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.

In 2001 and 2002, 235 outbreaks of bluetongue were observed in the Lazio and Tuscany regions of central Italy. During entomological surveillance Culicoides imicola, the main vector of bluetongue virus in the Mediterranean region, was detected in only 14 of 28 municipalities affected by outbreaks; Culicoides obsoletus was the most abundant species, contributing 83 per cent of individuals in catches, whereas C. imicola contributed only 2 per cent. In affected municipalities the maximum catch of C. obsoletus was 18,000 specimens, compared with 54 of C. imicola. In October 2002 bluetongue virus serotype 2 was isolated from a single pool of wild-caught, non-blood-engorged parous C. obsoletus inoculated on to BHK-21 cells. Its identity was confirmed by reverse transcriptase-PCR.

Equine arteritis viruses (EAV) from Europe and

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Serological diagnosis of equine infectious anaemia virus (EIAV) infections has depended mainly on the agar gel immunodiffusion test (AGIDT). This study documents the presence of EIAV genetic sequences in a number of persistently infected horses and mules whose serums were interpreted as negative/equivocal on AGIDT, but positive on more than one ELISA test and in immunoblot tests. Strategies designed to take advantage of the combined strengths of the ELISA and AGIDT are shown effective in a national surveillance program for EIA in Italy where 17 per cent (25/149) of the equids considered to be infected with EIAV on combined/ comparative serological data had reactions in the AGIDT that were interpreted as negative or equivocal. These data document the benefits of using a three-tiered laboratory system for the diagnosis of EIA. Although the ELISA-first strategy introduces some confusing results, the discovery of up to 20 per cent more cases of EIA makes it compelling. In our opinion, it is better and more defensible to find two samples in 1000 with resolvable but falsely positive ELISA tests for EIA than to release two to three horses in 10,000 with falsely negative test results for EIA (the rates seen in the Italian surveillance presented here).

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