Rift Valley fever in small ruminants, Senegal, 2003

Abstract

During the 2003 rainy season, the clinical and serologic incidence of Rift Valley fever was assessed in small ruminant herds living around temporary ponds located in the semi-arid region of the Ferlo, Senegal. No outbreak was detected by the surveillance system. Serologic incidence was estimated at 2.9% (95% confidence interval 1.0-8.7) and occurred in 5 of 7 ponds with large variations in the observed incidence rate (0%-20.3%). The location of ponds in the Ferlo Valley and small ponds were correlated with higher serologic incidence (p = 0.0005 and p = 0.005, respectively). Rift Valley fever surveillance should be improved to allow early detection of virus activity. Ruminant vaccination programs should be prepared to confront the foreseeable higher risks for future epidemics of this disease.

Figure 1

Location of the study of Rift Valley fever serologic incidence (Barkedji) and sentinel herds of the national surveillance system during the 2003 rainy season in Senegal.

Figure 2

Location of ponds and settlements for the study of Rift Valley fever serologic incidence in 610 small ruminants during the 2003 rainy season in the Barkedji area, Senegal.

Figure 3

Serologic incidence rate of Rift Valley fever in small ruminants (N = 610), according to the location of the pond (A, in Ferlo River bed; B, outside Ferlo River bed) and its maximum surface during the 2003 rainy season in the Barkedji area, Senegal. Points indicate observed pond-level serologic incidence. Solid line indicates population mean of the serologic incidence estimated with the best Bayesian information criterion mixed-effect logistic regression model. Dashed lines indicate pointwise 95% confidence interval corresponding to these estimates. ha , hectares.