Cycles of malaria associated with El Nino in Venezuela
M. J. Bouma and C. Dye
London School of Hygiene and Tropical Medicine, England. m.bouma@lshtm.ac.uk
CONTEXT: Malaria has been increasing globally, and epidemics tend to occur
when weather conditions favor this vector-borne disease. Long-term
meteorologic forecasting using El Nino Southern Oscillation (ENSO) may
assist in anticipating epidemics and targeting scarce resources. OBJECTIVE:
To determine whether malaria epidemics in Venezuela are related to ENSO and
rainfall and to determine whether such a relationship could be used to
predict outbreaks. DESIGN: Retrospective analysis of national malaria
morbidity (1975-1995) and mortality (1910-1935) data in the coastal zone
and interior of Venezuela in relation to El Nino events and rainfall. MAIN
OUTCOME MEASURE: Correlation between malaria mortality and morbidity and
sea surface temperatures (SSTs) in the Eastern Tropical Pacific, a
parameter of ENSO. RESULTS: Malaria mortality and morbidity have increased
by an average of 36.5% (95% confidence interval, 3.7%-69.3%; P=.004) in
years following recognized El Nino events. A moderate correlation was found
between Pacific tropical SST during a Nino event and malaria 1 year later
(r=0.50, P<.001). Malaria mortality is more strongly related to drought
in the year preceding outbreaks than to rainfall during epidemic years.
CONCLUSIONS: Historic and recent data from Venezuela demonstrate that
malaria increases by an average of about one third in the year following a
Nino event; change in malaria risk can be predicted from Pacific SSTs in
the previous year. Therefore, the occurrence of an El Nino event may help
predict malaria epidemics in this part of South America.
