Malaria models and temperature

With global warming a reality, we show how the projected changes in malaria transmission will depend on which Anopheles mortality model is used to make such predictions

Lunde TM, Bayoh NM and Lindtjørn B. How malaria models relate temperature to malaria transmission. Parasites & Vectors 2013, 6:20 doi:10.1186/1756-3305-6-20

Background It is well known that temperature has a major influence on the transmission of malaria parasites to their hosts. However, mathematical models do not always agree about the way in which temperature affects malaria transmission.

Methods In this study, we compared six temperature dependent mortality models for the malaria vector Anopheles gambiae sensu stricto. The evaluation is based on a comparison between the models, and observations from semi-field and laboratory settings.

Results Our results show how different mortality calculations can influence the predicted dynamics of malaria transmission.

Conclusions With global warming a reality, the projected changes in malaria transmission will depend on which mortality model is used to make such predictions.

Malaria incidence in south Ethiopia

We have now published the large malaria incidence study from Arba Minch: Loha E, Lindtjorn B. Predictors of Plasmodium falciparum Malaria Incidence in Chano Mille, South Ethiopia: A Longitudinal Study. Am J Trop Med Hyg. 2012. You find the publication at


We assessed potential effects of local meteorological and environmental conditions, indoor residual spray with insecticides, insecticide-treated nets (ITNs) use at individual and community levels, and individual factors on Plasmodium falciparum malaria incidence in a village in south Ethiopia. A cohort of 8,121 people was followed for 101 weeks with active and passive surveillance. Among 317 microscopically confirmed P. falciparum malaria episodes, 29.3% occurred among temporary residents. The incidence density was 3.6/10,000 person-weeks of observation. We observed higher malaria incidence among males, children 5–14 years of age, ITNs non-users, the poor, and people who lived closer to vector breeding places. Rainfall increased and indoor residual spraying with Deltamethrin reduced falciparum incidence. Although ITNs prevented falciparum malaria for the users, we did not find that free mass ITNs distribution reduced falciparum malaria on a village level.

Malaria mosquito larvae in the highlands of south-central Ethiopia

This study shows that streams serve as the main breeding sites of anopheline mosquitoes in the Butajira area of south-central Ethiopia. Density of larvae of An. arabiensis, the main malaria vector in the country, was highest along the Odamo stream (1817 m altitude) and decreased significantly along the streams with increasing altitude.

The following text contains the abstract of the article:

Abebe Animut, Teshome Gebre-Michael, Meshesha Balkew and Bernt Lindtjørn. Abundance and dynamics of anopheline larvae in a highland malarious area of south-central EthiopiaParasites & Vectors 2012, 5:117 doi:10.1186/1756-3305-5-117

Background: Malaria is a public health problem in Ethiopia, and increasingly so in highland areas, possibly because of global warming. This study describes the distribution, breeding habitat and monthly dynamics of anopheline larvae in Butajira, a highland area in south-central Ethiopia.

Methods: A study of the abundance and dynamics of Anopheles larvae was undertaken at different sites and altitudes in Butajira from July 2008 to June 2010. The sites included Hobe (1817m.a.s.l), Dirama (1995m.a.s.l.) and Wurib (2196m.a.s.l.). Potential anopheline larval habitats were surveyed once per month in each village. The recorded characteristics of the habitats included habitat type, pH, surface debris, emergent plants, algae, substrate, turbidity, temperature, length, width, depth, distance to the nearest house and anophelines. The Spearman correlation coefficient and Mann-Whitney U test were used to calculate the degree of association between the density of anopheline species and key environmental factors.

