The direct impacts of climate change depend mainly on exposure to heat or cold waves or extreme weather events. The former involves an alteration of heat- and cold-related illnesses and deaths. Although Latin America was not included in the five regions identified by IPCC (1990) for analysis of regional climate change simulation, Kattemberg et al. (IPCC 1996, WGI, Chapter 6) made generalized tentative assessments concerning extreme events. Studies in temperate and subtropical countries have shown increases in daily death rates associated with extreme outdoor temperatures. Mortality increases much more steeply with rising temperatures than with falling temperatures (Kalkstein, 1993). The lowest mortality occurs within a range of intermediate comfortable temperatures and humidities (between 21�C and 26�C and below 60% relative humidity, in these countries).
No references to studies and research on direct health impacts from projected warming in Latin America are included in the SAR; however, extrapolation of investigations performed in cities in the United States, China, The Netherlands, and the Middle East indicates that morbidity and mortality also could increase in this region as a result of the expected increase in the number of days with high daily temperatures (i.e., the persistence of days with higher-than-normal maximum and minimum temperatures) (Haines et al., 1993; Kalkstein, 1993; IPCC 1996, WG II, Section 18.2.1). The impacts would be exacerbated by high humidity rates, intense solar radiation, and weak winds. All of these factors affect the physiological mechanisms of human adaptation.
High temperatures and air pollutants, especially particulates, act synergistically to influence human mortality. This effect is occurring in large cities, such as Mexico City and Santiago, Chile, where such conditions enhance the formation of secondary pollutants (e.g., ozone) (Escudero, 1990; Katsouyanni et al., 1993; Canziani, 1994).
Global warming could increase the number and severity of extreme weather events such as storms, floods, and droughts, and related landslides and wildfires. Such events tend to increase death and pathology rates-directly through injuries or indirectly through infectious diseases, as well as through social problems that stem from the dislocation of people, adverse psychological effects, and other stresses (IPCC 1996, WG II, Section 18.2.2). A number of slums and shanty towns located on hills, as well as human settlements located in flood-prone areas, are subject to periodic natural disasters that adversely affect human health (Section 6.3.6). These overcrowded and poorly-serviced peri-urban settlements also provide a potential breeding ground for disease hosts (e.g., rats, mice, cockroaches, flies) and disease organisms, increasing the population's vulnerability. Communities surrounded by these poverty belts also become more vulnerable to periodic disease outbreaks (WHO Commission on Human Health and Environment, 1992).
Climate variability also may aggravate diseases resulting from water contamination. Increases in Salmonella infections following a flood in Bolivia resulted from the El Ni�o event of 1983 (Telleria, 1986).
Infectious and parasitic diseases are important causes of morbidity and mortality in Latin America, and the main cause of death in children (PAHO, 1994). Some infectious diseases are more common in tropical and subtropical areas than in temperate or cold areas. Therefore, global warming would tend to extend their area of influence or increase the importance of outbreaks. Some of these diseases are food- or water-related infections; after they are introduced into a region, they show a tendency to spread over the whole region. Viral, bacterial, and protozoan agents of diarrhea can survive in water-especially in warmer waters-for long periods of time and thus spread at increased rates in rainfall periods, enhancing their transmissibility among people. An example is cholera, which was introduced into Peru in 1993. It produced an outbreak that spread to most of the South American subcontinent, including places as far as Buenos Aires (PAHO, 1994). Cholera's relation to the ENSO phenomenon was proposed by Colwell (1996). This disease and other diarrheas and dysenteries are associated with the distribution and quality of surface water, as well as with flooding and water shortages. These conditions alter the population dynamics of organisms, impede personal hygiene, and impair local sewage systems. Increases in coastal algal blooming also may amplify the proliferation and transmission of Vibrio cholerae.
Algal blooming also may be associated with biotoxin contamination of fish and shellfish (Epstein et al., 1993). With ocean warming, temperature-sensitive toxins produced by phytoplankton could cause contamination of seafood more often, resulting in an increased frequency of poisoning. Thus, climate-induced changes in the production of aquatic pathogens and biotoxins may jeopardize seafood safety.
Other infectious diseases not included in the SAR have now achieved importance and could reach critical levels in South America. Some viruses have had unexpected outbreaks-such as arenaviruses in Argentina and Bolivia (PAHO, 1996) and hantaviruses in the south of Argentina; their relationship to climate change is not yet well understood. Fungi such as Paracoccidiodes brasiliensis-which require high humidity and generally are associated with rainfall regimes of 500-2,000 mm/yr and average temperatures of 14-30�C-are found in some areas of South America (e.g., Brazil, Venezuela, and northern Argentina) (Restrepo et al., 1972), where this mycosis is becoming endemic. It may spread if climate change provides adequate conditions to start the epidemiological chain. In this connection, increasing surface traffic that has resulted from commercial activity stemming from the new regional common market-Mercosur-may call for the development of appropriate sanitary barriers (e.g., disinfection of vehicles and their contents to block transport of harmful fungi) at borders.
A special category of infectious diseases-a group known as vector-borne diseases (VBDs)-already affect a large number of people in Latin America. These diseases could expand their geographic and elevational ranges because conditions would be more favorable for viruses and other living agents, reservoirs, and vectors as a result of global warming. The most important VBDs in Latin America are listed below, with indications of some of their main vectors:
Other viruses also affect human beings in this region. One produces Venezuelan equine encephalitis; it is transmitted by several mosquito species, and cases have been reported in Colombia and Venezuela (WHO, 1996). Its relation to climate change has not yet been demonstrated; however, warming could affect the geographical distribution and dispersion, as well as some behaviors and patterns, of vertebrate reservoirs (mammals and birds) and vectors.
Infective agents and vectors are sensitive to environmental changes, especially those conditioned by temperatures and humidity. Vectors also are sensitive to wind, soil moisture, surface water, and changes in vegetation and forest distribution (Bradley, 1993). Temperatures and humidity influence the geographical and elevational dispersion of vectors (Burgos et al., 1994; Curto de Casas et al., 1994), as well as their population dynamics and behavior. Precipitation is an important factor for vectors with aquatic stages, such as mosquitoes and blackflies, because breeding places are increased and maintained by rainfall. Winds may contribute to the dispersion of some flying insects, such as mosquitoes, blackflies, and sandflies (Ando et al., 1996).
Several years ago, VBDs were very critical in many areas of the region; during
recent years, however, some of them have been almost entirely controlled or
reduced in their endemicity. Malaria is prevalent in tropical and subtropical
areas of the American continent, from south of Mexico to northern Argentina.
Several species of mosquitoes of genus Anopheles are vectors of Plasmodium
vivax and Plasmodium falciparum, which are causal agents of the disease
that cannot survive at temperatures below 14-18�C, depending on the Plasmodium
species (see Figure 6-6). The normal type of epidemiological
curve of malaria in northeast Argentina has shown a peak in new cases every
1-4 years, particularly during the months of March to May or June, when Anopheles
darlingi has been present. During the period 1991-93, however, there were
cases every month of the year, and Anopheles darlingi were captured or
reported sighted during the whole period. Thus, more studies are needed to assess
the influence of new dams on the behavior of vector species and the epidemiology
of the disease, as well as the influence of increases in minimum temperatures
(Carcavallo et al., 1995). Martens et al. (1995) have predicted that temperature
increases of several degrees Celsius at higher elevations-which could occur
in Andean ranges under projected climate change-may produce seasonal epidemic
transmission in areas currently free of paludism.
|
| Figure 6-6: Distribution of principal malaria vectors in Latin America (WHO, 1996). |
(continues on next page...)
|
Other reports in this collection |
|
