The evolutionary history and spatiotemporal dynamics of the fever, thrombocytopenia and leukocytopenia syndrome virus (FTLSV) in China

Background

In 2007, a novel bunyavirus was found in Henan Province, China and named fever, thrombocytopenia and leukocytopenia syndrome virus (FTLSV); since then, FTLSV has been found in ticks and animals in many Chinese provinces. Human-to-human transmission has been documented, indicating that FTLSV should be considered a potential public health threat. Determining the historical spread of FTLSV could help curtail its spread and prevent future movement of this virus.

Method/Principal Findings

To examine the pattern of FTLSV evolution and the origin of outbreak strains, as well to examine the rate of evolution, the genome of 12 FTLSV strains were sequenced and a phylogenetic and Bayesian phylogeographic analysis of all available FTLSV sequences in China were performed. Analysis based on the FTLSV L segment suggests that the virus likely originated somewhere in Huaiyangshan circa 1790 (95% highest probability density interval: 1756–1817) and began spreading around 1806 (95% highest probability density interval: 1773–1834). Analysis also indicates that when FTLSV arrived in Jiangsu province from Huaiyangshan, Jiangsu Province became another source for the spread of the disease. Bayesian factor test analysis identified three major transmission routes: Huaiyangshan to Jiangsu, Jiangsu to Liaoning, and Jiangsu to Shandong. The speed of FTLSV movement has increased in recent decades, likely facilitated by modern human activity and ecosystem changes. In addition, evidence of RNA segment reassortment was found in FTLSV; purifying selection appears to have been the dominant force in the evolution of this virus.

Conclusion

Results presented in the manuscript suggest that the Huaiyangshan area is likely be the origin of FTLSV in China and identified probable viral migration routes. These results provide new insights into the origin and spread of FTLSV in China, and provide a foundation for future virological surveillance and control.

FTLSV is novel bunyavirus belonging to genus Phlebovirus and was first found in Huaiyangshan area. The epidemiology and pathogenesis of FTLSV remain poorly understood. This lack of information underscores the importance of analyzing the movement and genetic history of FTLSV in China. Recent advances in Bayesian coalescent phylogenetic analyses have resulted in more sophisticated methods being available for determining the relative age of emerging pathogens. In this study, a phylogenetic and Bayesian phylogeographic analysis was performed for FTLSV whole genomic sequences isolated from China. Results identified the Huaiyangshan area as the most probable origin of FTLSV and suggested migrating routes of the virus. These results offer the first description of the movement and history of FTLSV in China. RNA segment reassortment was found in FTLSV; purifying selection appears to have been the dominant force driving the evolution of this virus. The results of this study could be used to facilitate the development of new strategies for controlling FTLSV.

[Isolation and molecular characterization on Abbey Lake Orthobunyavirus (Bunyaviridae) in Xinjiang, China]

OBJECTIVE

To monitor and discover medically important mosquito-borne viruses circulating in Xinjiang, China.

METHODS

Mosquitoes were collected from Abbey Lake wetland in Bortala, in Northern Xinjiang. Viral isolates were obtained through inoculating and serial passaging into susceptible mammalian host cells (BHK-21), identified by cytopathogenic effect (CPE) observation and plague forming assay. Genetic identification of viral isolates was conducted by RT-PCR, sequencing and phylogenetic analysis.

RESULTS

A virus strain which causing CPE on BHK-21 cells, was isolated from the predominant Culex modestus (36.6%) and tentatively designated as Abbey Lake virus. Information on molecular identification revealed that Abbey Lake virus belonged to Orthobunyavirus genus within Bunyaviridae. Partial sequences (651 bp and 980 bp) of viral genomic S and M segment showed that Abbey Lake virus was phylogenetically related to Germiston virus that uniquely found in South Africa with 90.6% nucleotides and 95.0% amino acids similarities in S segment. However, viral M segment displayed much variability with 78.6% nucleotides and 86.1% amino acid similarities, suggesting a new member of Orthobunyavirus genus was discovered in the area.

CONCLUSION

In this study, Abbey Lake virus was isolated and characterized indicating its potential circulation nature of this newly-emerged mosquito-borne virus.

