Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus diseases, which is responsible for the greatly economic losses in the swine industry. The rate of nucleotide substitution within PCV2 is high, which keep the highest rate yet recorded for a single-stranded DNA virus. Although the oronasal route is considered the most likely route of infection, PCV2 can be shed in nasal, tonsillar, bronchial and ocular secretions, as well as in faeces, saliva, urine milk and semen. Pigs with PMWS have greater amounts of PCV2 in their serum and shed large quantities of virus than do non-affected pigs. The piglets which have high antibodies against PCV2 do not develop a viraemia until these antibodies wane. PMWS- affected pigs have depletion of T- and rMymphocytes, factors that are currently thought to influence the outcome of PCV2 infection include 4 main areas of focus: virus, host, coinfections, and immune modulation.%猪圆环病毒是猪圆环病毒病的主要致病因素,该病给养猪业带来很大的经济损失.猪圆环病毒变异较快,是单链DNA病毒中最高的;易感猪主要通过消化道和呼吸道水平传播而感染,猪圆环病毒Ⅱ型(PCV2)人工或自然感染猪的排泄物、鼻腔、口腔和扁桃体拭子和患畜的尿液和粪便中均能检测到PCV2.断奶仔猪多系统衰竭综合征(PMWS)的发病主要与猪体内PCV2含量有关.PCV2特异抗体对猪群的PCV2感染具有保护作用.PCV2诱导猪继发性免疫缺陷,淋巴细胞缺失,影响PCV2感染结果的因素有:病毒、宿主、混合感染和免疫调节等.
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