The Pirbright Institute, Ash Road, Pirbright, Surrey GU24 0NF, UK.
Viruses. 2021 May 1;13(5):814. doi: 10.3390/v13050814.
It is well known that approximately 50% of cattle infected with foot-and-mouth disease (FMD) virus (FMDV) may become asymptomatic carrier (persistently infected) animals. Although transmission of FMDV from carrier cattle to naïve cattle has not been demonstrated experimentally, circumstantial evidence from field studies has linked FMDV-carrier cattle to cause subsequent outbreaks. Therefore, the asymptomatic carrier state complicates the control and eradication of FMD. Current serological diagnosis using tests for antibodies to the viral non-structural proteins (NSP-ELISA) are not sensitive enough to detect all carrier animals, if persistently infected after vaccination and do not distinguish between carriers and non-carriers. The specificity of the NSP ELISA may also be reduced after vaccination, in particular after multiple vaccination. FMDV-specific mucosal antibodies (IgA) are not produced in vaccinated cattle but are elevated transiently during the acute phase of infection and can be detected at a high level in cattle persistently infected with FMDV, irrespective of their vaccination status. Therefore, detection of IgA by ELISA may be considered a diagnostic alternative to RT-PCR for assessing FMDV persistent infection in ruminants in both vaccinated and unvaccinated infected populations. This study reports on the development and validation of a new mucosal IgA ELISA for the detection of carrier animals using nasal, saliva, and oro-pharyngeal fluid (OPF) samples. The diagnostic performance of the IgA ELISA using nasal samples from experimentally vaccinated and infected cattle demonstrated a high level of specificity (99%) and an improved level of sensitivity (76.5%). Furthermore, the detection of carrier animals reached 96.9% when parallel testing of samples was carried out using both the IgA-ELISA and NSP-ELISA.
众所周知，大约有 50%感染口蹄疫病毒（FMDV）的牛可能成为无症状携带者（持续性感染）动物。尽管没有实验证明从带毒牛向无感染牛传播 FMDV，但来自现场研究的间接证据将 FMDV 带毒牛与随后的暴发联系起来。因此，无症状携带状态使 FMD 的控制和根除复杂化。目前使用针对病毒非结构蛋白（NSP-ELISA）的抗体检测进行的血清学诊断不够敏感，无法检测到所有持续性感染后的带毒动物，也无法区分带毒动物和非带毒动物。NSP ELISA 的特异性在接种疫苗后也可能降低，特别是在多次接种后。接种疫苗的牛不会产生 FMDV 特异性黏膜抗体（IgA），但在感染的急性期会短暂升高，并且可以在持续性感染 FMDV 的牛中检测到高水平的 IgA，无论其接种疫苗状态如何。因此，通过 ELISA 检测 IgA 可能被认为是评估接种疫苗和未接种疫苗的感染牛群中 FMDV 持续性感染的替代 RT-PCR 诊断方法。本研究报告了一种新的黏膜 IgA ELISA 的开发和验证，用于检测使用鼻腔、唾液和口咽液（OPF）样本的带毒动物。使用实验接种和感染牛的鼻腔样本进行的 IgA ELISA 诊断性能显示出高特异性（99%）和改进的敏感性（76.5%）。此外，当使用 IgA-ELISA 和 NSP-ELISA 同时平行检测样本时，检测带毒动物的比例达到 96.9%。
