Residual malaria transmission

Abraham M, Massebo F, Lindtjørn B: High entomological inoculation rate of malaria vectors in area of high coverage of interventions in southwest Ethiopia: Implication for residual malaria transmission. Parasite Epidemiology and Control 2017, 2:61-69.

Abstract
In Ethiopia, vector control is the principal strategy to reduce the burden of malaria. The entomological indicators of malaria transmission such as density, sporozoite rate and entomological inoculation rate (EIR) are parameters used to assess the impact of the interventions and the intensity of malaria transmission. The susceptibility of malaria vectors also determines the effectiveness of insecticide based vector control tools. Hence, the aim of the study was to assess the species composition, sporozoite rate and EIR, and insecticide susceptibility status of malaria vectors.

33 houses (18 for Centre for Disease Control and Prevention (CDC) light traps and 15 for exit traps) were randomly selected to sample Anopheles mosquitoes from October 2015 to May 2016. Plasmodium circum-sporozoite proteins (CSPs) of An. arabiensis and An. pharoensis were determined using Enzyme-Linked Immuno-Sorbent Assay (ELISA).

Five Anopheles species were identified from CDC Light traps and exit traps. An. arabiensis (80.2%) was the predominant species, followed by An. pharoensis (18.5%). An. pretoriensis, An. tenebrosus and An. rhodesiensis were documented in small numbers. 1056 Anopheles mosquitoes were tested for CSPs. Of which nine (eight An. arabiensis and one An. pharoensis) were positive for CSPs with an overall CSP rate of 0.85% (95% CI: 0.3–1.4). Five Anopheles mosquitoes were positive for P. falciparumand four were positive for P.vivax_210. P. falciparum CSP rate of An. arabiensis was 0.46% (95% CI: 0.13–1.2) and it was 0.54% (95% CI: 0.01–2.9) for An. pharoensis. The overall EIR of An. arabiensis was 5.3 infectious bites per/person (ib/p)/eight months. An. arabiensis was resistant to dieldrin (mortality rate of 57%) and deltamethrin with mortality rates of 71% but was fully susceptible to propoxur and bendiocarb. Based on the EIR of An. arabiensis, indoor malaria transmission was high regardless of high coverage of indoor-based interventions.

Finally, there was an indoor residual malaria transmission in a village of high coverage of bed nets and where the principal malaria vector is susceptibility to propoxur and bendiocarb; insecticides currently in use for indoor residual spraying. The continuing indoor transmission of malaria in such village implies the need for new tools to supplement the existing interventions and to reduce indoor malaria transmission.

The epidemiology of highland malaria in Ethiopia: a study from Butajira area

On May 30th, 2013, Adugna Woyessa defended his PhD thesis at Addis Ababa University. The PhD thesis The epidemiology of highland malaria in Ethiopia: a study from Butajira area aims to  describe human malaria transmission  in rural south central Ethiopian highlands.

Abstract

Background:In Ethiopia, malaria is a major public health problem with seasonal and unstable distribution. Because of the country’s diverse topography and climate, transmission of malaria varies with space and time; while the variability is more pronounced in highlands with low transmission. This calls for better understanding of malaria. However, there is paucity of information on magnitudeof malaria, risk factors, effective use of vector control measures such as insecticide-treated nets in relationship with malaria infection and performance of multi-species detecting malaria rapid diagnostic tests (RDTs) where Plasmodium falciparum and Plasmodium vivax co-exist at highlands of low-endemicity.

Objectives:To describe the epidemiology of highland malaria with emphasis to the magnitude and associated factors as well as interventions in various altitudesof Butajira area, south-central Ethiopia.