Risk factors for malformations and impact on reproductive performance and mortality rates of Schmallenberg virus in sheep flocks in the Netherlands

In Northwestern Europe, an epizootic outbreak of congenital malformations in newborn lambs due to infection with Schmallenberg virus (SBV) started at the end of 2011. The objectives of this study were to describe clinical symptoms of SBV infection, the effect of infection on mortality rates, and reproductive performance in sheep, as well as to identify and quantify flock level risk factors for SBV infections resulting in malformations in newborn lambs. A case-control study design was used, with 93 case flocks that had notified malformed lambs and 84 control flocks with no such lambs. Overall animal seroprevalence in case flocks was estimated at 82.0% (95% CI: 74.3–87.8), and was not significantly different from the prevalence in control flocks being 76.4% (95% CI: 67.2–83.6). The percentages of stillborn lambs or lambs that died before weaning, repeat breeders, and lambs with abnormal suckling behaviour were significantly higher in case flocks compared to control flocks. However, effect of SBV infection on mortality rates and reproductive performance seemed to be limited. Multivariable analysis showed that sheep flocks with an early start of the mating season, i.e. before August 2011 (OR = 33.1; 95% CI: 10.0–109.8) and in August 2011 (OR = 8.2; 95% CI: 2.7–24.6) had increased odds of malformations in newborn lambs caused by SBV compared to sheep flocks with a start of the mating season in October 2011. Other flock-level risk factors for malformations in newborn lambs were purchase of silage (OR 5.0; 95% CI: 1.7–15.0) and flocks with one or more dogs (OR = 3.3; 95% CI: 1.3–8.3). Delaying mating until October could be a potential preventive measure for naïve animals to reduce SBV induced losses. As duration of immunity after infection with SBV is expected to last for several years, future SBV induced congenital malformations are mainly expected in offspring of early mated seronegative animals.

The emergence of Schmallenberg virus across Culicoides communities and ecosystems in Europe

Schmallenberg virus (SBV), a novel arboviral pathogen, has emerged and spread across Europe since 2011 inflicting congenital deformities in the offspring of infected adult ruminants. Several species of Culicoides biting midges (Diptera: Ceratopogonidae) have been implicated in the transmission of SBV through studies conducted in northern Europe. In this study Culicoides from SBV outbreak areas of mainland France and Italy (Sardinia) were screened for viral RNA. The role of both C. obsoletus and the Obsoletus complex (C. obsoletus and C. scoticus) in transmission of SBV were confirmed in France and SBV was also discovered in a pool of C. nubeculosus for the first time, implicating this species as a potential vector. While collections in Sardinia were dominated by C. imicola, only relatively small quantities of SBV RNA were detected in pools of this species and conclusive evidence of its potential role in transmission is required. In addition to these field-based studies, infection rates in colony-derived individuals of C. nubeculosus and field-collected C. scoticus are also examined in the laboratory. Rates of infection in C. nubeculosus were low, confirming previous studies, while preliminary examination of C. scoticus demonstrated that while this species can replicate SBV to a potentially transmissible level, further work is required to fully define comparative competence between species in the region. Finally, the oral competence for SBV of two abundant and widespread mosquito vector species in the laboratory is assessed. Neither Aedes albopictus nor Culex pipiens were demonstrated to replicate SBV to transmissible levels and appear unlikely to play a major role in transmission. Other vector competence data produced from studies across Europe to date is then comprehensively reviewed and compared with that generated previously for bluetongue virus.

No evidence for the persistence of Schmallenberg virus in overwintering mosquitoes

In 2011, Schmallenberg virus (SBV), a novel member of the Simbu serogroup, genus Orthobunyavirus, was identified as the causative agent of a disease in ruminants in Europe. Based on the current knowledge on arthropods involved in the transmission of Simbu group viruses, a role of both midges and mosquitoes in the SBV transmission cycle cannot be excluded beforehand. The persistence of SBV in mosquitoes overwintering at SBV-affected farms in the Netherlands was investigated. No evidence for the presence of SBV in 868 hibernating mosquitoes (Culex, Anopheles, and Culiseta spp., collected from January to March 2012) was found. This suggests that mosquitoes do not play an important role, if any, in the persistence of SBV during the winter months in northwestern Europe.

