| Rabies is a fatal zoonotic disease with almost 100% fatality rate. As both reservior hosts and transmitting vectors, variety of animals maintain and spread this disease worldwide. During the recent years, the number of human rabies cases increased consecutively in China. Since 2003, there have been more than 2000 human rabies cases annually, and in 2007, the number has been reached 3302. Cases are in Most of provinces and autonomous regions except Qinghai and Xizang. Despite carrying out several epidemiologic investigations about the factors resulting in high incidence rate, more attention and investigations were not carried out in middle-and low-incidence regions where epidemic situation dramatically rose and spread. Therefore, in order to investigate the genetic features and the relationship between epidemic situation and distribution of rabies virus derived from different host animals, genetic variation properties and phylogenesis of rabies virus N gene were analyzed and compared with that of high-incidence provinces based on the epidemic situation in 2007, which provides pathogenic evidences for effective control and prevention of rabies spread in China.The epidemic situation in 2007 showed that the epidemic situation still rose and the trend was from south to north, from high-incidence to low-incidence regions, and most cases happened in summer, male cases were more that female cases. We collected 382 brain specimens from different host animals in five provinces with middle- and low-incidence rate. The brain tissues were detected with both direct immunofluorescence assay (IFA) and RT-PCR. Finally we got 81 positive dog brain samples. By amplification and sequence, the partial N gene(634-1353 N-coding nucleotide) was obtained from 34 positive samples. Sequences comparison showed that they share a high degree of homology in nucleotide acid(87.5%-100%) and deduced amino acid(93.3%-99.6%). This indicates that the variations in this region are synonymous mutations. Antigenic sitesâ… ,â…¢,â…£and Th cell epitopes on N gene were highly conserved, and all of the 34 positive samples had the phosphorylation site of serine at position 389 and Threonine at position 375.This indicates that the invariantion of functional sites on N gene is related with its stability in heredity.The analysis of phylogenetic trees indicates that all of the 34 positive samples belong to genetype 1 Lyssavirus and distribute regionally. It is likely that the infection was existed between wild animals and livestock, and the evolution trend is likely from western to eastern part, even to southeast. This is coincident with the distribution and spread trend in recent years, which shows that there is derect relationship between them. Compared with international rabies virus strain, the investigated samples are basically divided into 3 subgroups (â… ,â…¡,â…¢) which are in the same large group including another two strain of rabies virus from Indonesia and Thailand. It shows that rabies virus in China is different from rabies virus in other countries but is similar to the neighboring countries. In Subgroupâ…¡, close genetic relationship is existed in Yunnan strain and Tailand strain. Otherwise, other 33 strians of rabies virus (subgroupâ… andâ…¢) from China keep distant genetic relationship. Based on the information, the transmission may be existed between Southeast Asia and China.The results indicate that the reason for epidemic situation quickly spread may be the epidemic situation is still rise and spread in recent years, and prevalent in middle-and low-incidence regions. The variation of N gene of rabies virus has geographic characteristics and the deduced amino acids are highly conserved. The analysis of phylogenetic trees in N gene indicates that all the isolates belong to genetype 1 Lyssavirus and higher genetic relationship in the same province. All the analysis show that it exists the transmission form wild animals to livestock, from domestic animals to that of neighboring countries.In conclusion, the genetic features and the relationship between epidemic situation and distribution of rabies virus derived from different host animals, genetic variation properties and phylogenesis of rabies virus N gene were analyzed and compared with that of high-incidence provinces based on the epidemic situation in 2007, which provides pathogenic evidences for effective control and prevention of rabies spread in China. |
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