METHODS: Community-based repeated cross-sectional studies were conducted in six rural kebeles of Meskan and Mareko Districts from October 2008 to June 2010in Butajira area, Ethiopia. The kebeles (Hobe, Bati Lejano, Dirama, Shershera Bido, Yeteker and Wurib) were selected in such a way that two were from one altitudinal stratum thus making a total of three strata: low (1,800-1,899 meters above sea level), mid-level (1,900-1,999 meters above sea level), and high (2,000-2,300 meters above sea level) altitudes. These kebeles are part of Demographic Surveillance System Site of the Butajira Rural Health Program). A multi-stage sampling method was used to recruit study participants. The various stages were kebeles as first-stage, villages as second-stage, and households as third-stage units.   A total of 3,393 individuals were recruited from randomly sampled 750 households in 16 villages. Probability proportion to size sampling method was applied to allocate the number of households to be sampled from each kebeleand village. The study obtained data from household interview, survey and recruiting all self-reported febrile cases.  Household interview was undertaken by trained data collectors using pre-tested structured questionnaire. Household altitude reading and geo-reference was recorded from geographical positioning system location. Seasonal blood surveys were made on quarterly basis between Oct. 2008 and Jun. 2010. From the sampled households, all family members who consented to participate were requested for blood films. Besides, self-reported febrile cases were simultaneously checked for malaria infection using RDTs. CareStartTMMalaria Plasmodium falciparum/ Plasmodium vivax combo test result was compared with microscopy. Analytical tools including descriptive statistics, multilevel analysis, principal component analysis, and complex sample analysis were employed.

Main findings: The unadjusted prevalence of malaria was found to be 0.93 % [95% CI 0.79-1.07]; of 19, 207 people, 178 were positive; adjusted prevalence of malaria was estimated at 0.78 (95% CI: 0.48-1.29); of 19, 199 people, 178 were positive. Plasmodium vivax was dominant (86.5%, n=154) and the rest of the cases were due to Plasmodium falciparum (12.4%, n=22, seven with gametocyte) and mixed infections (1.1%, n=2).The prevalence varied among villages with the highest prevalence of 2.8% in Dadesso and Horosso villages (both <1,850 masl), and the lowest prevalence of 0.0% in Sunke Wenz and Akababi village (2,100-2,180 masl). Malaria prevalence decreased with altitude: 1.91% [95% CI (1.55-2.27)] in low, 1.37% [95% CI (0.87-1.87)] in mid-level and 0.36% [95% CI (0.25-0.47)] in high altitude zones; the highest prevalence was found at low altitude between October and November 2009. Moreover, malaria varied among age groups and the variation was different at different at altitudes. It reached its peak in children aged one to four yearsYonkers at mid-level and one to nine years at low altitudes. However, its prevalence at higher altitude was low and was similar across all age groups. Plasmodium falciparum malaria occurred rarely throughout the survey periods, with relatively more cases in October-November 2009 in the low altitude zone. Plasmodium vivax was found in all survey periods. However, its prevalence differed with respect to survey period and altitude. Variables like age (children aged below five and 5-9 years), altitude (low and mid-level altitude), and in houses with holes as individual-level factors; and village-level variables explained most of the variation (ICC= 94%) in individual malaria infection. The estimates of village-level variances showed well marked differences in malaria infection.

Only 28.5% [95%CI 25.8-31.4] of the 739 households surveyed owned at least an ITN.  Household ITN ownership was associated with household heads with no formal education, male-headed households, more beds in the house, absence of mosquito source reduction, and nonexistence of main water body. Male-headed households were also more associated with increased ITN ownership than female-headed ones. Households with ITN observed hanging, two and more number of ITN owned, not doing source reduction and less than a kilometredistance from main water body showed high association with use of ITN while the presence of more ITN observed hanging was a good predictor. Higher prevalence was found among people surveyed from ITN-owning than non-ITN-owning households (2.1% versus 0.5%). Malaria infection was more often observed in households owning at least an ITN than in their counterparts (unadjusted OR 4.1 [95% C.I. 2.2-7.6]; F (1, 22) =25.2, P<0.001).

