Cutting surveillance for mosquito-borne diseases would likely lead to an exponential increase in both the number of human cases and the financial costs when a disease outbreak occurs, according to an analysis by Emory researchers.

The Public Library of Science published the research, led by disease ecologist Gonzalo Vazquez-Prokopec.

“Our analysis shows that halting mosquito surveillance can increase the management costs of epidemics by more than 300 times, in comparison with sustained surveillance and early case detection,” he said.

The research was prompted by a U.S. government proposal last spring to slash funding for the vector-borne disease program of the Centers for Disease Control and Prevention. Congress ultimately voted to retain the program’s budget at the same levels, for 2011.

“This analysis provides scientific-based evidence of the need for more funding of mosquito surveillance, not less,” said Uriel Kitron, a co-author of the study and the chair of Emory’s Department of Environmental Studies.

High-risk across the globe
Diseases spread by mosquitoes and other blood-sucking vectors are major public health risks worldwide. They include a wide variety of bacterial, parasitic and viral infections, such as malaria, West Nile virus, dengue fever and Lyme disease.

The Emory analysis used data from two outbreaks of dengue fever in Cairns, Australia, that occurred in 2003 and 2009. (Dengue fever, an extremely debilitating viral disease spread by mosquitoes, can be fatal.)

A mathematical model used the Cairns data to evaluate the economic impact of hypothetical epidemics and different response times to them.

A response within two weeks of the outbreak was assumed to occur when there was active disease surveillance. And a delay of six to eight weeks was assumed when there was no active surveillance.

In Cairns, where mosquito surveillance is active, the reactions to the dengue fever outbreaks were rapid. The costs of the epidemics – including vector control, case diagnosis, blood screening and work days lost to disease – totaled US$150,000 for the 2003 outbreak and US$1.1 million for the 2009 outbreak.

The analysis showed that a delayed response of four to six weeks to both Cairns dengue outbreaks would have resulted in drastically escalated costs of up to US$382 million. A slight increase in the virulence of the strain could have multiplied the cost by another 10 times.

Cairns has a tropical climate similar to South Florida, where a dengue fever outbreak occurred in 2009, Vazquez-Prokopec noted. “Predictions based on our analysis show that, if the Miami area had not had a surveillance system in place, the costs to control the Florida outbreak could have been higher than the entire U.S. budget for mosquito surveillance,” he said.

Emerging threats

While the modern-day United States has been relatively unscathed by vector-borne disease, it is not immune to a host of new and emerging pathogens, the researchers warned.

The emergence of West Nile virus in New York City in 1999 spurred better mosquito surveillance, and serves as an example of the consequences of a delayed response. By the time a correct diagnosis was made and proper controls were initiated, the pathogen had spread throughout the country. By the end of 2008, West Nile had generated 28,961 known cases and 1,130 fatalities.

Co-authors for the study also include Emory disease ecologist Luis Chaves and S. Ritchie and J. Davis from the Cairns Tropical Public Health Unit.

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