[Preparation and characterization of a monoclonal antibody against the nucleocapsid protein of Schmallenberg virus]

OBJECTIVE

The present study was conducted to prepare and characterize a monoclonal antibody (mAb) against the nucleocapsid (N) protein of Schmallenberg virus (SBV).

METHODS

The SBV N gene was cloned into pET-28a-c(+ and pMAL-c5X vectors and then transformed into E.coli BL21. Histidine (His)-tagged (His-SBV-N) and maltose-binding protein (MBP)-tagged (MBP-SBV-N) fusion proteins were respectively induced to express by IPTG and purified by nickel-nitrilotriacetic acid (Ni-NTA) agarose and amylose resin. His-SBV-N was used to immunize BALB/c mice to prepare mAb, and MBP-SBV-N was used as the coating antigen in ELISA to screen mAb-secreting hybridomas and to determine mAb titers. The mAb against SBV N protein was purified from the ascitic fluids using protein G sepharose. Western blotting and indirect immunofluorescence assay were utilized to analyze the reactivity and specificity of the mAb.

RESULTS

One mAb specific for SBV N protein (named 1F2) was successfully screened and purified. The titer of 1F2 was 1:32 000. Besides, the isotype of 1F2 was determined to be IgG2α/κ. 1F2 reacted with both recombinant SBV N proteins and SBV isolates. It was also cross-reactive with the N proteins of genetically related Shamonda, Douglas and Akabane viruses, but not with the Rift Valley fever virus N protein.

CONCLUSION

One mAb specific for the SBV N protein was successfully prepared, it provides a useful tool for the serological detection of SBV.

[Pathologic-anatomical changes in newborn goats caused by an intrauterine Schmallenberg virus infection]

A complex of various malformations in newborns was observed to an increased extent in sheep farms in the 2011/2012 lambing season. An intrauterine Schmallenberg virus (SBV) infection was identified as the cause of these malformations. To date, a detailed pathological description of the deformity complex has only been given for bovine and ovine newborns.The aim of this study was therefore to provide a description of pathologic-anatomical congenital malformations in goat kids caused by intrauterine SBV infection. To this end, pathologic-anatomical and molecular biological investigations by PCR were carried out on 37 goat kids and 457 lambs from 238 sheep and goat farms in order to carry out an interspecies comparison. Of the 37 goat kids dissected, it was possible to identify a SBV infection in twelve animals (32.4%) by RT-PCR. In nine animals (24.3%) displaying pathological-anatomical malformations SBV could not be detected by PCR. The following malformations were observed: athrogryposis, deformation of spinal column, torticollis, asymmetry of the skull, brachygnathia inferior, cerebellar hypoplasia, cerebellar aplasia and internal hydrocephalus. Arthogryposis was the most common malformation, both in animals with positive PCR results and those with negative PCR results. This study documents congenital malformations caused by an intrauterine SBV infection for the first time on a large number of newborn goats.

Schmallenberg virus circulation in culicoides in Belgium in 2012: field validation of a real time RT-PCR approach to assess virus replication and dissemination in midges

