Embodiments of the presently-disclosed subject matter provide an isolated polypeptide comprising the sequence of SEQ ID NO: 1, fragments thereof, and/or epitopes thereof. Embodiments of the presently-disclosed subject matter also provide methods for diagnosing a Strongylus vulgaris infection in a subject that comprises providing a biological sample from the subject and contacting the sample with the present isolated polypeptide, fragment thereof, and/or epitope thereof. In some embodiments the Strongylus vulgaris infection can be detected during a prepatent period. In further embodiments the subject is a horse.