West Nile virus epidemic in horses, Tuscany region, Italy

Abstract

During the late summer of 1998, veterinary authorities in Tuscany, Italy, received reports of cases of neurologic disease among horses residing in a large wetland area located in the provinces of Florence and Pistoia. West Nile virus was isolated from two of the six horses that died or were euthanized. A retrospective epidemiologic study identified 14 clinical neurologic cases that occurred from August 20 to October 6 (attack rate of 2.8%). A serologic survey conducted over a 700-km2 area in stables with and without apparent clinical cases confirmed a wider spread of the infection, with an overall seroprevalence rate of 38% in the affected area. No significant differences in age-specific prevalence were observed, suggesting that the horses residing in the area had not been exposed previously to West Nile virus and supporting the hypothesis of its introduction in the wetland area during the first half of 1998.

Figure 1

Map of the study area, showing the inner polygon within the restricted zone (zone A), the corridor area (zone B), and the redrawn corridor area (zone C), in the provinces of Firenze, Lucca, and Pistoia, Tuscany Region, Italy.

Figure 2

Number of neurologic cases in horses by week of onset, Valdinievole District, Tuscany, Italy, August–October 1998.

Figure 3

West Nile virus age-specific prevalence (n=282) in horses, Tuscany Region, 1998–1999.