Data obtained from a total of 2,394 self-reported febrile cases: 66.8% (n=1,598) from health facilities and the rest 33.2% (n=796) from surveys. Higher proportionof Plasmodium positives and both Plasmodium falciparum and Plasmodium vivaxwere detected at health facilities compared to what was seen in the survey. However, more mixed infections were observed in the latter. Low sensitivity of the test was observed in all Plasmodium species (90.8%, 95% CI: 82.9-95.3), and Plasmodium falciparum (87.5%, 52.9-97.8) in survey; and Plasmodium vivax (92.8%, 95% CI: 89.3-95.2) at health facilities. Low specificity of Plasmodium vivax (87.5%, 95% CI: 52.9-97.8) was found at the survey and all Plasmodium species (82.7%, 95% CI: 80.5-84.8) at health facilities. Very low PPV was detected in all Plasmodium species (76.7%, 95% CI: 67.7-83.8), and Plasmodium falciparum (87.5%, 95% CI: 52.9-97.8) at the survey and all Plasmodium species (64.3%, 95% CI: 60.5-68.1) and Plasmodium falciparum (77.2%, 95% CI: 67.6-84.5) at health facilities.  Low NPV was observed in Plasmodium vivax both in the survey (87.5%, 95% CI: 52.9-97.8) and health facilities (77.2: 67.6-84.5).The measure of agreement or kappa score was almost perfect agreement in all categories, except in all Plasmodium species with substantial agreement.

Conclusions and recommendations: This thesis demonstrates that low prevalence of malaria with age and altitude dependent distribution was found in highlands with low transmission in south-central Ethiopia. Plasmodium vivax was the dominant species more prevalent throughout the survey. There was very low ITN use that might have also hardly protected children in ITN-owning households. Performance of malaria RDT detecting Plasmodium falciparum and Plasmodium vivax vary between health facility-based and survey setting for both species. A malaria intervention that prioritises children below 10 years appears to be practically feasible to reduce malaria transmission. Strengthening surveillance to help in evidence-informed decision of vector control is recommendable. Furthermore, future studies should target designing more frequent survey and application of PCR for evaluation of RDT performance.

Publications:

Woyessa A, Deressa W, Ali A, Lindtjorn B. Ownership and use of long-lasting insecticidal nets for malaria prevention in Butajira area, south-central Ethiopia: complex samples data analysis. BMC public health 2014; 14: 99.

Woyessa A, Deressa W, Ali A, Lindtjørn B. Evaluation of CareStartTM malaria Pf/Pv combo test for Plasmodium falciparum and Plasmodium vivax malaria diagnosis in Butajira area, south-central Ethiopia. Malaria Journal 2013, 12:218 doi:10.1186/1475-2875-12-218

Woyessa A, Deressa W, Ali A, Lindtjørn B. Malaria risk factors in Butajira area, south-central Ethiopia: a multilevel analysis. Malaria Journal 2013, 12:273. 

Woyessa A, Deressa W, Ali A, Lindtjørn B. Prevalence of malaria infection in Butajira area, south-central Ethiopia. Malaria Journal 2012, 11:84

The full-text thesis can be downloaded here. 

Many patients remain untreated for tuberculosis

Hamusse S, Demissie M, Teshome D, Hassen MS, Lindtjorn B: Prevalence and Incidence of Smear-Positive Pulmonary Tuberculosis in the Hetosa District of Arsi Zone, Oromia Regional State of Central Ethiopia. BMC Infect Dis 2017, 17:214.

Background  The real burden of smear-positive (PTB+) and bacteriologically confirmed tuberculosis (BCTB) in Ethiopia is not known. Thus, the aim of this community-based study was to measure the prevalence and incidence of tuberculosis in the Hetosa District of Oromia Region, Ethiopia.

Methods  First, a population-based cross-sectional survey was conducted on a total of 33,073 individuals aged ≥ 15 years to determine the prevalence of PTB+ and BCTB cases. Then, in order to determine the incidence, a prospective follow-up was carried out on 32,800 individuals found to be either free from symptoms suggestive of TB (SSTB) during the baseline survey or had symptoms suggestive of TB but yielded negative bacteriological examination results. We identified 1,041 presumptive TB cases at the baseline survey, and 1,468 in the follow-up study. Each participants with cough of more than two weeks were provided spot and morning sputum samples for acid-fast bacilli sputum microscopy and culture.

