Studies On Strongyloid Nematodes Of The Donkeys In Henan Province

Strongyloid nematodes belong to family Strongylidae, suborder Strongylina, order Rhabditida. Infections of equids (inculding horse, donkey, mule and zebra) with strongyloid nematodes are of major veterinary importance. Adult strongyles inhabit in the large intestine of equids, leading to severe disease or death. Many studies on equine parasites have been carried out in various parts of the world, but there is no detailed survey except taxonomy in China. This study is the first report about the species, morphological description, epidemiology and phylogeny of strongyloids nematodes in the large intestine of donkeys in Henan Province, China.Thirty-four donkeys from Henan Province were examined at necropsy for strongyloid nematodes in the large intestine from February 2006 to January 2007. Twenty-two species belonging to 8 genus and 2 subfamilies were identified. Of all strongyloid nematodes, some species are of large number, for example, Delafondia vulgaris, Cylicocyclus nassatus, Coronocyclus labratus, Cyathostomum tetracanthum and Cylicocyclus auriculatus. However, other species are of small number, for example, Cylicocyclus elongatus, Cylicostephanus calicatus, Cylicocyclus adersi, Parapoteriostomum euproctus, Triodontophorus nipponicus, Triodontophorus serratus and Alfortia edentatus.Twenty-two species of strongyloid nematodes were measured, redescribed and photographed through observation under light microscopy and scanning electron microscopy (SEM). SEM observations of strongyles were made at first time in China and the results will provide new characters for the identification and taxonomy. Morphological characters of strongyles in this study were similar to that reported in previously reported, but differences were also found in the numbers of external leaf crown and the length of body, esophagus, spicules, vagina and tail. These differences were considered as intraspecific variation, which can be related to the host, geographical location and climatic conditions.Epidemiological investigation showed that total numbers of strongyles ranged from 120 to 1939 worms, with a mean of 499 worms per donkey. The numbers of species ranged from 1 to 15 worms per donkey. Only 5.9% of donkeys were infected by a single species, the other were infected with multiple species. Of 22 strongyles, the four most prevalent species are D. vulgaris (88.2%) C. nassatus (73.5%), C. labratus (70.6%) and Coronocyclus labiatus (67.6%). Whereas C. labratus (175.9±291.3), C. tetracanthum (156.0±251.7), C. auriculatus (127.2±221.7) and C. nassatus (110.1±124.4) are the species with the greatest mean intensity. The three most abundant species are C. labratus (124.2±256.4), C.tetracanthum (96.4±210.5) and C. nassatus (80.9±117.1). In addition, season was a significant factor on the effect of species distribution, the prevalence and mean abundance of 22 strongyles. The species richness of strongyles examined are the most in autumn, followed by spring, summer and winter. The major of the species has much higher prevalence and mean abundance in spring and autumn than in summer and winter. Epidemiological investigation on strongyloid nematodes was the first study in China.Internal transcribed spacer (ITS) and 5.8S of ribosomal DNA (rDNA) of 7 species of the genus Cylicocyclus (C. radiatus, C. adersi, C. ashworthi, C. auriculatus, C. elongatus, C. insignis and C. nassatus) were amplified and sequenced using polymerase chain reaction (PCR) techniques. The length of the ITS1-5.8S-ITS2 sequences ranged from 829 to 843bp, and there are 88 variable sites and 56 parsimony informative sites. The length of the ITS1 sequences ranged form 366 to 370bp, with 22 variable sites and 14 parsimony informative sites. The length of the ITS2 sequences ranged from 307 to 321bp, with 66 variable sites and 42 parsimony informative sites. The 5.8S gene sequences of all 7 species are identical. For all 7 species, the G+C content is higher in the ITS1 (45.8-47.7%) than in the ITS2 (39.2-41.9%). Pairwise comparison revealed differences in sequences ranging from 1.4 to 3.8% in the ITS1 and from 3.1 to 14.3% in the ITS2.Based on ITS1 and ITS2 sequences from the above 7 species and 5 species of the genus Cylicocyclus (C. ashworthi, C. brevicapsulatus, C. insignis, C. leptostomus and C. nassatus) from Genebank, neighbor-joining (NJ) tree and maximum-parsimony (MP) tree were built using Cylicostephanus longibursatus as outgroup employing PAUP 4.0 (Phylogenetic Analysis Using Parsimony. 4.0 beta version) software. The results showed that C. brevicapsulatus was always on a branch external to the other species in the NJ and MP tree, as indicated that there was a distant relationship between C. brevicapsulatus and the other species. While C. nassatus, C. radiatus, C. ashworthi and C. leptostomus always clustered together, and this demonstrated they have a closed relationship. However, C. leptostomus always clustered with 3 individuals of C. ashworthi, and they could not be completely separated in the NJ and MP tree. This suggested that cryptic species may be existent within C. ashworthi or C. ashworthi and C. leptostomus are the same species. Of course, this problem still need to be further studied.