Rift Valley Fever in Kenyan pastoral
livestock: Simulation with an individual-
based demographic model
S. Fuhrimann1,2, T. Kimani3, F. Hansen3, B. Bett3, J. Zinsstag1,2, E. Schelling1,2
(1) Swiss Tropical and Public Health Institute, Basel, Switzerland
(2) University of Basel, Basel, Switzerland
(3) International Livestock Research Institute, Kenya
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Rift Valley Fever (RVF) is a viral mosquito-borne zoonosis caused by a phlebovirus. It affects livestock, humans and wildlife. In
East Africa, RVF epidemics occur after unusually heavy rainfalls and flooding and in cycles of 5-15 years. The epidemics are
associated with significant human morbidity and mortality and considerable economic losses throughout the livestock value
chains.
Objective Methods
Establishment of a pastoral livestock demographic model • Data on demographic dynamics of livestock in
and simulate: normal and drought periods ; RVF epidemics ; northeastern Kenya obtained in group discussions and
and alternate prevention and control options. interviews with livestock keepers in 12 villages
• Secondary data on livestock populations, dynamics and
on RFV-specific transmission parameters obtained from
Results and conclusions experts and literature
The model was used to estimate proportions of RVF • Model programmed in the C++ language with the Borland
infections (Figure 1); baseline and RVF-attributable C++ Builder
abortions (Figure 2) and baseline and RVF-attributable • Model used to simulate the following scenarios (i) the
mortalities and offtake under alternate prevention and demographic dynamics of cattle, camels, sheep and goats
control measures. The proportions are grouped in species, in North Eastern-Province; (ii) an RVF outbreak in
age classes and sex. livestock and the RVF immunity status afterwards; and (iii)
Sheep are mostly infected. Sheep and goats are most likely impacts of control measures (combinations of vaccination,
to spread the disease through livestock trade. Slaughtered sanitary measures, surveillance, vector control and
infected sheep are an important risk factor to human RVF awareness campaigns).
infection. The results are further used in the assessment of
cost-benefit and cost-effectiveness of interventions which
should improve future intersectoral livestock – public health
contingency planning. The ratio of susceptible/immune
hosts can further support the prediction system by
.3
consideration of the immunity levels years after a previous
No. abortions / Total pregnancies
outbreak.
.25
.2
Proportions of infected animals
.8
.15
.7
.6
.1
.5
.4
.05
.3
.2
0
.1
Cattle Sheep Goats Camels
0
Cattle Sheep Goats Camels
Figure 2 Modelled baseline abortion
and RVF- without control induced abortions
Figure 1 Modelled proportions of RVF infections by species
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