Indigenous Culicoides biting midges are suggested to be putative vectors for the recently emerged Schmallenberg virus (SBV) based on SBV RNA detection in field-caught midges. Furthermore, SBV replication and dissemination has been evidenced in C. sonorensis under laboratory conditions. After SBV had been detected in Culicoides biting midges from Belgium in August 2011, it spread all over the country by the end of 2011, as evidenced by very high between-herd seroprevalence rates in sheep and cattle. This study investigated if a renewed SBV circulation in midges occurred in 2012 in the context of high seroprevalence in the animal host population and evaluated if a recently proposed realtime RT-PCR approach that is meant to allow assessing the vector competence of Culicoides for SBV and bluetongue virus under laboratory conditions was applicable to field-caught midges. Therefore midges caught with 12 OVI traps in four different regions in Belgium between May and November 2012, were morphologically identified, age graded, pooled and tested for the presence of SBV RNA by realtime RT-PCR. The results demonstrate that although no SBV could be detected in nulliparous midges caught in May 2012, a renewed but short lived circulation of SBV in parous midges belonging to the subgenus Avaritia occured in August 2012 at all four regions. The infection prevalence reached up to 2.86% in the south of Belgium, the region where a lower seroprevalence was found at the end of 2011 than in the rest of the country. Furthermore, a frequency analysis of the Ct values obtained for 31 SBV-S segment positive pools of Avaritia midges showed a clear bimodal distribution with peaks of Ct values between 21–24 and 33–36. This closely resembles the laboratory results obtained for SBV infection of C. sonorensis and implicates indigenous midges belonging to the subgenus Avaritia as competent vectors for SBV.

Schmallenberg virus experimental infection of sheep

Since late 2011, a novel orthobunyavirus, named Schmallenberg virus (SBV), has been implicated in many cases of severely malformed bovine and ovine offspring in Europe. In adult cattle, SBV is known to cause a mild transient disease; clinical signs include short febrile episodes, decreased milk production and diarrhoea for a few days. However, the knowledge about clinical signs and pathogenesis in adult sheep is limited. In the present study, adult sheep of European domestic breeds were inoculated with SBV either as cell culture grown virus or as virus with no history of passage in cell cultures. Various experimental set-ups were used. Sampling included blood collection at different time points during the experimental period and selected organ material at autopsy. Data from this study showed, that the RNAemic period in sheep was as short as reported for cattle; viral genome was detectable for about 3-5 days by real-time RT-PCR. In total, 13 out of 30 inoculated sheep became RNAemic, with the highest viral load in animals inoculated with virus from low cell culture passaged or the animal passaged material. Contact animals remained negative throughout the study. One RNAemic sheep showed diarrhoea for several days, but fever was not recorded in any of the animals. Antibodies were first detectable 10-14 days post inoculation. Viral RNA was detectable in spleen and lymph nodes up to day 44 post inoculation. In conclusion, as described for cattle, SBV-infection in adult sheep predominantly results in subclinical infection, transient RNAemia and a specific antibody response. Maintenance of viral RNA in the lymphoreticular system is observed for an extended period.

[The Khurdun virus (KHURV): a new representative of the orthobunyavirus (Bunyaviridae)]

Unidentified Khurdun virus (KHURV) was isolated in 2001 from coot (Fulica atra, Linnaeus, 1758) in the Volga River delta (Astrakhan Region, Russian Federation). Here we report that the KHUV genome was de novo sequenced (on Illumina platform) and the KHURV was classified as a novel prototypic bunyavirus. The KHURV genome comprises three negative-sense RNA segments (L, M, and S); its terminal nucleotide sequences are canonical for the Orthobunyavirus genus. Based on the results of the molecular-genetic and phylogenetic analysis we suggest that the KHURV belongs to the genus Orthobunyavirus (Bunyaviridae).

Could drought conditions trigger Schmallenberg virus and other arboviruses circulation?

BACKGROUND

In 2011, a new orthobunyavirus, named the Schmallenberg virus (SBV), was discovered in Europe. Like the related Shamonda virus, SBV is an arbovirus (arthropod-borne virus). After its discovery, the virus was detected in a wide area in north-western Europe, an unexpected finding in a territory where climatic conditions would not seem ideal for arbovirus transmission. This sudden expansion suggests the effect of 2011 drought as a key factor that may have triggered SBV circulation. The possible influence of drought, recorded in north-western Europe in early 2011, on virus circulation was evaluated.

METHODS AND RESULTS

The locations of SBV detections in Europe until April 2012 were obtained, and area of virus circulation was evaluated by kernel density estimation. Precipitation data in SBV circulation area, summarized by the 3 month precipitation indexes of May, were compared with precipitation data outside that area, confirming driest conditions in that area.

