Purpose: The purpose of the study was to survey African Horse Sickness (AHS) virus prevalence in healthy horses and identify the serotypes circulating in Senegal. This study was conducted one month prior to the notification of the first AHS clinical case in northern Senegal and before mass vaccination against eight serotypes took place. Methods & Materials: Between 12-19 August 2007, 414 horses were randomly sampled in three zones in the Senegal River delta: St.-Louis, Ross Bethio and Richard Toll. The blood samples collected from 138 horses in each zone were centrifuged, stored at -20 °C, and later tested by competitive ELISA. A random sample of 71 positive horse sera was analyzed by Plaque Reduction Neutralization Test (PRNT) on Vero cells against African Horse Sickness Virus (AHSV) serotypes. Cytopathogenic effects were read four days later. Statistical data analysis was done using R software. Results: The overall true seroprevalence rate by ELISA test was 89.5% in 414 horse sera. In the subset of 71 infected horses, antibodies against AHSV 2 were detected in 67.5%, against AHSV 7 in 92.96% and against AHSV 9 in 100% of horses. AHSV 7 antibodies were found in 80.95% of the positive horses from Ross-Bethio, 95.45% from St.-Louis, and 100% in Richard-Toll zones. Conclusion: Prior to this study, only the monovalent vaccine against AHSV serotype 9 was used on horses in the area. The polyvalent vaccine against eight types of AHSV was first used after our sampling. Our results reveal the presence of antibodies against AHSV 7, which suggests that Serotype 7 virus had been circulating prior to the mass vaccination. Chi-square test for the three serotypes showed that they are not independent. Based on these results we hypothesize that the vectors of AHSV 9 in the Senegal River delta may be the same vectors that introduced and spread AHSV 2 and AHSV 7. This work is the first description of AHSV 7 in Senegal.