Winter has reached its end, at least in the southern hemisphere, and although in São Paulo it is only moderately cold, people appreciate the arrival of summer. Summer brings with it heat, the necessary rainfall, and outdoor activities, but also one of the worst threats, dengue fever.
In the first eight months of 2015, dengue fever has already infected over 650,000 people in the state of São Paulo, causing the death of more than 300. The figures exceed any previously known record and position São Paulo as the Brazilian state most affected by the disease, responsible for 30% of the total number of cases on the American continent. The most surprising thing is that this occurs in the midst of the most serious drought in memory. It seems contradictory, but it isn’t.
Dengue fever is a viral infection with high fever and which is fatal in its most serious haemorrhagic presentation. There is no treatment other than adequate hydration and symptomatic treatment and to date no effective vaccine has been developed.
The transmission of dengue fever between humans only occurs through mosquito bites, mainly Aedes aegypti and, to a lesser extent, Aedes albopictus (yes, the one already known in Spain as the “tiger mosquito”). These mosquitoes lay their eggs in clean, stagnant water, not in wastewater, and therefore warm tropical and subtropical climates, with abundant rainfall in summer, represent an excellent ecosystem for the development of the mosquito and, consequently, of the disease.
São Paulo has traditionally been a state with a low risk of dengue fever, mainly thanks to its cold winters, which temporarily reduce the population of the mosquito, and secondly to its economic development, which allows a better urban infrastructure and a population which is better educated to fight against the disease.
This being the case, how is it possible that in recent years the cases of dengue fever have rocketed in São Paulo? Why didn’t the lack of rainfall hinder the development of the mosquito?
Indeed, the lack of water in São Paulo appears to have had an important effect, but not in the direction expected. The progressive tariffs with high penalties for those who increase their consumption, and the supply problems arising from pressure management, modified people’s behaviour. During some months of 2014, the big construction stores exhausted their stocks of plastic tanks and buckets. Any small quantity of water can be used and stored in small improvised containers in thousands of houses, which in many cases are potential breeding grounds for mosquitoes.
The situation is so serious that the municipalities have created inspection units which search the neighbourhoods most affected for concentrations of mosquitoes and educate the population about how to safely accumulate water. In May, the municipality of São Paulo passed a law which authorizes entry by force into homes where it is suspected that there is a concentration of dengue fever mosquitoes.
The connection between the dengue fever epidemic and the water crisis may seem surprising, but it isn’t. All too often we forget that water supply and urban sewerage are two essential services for the health of people. The home water supply was not created for convenience but rather to guarantee the drinking water quality right up to the end user. Likewise, urban sewerage is not only a question of being environmentally friendly, but also of preventing the development of disease.
In this respect, as water management specialists, we have made a firm commitment to the UN’s new Sustainable Development Goals (SDG). The specific mandate of goal 6 leaves no room for doubt. But it is our responsibility to go even further. From our sphere focused on water, we are working to ensure that they are attained. Human development can only be achieved across the board, because the different goals are completely interrelated.
Water is health, and it is not enough to have a sufficient quantity of water. It is equally or more important to manage the water adequately and safely.
Professionalism and rigour must always be present in decisions on the management of this resource if we do not want to endanger our health. And, as my grandmother used to say, “don’t take chances with your health”.