World Health Day 2014: Small Bites, Big Threats

Vector-borne diseases are infectious diseases spread by intermediate organisms, such as insects and snails that transmit viruses, parasites, and bacteria to humans. These diseases cause a high burden of illness and death for individuals, their families, and communities, especially in poorer countries; they lead to school absenteeism, worsening of poverty, a negative impact on the economic productivity, high health costs and overloaded health systems in countries. Vector-borne diseases exercising significant impact in the Americas are mainly malaria, dengue, Chagas disease, leishmaniasis, lymphatic filariasis, schistosomiasis, and trachoma. Vector-borne diseases is the theme for World Health Day 2014 which is celebrated every 7th of April.

"Step up the fight against vector-borne diseases in the Americas"

Vector-borne diseases—diseases carried by insects, ticks, and small animals—are a serious and shifting public health threat in the Americas. They include long-established diseases such as malaria, yellow fever, Chagas disease, and dengue as well as newer imports such as West Nile virus, which arrived in North America in 1999, and chikungunya, first reported in the Caribbean in December 2013. An estimated 545 million people in the Americas are at risk of dengue, and some 145 million are at risk of malaria, with millions more at risk of other vector-borne diseases. The risk and range of these diseases could grow as globalization, increased travel and shipping, climate change, and urban sprawl expand the range of some vectors beyond their traditional areas.

In the Americas, deaths from vector-borne diseases have declined dramatically in recent decades. However, they continue to cause misery and hardship as a result of illness and disabilities that can include heart failure, paralysis, blindness, and disfigurement. Major outbreaks—as with dengue fever and chikungunya—can overburden hospitals and local health services. Although the impact of these diseases is greatest on low-income countries and people, no one is immune. All of us—rich and poor, from North and South—are at risk when these diseases are not controlled.

The countries of the Americas have a long tradition of working together to fight shared public health threats, and today we have the tools and knowledge needed to tackle these diseases. Publicly funded programs to control mosquitoes and other disease-carrying insects have proven key to reducing their impact. Large-scale drug treatment of communities in combination with vector control can even eliminate some of these diseases. Investing in these prevention and control programs is an urgent priority.

The successes achieved so far are today being threatened by the expansion of mosquitoes and other vectors into new habitats and by the emergence of insecticide and drug resistance. To protect our achievements and ensure further progress, the Pan American Health Organization/World Health Organization (PAHO/WHO) and its partners are calling for stepped-up action in the fight against vector-borne diseases in the Americas. Everyone has a role to play. We urge…

Governments to

Ensure political commitment and public funding for vector-control programs based on an integrated approach.
Invest in water and sanitation, waste collection, and urban drainage, especially in areas that are currently underserved.
Share proven strategies and lessons learned through country-to-country cooperation initiatives.

Health authorities to

Improve surveillance and monitoring of vector-borne diseases.
Integrate prevention and control of vector-borne diseases with programs to control other diseases.
Strengthen monitoring of insecticide and drug resistance, and ensure an effective response.
Collaborate with other government agencies and sectors, especially the environment, tourism, and education, to strengthen action for prevention and control of vector-borne diseases.
Work with local authorities to implement vector-control and elimination measures, including safe water supply, sanitation and drainage, control of breeding sites, healthy housing, and garbage collection.

Individuals and families to

Clean up around their homes and offices to eliminate vegetation, rubbish, and standing water that can serve as breeding sites for mosquitoes and other vectors.
Protect oneself by wearing long-sleeved clothing, applying insect repellent, and using window screens or bed nets as appropriate.
Work with governments to improve social and environmental conditions, especially sanitation, waste management, and protection of water sources.

International partners and donors to

Support the strengthening and sustainability of programs for control and elimination of vector-borne diseases.
Where needed, provide donations or subsidies of medicines for the control of vector-borne diseases.
Provide incentives for research and development of new, safer, and more environmentally adapted insecticides; next-generation vector-control tools; and innovative medicines and diagnostics.

Protect yourself and your environment

Vector-borne diseases can be prevented by:
- Wearing clothing that acts as a barrier to exposure to bites
- Using mechanisms to keep vectors out of houses such as screens on doors, windows, and eaves
- Reducing breeding sites near houses or in communities by:
  - covering water storage containers,
  - eliminating puddles and drainage of places where water accumulates,
  - eliminating unusable containers where water pools, and
  - controlling garbage in yards and gardens.

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—causing some 28,000 new cases annually—and in 2010, an estimated 6 million people had the disease.
Dengue is an example of a vector‐borne 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‐1, ‐2, ‐3, and ‐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‐borne 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‐resistant 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‐borne 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).