Species distribution of encysted cyathostome larvae and attribution of cyathostome species to larval cyathostominosis in the Netherlands
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Cyathostomes are the most common nematodes of the horse and are pathogenic parasites in horses. Over 50 species of cyathostomes are known. These parasites can cause a disease called larval cyathostominosis. This disease is caused by the en masse emergence of encysted larvae from the mucosa. Symptoms of this disease are, amongst other things, diarrhea, losing weight, subcutaneous edema, the presence of fourth stage larvae in the faeces and death. Treatment of larval cyathostominosis can consist of deworming with moxidectin and supportive therapy. Fourth stage larvae expelled with the faeces of horses with larval cyathostominosis were supposed to be isolated with the Baermann method and differentiated with reverse line blot (RLB). Also, third and fourth stage larvae from the (sub)mucosa of slaughtered horses and L3s cultured from the faeces of these horses were differentiated. The hypothesis is that these species match, since only species that can inhibit development are likely to be involved with larval cyathostominosis. The Baermann method was tested for isolation of L4s from the faeces, but unfortunately no cases of larval cyathostominosis were used in this study. Numbers of larvae recovered after overnight storage at 4 °C were lower than samples that were used immediately. We sampled 11 slaughtered horses to count and differentiate mucosal larvae. Of these horses, mucosal samples were taken and faecal cultures were made to differentiate larvae that represent the adult cyathostomes in the lumen. In 27.3 percent of the horses, no cyathostomes were found in the (sub)mucosa, nor in the faecal cultures. Additionally, in 36.3 percent of the horses only cultured L3s were found and in 36.3 percent of the horses, cyathostomes were found in the (sub)mucosa and in the faecal cultures. The age of horses in which cyathostomes were found in the mucosa was significantly lower than the age of horses where no cyathostomes were found. The 5 most prevalent species in the faeces were Cylicocyclus (Cyc.) nassatus, Coronocyclus (Cor.) coronatus, Cyc. ashworthi, Cyathostomum (Cya.) catinatum and Cyc. leptostomum. They comprised 74 percent of the total amount of larvae recovered. The 5 most prevalent species in the mucosa were Cyc. insigne, Cyc. nassatus, Cylicostephanus (Cys.) longibursatus, Cor. coronatus and Cya. catinatum. They comprised 86.9 percent of the total amount of larvae recovered. In conclusion, the Baermann method is useful for recovering L4s of the faeces when the faeces is fresh. Larvae from faeces that has been cooled or stored for more than a day should be recovered using direct microscopic examination of the faeces. As a conclusion for species distribution, there was a prominent difference in the finding of Cyc. insigne in the faeces and the mucosa, but more slaughtered horses should be sampled.