Mosquitoes, urban man and disease: a new look

Humans are a peripatetic bunch, and that creates real problems for controlling diseases--particularly mosquito-borne diseases like dengue.

When an infected person travels, say, from home to a workplace on the other side of the island, a mosquito feeding at the new location suddenly introduces the disease there.

(Image: The mosquito Aedes aegypti feeding. This mosquito, sometimes called the Yellow Fever Mosquito is implicated in dengue fever as well. It is a day-biting mosquito present in Hawai'i, but other mosquito species can also spread such diseases. Credit: Centers for Disease Control and Prevention.)

“Even a short visit to an infected patch of mosquitos, say at a lunch venue or open market, may be enough to keep the virus circulating,” said University of Hawai'i researcher Durrell D. Kapan.

And when another worker gets bit, and goes to home to a different part of the island, the disease leapfrogs once more.

Researchers from the University of Hawai'i and elsewhere reviewed these problems in a paper, Man Bites Mosquito: Understanding the Contribution of Human Movement to Vector-Borne Disease Dynamics.

The authors are Kapan, of the Center for Conservation and Research Training, Pacific Biosciences Research Center, University of Hawaii at Manoa, and mathematician Ben Adams, of the Department of Biology, Kyushu University, in Fukuoka, Japan, and the University of Bath in the United Kingdom. The paper is available at http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0006763

Dengue, also known as break-bone fever for the kind of pain it inflicts, has been a problem in Hawai'i, and is even more prevalent elsewhere in the Pacific. Between 50 million and 100 million people are infected each year.

“Even a small number of infected people who remain active can move a virus such as dengue between different parts of the community, where it will be picked up by mosquitos and, after an incubation period, be passed on to another unsuspecting passerby,” Kapan said in a University of Hawai'i news release.

So how do you deal with a leapfrogging virus in a modern commuting population?

“Our research examined whether the standard practice of eliminating mosquito vectors at residences would be sufficient to control dengue if other areas in the community still had several large patches of mosquitos that could become infected by commuters,” Kapan said.

The authors sought out the support of UH Mānoa’s Pacific Center for Emerging Infectious Diseases Research Center of Biomedical Research Excellence program (http://www.hawaii.edu/pceidr/), and UH Mānoa’s National Science Foundation Integrative Graduate Research Traineeship (IGERT) in Ecology, Conservation and Pathogen Biology (http://www2.jabsom.hawaii.edu/igert/).

Their conclusion was that traditional vector control programs may not be sufficient, and new approaches are needed.

“Our primary objective with this paper is to prompt researchers, public health practitioners and others concerned with vector control to ...consider novel ways to control community transmission of vector-borne diseases that account for great morbidity and mortality worldwide,” says Kapan.

An example of the problem: “Singapore, for example, has for many years implemented a vigorous program of domestic vector source reduction and insecticide spraying in a full GIS-enabled public health protection effort. Nevertheless dengue continues to circulate and, after a brief period of respite, outbreaks are becoming increasingly severe,” their paper says.

In someways, the authors suggest, it is the humans who are the vectors, hauling the disease from one mosquito population to another.

“When someone gets infected we need to look at their recent travel patterns to figure out from which group of mosquitoes they got the disease, and to which groups they may have passed it on,” Adams said.

© Jan TenBruggencate 2009