No specific treatment exists for a serious mosquito-borne disease that is sweeping into new parts of the globe. Nor are there any vaccines to prevent infection in the first place.
Combating the disease — dengue — largely depends on controlling the mosquitoes that spread it. To that end, a Canadian-funded effort to stem transmission and deaths from dengue in one hot spot for the disease in Bangladesh could help communities worldwide develop strategies to fend it off.
Dengue is a growing global public health concern. Before 1970, severe dengue epidemics had been recorded in only nine countries. Now the disease is endemic in more than 100 countries in Asia, Africa, and the Americas. The World Health Organization reports that half of the world’s population is at risk. Hundreds of thousands of severe cases and more than 20,000 deaths occur annually.
Dengue is caused by any one of four viruses transmitted by Aedes mosquitoes. These mosquitoes were originally found in tropical and sub-tropical regions, but now exist on all continents except Antarctica. They have caused outbreaks of dengue in the southern United States, and been seen as far north as New York and Chicago.
While dengue exists in both rural and urban areas, city dwellers are most at risk. The mosquito disease-carriers reproduce in standing water, which is common wherever people store water at home for drinking and bathing purposes. The rapid growth of cities in tropical countries has led to overcrowding, allowing more dengue-carrying mosquitoes to live closer to more people.
Because of poor knowledge about dengue transmission and lax regulations, construction sites in the booming cities offer ideal breeding grounds. Uncollected garbage also poses a danger, as discarded plastic packaging, tires, and other containers allow water to accumulate and remain stagnant for days. And if there’s no water for hatching, mosquito eggs can survive in dry conditions for more than year.
Humans help spread the virus in other ways — for example, by shipping tires and other containers to faraway places. Increased air travel means the virus can readily travel with its human host to new and distant locations.
Fighting dengue is an uphill battle, made difficult in many areas by weak surveillance systems, inadequate public health services, and a lack of resources to control the mosquito vectors. A more fundamental problem is that little is known about disease transmission dynamics — how changes in land use, in population, climate, pathogen evolution, and international travel and trade can trigger or exacerbate the spread of the disease.
All these factors are at play in the major cities of Bangladesh. The capital, Dhaka, with a population of 17 million, has experienced repeated devastating outbreaks of the severe form of dengue in recent years. But poor public health infrastructure and a lack of resources mean this poor, rapidly growing city lacks even basic knowledge about how much dengue there is, what strains are circulating, and where and when the infected mosquitoes are to be found.
That could soon change thanks to research being carried out by Bangladeshi and Canadian researchers, funded by Canada’s International Development Research Centre. The team brings together Bangladesh’s Ministry of Health and Family Welfare with strong scientific organizations (North South University, International Centre for Diarrhoeal Disease Research, Bangladesh and Jahangirnagar University in Bangladesh with the University of Manitoba and the Public Health Agency of Canada). Also participating are a civil society organization with presence and credibility in city slums, and city ward governments.
Their goal, simply put, is to better understand how dengue is transmitted in the city, focusing on many factors — health, the environment and climate, human behaviour, and urban planning, among others. This knowledge is critical for preventing the spread of the mosquito vector and controlling the virus.
That knowledge can then lead to more strategic investments in public health and healthier working and living environments. Good working relationships between community groups and government agencies will help ensure that solutions work well in the affected areas of the city. Dhaka’s experience and new knowledge gained could also benefit other cities and regions facing similar problems.
By building the capacity of local researchers and government institutions to understand and respond to dengue, and by strengthening international collaboration, the research will not only reduce suffering in the short term, but limit opportunities for new diseases to emerge.
Canadians well understand the potential threat these diseases pose, having dealt with invasions by Severe Acute Respiratory Syndrome and West Nile Virus in the recent past. The more Canada can do to assist developing countries control diseases such as dengue, the better for them and for us.
Dominique Charron and Andrés Sanchez work on ecohealth — the field of ecosystem approaches to human health at the Ottawa-based Canada’s International Development Research Centre. Zapped: the buzz about mosquitoes, a documentary featuring this research, aired January 17 on CBC’s The Nature of Things (video only available in Canada).