Morphological Identification,phylogenetic Analysis And Therapeutic Effect Analysis Of Gasterophilus Third Instars Of Ili Horse

Larvae of flies belonging to the genus Gasterophilus(Diptera: Gasterophilidae,Gasterophilus)are parasites of gastrointestinal mucosa and stomachus cardiacus of equus(horses,donkeys,zebras,etc.)and can cause a series of parasitic diseases such as restlessness,decreased food appetite and gastric mucosal ulcer and inflammation.The commonly seen Gasterophilus larvae include Gasterophilus nasalis,Gasterophilus pecorum,Gasterophilus intestinalis and Gasterophilus haemorrhoidalis.The horse breeding industry is developed in Xinjiang,with the amount of livestock on hand ranking first in the country,and Ili horse is the major horse species in this region.Due to natural grazing and other factors such as frequent contact with flies,leading to high incidence rate and prevalence of parasitic diseases,which seriously affected the healthy development of Ili horse industry.Therefore,in this study,with part of the horse ranches in producing area of Ili horses as the test spots,methods of ultrastructure,phylogenetic taxonomy and statistics were used to carry out species identification and analysis of community composition and genetic evolution on the third-stage larvae of Gastrophilus parasitizing in Ili horses,meanwhile,horses in the epidemic area were treated by ivermectin and the effect was observed and studied.The main species of house fly larvae parasitizing in Ili horses were investigated and the phyletic classification and community composition of the fly larvae was analyzed;the occurrence and epidemic characteristics of the disease and the necessity of drug therapy were revealed,which provided a scientific basis for comprehensive prevention and treatment of the disease.1.Based on the pathogenic identification of third-stage larvae of Gastrophilus,ultramicro observation and identification by scanning electron microscope were carried out.The experimental results showed that a total of 4 types of third-stage larvae of Gastrophilus were identified,those are,G.nasalis,G.pecorum,G.intestinalis and G.haemorrhoidalis.Parts with identification significance include body surface acanthotaxy,leaf segment of mandible on the head and surface groove of mouth hook.The third-stage larvae of G.pecorum have clapboard like protrusion on the first thoracic segment,the acanthotaxy has single row and the thoracic first acanthotaxy has two rows,in addition,the surface texture of the mouth hook is obvious,and cilium like objects exist in the surface groove;the dorsal mandible of the third-stage larvae of G.nasalis is extended into leaf,and the top of the leaf segment is smooth;the top part of the leaf segment of other three types of third-stage larvae of Gasterophilus is zigzag;no significant difference was found in morphological features between G.haemorrhoidalis and G.intestinalis,but the parasitic site and acanthotaxy characteristics can be used as the basis for identification.2.In this experiment,the phylogenetic tree of G.nasalis,G.pecorum,G.intestinalis and G.haemorrhoidalis was drawn based on COI gene,and the results showed that the nucleotide consistency ofthe measured COI gene sequences(GenBank accession numbers are GU265752.1,KR230402.1,KU578262.1 and KT946620.1,respectively)is 99%,99%,99% and 100%,respectively;the 4 species of Gastrophilus have similar base composition,thereinto,the average contents of A,T,C and G bases are30.65%,24.18%,19.10% and 16.10%,respectively,the average content of A+T is 64.83%,which is significantly higher than that of C+G,so obvious bias of A/T base is manifested.3.In this study,casual inspection(N=10)was carried out on horses in the epidemic area and definitive therapy was performed(ivermectin).The drug effectiveness was analyzed and observed by drug administration twice.The results showed that the deworming peak appeared with 50 h after the drug administration and the deworming gradually declined after 85 h and finally disappeared;no larva was expelled in feces after drug administration twice,indicating that ivermectin has some curative effect;the curative effect in horses(N=118)in the epidemic area,including 70 horses undergoing medicaments deworming and 48 horses undergoing necropsy,was observed.The results showed that 16775 horses were infected by the third-stage larvae of Gasterophilus,of which G.nasalis,G.pecorum,G.intestinalis and G.haemorrhoidalis were the dominant species,and the relative dominance was respectively 53.17%(N=8920),22.71%(N=3809),12.14%(N=2037)and 11.98%(N=2009).No significant difference was found in age of the host horses and parasitic species of Gastrophilus larvae,The different parasite that larvae of G.nasalis tend to parasitic in cardia,while larvae of the other three species are parasitic in pylorus.