Category Archives: Malaria

How bednets and indoor residual spraying influence spatio-temporal clustering of malaria

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Loha E, Lunde TM, Lindtjørn B. Effect of Bednets and Indoor Residual Spraying on Spatio-Temporal Clustering of Malaria in a Village in South Ethiopia: A Longitudinal Study. PLoSONE 2012; 7(10): e4735.

Background

Understanding the spatio-temporal pattern of malaria transmission where prevention and control measures are in place will help to fine-tune strategies. The objective of this study was to assess the effect of mass distribution of bednets and indoor residual spraying (IRS) with insecticides on the spatio-temporal clustering of malaria in one malaria endemic village in south Ethiopia.

Methods

A longitudinal study was conducted from April 2009 to April 2011. The average population was 6631 in 1346 locations. We used active and passive searches for malaria cases for 101 weeks. SatScan v9.1.1 was used to identify statistically significant retrospective space–time clusters. A discrete Poisson based model was applied with the aim of identifying areas with high rates. PASW Statistics 18 was used to build generalized Poisson loglinear model.

Results

The total number of both types of malaria episodes was 622, giving 45.1 episodes per 1000 persons per year; among these, episodes of Plasmodium falciparum and vivax infection numbered 316 (22.9 per 1000 per year) and 306 (22.2 per 1000 per year), respectively. IRS with Dichlorodiphenyltrichloroethane (DDT) and later with Deltamethrin and free mass distribution of insecticide-treated nets (ITNs) were carried out during the study period. There was space–time clustering of malaria episodes at a household level. The spatio-temporal clustering of malaria was not influenced by free mass distribution of ITNs; however, the time-span of the spatio-temporal clustering of malaria cases ended after IRS with Deltamethrin. The presence of clusters on the south-east edge of the village was consistent with the finding of an increasing risk of acquiring malaria infection for individuals who lived closer to the identified vector breeding site.

Conclusion

The risk of getting malaria infection varied significantly within one village. Free mass distribution of ITNs did not influence the spatio-temporal clustering of malaria, but IRS might have eliminated malaria clustering.

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(This paper was also been presented at a conference that BioMed Central, in conjunction with its journals Malaria Journal and Parasites & Vectors, hosted. The second malaria conference “Challenges in Malaria Research: Progress Towards Elimination” was held in Basel, Switzerland from 10 – 12 October 2012).

Malaria incidence in south Ethiopia

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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 http://www.ajtmh.org/content/87/3/450.full

Abstract

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.

New malaria control research in Ethiopia

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We recently received the good news the Research Council of Norway will fund the project: “Combining indoor residual spraying and long-lasting insecticidal nets for preventing malaria: Cluster randomised trial in Ethiopia”.

This research aims to improve malaria control by evaluating the combined effect of indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) on malaria incidence in Ethiopia. This project addresses how to promote uptake of research findings into public health programmes by enhancing our knowledge on interventions that will improve the effectiveness and coverage of malaria control programmes. It includes community randomised controlled trials to assess effectiveness of multiple interventions in combination versus one method alone within routine malaria control settings.

The clinical study objectives are to examine if IRS with insecticide and LLINs provide added protection against clinical malaria compared with LLINs alone. In the health economic part we shall estimate the costs of LLINs alone or combined with IRS, compared with current standard practice in the study settings. The study will also include studies on the anopheles mosquito where we aim to assess whether IRS with insecticide plus LLINs reduces vector biting and resting preference and density, longevity, infection and entomological inoculation rates inside houses when compared with LLIN alone.

We plan to start preliminary studies in late 2012, with start of the trial during the main malaria season in 2013. The planned study site is in the Adami Tullu area in the central part of the Rift valley in Ethiopia. This research will build up on the already established research collaboration between the University of Bergen, Addis Ababa University (School of Public Health and Aklilu Lemma Institute of Pathobiology), Hawassa University, and the Ethiopian Ministry of Health (Malaria Control).

Malaria mosquito larvae in the highlands of south-central Ethiopia

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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 Ethiopia. Parasites & 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.

Forecasting Malaria

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On March 30, Kjersti Brown from SIU presented our malaria research in Ethiopia:

Researchers from Ethiopia and Norway have developed a new model for forecasting malaria epidemics.

Climate change is presenting major challenges in Africa. Malaria, one of the big killers of African children, is a disease directly linked to temperature and rainfall. In Ethiopia, malaria occurs seasonally. Every four to six years there are huge epidemics, affecting as many as several hundred thousand people. Global warming now seems to be changing the pattern of malaria. Will high-land Ethiopia experience more malaria in the future? And if so, will it be possible to predict epidemics in time for people to prepare?

 

You can read the full presentation here.

Malaria mortality

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A new study published in The Lancet suggests that malaria kills almost twice as many people as the World Health Organisation estimates 1.

The researchers, led by Professor Christopher Murray at the University of Washington, assessed death statistics for 105 countries since 1980. Their method included examining registration statistics and verbal autopsy data, and correcting possible misclassifications of deaths from categories such as “fever” and attributing them to malaria.

They concluded there were 1.24 million deaths from malaria in 2010, nearly double the 655,000 given by the WHO. The authors found that were also far more adult deaths outside Africa, than were previously estimated.

In a study from rural Ethiopia, we found that malaria represents the leading cause of death among people aged 10 to 24 years old 2. Our study showed the leading perceived causes of death were malaria (0.85 per 1,000 person years), diarrhoea (0.5 per 1,000 PY) and tuberculosis (0.36 per 1,000 PY). Other causes accounted for 1.25 deaths per 1,000 PY and unknown causes for 0.39 deaths per 1,000 PY, as reported by family care givers.

I hope future malaria studies in Africa and Asia also try to estimate malaria deaths.

If these findings are accepted, there will be important consequences for global funding of initiatives to combat the parasite.

References 

1.         Murray CJL, Rosenfeld LC, Lim SS, et al. Global malaria mortality between 1980 and 2010: a systematic analysis. The Lancet 2012;379:413-31.

2.         Molla M, Byass P, Berhane Y, Lindtjorn B. Mortality Decreases among Young Adults in Southern Central Ethiopia. Ethiopian Journal of Health Development 2008;22:218-25.

Malaria in a highland-fringe area of Ethiopia

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

Adugna Woyessa, Wakgari Deressa, Ahmed Ali and Bernt Lindtjorn

Malaria Journal 2012, 11:84

Abstract

Background

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.

Methods

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).

Results

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.

Conclusion

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

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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

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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.