Estimating the annual entomological inoculation rate for Plasmodium falciparum transmitted by Anopheles gambiae s.l. using three sampling methods in three sites in Uganda

Abstract

BackgroundThe Plasmodium falciparum entomological inoculation rate (PfEIR) is a measure of exposure to infectious mosquitoes. It is usually interpreted as the number of P. falciparum infective bites received by an individual during a season or annually (aPfEIR). In an area of perennial transmission, the accuracy, precision and seasonal distribution (i.e., month by month) of aPfEIR were investigated. Data were drawn from three sites in Uganda with differing levels of transmission where falciparum malaria is transmitted mainly by Anopheles gambiae s.l. Estimates of aPfEIR derived from human-landing catches – the classic method for estimating biting rates – were compared with data from CDC light traps, and with catches of knock down and exit traps separately and combined.MethodsEntomological surveillance was carried out over one year in 2011/12 in three settings: Jinja, a peri-urban area with low transmission; Kanungu, a rural area with moderate transmission; and Nagongera, Tororo District, a rural area with exceptionally high malaria transmission. Three sampling approaches were used from randomly selected houses with collections occurring once a month: human-landing collections (eight houses), CDC light traps (100 houses) and paired knock-down and exit traps each month (ten houses) for each setting. Up to 50 mosquitoes per month from each household were tested for sporozoites with P. falciparum by ELISA. Human biting rate (HBR) data were estimated month by month. P. falciparum Sporozoite rate (PfSR) for yearly and monthly data and confidence intervals were estimated using the binomial exact test. Monthly and yearly estimates of the HBR, the PfSR, and the PfEIR were estimated and compared.ResultsThe estimated aPfEIR values using human-landing catch data were 3.8 (95% Confidence Intervals, CI 0-11.4) for Jinja, 26.6 (95% CI 7.6-49.4) for Kanungu, and 125 (95% CI 72.2-183.0) for Tororo. In general, the monthly PfEIR values showed strong seasonal signals with two peaks from May-June and October-December, although the precise timing of the peaks differed between sites. Estimated HBRs using human-landing catches were strongly correlated with those made using CDC light traps (r2 = 0.67, p < 0.001), and with either knock-down catches (r2 = 0.56, p < 0.001) and exit traps (r2 = 0.82, p < 0.001) or the combined catches (r2 = 0.73, p < 0.001). Using CDC light trap catch data, the PfSR in Tororo was strongly negatively correlated with monthly HBR (r2 = 0.44, p = 0.01). In other sites, no patterns in the PfSR were discernible because either the number P. falciparum of sporozoite positive mosquitoes or the total number of mosquitoes caught was too low.ConclusionsIn these settings, light traps provide an alternative method for sampling indoor-resting mosquitoes to human-landing catches and have the advantage that they protect individuals from being bitten during collection, are easy to use and are not subject to collector bias. Knock-down catches and exit traps could also be used to replace human-landing catches. Although these a...

Novel serologic biomarkers provide accurate estimates of recent Plasmodium falciparum exposure for individuals and communities

“…Participants consisted of 186 children from cohort studies in two districts of Uganda: Kanungu, where transmission is moderate (annual entomological inoculation rate = 27), and Tororo, where transmission is intense (annual entomological inoculation rate = 125) (59). All participants were followed by active and passive surveillance for at least 1 y before the collection of the plasma samples analyzed here, allowing evaluation of recent exposure.…”

Malaria Transmission, Infection, and Disease at Three Sites with Varied Transmission Intensity in Uganda: Implications for Malaria Control

“…arabiensis. 19 Malaria transmission is perennial, with two annual peaks following the two rainy seasons (March-May and August-October).…”

“…Methods used for the processing of mosquito specimens and identification of sporozoites were as described previously (processing of mosquito specimens in methods section). 19 Enrollment and follow-up of cohort study participants. All children from each household were enrolled into the cohort study if they met the following eligibility criteria: 1) documented age between 6 months and less than 10 years, 2) fulltime resident of the household, 3) no intention to move out of the subcounty for the next 2 years, 4) agreement to come to a dedicated study clinic located within the subcounty for any febrile illness, 5) agreement to avoid antimalarial medications administered outside the study, and 6) provision of written informed consent from parent or guardian.…”

Impact of Antimalarial Treatment and Chemoprevention on the Drug Sensitivity of Malaria Parasites Isolated from Ugandan Children

“…All studied parasites were from subjects enrolled in two clinical trials conducted in Tororo, Uganda, a region with very high malaria transmission intensity, with an entomological inoculation rate recently estimated at 125 infectious bites per year (32). In the PROMOTE-1 trial (registered at ClinicalTrials.gov under registration no.…”