Evolution and host adaptation strategy of carnivorous parvoviruses

这项研究的最终目标是定义肉食性细小病毒的进化(突变)，并分析病毒获得感染和在新宿主物种中复制的能力的机制。在研究过程中，我们获得了以下几点新发现：1)利用越南猫新的抗原变异体V203株和从越南猫和日本狗分离的抗原型CPV2b株对非结构蛋白基因进行了序列分析。与日本毒株相比，越南毒株在545.2位氨基酸发生了唯一的替换(Glu到Val)，产生了4株新的抗V203毒株的单抗。根据对各抗原型毒株的反应性，将这些单抗分为三组。抗性变异体的分析结果表明，两株mAb识别抗原位点A，另外两株识别抗原位点B或邻近区域。3)从越南河内和胡志美市的狗和猫的126份直肠拭子样本中，从狗身上分离出8株细小病毒株，从猫身上分离出1株细小病毒株。4)利用mAb对越南新分离株的抗原类型进行了检测。HNI-4-1毒株在VP2的第426位有氨基酸替换，提示HNI-4-1毒株是CPV-2b的新的抗原株。综上所述，本研究制备的单抗有望用于微小病毒的检测和分型，包括新出现的抗原变异株，因为肉食性细小病毒仍被认为是通过突变而进化的。

The final goal of this study is to define evolution (mutation) of carnivorous parvoviruses and to analyze mechanisms lying for the viruses to gain ability to infect and replicate in new host species. During the study, we obtained several new findings as follows.1)Sequence analysis on the nonstructural protein gene was performed using a new antigenic variant V203 strain from a Vietnamese cat and antigenic type CPV2b strains isolated from Vietnamese cats and Japanese dogs. Compared with Japanese strains, all the Vietnamese strains had a unique substitution (Glu to Val) at the amino acid position 545.2)Four new monoclonal antibodies (mAbs) were produced against V203 strain. These mAbs were categorized into three groups according to the reactivity to each of the antigenic type strain. Results of the analysis using resistant variants showed that two mAbs recognized the antigenic site A and that the other two recognized the antigenic site B or its neighborhood.3)Out of the 126 rectal swab samples obtained from dogs and cats in Hanoi and Ho Chi Meth cities in Vietnam, eight parvovinus strains were isolated from dogs and one from a cat.4)The new Vietnamese isolates were examined on their antigenic types using the mAbs. Eight strains including one from a cat were clearly shown to be CPV-2b, but HM-4-1 strain isolated from a dog in Hanoi city showed much lower reactivity to two of the mAbs.5)HNI-4-1 strain had an amino acid substitution at a position 426 in VP2, suggesting that HNI-4-1 strain was a novel antigenic variant of CPV-2b.In conclusion, the mAbs produced in this study are expected to be useful for the detection as well as typing of parvoviruses including newly emerging antigenic variants, because carnivorous parvoviruses are still considered to be evolving by mutations.