Seroepidemiological Survey, Insect Vector Investigation, Isolation, Identification And Preliminary Study On Pathogenicity Of Akabane Virus Of Cattle And Goats In Guangxi

Akabane disease(AKAD)is an insect-bone infectious disease,which is caused by Akabane virus(AKAV),the main hosts is ruminants such as cows,sheep and goats.Clinical manifestations in miscarriage,premature birth,stillbirth and congenital arthrogryposis-hydraencephaly syndrome(AH syndrome),also can have some strains of newborn animals non suppurative encephalomyelitis.The disease is widespread in Africa,Asia and Oceania and is spread by blood-thirsty insects.In this study,2411 bovine and goat serum samples(Including 1428 goat serum samples were collected from 12 cities Guangxi;983 bovine serum sarrples were collected from 13 cities).The results showed that AKAV infection was found in cattle and goats in all 14 cities of Guangxi,and the infection was different in different places,and the positive rate of cattle was significantly higher than that of goats,the total positive rate of cattle was 63.89%,and the total positive rate of goats was 36.48%.By comparing the positive rate of AKAV antibody in different regions,it was found that the highest positive rate of AKAV antibody in goats was 62.50%in Wuzhou.The positive rate of AKAV antibody in cattle was the highest in Nanning(82.29%).When analyzing the environmental factors affecting the positive rate of AKAV antibody,it was found that the infection of cattle and goats with AKAV in Guangxi was affected by geographical location(latitude)and climatic factors(temperature and rainfall)In this study,we set up three monitoring sites in Danznang village and Banwai village in Dahua county;Longqi village,Putang town in Xingye county to collect the insect vector.The identification of the insect shows that there were five kinds of Culicoides,respectively Culicoides oxystorma,Culicoides peregrinzus,Culicoides arakawae,C.ulicoides humeralis and Culicoides homotomus.Among them,Culicoides oxystoma and Culicoides peregrinus were the dominant speciesIn this study,a strain of AKAV,named GXDH01,was isolated from the blood of goat from Danzhang monitoring point in Dahua,which was the first AKAV strain isolated from goat in China.The whole gene sequence of GXDH01 strain was obtained by subsection amplification,in which the length of L segment was 6968bp,the length of M segment was 4309bp,and the length of S segment was 856bp.Genetic and evolutionary analysis of the gene sequence showed that the virus isolated from bovine strains from Japan and Korea were closely related and belonged to the Asian group.However,L segment,M segment and S segment belong to different branches,which may lead to gene recombination.The pathogenicity of GXDH01 strain on suckling mice,adult mice and bamboo rat was studied.GXDH01 strain can make suckling mices die by intracranial inoculation,LD50 was 104 6TCID50;however,it could not cause symptoms in adult mice.The results of this test were the same as those of the challenge test of AKAV standard strain OBE-1.The GXDH01 strain was inoculated subcutaneously into young bamboo rats at the age of 50 days,resulting in neurological symptoms and death of bamboo rats.At vaccination dose was 106'9 TCID50,the mortality was 66.7%.The vaccination dose was 105.9 TCID50,the mortality was 33.3%.Necropsy showed hemorrhage of brain and lung,necrosis of liver.Pathological examination showed that there was a single layer or multiple layers of cells infiltrating around the blood vessels of brain tissue,forming a "blood vessel sheath,".There were several necrotic foci in the liver tissue,in which liver cells were degenerated and necrotic,a large number of inflammatory cells were infiltrated and necrotic,and a large number of inflammatory cells were infiltrated around the blood vessels.A large number of neutrophils were found in the bronchus and alveolar cavity,local hemorrhage was found in the lung tissue,and alveolar septum was thickened.