Rift valley fever risk mapping and modelling in Tanzania
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Date
2015
Authors
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Publisher
Sokoine University of Agriculture
Abstract
Rift Valley fever (RVF) was first reported in Tanzania in 1930 and the last outbreak
occurred in the country in 2006/07. Besides the long history of RVF in the country, little is
known about its spatial and temporal epidemiology and habitat suitability for its
occurrence. This study was conducted to determine potential risk factors and develop the
country RVF risk map. Enzyme-linked immunosorbent assay was used to examine the
presence of antibodies specific to RVF virus (RVFV) in serum samples from domestic
ruminants, humans and wild animals. Logistic regression modelling was used to analyze
RVF outbreak data and RVFV seropositivity. Space-time permutation and MaxEnt
modelling were used to identify clusters and habitat suitability for RVF occurrence,
respectively. Between 1930 and 2007, there were a total of 10 RVF outbreaks with
overlapping of clusters that continuously covered more parts of the country. Overall, the
seroprevalence of IgG specific to RVFV in domestic ruminants (n = 1435) was 25.8%
(95% CI: 23.52, 28.05) and in humans (n = 541) was 10.7% (95% CI: 8.11, 13.34). The
IgG specific to RVFV was detected in nine (n = 22) and one (n = 3) serum samples from
African buffalo and African elephant, respectively. The potential risk factors for RVF
occurrence included eastern Rift Valley ecosystem (OR = 6.14, CI: 1.96, 19.28), rainfall
during the previous two months >405.4mm (OR = 12.36, CI: 3.06, 49.88), clay (OR
=8.76, CI: 2.5, 30.5) and loam (OR = 8.8, CI: 2.0, 37.8) soil texture, introduction of
domestic ruminants into the herd (OR = 5.08, CI: 2.74, 9.44; p< 0.001), human contact
with aborted foetus materials (OR = 2.89, CI: 1.48, 5.60), human participation in the
slaughtering of animals (OR = 2.65, CI: 1.39, 5.04), human having consumed meat from
dead animals (OR = 2.06, CI: 1.05, 4.00). The findings of this study have shown that the
north-eastern, central and lake zones of the country have larger amount of suitable habitat
for RVF occurrence than the north-western and southern zones. These research findingsiii
can be applied to guide risk-based cost-effective RVF surveillance and interventions
strategies in the country.
Description
PhD Thesis
Keywords
Rift valley fever, risk mapping, Tanzania, risk modelling, temporal epidemiology, spatial epidemiology