Population Matters

Urbanization’s Effects on Dengue Fever and Malaria

July 19th, 2011

As the world population approaches 7 billion, our global society faces new challenges.  Rising energy and food prices as well as increasing water scarcity can be directly linked to a larger population and ever rising consumption levels.  However, crowding our planet may also have less obvious, although not necessarily less direct, effects on humans, including implications for urbanization and deforestation.  And the effects of such activities may extend farther than initially observed.

The percentage of people living in urban areas in Latin America has jumped from just over 41% in 1950 to 75% in 2000.  By 2025, 82% of the people in the region are projected to live in urban areas.  While cities have the potential to provide economic opportunities for more people, when infrastructure does not keep pace with this rapid pace of urbanization, slums or shantytowns often result, leading to poor living conditions.  In Latin America, 150 million people, or 40% of the urban population, lack adequate sanitation, due in large part to this rapid urbanization.

Without adequate infrastructure, urban residents are put at a much higher risk of contracting many diseases, ranging from cholera to tuberculosis.  One of these diseases is dengue fever, which is spread by mosquitos.  This incapacitating and, at times, deadly disease has been on the rise in Latin American cities since the 1980s.  While the population of the particular mosquito vector was controlled in many places in Latin America from the 1950s until the mid-1970s, as the vector found more and more breeding grounds in the low-quality city conditions in which they thrive, disease rates increased.  In Mexico, by 1998, more than 75% of the population (around the regional average) lived in urban areas.  In the decade or so that followed, the number of dengue cases in the country increased by more than 600%.

Similarly, deforestation, which is driven by urbanization and the growing demand for cropland, has had negative impacts on human health—impacts that extend beyond the effects of reduced carbon sequestration and overall climate change.

While deforestation has slowed in recent years, dropping from an annual loss of 8 million hectares to 5 million hectares between 1990 and 2011, Brazil experienced a 27% jump in deforestation in the 8 month period between August 2010 and April 2011.  As trees are cut in order to accommodate a larger population and the land and timber are used for farming, development, building, or the production of biofuel, it is not simply the plant and animal life that suffers.

Deforestation and urbanization have not only driven dengue rates higher but have also increased rates of malaria.  Malaria, a disease that infects 250 million people every year, has been found to increase in deforested areas.  In fact, a Brazilian study published in the journal Emerging Infectious Diseases found that a 4.2% increase in deforestation yielded a 48% increase in malaria incidence.  The malaria mosquito vector thrives in the open pools of water that collect in deforested areas, while their growth is not nearly as efficient in the water that collects under the rainforest canopy.

As the pressures of urbanization and continued population growth stretch the current capacities of our society, it is important to anticipate new and re-emerging challenges, like malaria and dengue fever, before they reach epidemic proportions.

Fortunately, fertility rates in many parts of Latin America have fallen sharply in recent decades as family planning services and information have become more widely available.  Latin America, however, still suffers from widespread income inequalities, and health services for the poor still lag in many areas.  Without a greater commitment to meeting the reproductive health needs of poor women, Latin America will continue to suffer from unacceptably high maternal and infant mortality rates, while also wrestling with dengue, malaria, and other diseases that accompany urbanization and deforestation.

Posted by Hannah Ellison, Public Policy Fellow

Leave a Reply