International Institute for Zoonosis Control, Hokkaido University, Sapporo, Japan.
Virology Unit, Central Veterinary Research Institute, Lusaka, Zambia.
PLoS Negl Trop Dis. 2022 Jun 2;16(6):e0010420. doi: 10.1371/journal.pntd.0010420. eCollection 2022 Jun.
Rift valley fever (RVF) is a mosquito-borne disease of animals and humans. Although RVF outbreaks are usually reported at 5-15-year intervals in sub-Saharan Africa, Zambia has experienced an unusually long inter-epizootic/-epidemic period of more than three decades. However, serological evidence of RVF virus (RVFV) infection in domestic ruminants during this period underscores the need for comprehensive investigation of the mechanisms of virus perpetuation and disease emergence. Mosquitoes (n = 16,778) captured from eight of the ten provinces of Zambia between April 2014 and May 2019 were pooled (n = 961) and screened for RVFV genome by a pan-phlebo RT-PCR assay. Aedes mosquito pools (n = 85) were further screened by nested RT-PCR assay. Sera from sheep (n = 13), goats (n = 259) and wild ungulates (n = 285) were screened for RVFV antibodies by ELISA while genome detection in pooled sera (n = 276) from domestic (n = 248) and wild ungulates (n = 37) was performed by real-time RT-PCR assay. To examine the association between the long inter-epizootic period and climatic variables, we examined El Niño-Southern Oscillation indices, precipitation anomalies, and normalized difference vegetation index. We then derived RVF risk maps by exploring climatic variables that would favor emergence of primary RVFV vectors. While no RVFV genome could be detected in pooled mosquito and serum samples, seroprevalence was significantly high (OR = 8.13, 95% CI [4.63-14.25]) in wild ungulates (33.7%; 96/285) compared to domestic ruminants (5.6%; 16/272). Retrospective analysis of RVF epizootics in Zambia showed a positive correlation between anomalous precipitation (La Niña) and disease emergence. On risk mapping, whilst northern and eastern parts of the country were at high risk, domestic ruminant population density was low (< 21 animals/km2) in these areas compared to low risk areas (>21 animals/km2). Besides evidence of silent circulation of RVFV and the risk of disease emergence in some areas, wildlife may play a role in the maintenance of RVFV in Zambia.
裂谷热（RVF）是一种动物和人类的蚊媒疾病。尽管 RVF 暴发通常在撒哈拉以南非洲每 5-15 年报告一次，但赞比亚经历了异常长的超过三十年的间疫期/流行期。然而，在此期间，国内反刍动物中 RVF 病毒（RVFV）感染的血清学证据强调了全面调查病毒持续存在和疾病出现机制的必要性。2014 年 4 月至 2019 年 5 月期间，从赞比亚的十个省中的八个省捕获了 16778 只蚊子（n = 16778），将其汇集（n = 961）并通过 pan-phlebo RT-PCR 检测 RVFV 基因组。用巢式 RT-PCR 检测进一步筛选伊蚊池（n = 85）。用 ELISA 检测绵羊（n = 13）、山羊（n = 259）和野生有蹄类动物（n = 285）的 RVFV 抗体，用实时 RT-PCR 检测来自国内（n = 248）和野生有蹄类动物（n = 37）的汇集血清（n = 276）中的基因组。为了研究长间疫期与气候变量之间的关系，我们检查了厄尔尼诺-南方涛动指数、降水异常和归一化植被指数。然后，通过探索有利于 RVFV 主要媒介出现的气候变量，得出 RVF 风险图。虽然在汇集的蚊子和血清样本中均未检测到 RVFV 基因组，但野生有蹄类动物（33.7%；285 头中有 96 头）的血清阳性率明显高于国内反刍动物（5.6%；272 头中有 16 头）（OR = 8.13，95%CI [4.63-14.25]）。对赞比亚 RVF 流行情况的回顾性分析表明，异常降水（拉尼娜）与疾病的出现呈正相关。在风险图上，虽然该国北部和东部地区风险较高，但与低风险地区（> 21 头/平方公里）相比，这些地区的国内反刍动物种群密度较低（< 21 头/平方公里）。除了 RVFV 沉默循环的证据和某些地区疾病出现的风险外，野生动物可能在赞比亚维持 RVFV 方面发挥作用。
