In the Americas, nearly 106 million people in 21 countries live in areas at risk for malaria transmitted by the bite of the different Anopheles mosquito species. Almost the entire population of the Region, 35 countries in all, with the exception of Canada and mainland Chile, lives with the Aedes aegypti mosquito, capable of transmitting dengue, chikungunya, and yellow fever viruses.
The Lutzomyia sand fly, with different species, is the principal vector for leishmaniasis transmission. Likewise, lymphatic filariasis is transmitted by mosquitoes of the Culex genus, while triatomine species (known as kissing bugs, among other names), such as R. prolixus and T. dimidiata, are the main vehicle for Chagas disease transmission. Similarly, snails of the Biomphalaria genus are the main intermediate host for schistosomiasis.
It is estimated that nearly 13 million people in the Americas are at risk of contracting lymphatic filariasis (elephantiasis). Plus, some 700,000 cases of leishmaniasis were reported from 2001 to 2011, and 1.6 million people, mainly in Brazil and Venezuela, required treatment for schistosomiasis. Every year, Chagas disease infects thousands of people鈥攃ausing some 28,000 new cases annually鈥攁nd in 2010, an estimated 6 million people had the disease.
Dengue is an example of a vector鈥恇orne disease that has an enormous negative impact on the public health and the economy. Before the 1970s, dengue epidemics had only been reported in nine countries, mostly in Southeast Asia. In the second half of the 1970s, reports of dengue epidemics began to increase in South America, North America, and the Caribbean. In recent decades, Latin America has become the region with the highest reported annual figures in the world.
Aedes aegypti is capable of transmitting the four different dengue serotypes (DENV鈥1, 鈥2, 鈥3, and 鈥4), and is fully adapted to urban conditions. Reinfections with the different serotypes can occur and depending on the sequence of the virus involved, frequency, and conditions at the time of reinfection, dengue can present serious hemorrhagic symptoms, which can lead to death if not properly treated. There is still no vaccine available against the virus, and consequently disease prevention actions are more aimed at vector control (chemical, environmental management, individual protection).
The life cycle of vectors, as well as the chain of disease transmission, is closely related to the environmental dynamics of the ecosystems they inhabit. Moreover, the limitations on their development are determined by environmental variables such as temperature, precipitation, moisture, and land use, among others. Climate variability has shown a direct influence on vector biology and ecology, and consequently an impact on the risk of transmission of these diseases.
At present, climate change is raising concerns over the possible expansion in incidence of these diseases. The effect of climate change is seen in extreme events, which are introducing major fluctuations in weather cycles. For example, an increase in rainfall patterns has the potential to increase the number (and ideal conditions) of breeding sites where vectors such as mosquitoes, ticks, and snails reproduce. Extreme temperatures can slow down or speed up the development and survival of insect vectors, as well as the incubation period of some pathogens.
Climate alone cannot explain the entire natural history of vector鈥恇orne diseases, but it is an important component in the temporal and spatial distribution of disease vectors, whether limiting their expansion or influencing the dynamics of their transmission.
Migration, increases in air and land traffic, and urban sprawl have also facilitated the reproduction and expansion of some of these vectors and the spread of disease. Characteristics such as population density and adaptability of the vector to a human environment are correlated with infection distribution and frequency. In large cities, especially where urban infrastructure is poor (substandard housing, uncovered water containers, lack of sanitation etc.), the irregular use of space enables the creation of habitats favorable to vectors and their consequent spread.
It is also worth mentioning that some countries have documented and reported on patients who do not respond well to treatments to cure these diseases, and on insecticide鈥恟esistant vectors, which are signs of serious challenges in the struggle to control and eliminate these diseases.
In view of the serious health risks and harm from the vectors that transmit these diseases, and recognizing the limited availability of effective drugs and vaccines for the treatment of some of them, infection prevention and vector control are essential to reducing the burden of vector鈥恇orne diseases.
Integrated vector control can decrease the risk of disease transmission, since these diseases cannot spread if there is no contact between the host (human beings) and the vector. Integrated vector control is aimed at optimizing and rationalizing the use of resources and tools by building country capacity, including surveillance, case monitoring, and evaluation of actions, along with community health education and promotion, and working together with partners and allies. Integrated vector control is also geared to the control or elimination of vectors, through rational insecticide use, legal instruments (regulations and laws), and a combination of these, using methods that are less hazardous to the environment and to the health of agricultural workers and communities in areas where transmission occurs.
To ensure the sustainability of these actions, changes should also be made that impact health determinants associated with the persistence of these diseases, such as improving access to safe water, waste collection services, basic sanitation, education, hygiene, and adequate housing, among others.
Finally, people and communities have an equally essential role in infection prevention actions. This includes individual protective actions such as wearing clothing that acts as a barrier to exposure to bites, using mechanisms to keep vectors out of houses (screens on doors, windows, and eaves), and taking action to reduce breeding sites near houses or in communities (covering water storage containers, elimination of puddles and drainage of places where water accumulates, elimination of unusable containers where water pools, and refuse control in yards and gardens).
