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Abstract：
Chicken infectious anemia (CIA) is caused by chicken anemia virus (CAV). Recently, severe anemia has emerged in layer chickens (8 to 10-week-old) on poultry farms in China. However, the etiological characteristics and pathogenic potential of CAV in chickens at 6 weeks or older are not well understood. In this study, we isolated a CAV strain, termed SD15, from two-month-old chicken with severe anemia and analyzed the genetic evolution relationship. We found that strain SD15 had the highest homology (98.9%) with CAV18 strain. Comparison with 33 reference strains revealed 16 amino acid mutations in strain SD15, two of which were previously unknown (F210S in VP1 and L25S in Vp3). Compared with low pathogenic strains (Cux-1 and C14), highly pathogenic strains (SDLY08 and SD15) had three base mutations in their noncoding region. To further understand its pathogenicity, 10-week-old specific-pathogen-free (SPF) chickens were challenged with the novel strain and SDLY08. No obvious clinical symptoms were observed in the SDLY08 group. However, SD15-infected chickens showed significant growth retardation and immunosuppression. The main manifestations of immunosuppression were the significantly reduced thymus and bursa indices and AIV-H9 vaccine-induced antibody levels (P < 0.05). The lowest number of red blood cells in the SD15 group was just 60% of that in the control group. Taken together, the novel strain SD15 not only showed higher pathogenicity but also exhibited the potential ability to break the age resistance of older chickens to CAV. Our study enhanced the understanding of the epidemiological characteristics of chickens infected with severe anemia and can facilitate the development of improved control strategies of CIA in China.
摘要：
鸡传染性贫血（CIA）是由鸡贫血病毒（CAV）引起的。最近,中国家禽养殖场的蛋鸡（8至10周龄）出现了严重的贫血。然而,在6周龄或以上的鸡中，CAV的病因特征和致病潜力尚不清楚。在这项研究中,我们分离出一个CAV菌株,SD15，来自两个月大的严重贫血鸡，并分析了遗传进化关系。我们发现菌株SD15与CAV18菌株具有最高的同源性(98.9%)。与33个参考菌株的比较揭示了菌株SD15中的16个氨基酸突变,其中两个是先前未知的(VP1中的F210S和Vp3中的L25S)。与低致病性菌株(Cux-1和C14)相比，高致病性菌株(SDLY08和SD15)在其非编码区存在3个碱基突变。为了进一步了解其致病性，用新型菌株和SDLY08攻击10周龄的无特定病原体(SPF)鸡。SDLY08组未见明显临床症状。然而,感染SD15的鸡表现出明显的生长迟缓和免疫抑制。免疫抑制的主要表现为胸腺和法氏囊指数显著降低以及AIV-H9疫苗诱导的抗体水平(P<0.05)。SD15组的红细胞数量最低，仅为对照组的60%。一起来看,新型菌株SD15不仅表现出更高的致病性，而且还表现出打破老年鸡对CAV的年龄抗性的潜在能力。我们的研究增强了对感染严重贫血的鸡的流行病学特征的了解，并有助于在中国制定改进的CIA控制策略。
