Evolution and host adaptation strategy of carnivorous parvoviruses

本研究的最终目标是确定肉食性细小病毒的进化（突变），并分析病毒在新宿主物种中获得感染和复制能力的机制。在研究过程中，我们获得了以下几个新的发现。1)利用越南猫新抗原变异株V203和越南猫、日本犬抗原型CPV2b进行非结构蛋白基因序列分析。与日本株相比，越南株在545.2氨基酸位置均有独特的Glu取代Val。根据对每种抗原型菌株的反应性，将这些单克隆抗体分为三组。使用耐药变异体的分析结果显示，两个单抗识别抗原位点A，另外两个单抗识别抗原位点B或其邻近区域。3)在越南河内和胡志明市采集的126份猫狗直肠拭子样本中，分别从狗和猫身上分离出8株和1株细小病毒。4)利用单克隆抗体检测越南新分离株的抗原类型。8株CPV-2b（其中1株来自猫）被明确显示为CPV-2b，但从河内市一只狗身上分离的HM-4-1株对其中两种单克隆抗体的反应性要低得多。5)HNI-4-1菌株在VP2的第426位有一个氨基酸取代，提示hni -1 -1菌株是CPV-2b的一个新的抗原变体。总之，本研究中产生的单克隆抗体有望用于细小病毒的检测和分型，包括新出现的抗原变异，因为肉食性细小病毒仍然被认为是通过突变进化的。

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.