Critical points in morphological descriptions of adults and larvae of Strongylidae in equids

AIM – Strongylidae, which includes the most common parasites of equids, have been historically difficult to identify. Molecular methods, whose use is taking place in recent years, have the disadvantage of being expensive and have been developed only for the most prevalent strongylid species. That is why, more extensive studies of the strongylids by classical morphological methods are still necessary. The aim of this study is to update the knowledge about the species of nematode parasites affecting Italian donkeys and give a critical review about identification keys for larvae (Euzeby J, 1981, Diagnostic experimental des Helminthoses animales, Information Technique des Services Veterinaires, Ministère de l’Agricolture, Paris, F) and adults (Lichtenfels JR et al, 2008, Vet Parasitol, 156: 4-161) of Strongylidae. MATERIALS AND METHODS – Between November 2009 and April 2010, the intestine of ten donkeys was collected from a slaughterhouse. All animals, five male foals and five adult females, belonged to an organic farm and never had anthelmintic treatments. Following a proven technique for parasites’ isolation in Equidae (Bu Y et al, 2009, Acta Parasitol, 54: 263-268; Matthee S et al, 2000, J of Parasitol, 86:756-762), after dilution in water, 10% of the whole intestinal content was collected by each intestinal tract and repeatedly washed before parasite isolation. Adult parasites were identified following Lichtenfels’ keys. If available, a faecal specimen was collected from rectum for coprocolture (seven animals); 100 larvae were identified for each faecal specimen following Euzeby’s keys. RESULTS – Adult parasites: 21 species of Strongylidae were identified (Strongylus vulgaris, Strongylus edentatus (first report in Italian donkeys: frId), Triodontophorus serratus, Triodontophorus brevicauda (frId), Triodontophorus minor (frId), Cyathostomum alveatum, Cyathostomum catinatum, Cyathostomum tetracanthum, Coronacyclus coronatus, Coronocyclus labratus, Cylicocyclus adersi (frId), Cylicocyclus asini (frId), Cylicocyclus auriculatus, Cylicocyclus leptostomum, Cylicocyclus nassatus, Cylicocyclus radiatus, Cylicostephanus calicatus, Cylicostephanus goldi, Cylicostephanus longibursatus, Cylicostephanus minutus, Cylicodontophorus bicoronatus). Critical points verified in Lichtenfels’ keys and descriptions were the following:  the key for the identification on the genus Cyathostomum report that the insertion point of the internal leaf crown is at about ¼ - ½ of buccal capsule depth; actually it is not true for C. alveatum, as clearly appears from the figures and description of this species;  the dorsal gutter of C. asini is described as short, little, button-like. It is clearly a mistake as, consistently with other descriptions of this species (Matthee S et al, 2002, Syst Parasitol, 51: 29-35) and with the photos and pictures of Lichtenfels himself, the dorsal gutter is long and well developed;  the photos of C. radiatus are not consistent with its descriptions;  C. calicatus and C. minutus are very difficult to distinguish as the only morphological difference regards the number of external leaf crown elements (12-18 vs. 8). Larvae: 3 types of strongylid larvae were observed. According to Euzeby’s descriptions they were Cyathostomum spp. sensu lato, Oesophagodontus spp. and Strongylus vulgaris. However the following critical points, verified comparing larval identification with adult parasites isolated in the same host, were observed:  larval length of Strongylus vulgaris was constantly less than the length reported; it is remarkably critical given that the larval length is the starting dichotomous character for identification in Euzeby’s keys;  larvae with 16 intestinal cells couldn’t be Oesophagodontus spp. larvae, as suggested by Euzeby, as there were no adult specimens in the corresponding faecal samples; they probably belong to the species Triodontophorus serratus (isolated..