Virology Department, Animal and Plant Health Agency, Woodham Lane, Surrey, UK.
Institute of Infection and Global Health, University of Liverpool, Liverpool, UK.
Parasit Vectors. 2020 Nov 26;13(1):596. doi: 10.1186/s13071-020-04481-9.
West Nile virus (WNV) is a single-stranded RNA virus that can cause neurological disease in both humans and horses. Due to the movement of competent vectors and viraemic hosts, WNV has repeatedly emerged globally and more recently in western Europe. Within the UK, WNV is a notifiable disease in horses, and vaccines against the virus are commercially available. However, there has been no investigation into the seroprevalence of WNV in the UK equine population to determine the extent of vaccination or to provide evidence of recent infection.
Equine serum samples were obtained from the Animal and Plant Health Agency's equine testing service between August and November 2019. A total of 988 serum samples were selected for horses resident in South East England. WNV seroprevalence was determined using two enzyme-linked immunosorbent assays (ELISAs) to detect total flavivirus antibodies and WNV-specific immunoglobulin M (IgM) antibodies. Positive IgM results were investigated by contacting the submitting veterinarian to establish the clinical history or evidence of prior vaccination of the horses in question.
Within the cohort, 274 samples tested positive for flavivirus antibodies, of which two subsequently tested positive for WNV-specific IgM antibodies. The follow-up investigation established that both horses had been vaccinated prior to serum samples being drawn, which resulted in an IgM-positive response. All the samples that tested positive by competition ELISA were from horses set to be exported to countries where WNV is endemic. Consequently, the positive results were likely due to previous vaccination. In contrast, 714 samples were seronegative, indicating that the majority of the UK equine population may be susceptible to WNV infection.
There was no evidence for cryptic WNV infection in a cohort of horses sampled in England in 2019. All IgM-seropositive cases were due to vaccination; this should be noted for future epidemiological surveys in the event of a disease outbreak, as it is not possible to distinguish vaccinated from infected horses without knowledge of their clinical histories.
西尼罗河病毒（WNV）是一种单链 RNA 病毒，可导致人类和马的神经疾病。由于有能力的媒介和带毒宿主的移动，WNV 在全球范围内多次出现，最近在西欧也出现了。在英国，WNV 是马的法定报告疾病，并且有针对该病毒的商业疫苗。然而，尚未对英国马群进行 WNV 的血清流行率调查，以确定疫苗接种的程度或提供最近感染的证据。
2019 年 8 月至 11 月期间，从动植物卫生署的马匹检测服务中采集了马血清样本。总共选择了东南英格兰的 988 份血清样本。使用两种酶联免疫吸附测定法（ELISA）检测总黄病毒抗体和 WNV 特异性免疫球蛋白 M（IgM）抗体来确定 WNV 的血清流行率。通过联系提交兽医，对阳性 IgM 结果进行调查，以确定有关马匹的临床病史或先前接种疫苗的证据。
在该队列中，274 份样本检测出黄病毒抗体呈阳性，其中两份随后检测出 WNV 特异性 IgM 抗体呈阳性。后续调查确定，这两匹马在采集血清样本之前均已接种疫苗，这导致了 IgM 阳性反应。所有通过竞争 ELISA 检测出阳性的样本均来自计划出口到 WNV 流行地区的马匹。因此，阳性结果可能是由于先前的接种。相比之下，714 份样本呈血清阴性，这表明英国马群的大多数可能容易感染 WNV。
在 2019 年英格兰采样的马群中，没有发现隐匿性 WNV 感染的证据。所有 IgM 血清阳性病例均归因于疫苗接种；如果发生疾病暴发，这一点应在未来的流行病学调查中引起注意，因为如果不知道其临床病史，则无法区分接种疫苗的马匹和感染的马匹。
