14.2.5.4. Effects of El Niño Phenomenon on Health
There is good evidence that the ENSO cycle is associated with increased risk
of certain diseases (PAHO, 1998b). ENSO events may affect the distribution (reproduction
and mortality) of disease vectors (Epstein et al., 1998). El Niño
events raise SST over the tropical Pacific, affecting some pathogenic agents.
McMichael and Kovats (1998b), Patz (1998), and Instituto Nacional de Salud (1998a,b)
have speculated that the last cholera outbreak in Peru, beginning in 1991, was
linked with an El Niño phenomenon (1990-1995). The outbreak spread
to most of the South American subcontinent, including places as far away as
Buenos Aires (OPS, 1999). de Garín et al. (2000) have reported
that El Niño has important impacts in andean population; they found large
amounts of the insect, as well as eggs for the next period, in the northern
part of Argentina.
Higher temperatures over coastal Peru associated with ENSO may have an impact
on gastrointestinal infections. Salmonella infections increased after a flood
in Bolivia, which resulted from the El Niño event of 1983 (Valencia Tellería,
1986). Salazar-Lindo et al. (1997) report that the number of patients
with diarrhea and dehydration admitted to a rehydration unit in Lima, Peru,
was 25% higher than usual during 1997, when temperatures where higher than normal
as a result of the emerging El Niño. Increases in the incidence of acute
diarrheas and acute respiratory diseases were recorded in Bolivia (Valencia
Tellería, 1986) and Peru (Gueri et al., 1986).
The effects of natural events vary by region, and the same weather condition
may have the opposite effect in different areas for the same disease (e.g.,
a dry year may induce malaria epidemics in humid regions but cause malaria decreases
in arid regions) (McMichael and Kovats, 1998b). For example, ENSO has been associated
with severe drought in Iquitos, Peru, and the state of Roraima, Brazil, where
malaria cases have drastically decreased (OPS, 1998; Confalonieri and Costa-Díaz,
2000). In Venezuela, malaria mortality has been shown to be more strongly related
to the occurrence of drought in the year preceding outbreaks than to rainfall
during epidemic years (Bouma and Dye, 1997). The El Niño phenomenon appears
to be responsible in particular for serious epidemics in Peru, including one
of malaria in 1983 (Moreira, 1986; Russac, 1986; Valencia Tellería, 1986),
as well as cutaneous diseases, leptospirosis, and respiratory infections in
1998 (Instituto Nacional de Salud, 1998b). Compared with other years, malaria
cases in Colombia increased 17.3% during an El Niño year and 35.1% in
the post-El Niño year. Upsurges of malaria in Colombia during El Niño
events are associated with its hydrometeorological variables—in particular,
the increase in air temperature that enhances reproductive and biting rates
and decreases the extrinsic incubation period, as well as changes in precipitation
rates that favor formation of ponds and stagnant pools and thus create more
mosquito breeding sites (Poveda and Rojas, 1997; Poveda et al., 1999a,b).
Global analyses have shown no association between ENSO and the number of flood
disasters (Dilley and Heyman, 1995) or between ENSO and the numbers of persons
affected by floods and landslides (Bouma et al., 1997). However, the
number of persons affected by landslides, particularly in South America, increases
in the year after the onset of El Niño (Bouma et al., 1997). In
1983, the impacts of El Niño in Peru increased total mortality by nearly
40% and infant mortality by 103% (Toledo-Tito, 1997).
Predicting malaria risk associated with ENSO and related climate variables
may serve as a short-term analog for predicting longer term effects posed by
global climate change. The ability to predict years of high and low risk for
malaria can be used to improve preventive measures (Bouma et al., 1997).
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