Results: Among the different types of habitat surveyed, the Odamo, Akamuja and Assas streams and Beko swamp were positive for anopheline larvae. A total of 3,957 third and fourth instar larvae were collected from the three localities, and they represented ten species of anophelines. These were: Anopheles cinereus (32.5%), An. arabiensis (31.4%), An. chrysti (23%), An. demeilloni (12.2%), An. pretoriensis (0.6%), An. azaniae (0.1%), An. rufipes(0.1%), An. sergentii (0.06%), An. garnhami (0.06%) and An. pharoensis (0.03%). The density of anopheline larvae was highest during the dry months. An. arabiensis was widely distributed, and its density decreased from the lowest elevation in Hobe to the highest in Wurib. The density of An. arabiensis larvae was correlated positively with larval habitat temperature (r = 0.33, p < 0.05) and negatively with depth of larval habitat (r = 0.56, p < 0.05).

Conclusion: Ten species of anophelines were identified, including two known vectors of malaria (An. arabiensis and An. pharoensis), along streams in Butajira. Larvae of An. arabiensis were found in streams at 2200m.a.s.l. This possible expansion of the malaria vector to highland areas indicates an increasing risk of malaria because a large proportion of the Ethiopian population live above this altitude.

Malaria in a highland-fringe area of Ethiopia

Prevalence of malaria infection in Butajira area, south-central Ethiopia

Adugna Woyessa, Wakgari Deressa, Ahmed Ali and Bernt Lindtjorn

Malaria Journal 2012, 11:84



In 2005, the Ethiopian government launched a massive expansion of the malaria prevention and control programme. The programme was aimed mainly at the reduction of malaria in populations living below 2,000 m above sea level. Global warming has been implicated in the increase in the prevalence of malaria in the highlands. However, there is still a paucity of information on the occurrence of malaria at higher altitudes. The objective of this study was to estimate malaria prevalence in highland areas of south-central Ethiopia, designated as the Butajira area.


Using a multi-stage sampling technique, 750 households were selected. All consenting family members were examined for malaria parasites in thick and thin blood smears. The assessment was repeated six times for two years (October 2008 to June 2010).


In total, 19,207 persons were examined in the six surveys. From those tested, 178 slides were positive for malaria, of which 154 (86.5%) were positive for Plasmodium vivax and 22 (12.4%) for Plasmodium falciparum; the remaining two (1.1%) showed mixed infections of Plasmodium falciparum and Plasmodium vivax. The incidence of malaria was higher after the main rainy season, both in lower lying and in highland areas. The incidence in the highlands was low and similar for all age groups, whereas in the lowlands, malaria occurred mostly in those of one to nine years of age.


This study documented a low prevalence of malaria that varied with season and altitudinal zone in a highland-fringe area of Ethiopia. Most of the malaria infections were attributable to Plasmodium vivax.

New publication: EMAPS project on climate and malaria

Ellen Viste and Asgeir Sorteberg. Moisture transport into the Ethiopian highlands. Int. J. Climatol. (2011)  DOI: 10.1002/joc.3409 (pdf file)

ABSTRACT: The Ethiopian summer rains occur as air masses of various origins converge above the Ethiopian plateau. In this study, the relative importance of different moisture transport branches has been estimated using the Lagrangian trajectory model FLEXPART, and ERA-Interim reanalysis data, to backtrack air reaching the northern Ethiopian highlands in July–August 1998–2008. The Indian Ocean, the Congo Basin and the Red Sea were found to be important moisture source regions; for air from the Indian Ocean aided by a considerable moisture uptake along routes across the African continent. The following main transport branches were identified: (1) Flow from the Gulf of Guinea, (2) Flow from the Indian Ocean, and (3) Flow from the north; from the Mediterranean region across the Red Sea and the Arabian Peninsula. The largest contribution to the moisture transport into, and release of moisture within, the northern Ethiopian highlands, was associated with air traveling from the Indian Ocean and from the north. This was partly due to the relatively high mean specific humidity of this air, and partly because a large proportion of the air that reaches the highlands, follows these routes. As a total, the amount of moisture brought into the highlands from the north is 46% higher than from the south, whereas the contribution to moisture release within the highlands is about equal for air coming from the south and from the north. While previous studies have emphasized the importance of the Gulf of Guinea, we find that despite the high specific humidity of the low-level flow of air from the Gulf of Guinea, the amount of moisture carried into and released within the northern Ethiopian highlands through this branch, is much smaller than from the other branches – about 1/8 of that from the Indian Ocean. This is due to the fact that normally only a small proportion of the air reaching Ethiopia comes from the Gulf of Guinea

