Epidemiological, virological, and pathogenic insights into Nairobi sheep disease virus infection in sheep and goats in China.

Nairobi sheep disease virus (NSDV), a tick-borne pathogen in the Orthonairovirus genus of the Nairoviridae family, causes Nairobi sheep disease (NSD), which has mortality rates over 90% in sheep and goats. Historically, NSD outbreaks in East Africa and South Asia have led to considerable economic losses. Although NSDV genomic fragments have been detected in ticks in China, there has been a notable absence of reported infections in local sheep and goats. In this study, we report the first identification of NSDV infection in sheep and goats in China. Through meta-transcriptomics sequencing, NSDV was found in infected spleen tissue with high viral abundance. Epidemiological investigations indicated a 4.1% positive rate for NSDV RNA and a 29.9% seroprevalence rate, confirming the presence of NSDV infection in these herds. Sequence analyses showed that the identified NSDV clustered with those previously found in ticks in China but were distinct from Africa or India strains. Furthermore, these viruses could be categorized into different sub-clades, suggesting the genetic diversity of NSDV in China. Remarkably, NSDV was isolated from infected sheep for the first time in China, and the isolated virus could cause severe clinical signs, leading to sheep mortality. In summary, this study represents the initial identification of NSDV in vertebrate hosts in China and highlights the importance of NSDV surveillance to prevent outbreaks of NSD within the country.IMPORTANCEAs a significant tick-borne virus, Nairobi sheep disease virus (NSDV) has caused devastating disease known as Nairobi sheep disease (NSD) in small ruminants in East Africa and South Asia. Although NSDV genomic fragments have been detected in ticks within China, there has been little information on its infection in local sheep or goats. This study confirms, for the first time, the infection of NSDV among these animals in China. Additionally, the successful isolation of NSDV from infected sheep highlights its capacity to replicate in various cell lines, including those of human origin, thereby underscoring its broad host range and potential for cross-species transmission. Notably, animal experiments demonstrated that the isolated virus strain could cause severe clinical signs in sheep. These findings provide the first evidence for the presence of NSDV infection among sheep and goats in China, underscoring the critical need for NSDV surveillance to prevent outbreaks of NSD within the country.