Results  At the baseline survey, 43 BCTB cases were identified. Thirty six of these were both smear- and culture-positive while seven were only culture-positive. In the follow-up study, however, 76 BCTB cases were diagnosed and 70 of these were found to be both smear- and culture-positive while six were culture-positive only. The adjusted prevalence of PTB+ and BCTB in the study area was 109 and 132/100,000 persons, respectively. Moreover, the incidences of PTB+ and BCTB were 214 and 232/100,000 persons per year (py), respectively. The ratio of the passive to active case finding was 1:0.96 (45/43). For every TB case identified through the existing passive case diagnosis, there was an almost equal number (0.96) of undiagnosed infectious TB cases in the community. A family history of TB contact was independently associated with a high risk of TB (TB prevalence, AOR, 13; 95% CI: 6.55–15.33) and (TB incidence, aIRR 4.11, 95% CI: 2.18–7.77).

Conclusions and recommendations  The prevalence and incidence of smear-positive and bacteriologically confirmed TB cases were high in the study area. For every case of smear-positive TB receiving treatment, there was an almost equal (0.96) number of undetected infectious bacteriologically confirmed TB case in the community. The high proportion of undetected infectious TB cases in the community could possibly be due to the sub-optimal performance of Directly Observed Treatment Short-course (DOTS) in detecting 70% of infectious TB cases, as well as attaining a cure rate of 85% in the study area. Family history of TB contact has substantaially increased the risk of developing the disease, and there is a need to improve ways of identifying TB cases and intensify mechanisms of tracing contacts among household members of PTB+ cases.

Anaemia, drought and malaria in Ethiopia

Gari T, Loha E, Deressa W, Solomon T, Atsbeha H, Assegid M, Hailu A, Lindtjørn B. (2017) Anaemia among children in a drought affected community in south-central Ethiopia. PLoS ONE 12(3): e0170898. doi:10.1371/journal.pone.0170898

Introduction  As part of a field trial (PACTR201411000882128) to provide evidence on the combined use of long-lasting insecticidal nets and indoor residual spray for malaria prevention, we measured haemoglobin values among children aged 6 to 59 months. The aim of this study was to estimate the prevalence of anaemia, and to determine the risk factors of anaemia and change in haemoglobin value in Adami Tullu district in south-central Ethiopia.

Methods  Repeated cross-sectional surveys among 2984 children in 2014 and 3128 children in 2015; and a cohort study (malaria as exposure and anaemia as outcome variable) were conducted. The study area faced severe drought and food shortages in 2015. Anaemia was diagnosed using HemoCue Hb 301, and children with haemoglobin <11 g/dl were classified as anaemic. Multilevel and Cox regression models were applied to assess predictors of anaemia.

Results  The prevalence of anaemia was 28.2% [95% Confidence Interval (CI), 26.6–29.8] in 2014 and increased to 36.8% (95% CI, 35.1–38.5) in 2015 (P<0.001). The incidence of anaemia was 30; (95% CI, 28–32) cases per 100 children years of observation. The risk of anaemia was high (adjusted Hazard Ratio = 10) among children with malaria. Children from poor families [Adjusted Odds Ratio (AOR); 1.3; 95% CI, 1.1–1.6)], stunted children (AOR 1.5; 95% CI; 1.2–1.8), and children aged less than 36 months (AOR; 2.0; 95% CI, 1.6–2.4) were at risk of anaemia compared to their counterparts. There was no significant difference in risk of anaemia among the trial arms.

Conclusions  Young age, stunting, malaria and poverty were the main predictors of anaemia. An increase in the prevalence of anaemia was observed over a year, despite malaria prevention effort, which could be related to the drought and food shortage. Therefore, conducting trials in settings prone to drought and famine may bring unexpected challenges.

Entomological evaluation of vector control

oljira-phd-thesis-cover

Kena, O. 2017. Entomological impact of combined and separate use of indoor residual spraying and long-lasting insecticidal nets for malaria prevention in Adami Tullu district, South-Central Ethiopia. PhD thesis. Addis Ababa University.

Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key frontline malaria prevention interventions in Ethiopia. Both target Anopheles arabiensis, the sole primary malaria vector. Universal coverage of both interventions has been promoted and there is a growing demand in combination of interventions for malaria control and elimination. However, available evidence is contradictory wether the combined intervention is better than either IRS or LLINs alone. To investigate whether IRS and LLINs combination provides added protective impact on An. arabiensis compared to either IRS or LLINs alone, a cluster randomized controlled trial was carried out in Adami Tullu district, south-central Ethiopia. Villages were randomly allocated to four study arms: IRS+LLINs, IRS, LLINs, and control. All households in the IRS+LLINs and LLINs arms were provided with LLINs (PermaNet 2.0) free of charge. Households in the IRS+LLINs and IRS arms were applied with propoxur before the main malaria transmission season in 2014 and 2015. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD) of the anophelines. Human landing catch (HLC) was performed in selected villages to monitor the impact of the interventions on local mosquito biting behaviours (biting location, time and host preference).

Collected anophelines were identified to species by use of standard morphological keys and additional use of molecular methods to separate sibling species of the An. gambiae complex. Enzyme-linked immunosorbent assay (ELISA) was used to detect malaria infections in mosquitoes and the sources of mosquito blood meals. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. Parity rate (percentage of parous females) was also determined by ovarial dissection. Human blood index (HBI) was expressed as the proportion of mosquitoes with human blood divided by the total number of blood-fed mosquitoes tested.

A total of 1786 female anophelines of four species (An. arabiensis, An. pharoensis, An. ziemanni and An. funestus s.l.) were collected over two transmission seasons during the intervention period (2014-2015). Anopheles numbers were highest in the control arm (41.3% of total) followed by LLINs (25.4%), IRS (18.0%), and IRS+LLINs (15.8%). In most of the vector parameters estimated, the impact of IRS and LLINs combined and separate interventions were significantly higher in communities that recieved the interventions (in experimental groups) compared with untreated communities (control group). The mean HSD of An. arabiensis in the IRS+LLINs arm was similar to the IRS arm (0.03 vs. 0.03/ house/LTC/night) but lower than the LLINs arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS+LLINs compared to the IRS arm. However, both IRD and ORD of An. arabiensis were higher in LLINs compared to IRS+LLINs (p < 0.001 for indoors). Parity rate of An. arabiensis were similar among the intervention arms. None of the 1786 samples of four species tested by ELISA was positive for P.  falciparum and P. vivax CSP infection in all of the study arms. Anopheles arabiensis preferred mainly bovine and human hosts for blood meal sources with high HBI in the LLIN alone. Indoor resting habit of An. arabiensis was less impacted by LLINs alone intervention compared to IRS + LLINs or IRS alone.

In conclusion, the IRS+LLINs and the IRS alone each was similarly most effective against An. arabiensis as compared to the LLINs alone. The IRS+LLINs provided added impact on An. arabiensis compared to LLINs alone. The LLINs alone had poor impact on densities and human biting rates of An. arabiensis in this study setting.

You can download the thesis here: Oljira-Kenea-thesis

Clustering of chronic malnutrition among Ethiopian children

journal-pone-0170785-g001Hagos S, Hailemariam D, WoldeHanna T, Lindtjørn B (2017) Spatial heterogeneity and risk factors for stunting among children under age five in Ethiopia: A Bayesian geo-statistical model. PLOS ONE 12(2): e0170785. doi: 10.1371/journal.pone.0170785

Background  Understanding the spatial distribution of stunting and underlying factors operating at meso-scale is of paramount importance for intervention designing and implementations. Yet, little is known about the spatial distribution of stunting and some discrepancies are documented on the relative importance of reported risk factors. Therefore, the present study aims at exploring the spatial distribution of stunting at meso- (district) scale, and evaluates the effect of spatial dependency on the identification of risk factors and their relative contribution to the occurrence of stunting and severe stunting in a rural area of Ethiopia.

Methods  A community based cross sectional study was conducted to measure the occurrence of stunting and severe stunting among children aged 0–59 months. Additionally, we collected relevant information on anthropometric measures, dietary habits, parent and child-related demographic and socio-economic status. Latitude and longitude of surveyed households were also recorded. Local Anselin Moran’s I was calculated to investigate the spatial variation of stunting prevalence and identify potential local pockets (hotspots) of high prevalence. Finally, we employed a Bayesian geo-statistical model, which accounted for spatial dependency structure in the data, to identify potential risk factors for stunting in the study area.