CONCLUSIONS

The onset of drought conditions recorded in the SBV detection area in early 2011 may have promoted the circulation of this virus. A correlation between circulation of some arboviruses and drought has been reported elsewhere. This was mainly explained by an effect of water deficit on the environment, which altered the relationships between vectors and reservoirs, but this correlation might be also the result of unknown effects of drought on the vectors. The effect of drought conditions on arbovirus circulation is most likely underestimated and should be considered, since it could promote expansion of arboviruses into new areas in a global warming scenario.

In vivo and in vitro identification of a hypervariable region in Schmallenberg virus

Detected for the first time in 2011, Schmallenberg virus (SBV) is an orthobunyavirus of the Simbu serogroup that caused a large outbreak in European ruminants. In a tight time frame, data have been obtained on SBV epidemiology and the clinical pictures associated with this new viral infection, but little information is available on the molecular biology of SBV. In this study, SBV sequence variability was characterized from the central nervous system of two stillborn lambs in a naturally infected herd. A hypervariable region (HVR) was detected in the N-terminal region of the SBV Gc glycoprotein through sequencing and analysis of the two full-length genomes representative of intra-herd SBV dissemination. In vitro growth assays coupled with full-length genome sequencing were performed on the two isolates after successive cellular passages, showing an in vitro adaptation of SBV and mutation accumulation inside the HVR in the absence of immune selective pressure.

Schmallenberg virus pathogenesis, tropism and interaction with the innate immune system of the host

Schmallenberg virus (SBV) is an emerging orthobunyavirus of ruminants associated with outbreaks of congenital malformations in aborted and stillborn animals. Since its discovery in November 2011, SBV has spread very rapidly to many European countries. Here, we developed molecular and serological tools, and an experimental in vivo model as a platform to study SBV pathogenesis, tropism and virus-host cell interactions. Using a synthetic biology approach, we developed a reverse genetics system for the rapid rescue and genetic manipulation of SBV. We showed that SBV has a wide tropism in cell culture and “synthetic” SBV replicates in vitro as efficiently as wild type virus. We developed an experimental mouse model to study SBV infection and showed that this virus replicates abundantly in neurons where it causes cerebral malacia and vacuolation of the cerebral cortex. These virus-induced acute lesions are useful in understanding the progression from vacuolation to porencephaly and extensive tissue destruction, often observed in aborted lambs and calves in naturally occurring Schmallenberg cases. Indeed, we detected high levels of SBV antigens in the neurons of the gray matter of brain and spinal cord of naturally affected lambs and calves, suggesting that muscular hypoplasia observed in SBV-infected lambs is mostly secondary to central nervous system damage. Finally, we investigated the molecular determinants of SBV virulence. Interestingly, we found a biological SBV clone that after passage in cell culture displays increased virulence in mice. We also found that a SBV deletion mutant of the non-structural NSs protein (SBVΔNSs) is less virulent in mice than wild type SBV. Attenuation of SBV virulence depends on the inability of SBVΔNSs to block IFN synthesis in virus infected cells. In conclusion, this work provides a useful experimental framework to study the biology and pathogenesis of SBV.

Schmallenberg virus (SBV) was discovered in Germany (near the town of Schmallenberg) in November 2011 and since then has been found to be the cause of malformations and stillbirths in ruminants. SBV has spread very rapidly to many European countries including the Netherlands, Belgium, France and the United Kingdom. Very little is known about the biological properties of this virus and there is no vaccine available. In this study (i) we developed an approach (called reverse genetics) that allows the recovery of “synthetic” SBV under laboratory conditions; (ii) we developed a mouse model of infection for SBV; (iii) we showed that SBV replicates in neurons of experimentally infected mice similar to naturally infected lambs and calves; (iv) we developed viral mutants that are not as pathogenic as the original virus due to the inability to counteract the host cell defenses; and v) we identified mutations that are associated with increased virulence. This work provides the experimental tools to understand how this newly emerged virus causes disease in ruminants. In addition, it will now be possible to manipulate the SBV genome in order to develop highly effective vaccines.

