Gasterophilus larvae in association with primary parasitic periodontitis

Abstract

parasite and usage of targeted selective therapy regimens basing treatment decisions on individual fecal egg counts from all horses on the farm. The established diagnostic method for S. vulgaris involves larval culture and subsequent morphological identification of third stage larvae under the microscope. Recently, a real-time PCR assay was developed and validated for the detection and semi-quantification of S. vulgaris eggs in equine fecal samples. The purposes of the present study were a) to determine the presence of S. vulgaris by real-time PCR in Danish and American horses on farms using vastly different anthelmintic treatment regimens and b) to evaluate the association between larval culture results and the PCR. A total of 991 horses representing 53 different horse farms in Denmark and Central Kentucky were studied. Fresh fecal samples were collected from all horses, and strongyle eggs retrieved for DNA extraction and subsequent real-time PCR analysis. Individual larval cultures were performed on the Danish part of the data set (662 horses on 42 farms). On the Danish farms, the S. vulgaris PCR prevalencewas found to be 9.2% on farms not basing parasite control on fecal egg counts, and 14.1% on farms using selective therapy. None of the 328 horses evaluated on 11 farms in Central Kentucky were PCR positive. Kappa-values indicated a moderate agreement between PCR and larval culture results, while a McNemar’s test revealed no statistical difference between the paired proportions. Statistically significant associations were found between PCR cycle of threshold (Ct) value groups and larval culture counts. Results indicate that both diagnostic methods can be useful for determining the occurrence of S. vulgaris in horses on farms, but that they both are affected by potential sources of error. Agreement between tests was moderate and no direct linear association could be found. The PCR results confirmed previous findings suggesting that S. vulgaris is highly dependent on the anthelmintic treatment intensity, and that selective therapy regimens can be associated with higher occurrence of this parasite.