Results  Overall, the prevalence of stunting and severe stunting in the district was 43.7% [95%CI: 40.9, 46.4] and 21.3% [95%CI: 19.5, 23.3] respectively. We identified statistically significant clusters of high prevalence of stunting (hotspots) in the eastern part of the district and clusters of low prevalence (cold spots) in the western. We found out that the inclusion of spatial structure of the data into the Bayesian model has shown to improve the fit for stunting model. The Bayesian geo-statistical model indicated that the risk of stunting increased as the child’s age increased (OR 4.74; 95% Bayesian credible interval [BCI]:3.35–6.58) and among boys (OR 1.28; 95%BCI; 1.12–1.45). However, maternal education and household food security were found to be protective against stunting and severe stunting.

Conclusion  Stunting prevalence may vary across space at different scale. For this, it’s important that nutrition studies and, more importantly, control interventions take into account this spatial heterogeneity in the distribution of nutritional deficits and their underlying associated factors. The findings of this study also indicated that interventions integrating household food insecurity in nutrition programs in the district might help to avert the burden of stunting.

 

 

PhD in malaria entomology, and first and second opponents from Africa

img_1060On Friday, January 27, Fekadu Massebo  defended his PhD thesis at the University of Bergen. This was a good defence with a thorough  scientific discussion. For the first time at the University of Bergen, the first and second opponents were African. This is a testimony to the emerging strength of African scientists.

The picture shows the candidate after the defence, the  opponents, and the supervisors. From left: Professor Sven Gudmund Hinderaker (Acting Dean), Fekadu Massebo, Dr Silas Majambere (First opponent), Professor Tehmina Mustafa from UiB, Professor Bernt Lindtjørn (supervisor), Dr Tarekegn Abeku (Second opponent) and Ass Professor Meshesha Balkew (supervisor) from Addis Ababa University.

New PhD: Malaria vectors in southern Ethiopia

fekadu-cover-pageMassebo F. Malaria vectors in southern Ethiopia. Some challenges and opportunities for vector control. PhD. University of Bergen, 2017. Bergen

Background: Malaria is a public health problem in Ethiopia, where more than 60% of the population lives in risky areas. Since 2005, malaria-related sicknesses and deaths have substantially decreased in the country, mainly due to the increasing coverage of vector control interventions and chemotherapy. On the other hand, resistance to most public health insecticides is widely spreading among the populations of the principal malaria vector Anopheles arabiensis. Therefore, assessing the susceptibility status of local malaria vectors is an essential activity to improve the effectiveness of the interventions, by introducing the appropriate insecticide resistance management strategies. There are also substantial gaps in knowledge regarding the entomological inoculation rate (EIR), which is an indicator of the intensity of malaria transmission, and are used to assess the impact of vector control interventions. Understanding the species composition, feeding and resting behaviours, parity rate, as well as human biting and sporozoite rates, are all important in evaluating the effectiveness of interventions and planning for supplementary vector control tools. Moreover, improving housing, such as screen doors and windows, and closing openings on walls and eaves, might reduce the entry of malaria vectors and provide protection from infectious bites of malaria vectors.

Objective: The study was carried out to help assess the species composition, age structure, feeding patterns, sporozoite infection rate, entomological inoculation rate and insecticide susceptibility status of An. arabiensis, and evaluate the impact of screened houses on its indoor density.

Methods: The study was done in the Chano Mille Kebele in southwestern Ethiopia. The longitudinal entomological study was conducted from May 2009-April 2010, whereas the house screening intervention was done between April-November 2011. Thirty houses (10 houses for each collection method) were randomly selected for biweekly Anopheles mosquito sampling. The Anopheles mosquitoes were collected by the Centers for Disease Control and Prevention (CDC) light traps, pyrethrum spray catches (PSC) and from artificial pit shelters by aspirating. Enzyme-linked-immunosorbent assay (ELISA) was used to analyse the blood meal origins and circumsporozoite proteins. The EIR of P. falciparum and P. vivax of An. arabiensis was calculated by multiplying the sporozoite and human biting rates from CDC light traps and PSC collections.