Complete genome sequencing of mosquito and human isolates of Ngari virus

Ngari virus (NRIV) is a recently described, naturally occurring reassortant between two other orthobunyaviruses, Bunyamwera virus (BUNV) and Batai virus (BATV). Intriguingly, this reassortment was associated with the acquisition of heightened virulence, although the molecular basis for this is not understood. Here we report the first complete genome sequences of Ngari virus. We include five isolates from various geographical locations, as well as samples isolated from both mosquitos and human cases. Based on an analysis of these sequence data, NRIVs are clearly genetically distinct from all known BUNV and BATV strains but are very closely related to one another regardless of their source.

[Survey on ticks and detection of new bunyavirus in some vect in the endemic areas of fever, thrombocytopenia and leukopenia syndrome (FTLS) in Henan province]

OBJECTIVE

To investigate the distribution, species, seasonal fluctuation of ticks and detect new bunyavirus in some hematophagus in the endemic areas of fever thrombocytopenia and leukopenia syndrome (FTLS) in Henan province.

METHODS

From March to December 2011, the free ticks were collected manually with white cloth from the grassland and the parasitic ticks were collected from the host skin by hand searching in Xinyang and Jiyuan. The density and seasonal fluctuation of ticks were analyzed after classification of the specimen. The hematophagus were collected including gadfly (38 in 16 groups), cattle lice (224 in 16 groups), mosquitoes (238 in 17 groups) and ticks (825 in 77 groups), then RNA of new bunyavirus were detected by RT-PCR.

RESULTS

A total of 12 388 ticks were collected in Xinyang and Jiyuan, consisting of 2 families, 5 geniuses and 6 species. In Xinyang city, 622 ticks were identified, consisting of 2 families, 3 geniuses and 3 species, including 2 (0.32%) Ornithodoros lahorensis, 451 (72.51%) Haemaphysalis longicornis and 117 (18.81%) Boophilus microplus. In Jiyuan city, 11 766 ticks were identified, consisting of 1 family, 4 geniuses and 5 species, including 7718 (65.60%) Haemaphysalis longicornis, 164 (1.39%) H.anatolicum anatolicum and 710 (6.03%) other ticks such as H. detritum, Boophilus microplus and Rhipicephalus sanguineus. Haemaphysalis longicornis were found in both districts as the predominant species in Henan province. Ticks were active from March to October. The average density was 160 per person hour and the peak was from May to July with density 278, 209 and 542 per person hour respectively. The results was positive in RNA detection of new bunyavirus in 11 groups of tick and 3 groups of gadfly by RT-PCR. The results were negative in all other hematophagus.

CONCLUSION

Ornithodoros lahorensis, Haemaphysalis longicornis, Boophilus microplus, H.anatolicum anatolicum, Rhipicephalus sanguineus and H. detritum were found in Henan province. Haemaphysalis longicornis was the predominant species. The density of ticks varied with the seasons. The detection of new bunyavirus by PCR was positive in some ticks and gadflies.

Organ distribution of Schmallenberg virus RNA in malformed newborns

A novel orthobunyavirus was first detected in German dairy cows in autumn 2011 and was subsequently found in the brains of malformed lambs, kids and calves in the Netherlands, Germany, Belgium, France, Italy, Great Britain, Luxembourg and Spain. For rapid detection of this novel virus, named Schmallenberg virus, a real time quantitative reverse transcription PCR (RT-qPCR) was developed at the Friedrich-Loeffler-Institut and provided to the federal veterinary state laboratories in Germany. For diagnostic purposes, the organ distribution of this new virus was analyzed in several organs and body fluids of 15 lambs and two calves showing typical malformations. Spleen, cerebrum, meconium, spinal cord, rib cartilage, umbilical cord, placental fluid out of the stomach as well as external placental fluid scraped from the coat of the foetuses were collected during necropsy. All animals were tested RT-qPCR positive in the external placental fluid, and all but one were also RT-qPCR positive in the cerebrum, the umbilical and the spinal cord. Our results suggest that both the external placental fluid and the umbilical cord could be suitable sample materials for the confirmation of an infection with Schmallenberg virus in malformed newborns, at least in lambs. This is of special interest since those samples can be collected very easily on the farm without the need of a necropsy.