Date Published: October 20, 2015
Publisher: Public Library of Science
Author(s): Yongjun Jiao, Xian Qi, Dapeng Liu, Xiaoyan Zeng, Yewu Han, Xiling Guo, Zhiyang Shi, Hua Wang, Minghao Zhou, Rosemary C Sang. http://doi.org/10.1371/journal.pntd.0004092
Abstract: BackgroundSevere fever with thrombocytopenia syndrome virus (SFTSV), the causative agent for the fatal life-threatening infectious disease, severe fever with thrombocytopenia syndrome (SFTS), was first identified in the central and eastern regions of China. Although the viral RNA was detected in free-living and parasitic ticks, the vector for SFTSV remains unsettled.Methodology/Principal FindingsFirstly, an experimental infection study in goats was conducted in a bio-safety level-2 (BSL-2) facility to investigate virus transmission between animals. The results showed that infected animals did not shed virus to the outside through respiratory or digestive tract route, and the control animals did not get infected. Then, a natural infection study was carried out in the SFTSV endemic region. A cohort of naïve goats was used as sentinel animals in the study site. A variety of daily samples including goat sera, ticks and mosquitoes were collected for viral RNA and antibody (from serum only) detection, and virus isolation. We detected viral RNA from free-living and parasitic ticks rather than mosquitoes, and from goats after ticks’ infestation. We also observed sero-conversion in all members of the animal cohort subsequently. The S segment sequences of the two recovered viral isolates from one infected goat and its parasitic ticks showed a 100% homology at the nucleic acid level.Conclusions/SignificanceIn our natural infection study, close contact between goats does not appear to transmit SFTSV, however, the naïve animals were infected after ticks’ infestation and two viral isolates derived from an infected goat and its parasitic ticks shared 100% of sequence identity. These data demonstrate that the etiologic agent for goat cohort’s natural infection comes from environmental factors. Of these, ticks, especially the predominant species Haemaphysalis longicornis, probably act as vector for this pathogen. The findings in this study may help local health authorities formulate and focus preventive measures to contain this infection.
Partial Text: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS bunyavirus (SFTSV) . This virus was originally identified in 6 provinces of central and northeastern China . Later on, 10 more provinces have been added to the list of endemic regions . Moreover, similar viruses have recently been found to circulate in the United States, South Korea and Japan [3, 4, 5], indicating the genus phlebovirus worldwide distribution. Although most human cases in China are sporadic, SFTS constitutes a threat to public health in China because of its epidemic potential, high fatalities (10–16%), potential for family cluster or nosocomial outbreaks by means of direct infectious blood or secretion contact, and the difficulties in treatment and prevention [6–10].
In this study, an experimental as well as a natural infection studies in goats were conducted to investigate the role of ticks in the natural cycle of SFTSV. In the natural infection study, we were able to detect the viral RNA in ticks and goats, observe sero-conversion in goats, and also isolate two virus strains from one infected goat serum and one of its parasitic tick samples, respectively, which share a high sequence homology. These findings help to understand the virus transmission mechanism in the natural settings.