Researchers at the Johns Hopkins
Bloomberg School of Public
Health studying dengue hemorrhagic fever epidemics in
Thailand have determined that the disease radiates outward
in a traveling wave from Bangkok, the nation's largest
city, to infect every province in the country. According to
the researchers' analysis, the spatial-temporal wave
travels at a speed of 148 kilometers per month and takes
about eight months to spread through the entire country.
The analysis appears in the Jan. 22 edition of the journal
Nature.
"We used a new mathematical technique developed by
NASA for analysis of waves in physical materials —
like water waves and sound waves — to study "epidemic
waves" of dengue cases. Our study is the first step to
understanding the mechanism of how a disease like dengue
spreads through the country," said lead author Derek
Cummings, a doctoral candidate at the schools of
Public Health and
Engineering.
"Anticipating dengue epidemics and determining the causes
of those epidemics could help us plan control strategies
more effectively."
Dengue fever is a mosquito-borne illness that infects
50 million to 100 million people worldwide each year, many
of them children. Epidemics of the most serious and
life-threatening form of the disease, dengue hemorrhagic
fever, place a heavy burden on public health systems.
The number of cases of dengue hemorrhagic fever in
Thailand varies widely from year to year. Cummings and his
colleagues examined the spatial-temporal dynamics of dengue
hemorrhagic fever in a data set describing 850,000
infections that occurred between 1983 and 1997. Their
analysis showed that outbreaks in provinces surrounding
Bangkok were either synchronous or lag behind Bangkok,
which indicated a repeating spatial-temporal wave emanating
from the city. The researchers do not know exactly why the
wave occurs, but they believe it is related to the movement
of people. Bangkok is heavily populated, and it is the
cultural and economic center of Thailand.
Donald S. Burke, co-author of the study and professor
of international health
at the School of Public Health, said, "Disease surveillance
and control in Bangkok may help surrounding regions prepare
for future outbreaks of dengue fever. Our results suggest
that high priority should be placed on surveillance and
control systems in urban areas of Southeast Asia."
Research was supported by grants from the National
Oceanic and Atmospheric Administration's Joint Program on
Climate Variability and Human Health and the Bill and
Melinda Gates Foundation.
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