Sensitivity of SWAT simulated streamflow to climatic changes within the Eastern Nile River basin

Recently Dereje T. Mengistu and Asgeir Sorteberg published a paper on the river flows in the Eastern Nile basin. This study is a part of the EMAPS research. (pdf file)

The paper is published in:Hydrology and Earth System Sciences 2012; 16: 391–407.

The Abstract of the paper is.

The hydrological model SWAT was run with daily station based precipitation and temperature data for the whole Eastern Nile basin including the three subbasins: the Abbay (Blue Nile), BaroAkobo and Tekeze. The daily and monthly streamflows were calibrated and validated at six out- lets with station-based streamflow data in the three different subbasins. The model performed very well in simulating the monthly variability while the validation against daily data revealed a more diverse performance. The simulations in- dicated that around 60 % of the average annual rainfalls of the subbasins were lost through evaporation while the esti- mated runoff coefficients were 0.24, 0.30 and 0.18 for Ab- bay, BaroAkobo and Tekeze subbasins, respectively. About half to two-thirds of the runoff could be attributed to surface runoff while the other contributions came from groundwater.

Twenty hypothetical climate change scenarios (perturbed temperatures and precipitation) were conducted to test the sensitivity of SWAT simulated annual streamflow. The result revealed that the annual streamflow sensitivity to changes in precipitation and temperature differed among the basins and the dependence of the response on the strength of the changes was not linear. On average the annual streamflow responses to a change in precipitation with no temperature change were 19 %, 17 %, and 26 % per 10 % change in precipitation while the average annual streamflow responses to a change in temperature and no precipitation change were

47 temperature and precipitation scenarios from 19 AOGCMs participating inCMIP3 were used to estimate fu- ture changes in streamflow due to climate changes. The cli- mate models disagreed on both the strength and the direc- tion of future precipitation changes. Thus, no clear conclu- sions could be made about future changes in the Eastern Nile streamflow. However, such types of assessment are impor- tant as they emphasise the need to use several an ensemble of AOGCMs as the results strongly dependent on the choice of climate models.

Malaria research during 2011

The Ethiopian Malaria Prediction System (EMaPS) combines information about weather and water with demographic data to predict mosquito development and malaria risk.

Climate variability and changes may influence socio-economic development in Africa by affecting human health through extreme weather events and by bringing about changes in the ecology of infectious diseases. Malaria is a major climate sensitive public health problem in Ethiopia. Unfortunately, there are no practical tools for predicting malaria epidemics based on weather and climate information. Such tools would be useful in making a more efficient use of the limited resources for malaria control.

The project is a collaborative multidisciplinary research project. Researchers from Ethiopia and Norway work together to develop and validate models for predicting malaria transmission and set up an early warning by combining information on climate, water, epidemiological and entomological data. By the end of the project period, EMaPS will try to provide an implementation approach for early malaria warning. The project also aims to strengthen research, and improve interdisciplinary research capacity in Ethiopia and Norway.

The project contains several disciplines (see figure).

The project combined new population-based malaria transmission data with climate and land use variability data to develop early warning to predict malaria epidemics in Ethiopia. Such information is useful for the public and public institutions about the risk of malaria transmission and thus prevents malaria-related deaths.

Overall, eight PhD candidates (six Ethiopians and two Norwegians) take part in the project. The NUFU project funds four of these students, and four are funded by the University of Bergen. They collaborate and share data between the project parts.

We completed the data collection in 2010. During 2011, we mainly focused on data analysis, write-up and publication of the study findings. We expect all PhD candidates to defend their PhD thesis in 2012, and their works are briefly described below.

