Does Unplanned Urbanization Pose a Disease Risk in Asia? the Case of Avian Influenza in Vietnam

By Saksena, Sumeet; Finucane, Melissa et al. | Asia - Pacific Issues, January 2017 | Go to article overview

Does Unplanned Urbanization Pose a Disease Risk in Asia? the Case of Avian Influenza in Vietnam


Saksena, Sumeet, Finucane, Melissa, Tran, Chinh C., Duong, Nong Huu, Spencer, James H., Fox, Jefferson, Asia - Pacific Issues


All over Asia, rural dwellers are moving to urban centers in search of better economic opportunities, and cities are growing at an unprecedented rate. In the 50 years between 1965 and 2015, Asia's urban population increased nearly fivefold-from 430 million to 2.1 billion-and by 2015, nearly one-half of all people in Asia were living in cities.1

This urban expansion has been largely unplanned. In city after city, local governments struggle to provide housing, sanitation, healthcare, transportation, and other infrastructure to areas with rapidly growing populations. These "peri-urban" areas, which often surround a core urban zone, represent a transition between rural and urban land-use types. Here new migrants live in crowded conditions with few public services and a poorly developed sense of community.

The conditions that characterize these peri-urban areas have raised concerns about the potential rise of new and reemerging infectious diseases. These affect humans, economically important livestock, or both and include SARS, swine flu, and highly pathogenic avian influenza (HPAI, subtype H5N1). First detected in 1996 in geese in China, avian influenza has been described as the most significant newly emerging pandemic disease since HIV/AIDS.2

Highly Pathogenic Avian Influenza

Wild birds can carry the avian influenza virus without showing any signs of disease. Ducks and geese may also be infected without serious disease signs. But when domestic chickens become infected, the death rates can be catastrophic.

Although they may not be strongly affected themselves, ducks are thought to play an important role in disease transmission in Southeast Asia. Following the region's traditional integrated-farming practices, duck owners transport their birds to and from different rice paddies around a small region. The ducks provide a service to farmers because they eat insects that can damage rice plants and their manure helps fertilize rice paddies. As they travel from paddy to paddy, however, they are in contact with wild birds that carry avian influenza and also with domestic chickens that are highly susceptible to the virus.

Once avian influenza appears in a flock of domestic chickens, the disease can spread rapidly, affecting multiple internal organs and killing 90 to 100 percent of affected birds, often within 48 hours. Outbreaks are generally controlled by killing entire flocks where infection has been detected and monitoring and vaccinating flocks nearby.

Apart from the threat to poultry, avian influenza poses a risk to human populations. The virus was first detected in humans in 1997 during a poultry outbreak in Hong Kong, and since then it has killed more than 400 people in 16 countries.

Up to now, most human infections have occurred following close or prolonged contact with infected poultry. There is concern, however, that the virus could mutate and become transmissible between humans, possibly causing a pandemic worldwide.

To gain a better understanding of the potential link between land use and disease risk, beginning in 2010 the Center teamed with scientists at the Vietnam National University of Agriculture to study the role of unplanned urbanization in the emergence of infectious disease. The focus was on two of the worst outbreaks of avian influenza that occurred in Vietnam between late 2003 and early 2005, in which millions of poultry died from the virus or were culled in an effort to control the disease.

The research goal was to improve understanding of how land-use change associated with urbanization and agricultural intensification might contribute to outbreaks of avian influenza in poultry. Such understanding could help policymakers identify specific areas at highest risk of a disease outbreak, making government prevention programs more effective and more efficient in terms of cost.

Why Chickens? Why Vietnam?

By providing a valuable opportunity for poor families to improve their own nutrition and to generate a cash income, chickens play an important role in economic development. …

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