Taking a Bite out of Vector-Borne Diseases
April 10, 2014
Katherine E. Bliss, Senior Associate, Global Health Policy Center
Center for Strategic and International Studies
“Preventing vector-borne diseases” was the 2014 World Health Day (April 7) theme. The World Health Organization (WHO), which organizes the annual World Health Day, is using this year’s slogan, “Small bite: big threat,” to raise awareness about the long-term health, social and economic challenges posed by such debilitating diseases as malaria, dengue, leishmaniasis, and Lyme disease, which are transmitted to humans by mosquitoes, flies, ticks, and other vectors.
A look at what’s happening in the Americas provides a snapshot of how global challenges and progress in addressing vector-borne diseases play out in one region. As I wrote in January, local transmission of Chikungunya virus was reported in the Caribbean for the first time in December, 2013. Officials confirmed the first cases in the French territory of St. Martin, and as of last month, Chikungunya had been reported in 10 Caribbean countries and territories. Chikungunya is most often detected in Africa and South Asia and is transmitted by mosquitoes in the Aedes genus, which are also common throughout the Americas. By March 28, the Pan American Health Organization (PAHO), the regional arm of the WHO, had reported 3,112 confirmed cases in the Caribbean. So far, no cases involving local transmission have been reported on the mainland.
Other vector-borne diseases of concern in the Americas include malaria, dengue fever and Chagas disease. Thanks to strengthened malaria prevention and vector-control measures, countries across the region have made progress in reducing the number of malaria deaths by 70% since 2000, but there are still nearly one and a half million people in the region vulnerable to malaria infection. The incidence of Chagas disease, which follows a bite from the insect that transmits the parasite, trypanosoma cruzi, has also decreased through vector management and education campaigns. Between 1990 and 2006 the number of new cases of Chagas disease, which can cause an enlarged heart and other chronic conditions, decreased from 700,000 to 56,000 per year.
But despite some successes in preventing vector-borne illnesses, controlling the regional transmission of dengue, which causes fever, headache, and severe joint pain, remains a challenge. In 2013, laboratory confirmed cases of dengue, transmitted by the same Aedes mosquitoes as Chikungunya virus, had totaled 480,365 by the end of October. All four types of dengue virus circulate in the Americas, and previous infection with one type increases the chance of more severe illness following infection with a second type. There are currently no vaccines available to prevent infection with malaria, Chagas disease, or dengue, although research to develop vaccines for all three diseases is underway. Recent analysis focusing on the economic effects of dengue infection in eight countries in Asia and the Americas showed that an “average” dengue episode resulted in nearly 15 days of lost productivity and a cost of more than $520.
In Dallas, Texas, where I live, health officials have been gearing up for another season of West Nile Virus, also a vector-borne disease. The warmer weather and increasing humidity over the past few weeks have given rise to a new crop of mosquitoes, which are the vectors for West Nile. West Nile Virus was originally reported in Uganda in 1937 and first reported in North America, in New York, in 1999. The CDC reports more than 39,000 cases in the United States between 1999 and 2012. The majority of people who are infected with West Nile experience no symptoms, but about 20 percent experience headache, fever, and pain, and approximately one in 150 develop high fever and moderate to severe neurological symptoms.
Following an unprecedented number of reported West Nile Virus cases and deaths in North Texas, in 2012, officials began aerial spraying campaigns to kill mosquitoes and expanded community education initiatives regarding West Nile Virus and how to prevent it. Health officials also recognized the importance of regional cooperation, with Dallas, Tarrant, Denton and Collin county officials coordinating planning and response initiatives. Last year Texas reported a total of 172 total cases, with 13 deaths. Because of a change in “reporting requirements” having to do with how cases are defined, it is expected that the number of West Nile Virus cases reported this year reported will rise this year. Officials emphasize what they call the 4 D’s “dress” to avoid mosquito bites; “defend” yourself against bites by using insect repellents; avoid outside activities from “dusk to dawn” and “drain” standing water around the home to eliminate the environments in which mosquitoes breed.
With more than one billion people globally infected by vector-borne diseases each year, and with one million deaths occurring annually as a result, this year’s World Health Day message is that strengthening prevention activities and protecting the most vulnerable social sectors from vector-borne diseases are essential. Through international, regional, and local level cooperation in managing educational campaigns and vector-management activities, community members and public officials can work hand in hand to take a bite out of vector-borne diseases.