Impact of the El Niño/Southern Oscillation on Visceral Leishmaniasis, Brazil

Carlos Roberto Franke, Mario Ziller, Christoph Staubach, and Mojib Latif

Disclosures

Emerging Infectious Diseases. 2002;8(9) 

In This Article

Abstract and Introduction

We used time-series analysis and linear regression to investigate the relationship between the annual Niño-3 index from 1980 to 1998 and the annual incidence of visceral leishmaniasis (VL) in the State of Bahia, Brazil, during 1985-1999. An increase in VL incidence was observed in the post-El Niño years 1989 (+38.7%) and 1995 (+33.5%). The regression model demonstrates that the previous year's mean Niño-3 index and the temporal trend account for approximately 50% of the variance in the annual incidence of VL in Bahia. The model shows a robust agreement with the real data, as only the influence of El Niño on the cycle of VL was analyzed. The results suggest that this relationship could be used to predict high-risk years for VL and thus help reduce health impact in susceptible regions in Brazil.

Visceral leishmaniasis (VL) is a widespread parasitic disease in the Old and New Worlds, with a global incidence of 500,000 new human cases each year. VL is the most severe clinical form within the leishmaniasis complex, which is endemic in 88 countries with an at-risk population of approximately 350 million.[1] In Brazil, VL affects both humans and animals and is caused by Leishmania chagasi, a flagellate protozoan transmitted by the sand fly Lutzomyia longipalpis.[2] The disease occurs mainly in malnourished young children and is frequently fatal if untreated.[3,4] Periodic epidemic waves of VL, observed mainly in northeastern Brazil, have been associated with human migrations to urban areas after long periods of drought.[5,6,7,8] In this region, El Niño events are related to unusually dry conditions, widespread food scarcity, and migration.[9,10,11] El Niño periods in 1982-1983, 1986-1987, 1991-1993, and 1997-1998 coincided with long droughts recorded by the Superintendence for the Development of the Northeast Brazil (SUDENE). Data from the State of Bahia, analyzed in our study, show that 247 municipalities were affected during the strong El Niño of 1997-98, mainly in the semi-arid inland region, where approximately 200,000 people were included in SUDENE's emergency program, at a cost of an estimated US $62 million.

El Niño is the strongest interannual climate fluctuation worldwide, characterized by a large-scale warming of the eastern and central equatorial Pacific Ocean. El Niño (also known as El Niño/Southern Oscillation) can be understood as the warm phase of an irregular cycle with an average frequency of 3-4 years. Each event typically lasts for approximately a year, with the peak warming in boreal winter (December-February) and the following spring (March-May).[12] Some studies provide strong evidence of the relationship between El Niño and increased epidemic risk of vector-borne diseases in distinct regions throughout the world.[13,14] This observation is especially true for malaria.[15,16,17,18] We report the early results of our analysis of the relationship between the El Niño cycle and VL in Brazil.

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