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. 2008 Jul 24:7:140.
doi: 10.1186/1475-2875-7-140.

Epochal changes in the association between malaria epidemics and El Niño in Sri Lanka

Lareef Zubair  1 , Gawrie N Galappaththy, Hyemin Yang, Janaki Chandimala, Zeenas Yahiya, Priyanie Amerasinghe, Neil Ward, Stephen J Connor
Affiliations

Epochal changes in the association between malaria epidemics and El Niño in Sri Lanka

Lareef Zubair et al. Malar J. .

Abstract

Background: El Niño events were suggested as a potential predictor for malaria epidemics in Sri Lanka based on the coincidence of nine out of 16 epidemics with El Niño events from 1870 to 1945. Here the potential for the use of El Niño predictions to anticipate epidemics was examined using enhanced climatic and epidemiological data from 1870 to 2000.

Methods: The epidemics start years were identified by the National Malaria Control Programme and verified against epidemiological records for consistency. Monthly average rainfall climatologies were estimated for epidemic and non-epidemic years; as well El Niño, Neutral and La Niña climatic phases. The relationship between El Niño indices and epidemics was examined to identify 'epochs' of consistent association. The statistical significance of the association between El Niño and epidemics for different epochs was characterized. The changes in the rainfall-El Niño relationships over the decade were examined using running windowed correlations. The anomalies in rainfall climatology during El Niño events for different epochs were compared.

Results: The relationship between El Niño and epidemics from 1870 to 1927 was confirmed. The anomalies in monthly average rainfall during El Niño events resembled the anomalies in monthly average rainfall during epidemics during this period. However, the relationship between El Niño and epidemics broke down from 1928 to 1980. Of the three epidemics in these six decades, only one coincided with an El Niño. Not only did this relationship breakdown but epidemics were more likely to occur in periods with a La Niña tendency. After 1980, three of four epidemics coincided with El Niño.

Conclusion: The breakdown of the association between El Niño and epidemics after 1928 is likely due to an epochal change in the El Niño-rainfall relationship in Sri Lanka around the 1930's. It is unlikely that this breakdown is due to the insecticide spraying programme that began in 1945 since the breakdown started in 1928. Nor does it explain the occurrence of epidemics during La Niña phase from 1928 to 1980. Although there has been renewed coincidence with El Niño after 1980, this record is too short for establishing a reliable relationship.

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Figures

Figure 1
Figure 1
Topography of Sri Lanka is shown as shading along with locations of meteorological observatories. The homogeneous climate regions Eastern, Western and Northern and Southern Plains are also shown.
Figure 2
Figure 2
Annual island-wide morbidity and mortality due to Malaria for 1910 to 2003 is shown on a logarithmic scale. These are annual estimates from the Anti-Malaria Campaign of Sri Lanka and its predecessors.
Figure 3
Figure 3
The monthly average incidence of malaria in Sri Lanka for 1961–2000 compared with the monthly average rainfall for the same period. Malaria incidence peaks in January and July. Rainfall peaks in November and May.
Figure 4
Figure 4
(a) Monthly average rainfall climatology for epidemic start years (1877, 1880, 1884, 1891, 1906, 1911, 1914, 1919, 1923, 1928, 1934, 1939, 1943, 1945, 1967, 1986, 1990) and for non-epidemic years for the period of 1876 to 2000. (b) Average monthly rainfall, and that during El Niño and La Niña phases. The error bars represent the standard error of the estimate.
Figure 5
Figure 5
Annual average of SST anomalies in the NINO3.4 region. Black bars: epidemic start years. Grey bars: non-epidemic years.
Figure 6
Figure 6
Monthly average rainfall in Sri Lanka during El Niño, Neutral and La Niña phases from a) 1870 to 1927, b) 1928 to 1980, and c) 1981 to 2000.
Figure 7
Figure 7
The running correlation with a 30-year window between Sri Lankan average rainfall and the ENSO index of NINO3.4. The year shown in the x-axis represents the central year of the 31 year window.
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