Malaria models and temperature

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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.

Use of bed nets to prevent malaria

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The objective of this study was to characterize the pattern related to ITN use in one village in south Ethiopia. A huge discrepancy was reported between ownership versus utilization of insecticide-treated bed nets (ITNs). To acquire the benefits of ITNs, households need to use and not merely own them.

Eskindir Loha, Kebede Tefera and Bernt Lindtjørn. Freely distributed bed-net use among Chano Mille residents, south Ethiopia: a longitudinal study. Malaria Journal 2013, 12:23 doi:10.1186/1475-2875-12-23

Background:  A huge discrepancy was reported between ownership versus utilization of insecticide-treated bed nets (ITNs). To acquire the benefits of ITNs, households need to use and not merely own them. The objective of this study was to characterize the pattern of, and assess factors related to ITN use in one village in south Ethiopia.

Methods:  A prospective cohort study involving 8,121 residents (in 1,388 households) was carried out from April 2009 to April 2011 (101 weeks). Every week, individuals were asked whether they slept under an ITN the night before the interview. Descriptive statistics was used to report the availability and use of ITN. A negative, binomial, probability, distribution model was fitted to find out significant predictors of ITN use. Reasons for not using ITN were summarized.

Results:  The total number of ITNs available at the beginning of the study was 1,631 (1.68 ITNs per household). On week 48, 3,099 new ITNs (PermaNet2.0) were distributed freely (2.3 ITNs per household). The number of households who received at least one new ITN was 1,309 (98.4%). The percentage of children <5 years and pregnant women not using ITNs exceeded that of other adults. The mean (range; SD) ITN use fraction before and after mass distribution was 0.20 (0.15-0.27; 0.03) and 0.62 (0.47-0.69; 0.04), respectively. Before mass ITN distribution, the most frequent reason for not using ITN was having worn out bed nets (most complained the bed nets were torn by rats); and after mass ITN distribution, it was lack of convenient space to hang more than one ITN. Males, younger age groups (mainly 15–24 years) and those living away from the vector-breeding site were less likely to use ITN.

Conclusions:  The ITN use fraction reached to a maximum of 69% despite near universal coverage (98.4%) was achieved. Gender, age differences and distance from vector breeding site were associated with ITN use. Strategies may need to be designed addressing disproportions in ITN use, lack of convenient space to hang more than one ITN (for those receiving more than one), and measures to prolong usable life of ITNs.

High maternal mortality in rural south-west Ethiopia

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The Reducing Maternal Mortality project in south-west Ethiopia aims to reduce maternal and early child deaths. As part of this intervention project, we did several studies on estimating maternal mortality through a community-based birth registry, a retrospective 5-year recall period household survey, and a health facilities obstetric care quality study.

The abstract of the first publication is:

Yaya Y, Lindtjørn B (2012) High maternal mortality in rural south-west Ethiopia: estimate by using the sisterhood method. BMC Pregnancy and Childbirth 12: 136.

Background: Estimation of maternal mortality is difficult in developing countries without complete vital registration. The indirect sisterhood method represents an alternative in places where there is high fertility and mortality rates. The objective of the current study was to estimate maternal mortality indices using the sisterhood method in a rural district in southwest Ethiopia.

Method: We interviewed 8,870 adults, 15–49 years age, in 15 randomly selected rural villages of Bonke in Gamo Gofa. By constructing a retrospective cohort of women of reproductive age, we obtained sister units of risk exposure to maternal mortality, and calculated the lifetime risk of maternal mortality. Based on the total fertility for the rural Ethiopian population, the maternal mortality ratio was approximated.

Results: We analyzed 8503 of 8870 (96%) respondents (5262 [62%] men and 3241 ([38%] women). The 8503 respondents reported 22,473 sisters (average = 2.6 sisters for each respondent) who survived to reproductive age. Of the 2552 (11.4%) sisters who had died, 32% (819/2552) occurred during pregnancy and childbirth. This provided a lifetime risk of 10.2% from pregnancy and childbirth with a corresponding maternal mortality ratio of 1667 (95% confidence interval, 1564–1769) per 100,000 live births. The time period for this estimate was in 1998. Separate analysis for male and female respondents provided similar estimates.

Conclusion: The impoverished rural area of Gamo Gofa had very high maternal mortality in 1998. This highlights the need for strengthening emergency obstetric care for the Bonke population and similar rural populations in Ethiopia.

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).

Tuberculosis research in Ethiopia

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This  research team works mainly to improve control of tuberculosis in south Ethiopia. We have worked on methods to improve case finding, and improve access to diagnosis and treatment for rural populations.

Currently three PhD students and two experienced Ethiopian researchers work on these studies:

  1. Endrias Markos works to improve new tools to find tuberculosis cases in rural Sidama in Ethiopia. He also studies the potential effect of inn-door air pollution on tuberculosis occurrence
  2. Mesay Hailu works on a project to map how tuberculosis occurrence varies from year to year, and to describe the geographical variations in the occurrence of pulmonary tuberculosis
  3. Shallo Daba works on a project to look at the geographical distribution of tuberculosis in the Arsi area of south-central Ethiopia, and to measure tuberculosis prevalence and multidrug resistance pattern.

Two former PhD students at the University of Bergen (Dr Meaza Demissie, PhD 2002; and Dr. Daniel Gemechu, PhD 2011) also work on these studies, and serve as co-supervisors for the PhD students.

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.