Malaria transmission at high altitudes in Ethiopia

Daygena TY, Massebo F, Lindtjorn B. Variation in species composition and infection rates of Anopheles mosquitoes at different altitudinal transects, and the risk of malaria in the highland of Dirashe Woreda, south Ethiopia. Parasites & vectors. 2017;10(1):343.

Background  The transmission of malaria is heterogeneous, and varies due to altitude. The information on whether the transmission of malaria is indigenous or imported to highland areas is scarce. Therefore, this study aimed to assess the species composition and infection rates of Anopheles at different altitudinal transects, and the risk of malaria if any in the highland of Dirashe Woreda, South Ethiopia.

Methods  This study was conducted in Gato (low altitude; average elevation of 1273 m), Onota (mid-altitude; average elevation of 1707 m) and Layignaw-Arguba (high altitude; average elevation of 2337 m) from August 2015 to April 2016. Anopheles mosquitoes were sampled using Centers for Disease Control and Prevention (CDC) light traps from thirty houses (ten houses from each village). The circum-sporozoite proteins (CSPs) rate and entomological inoculation rate (EIR) of Anopheles mosquitoes were estimated. For the epidemiological survey, malaria cases were collected from laboratory registration books of selected health facilities from (August 2015-April 2016). A cross-sectional survey was done to collect data on malaria vector control activities in each village (August-September 2015).

Results  One thousand two hundred sixty-eight Anopheles mosquitoes comprising Anopheles arabiensis, An. demeilloni, An. cinereus, An. pharoensis, An. funestus-group, An. pretoriensis, An. christyi, An. ardensis and An. tenebrosus were identified in the study area. Anopheles arabiensis was the dominant species in Gato, whereas An. demeilloni was the dominant species in Layignaw-Arguba. Five mosquitoes, three An. arabiensis from Gato and two An. demeilloni from Layignaw-Arguba, were positive for Plasmodium falciparum CSPs. Plasmodium falciparum CSP rate was 0.4% (95% CI: 0.08–1.15) for An. arabiensis in Gato, and it was 0.64% (95% CI: 0.08–2.3) for An. demeilloni from Layignaw-Arguba. The P. falciparum EIR of An. arabiensis was 8.6 (95% CI: 2.4–33.4) infectious bites/person/nine-months in Gato. Plasmodium falciparum was dominant in Gato (88%) and Onota (57.5%), whereas in Layignaw-Arguba P. vivax (59.4%) occurred most frequently. Increased malaria cases were observed in children age 5–14 years in Gato (P < 0.05), whereas in Onota and Layignaw-Arguba there was no statistically significant difference in malaria cases among the age groups. Households owning at least one long lasting insecticidal net were 92.7% in the study area, and 77.6% slept under the net during the preceding night of the survey. About 64.4% of the households in Gato were protected by the indoor residual spray. However, the spraying was done when the density of local malaria vectors was low.

Conclusion  Incrimination of Plasmodium CSP positive Anopheles species and the presence of malaria in children under five years in high altitude Layignaw-Arguba may justify the existence of indigenous malaria transmission and the need for effective malaria control. Further investigation and confirmation using more sensitive molecular techniques are however needed to consider An. demeilloni as a proven vector of malaria in Ethiopia.

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.

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.

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


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

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.

Collecting malaria mosquitoes

Kenea O, Balkew M, Tekie H, Gebre-Michael T, Deressa W, Loha E, Lindtjørn B, Overgaard HJ: Comparison of two adult mosquito sampling methods with human landing catches in south-central Ethiopia. Malaria Journal 2017, 16

Background  The human landing catch (HLC) is the standard reference method for measuring human exposure to mosquito bites. However, HLC is labour-intensive, exposes collectors to infectious mosquito bites and is subjected to collector bias. These necessitate local calibration and application of alternative methods. This study was undertaken to determine the relative sampling efficiency (RSE) of light traps with or without yeast-produced carbon dioxide bait vs. HLC in south-central Ethiopia.

Methods  The experiment was conducted for 39 nights in a 3 × 3 Latin square randomized design with Anopheles arabiensis as the target species in the period between July and November 2014 in Edo Kontola village, south-central Ethiopia. Center for Disease Control and Prevention light trap catches (LTC) and yeast-generated carbon dioxide-baited light trap catches (CB-LTC) were each evaluated against HLC. The total nightly mosquito catches for each Anopheles species in either method was compared with HLC by Pearson correlation and simple linear regression analysis on log-transformed [log10(x + 1)] values. To test if the RSE of each alternative method was affected by mosquito density, the ratio of the number of mosquitoes in each method to the number of mosquitoes in HLC was plotted against the average mosquito abundance.

