Swiss TPH, Socinstrasse 57, P.O. Box, 4002 Basel, SwitzerlandT +41 61 284 81 11, F +41 61 284 81 01, www.swisstph.ch

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.

Rift Valley Fever in Kenyan pastoral livestock: Simulation with an individual-based demographic model

Results and conclusionsThe model was used to estimate proportions of RVF infections (Figure 1); baseline and RVF-attributable abortions (Figure 2) and baseline and RVF-attributable mortalities and offtake under alternate prevention and control measures. The proportions are grouped in species, age classes and sex. Sheep are mostly infected. Sheep and goats are most likely to spread the disease through livestock trade. Slaughtered infected sheep are an important risk factor to human RVF 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 consideration of the immunity levels years after a previous outbreak.

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

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Figure 2 Modelled baseline abortion and RVF- without control induced abortions

ObjectiveEstablishment of a pastoral livestock demographic model and simulate: normal and drought periods ; RVF epidemics ; and alternate prevention and control options.

Methods • Data on demographic dynamics of livestock in

northeastern Kenya obtained in group discussions and interviews with livestock keepers in 12 villages

• Secondary data on livestock populations, dynamics and on RFV-specific transmission parameters obtained from experts and literature

• Model programmed in the C++ language with the Borland C++ Builder

• Model used to simulate the following scenarios (i) the demographic dynamics of cattle, camels, sheep and goats in North Eastern-Province; (ii) an RVF outbreak in livestock and the RVF immunity status afterwards; and (iii) impacts of control measures (combinations of vaccination, sanitary measures, surveillance, vector control and awareness campaigns).

0.0

5.1

.15

.2.2

5.3

No.

abo

rtion

s/ T

otal

pre

gnan

cies

0.0

5.1

.15

.2.2

5.3

No.

abo

rtion

s/ T

otal

pre

gnan

cies

Cattle Sheep Goats Camels

Figure 1 Modelled proportions of RVF infections by species

Cattle Sheep Goats Camels

Pro

porti

ons

of in

fect

edan

imal

s0

.1.2

.3.4

.5.6

.8.7