The map extent exactly matches the area defined by Patz et al. In a recent article, Zhou et al.claim that increases in climate variance, rather than simple increases in climate mean values, have had an important role in the resurgence of malaria epidemics in the East African highlands since the early 1980s. Malaria resurgence in the East African highlands: Temperature trends revisited M. Pascual*†, J. PLoS ONE 6(9): The evidence that climate change is the most significant factor in recent malaria resurgences in the highlands of East Africa is at best equivocal, at worst unfounded. Because only the total number of rainy days is provided by the CRU records, we generated daily presence/absence data with a prescribed autocorrelation structure by using a Markov model with two states (rain and no rain) adapted from Caswell (43) and with the frequency of rainy days varying monthly as given by the CRU data. The role of climate change in the exacerbation of the disease has been controversial, and the specific influence of rising temperature (warming) has been highly debated following a previous study reporting no evidence to support a trend in temperature. AN is supported by the Wellcome Trust as a Research Training Fellow (# 081829). ↵ Although, malaria is decreasing through intensified interventions since mid 2000s onwards, these environmental changes might expose population in the highlands of east Africa to an increase risk of malaria and its epidemic particularly if the current interventions are not sustained. RS is supported by the Wellcome Trust as Principal Research Fellow (# 079080). Studies in this region have sparked a heated debate over the importance of climate change in the territorial expansion of malaria, where positions range from its neglect to the reification of correlations as causes. [19] across which CRU TS 2.1 and 3.0 data were tested: 4°S, 4°N, 28°E, 38°E. where Mi We also tested simpler AR models with independent and identically distributed random noise but found that these models failed to remove the autocorrelation of the residuals. 2 more...], Climate has a significant impact on malaria incidence and we have predicted that forecast climate changes might cause some modifications to the present global distribution of malaria close to its present boundaries. Based on the results of this analysis, two parameters (the slope of larval development and larval survival) were selected for their higher influence on RD and examined systematically for their effect on this quantity. Malaria resurgence in the East African highlands: Temperature trends revisited M. Pascual*†, J. Given our focus here on trends and not on the localization of specific frequencies, we chose one of these flexible decompositions, although we expect EMD to provide similar results. The trend coefficient for 1966-2006 is about the same as that for 1966-1995 with an implied increase over the full period of 40 cases per month but is significant at the 5% level. CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): Update TRENDS in Parasitology Vol.21 No.2 February 200552variability at the 95 % confidence level, and correction for multiple t testing would similarly reduce the number of ‘significant ’ results, in this case refuting the authors’ contention. [4], the actual temperature changes estimated by the trend component vary from 0.21 K for Kericho to 0.27 K for Gikongoro and Muhanga. Results of parametric (SARMA) time series model. Controversy over the cause of malaria resurgences reported in the late 1990s in some areas of highland East Africa continues despite reports of an overall global reduction in prevalence of the disease , marked declines across many well studied communities in East Africa , and at the majority of seventeen non-lakeside hospitals across Kenya . This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. In other words, this temperature pattern indicates a period of lower temperatures than expected without the nonlinear trend. Finally, regardless of its etiology, malaria in Kericho and many other areas of East Africa has decreased during periods of unambiguous warming. Finally, through the data collection initiatives of the Malaria Atlas Project (MAP, http://www.map.ox.ac.uk) [16] we are able to present information on more than 5000 geo-positioned, post-1985, malaria prevalence surveys that allow insights into the changing endemicity of malaria in several East African countries during the last 25 years and if these show any difference by altitude. We do not capture any email address. Hence, while high quality data is of value, use of the data from a single met station vs. use of the interpolated CRU database is not the reason that Hay et al. The following three models were considered In particular, the residuals were not independent, exhibiting significant autocorrelation. One central piece of evidence against a role of climate has been presented by Hay et al. 28 and 29; see figure 2 in ref. Summary time series plots for community parasite rate surveys in Kenya, Tanzania, Burundi, Rwanda, and Uganda are shown in Figure 5. None of these changes are statistically significant at the 5% level as determined by the tDAN statistics and only Muhanga and Gikongoro have a statistically significant trend at the 10% level. Temperature and precipitation in the highlands, as a result of predicted climate change, are expected to rise above the minimum temperature and precipitation thresholds of malaria transmission in xt 's mean temperature series. The International Panel on Climate Change has concluded that there is likely to be a net extension in the distribution of malaria and an increase in incidence within this range. