mendis and others 5 reported a negative correlation between the EIR and the distance from breeding sites. Figure 1 illustrates the progression of the transmission season from the start of the rains in October 2005, to peak indoor-resting density of An.…”

“…arabiensis in different ecologic zones in Eritrea. 37 Finally, in Senegal, EIRs over four consecutive years ranged from 7 to 63 infective bites per person per year, with An. arabiensis responsible for 66% of transmission, An.…”

“…arabiensis density and malaria transmission intensity display similar patterns in relation to rainfall, as well as spatial and seasonal heterogeneity among sites. 37 Although Chidakwa and Lupata communities were separated by approximately 5 km, indoor-resting density, human biting rate, and malaria transmission by An. arabiensis were all much higher in Lupata than in Chidakwa.…”

Spatio-temporal variation in malaria transmission intensity in five agro-ecosystems in Mvomero district, Tanzania

“…There is a paucity of data on the impact of other agro-ecosystems on malaria transmission in Africa with only a few studies on malaria among communities in sugarcane plantations and those producing cotton and vegetables (Packard, 1986;Ijumba, 1997;Shililu et al, 2003;Dongus et al, 2009). Studies in Kenya have reported a high sporozoite rate for Anopheles gambiae suggesting a high malaria transmission level in the area and low but perennial malaria transmission intensity in sugarcane growing zone (Githeko et al, 1993).…”

Habitat Partitioning of Malaria Vectors in Nchelenge District, Zambia

“…Heterogeneity in malarial risk has implications for developing and targeting interventions because a single vector control measure such as indoor residual spraying (IRS) may successfully interrupt transmission in a low transmission setting, whereas multiple vector control measures such as IRS, long-lasting insecticide-treated nets (LLINs), larviciding, and/or larval habitat source reduction may be needed to have an impact in high transmission settings. [10][11][12][13][14][15][16][17][18][19][20][21] Therefore, it is necessary to identify and characterize malarial vectors at a local scale to inform successful control strategies.…”