Disease
Reemergence
Despite great strides in schistosomiasis
control over the past several decades in
Sichuan
province,
China,
the disease has reemerged in areas in which it was previously
controlled. Up to the end of 2004, seven of 21 counties under
transmission control, and one of 25 under transmission interruption,
have been confirmed to have local disease transmission. This
project, supported by the
NIH National Institute of Allergy & Infectious Diseases,
explores
the determinants of schistosomiasis
re-emergence and aims to
understand:
1) Why disease reemergence occurs
2) Why reemergence occurs in some
populations earlier than others
3) What environmental and
socio-demographic factors are associated with disease reemergence.
Understanding the environmental and
socio-economic conditions that favor reemergence can aid in the design
and implementation of both sustainable disease control activities
and schistosomiasis
surveillance programs for its early detection
in the agriculturally rich
Sichuan
Province
and in other endemic areas of the world. We are using
epidemiological and environmental data from historical records and
remote sensing to compare the a sample of reemergent and non-reemergent
villages in China. We will test the hypothesis that the time of
reemergence of transmission is determined by internal potential and
connectivity.
Internal
Potential
The
internal potential of a village is a measurement of village-level social
and environmental conditions that facilitate human transmission, upon
introduction of a parasite into a village’s environment.
Examples of these conditions include
favorable
snail habitat, the number of human and animal hosts, crop-dependent
irrigation and fertilization practices, and water contact intensity.
(Top) | Methods:
Field epidemiology
Connectivity
This
variable
relates
to the degree to which each study
village is linked via social and environmental pathways to other
potentially endemic or re-emergent areas and, hence, how susceptible
each study village is
to the introduction of the parasite from external sources.
We hypothesize that the
key
pathways of connectivity are
hydrological, via irrigation channels and streams, or socioeconomic, via
the
movement
of infected individuals or animals. Some factors that
might determine connectivity include hydrological dynamics of the
upstream watershed and village-level accessibility as defined by the
density and nature of roads and trails.
(Top) | Methods: Geographic
Information Systems/ Remote Sensing,
Hydrology,
Field epidemiology
Temporality
Because the areas under study are not
static, we will use historical data to reconstruct conditions at time of
control through the time of re-emergence. Using administrative records
and images as well as data conducted at present, we can define measures
of internal potential and connectedness during each time point of
interest.
(Top) | Methods:
Geographic
Information Systems/ Remote Sensing
,
Field epidemiology