A randomized control trial was conducted to assess the impact of screening windows and doors with wire mesh, and closing openings on eaves and walls by mud on the indoor density of An. arabiensis. Baseline mosquito data was gathered biweekly from 40 houses by CDC light traps in March and April 2011 to randomize houses into both control and intervention groups. The windows and doors of 20 houses were screened by mosquito-proof wire mesh, and openings on the walls and eaves were closed by mud. The rest of the 20 houses were assigned to the control group. Mosquitoes were collected biweekly in October and November 2011 from both the control and intervention houses.

Results: Anopheles species, comprised of An. arabiensis, An. marshalli, An. garnhami, An. funestus group, An. pharoensis, An. tenebrosus, An. rhodensiensis, An. flavicosta, An. longipalpis, An. daniculicus, An. pretoriensis, An. chrysti, An. moucheti, An. distinctus and An. zeimanni, were documented in the area. Anopheles arabiensis was by far the most dominant species.

The overall human blood index (HBI) of An. arabiensis, including the mixed blood meals, was 44%, whereas the bovine blood index (BBI), including mixed blood meals, was 69%. The majority of An. arabiensis (65%) from the indoor-resting collection had bovine blood meal, which was unexpected. The higher proportion (75%) of indoor host-seeking An. arabiensis collected by CDC light traps had contact with humans. Only 13% An. arabiensis from pit shelters had human blood meal, while 68% had bovine blood meal. Anopheles arabiensis showed a consistently higher feeding pattern on cattle than on humans, regardless of collection sites and the high number of the human population. The human and bovine feeding patterns of An. arabiensis showed little change due to the number of cattle to human ratio of each household. Anopheles marshalli and An. garnhami showed similar feeding patterns.

Anopheles arabiensis was highly resistant to four pyrethroid insecticides tested (lambdacyhalothrin, cyfluthrin, alphacypermethrin and deltamethrin) and DDT, with a maximum mortality rate of 56% due to lambdacyhalothrin and a minimum of 10% due to DDT.

The circumsporozoite protein ELISA test revealed 11 P. falciparum infections out of 14 sporozoite positive An. arabiensis (the other three were P. vivax), thereby confirming that this species is the principal vector of P. falciparum and P. vivax parasites. The P. falciparum sporozoite rate of An. arabiensis was 0.32% for CDC light traps, 0.28% for pit shelters and 0.23% for PSCs. The overall estimated annual P. falciparum EIR of An. arabiensis from CDC light traps was 17.1 infectious bites/person/year (ib/p/y), but it varied between houses, from a 0 EIR in 60% of houses to 73.2 in a house close to the major breeding site. Hence, those houses nearest to the mosquito breeding sites had a higher risk of exposure to infectious bites. The P. falciparum EIR of An. arabiensis was 2.4 in the dry season and 14.7 in the wet season, indicating 6.1-fold more infectious bites in the wet- than in the dry season. The P. falciparum and P. vivax EIR of An. arabiensis from PSC was 0.1ib/p/y, while the P. vivax EIR of An. arabiensis from CDC light traps was 2.41ib/p/y.

The screening of doors and windows with wire mesh, and closing the openings on eaves and walls by mud, significantly reduced the indoor density of host-seeking An. arabiensis by 40%. The intervention was cheap, and can be incorporated into malaria vector control programmes by local communities.

Conclusion: Anopheles arabiensis showed a consistently higher feeding pattern on cattle than on humans regardless of collection sites and the high number of human population. It was the most abundant and the principal vector of P. falciparum and P. vivax, while An. marshalli and An. garnhami were the second and third most abundant species, but neither of them was positive for CSPs. The transmission of malaria is heterogeneous; those houses nearest to the mosquito breeding sites (hot spots) had a higher risk of exposure to the infectious bites of An. arabiensis. Anopheles arabiensis was resistant to pyrethroid insecticides, the only class of insecticides recommended for LLINs treatment; as a result, there should be an action programme to manage insecticide resistance. Finally, supplementary methods of vector control, such as the screening of houses, could be included to help improve malaria control in the area based on the principle of integrated vector management.

The thesis can be downloaded here.