Abebe Animut is studying malaria mosquitoes in the highlands. He has described the occurrence of Anopheles arabiensis at altitudes as high as 2200m. He has also described the risk of malaria transmission at varying altitudes between 1700 and 2200 m altitude. His study provides good evidence that malaria transmission often occurs in the Ethiopian highlands.

Dereje Tesfahun has evaluated how rainfall and other factors affect the flow of the major rivers in Ethiopia. He has used a model to assess how sensitive the flows of the major river basins are affected by the weather and by possible land use changes. His research shows that Ethiopian rivers are sensitive to precipitation with a 10% change in precipitation giving a 20-30% response in annual stream flow.

Diriba Korecha has studied seasonal weather forecast for Ethiopia. He has re-classified the climatic zones in Ethiopia, worked on models to improve seasonal weather forecasting and validated the result of 10 years of seasonal forecasting in Ethiopia. His research shows that seasonal weather forecasting in Ethiopia is difficult.

Adugna Woyessa has studied the prevalence and risks for malaria using prospective community-based surveys in Butajira in the south central Ethiopian Highlands. His study confirms that malaria is present at altitudes as high as 2200 m, and the malaria prevalence increases towards the lowlands. Malaria occurs throughout the year, but mainly after the main rains. One important finding is that he shows that malaria varies much between villages and within households at all altitudes.

Eskindir Loha studies malaria in the holoendemic Arba Minch area. One of his studies shows that models of climate-malaria link vary from place to place, and one model cannot fit all locations. Malaria modelling may need the inclusion of non-climatic causes. In a follow up study he shows that risk of getting malaria varies much both in time and space within villages. He now works on a paper to describe the influence on rainfall, temperature, socioeconomic factors on the incidence on malaria in these lowlands.

Fekadu Massebo is describing the association between resting behaviour, human blood index and entomological inoculation rates of Anopheles arabiensis in south Ethiopia. The studies include analysis on how mosquito density is associated with malaria cases and how it is influenced by temperature and rainfall. He also assesses insecticide resistance pattern, and if simple house screening will reduce risk of malaria infection.

Torleif Markussen Lunde works on the malaria prediction model. He uses information collected from several disciplines of our project. He has developed a validated malaria prediction model. In the coming months, he will produce malaria distribution maps for Ethiopia, and try to estimate how the new IPPC climate scenarios will affect malaria in the coming years.

Ellen Viste has used weather analysis to describe and analyse from where moisture to Ethiopia comes from.  The Indian Ocean, the Congo Basin and the Red Sea are important moisture source regions. The results suggest that most of the air – humid or not – that enters the Ethiopian highlands from the south has travelled through the Indian Ocean, by the African continent, reaching the Ethiopian highlands from the south-west, or through the Turkana channel.

Some conclusions:

The research will reach its research objectives by the end of 2012, and will have produced eight PhDs and over 20 master theses. Based on our experience we conclude the following challenges remain:

Research challenges include:

  • Improve seasonal weather forecasting for Ethiopia
  • Further develop and field-test malaria prediction in close collaboration with national meteorology and health authorities
  • Possibly add new disciplines such as studies on climate – food production and nutrition.

Educational challenges include:

  • Strengthen PhD training in advanced epidemiology and mathematical modelling (both in geophysics and in health research)
  • Strengthening training in medical entomology (masters level)

These are parts we wish to include in plans for a possible extension of our project.

EMAPS 2011 Annual Meeting

The Ethiopian Malaria Prediction System (EMAPS)  Annual Meeting will be on Monday and Tuesday January 10 and 11 at Ghion Hotel in Addis Ababa.

We plan the meeting as an open scientific meeting, and malaria interested scientists in Ethiopia are invited to take part in the meeting.

We will have one or two lectures at the start of the workshop. Our main emphasis is on forecasting malaria epidemics, and we aim to build our scientific meeting around our modelling efforts.

We shall discuss this in thematic areas such as: mosquito dynamics and behaviour, human host infection (highland, and lowland areas), environmental (hydrology and climate/meteorology), and modelling (captures the whole or part of the information collected so far).