Results  Overall, 7606 Anopheles females were collected by the three sampling methods. Among these 5228 (68.7%) were Anopheles ziemanni, 1153 (15.2%) An. arabiensis, 883 (11.6%) Anopheles funestus s.l., and 342 (4.5%) Anopheles pharoensis. HLC yielded 3392 (44.6%), CB-LTC 2150 (28.3%), and LTC 2064 (27.1%) Anopheles females. The RSEs of LTC and HLC for An. arabiensis were significantly correlated (p < 0.001) and density independent (p = 0.65). However, for outdoor collection of the same species, RSEs of LTC and CB-LTC were density dependent (p < 0.001). It was estimated that on average, indoor LTC and CB-LTC each caught 0.35 and 0.44 times that of indoor HLC for An. arabiensis respectively.

Conclusions  Results showed that HLC was the most efficient method for sampling An. arabiensis. LTC can be used for large-scale indoor An. arabiensis surveillance and monitoring when it is difficult to use HLC. CB-LTC does not substantially improve sampling of this major vector compared to LTC in this setting.

Presentation at 65th Annual meeting of the American Society of Tropical Medicine and Hygiene

Impact of combining Indoor Residual Spraying and Long-Lasting Insecticidal Nets on Anopheles arabiensis in Ethiopia: Preliminary findings of a randomized controlled trial

Oljira Kenea, Meshesha Balkew, Habte Tekie, Teshome Gebre-Michael, Wakgari Deressa, Eskindir Loha, Hans J. Overgaard, Bernt Lindtjørn


The current malaria vector control interventions, indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) have been used in combination in sub-Saharan Africa with inconclusive evidence that the combined intervention is more effective than either IRS or LLINs alone. In Ethiopia, both interventions target Anopheles arabiensis, the sole primary malaria vector. This study compared the impact of combining IRS and LLINs with either intervention alone in south-central Ethiopia. Villages were randomly allocated to four study arms: IRS + LLIN, IRS, LLIN, and control. LLINs (PermaNet 2.0) were provided free of charge. IRS with propoxur was applied 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). Human landing catch (HLC) was performed in selected villages to monitor An. arabiensis biting behaviors. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. A total of 1786 female anophelines of four species was collected of which An. arabiensis (n=574) was highest in the control arm (51.4%) followed by LLIN (31.5%), IRS (9.2%), and IRS+LLIN (7.9%). The mean HSD of An. arabiensis in the IRS+LLIN arm was similar to either the IRS arm (0.03 vs. 0.03/ house/LTC/night) or the LLIN arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS and LLIN compared to the IRS arm. However, both IRD and ORD were higher in LLIN compared to IRS+LLIN (p < 0.001 for indoors). In all study arms, An. arabiensis was actively biting indoors and outdoors throughout the night with an early night biting peak before the local people retire to bed. IRS+LLIN compared to IRS had equal powerful impact on resting density of An. arabiensis, but LLIN had the least impact.

Malaria control or elimination?

Malaria controlAbout ten years ago, the global health community was cautious about aiming at malaria eradication. The experiences from the 1960s and 1970s left some severe scars on such campaigns. Recently, the Gates Foundation has led the shift in approach and mobilised others to join efforts to end the disease. However, while malaria is preventable and treatable, eradication requires new tools (see figure).

A good vaccine would be highest on the agenda. Although vaccine trials show promising results, the vaccine efficacy is unfortunately too low to eradicate the disease.

Our recent study on the prevention of malaria in the Rift Valley of Ethiopia also shows some of the limited effects of insecticide-treated bed nets. In addition, we have observed that many of the mosquito bites take place at times when people do not use their bed nets. Our mosquito studies show that indoor residual spraying with insecticides can reduce the density of mosquitoes both inside the houses as well as outside the houses. Furthermore, a recent and unpublished study from south-west Ethiopia supporter previous findings that improving housing can reduce the entomological inoculation rates, which is a measure on how dangerous the mosquitoes are in transmitting malaria.

We, therefore, also support that several new tools are required. So, maybe the time is right to assess the combination of many interventions that would include active case finding, treatment, insecticide treated bed nets, indoor residual spraying, improved housing, and other vector control measures; such as reducing the out-door density of malaria mosquitoes.