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The incidence of malaria in the East African highlands has increased since the end of the 1970s. An interesting consequence of this pattern is that mosquito abundance in the model exhibits a larger jump between the end of the 1970s and beginning of the 1980s. They applied three different time series methods to CRU data interpolated for Kericho and find increases in temperature in the period from 1966 to 1996. In Kabale, for similar differences in the two temperature time series, the RD in the mosquito abundance is further amplified, with peak values well above 100%. Statistical analyses of time series patterns alone will not be sufficient to fully understand the subtleties of malaria transmission. EO is supported by the Wellcome Trust as a Research Training Fellow (# 086166). (2010). Clearly, trends in climate and resistance need not be independent and could interact through changing selective pressures. A comprehensive sensitivity analysis of the mosquito model has been presented elsewhere (18). The respective reconstructed components are shown in Fig. Trends are significant at the 5% level in all four locations but at the 1% level only in Kericho and Muhanga. Smoothed lines show the LOWESS-smoothed moving average. wrote the paper. [SANTIAGO] More people may contract malaria in the tropical highlands of Africa, Asia and South America as global warming makes the climate in these areas more suitable for the disease’s transmission, according to a study.. In the 1966 to 1995 period we find a 0.76 K temperature increase at Kericho, which is significant at the 1% level. For over a decade, the highlands of malaria endemic countries have been considered areas of special concern for the impacts of climate change [12]. Our results on (CRU) temperature data at four high-altitude sites support the occurrence of a significant warming trend since the end of the 1970s of ≈0.5°C. The influence of rainfall is simulated by increasing larval mortality as a function of accumulated days with no rain to represent the combined effects of increased competition and desiccation of breeding sites. Freely available online through the PNAS open access option. Malaria epidemics in the highlands of East Africa garner significant research attention, due, in part, to their proposed sensitivity to climate change. At a more regional level on land, evidence has also been reported for increasing monthly minimum (nighttime) surface temperatures and decreasing diurnal temperature ranges over Eastern Africa (e.g., ref. It consists of a nonlinear trend, with an inflection point in the 1970s followed by an increase in the 1980s and 1990s of ≈0.5°C. All of the J statistics used to test for stochastic trends in the data are highly significant at the 1% level allowing us to reject the null hypothesis of a unit root in the residuals of the trend regression. Additionally, none of the autoregressive (AR) or moving average components is a unit root (Table 1). Sensitivity analysis for the mean (a and b) and maximum (c and d) of RD values in Kericho (a and c) and Kabale (b and d), as a function of larval survival and development rate in the mosquito population model. 11 and refs. By contrast, Omumbo et al. Age patterns of severe paediatric malaria and their relationship to Plasmodium falciparum transmission intensity. Because of the importance of this debate [10], we apply a uniform methodology to test for trends in the various datasets used to date and time periods previously considered in the literature to determine whether differences in data or in methods are responsible for the variant findings. Caroline W. Kabaria, In a recent article, Zhou et al. There is only a marked decrease in the number of stations at all sites since 1997. The test compares statistics of simulated red-noise time series with those of the climatic time series (20). This project was conducted as part of the Working Group on Global Change and Infectious Disease, supported by the National Center for Ecological Analysis and Synthesis, a center funded by the National Science Foundation (Grant DEB 0072909) and University of California, Santa Barbara. The role of climate change in the exacerbation of the disease has been controversial, and the specific influence of rising temperature (warming) has been highly debated following a previous study reporting no evidence to support a trend in temperature. A response by Patz et al. In Southern Africa, countries have recently experienced malaria epidemics following unusual rainfall. In Kenya, the moving average lines for both low and high altitude regions display an overall decreasing trend across the period 1985-2008, although in low altitude regions this decline slows or reverses slightly during the period 1995-2000. The recommended value of b and the critical values of tDAN for a two-tailed test are as follows: b = 2.466, tDAN = 2.462 at 1%; b = 1.795, tDAN = 2.052 at 2.5%; b = 1.322, tDAN = 1.710 at 5% and b = 0.965, tDAN = 1.329 at the 10% significance level. Then the trend test statistic is given by:(2)where is the estimate of the slope parameter in (1) and its standard error. Controversy over the cause of malaria resurgences reported in the late 1990s in some areas of highland East Africa continues despite reports of an overall global reduction in prevalence of the disease [1], marked declines across many well studied communities in East Africa [2], and at the majority of seventeen non-lakeside hospitals across Kenya [3]. Thank you for your interest in spreading the word on PNAS. Inhabitants of southwest Uganda and parts of Zambia and Rwanda typically lack the genetic resistance to malaria developed by farmers in mosquito-prone areas. However, although the malaria cases observed at Kericho, Kenya rose during a period of resurgent epidemics (1994-2002) they have since returned to a low level. Similarly, seasonality is treated differently in our models, with fewer terms (and therefore parameters) whose number is determined by model selection itself. However, the new CRU TS 2.1 and CRU TS 3.0 datasets shows a highly significant temperature increase in Kericho in both the 1966-1996 period examined by Chavez and Koenraadt [6], in the shorter 1970-1995 period examined by Hay et al. Kabale’s temperatures are colder and result in a much larger amplification of the temperature difference. At five of the seven sites (Kericho, Kabale, Gikonko, Muhanga and Amani), climate has not changed significantly. An increase in temperature after 1995 is also apparent from both figures. 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