The emergence and cross species transmission of newly discovered tick-borne Bunyavirus in China

The immun function of dendritic cells in SFTS patients

OBJECTIVES

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by a novel bunyavirus in which host immune system suppression is thought to be crucial in disease development. Dendritic cells (DCs) are professional antigen-presenting cells (APCs) critical for initiation and orchestration of the immune response. And it have been suggested that functionally impaired DCs may mediate the suppression of host-specific T-cell immune responses and thus facilitate viral persistence and disease progression.This study was designed to improve the in vitro culture method for DCs and investigate the different immunologic functions of DCs between SFTS patients and healthy people.

METHODS

All confirmed SFTS patients (N = 10) were recruited from the Jinan Infectious Diseases Hospital in 2019; routine laboratory parameters were collected. The frequencies, phenotypes were analyzed by flow cytometry. And the levels of 8 cytokines in the cell culture supernatant were detected by flow cytometry.

RESULTS

On day 8 of the incubation period, cells were harvested and analyzed by flow cytometry. There were significant differences in the rates of CD1a-, CD83-positive cells between SFTS patients and healthy people (all P < 0.05). The detection of 8 cytokines in the culture supernatant showed that the expressions of IFN-α and IFN-γ in the culture supernatant of DC cells in SFTS patients were lower than those in normal people (P < 0.05, P < 0.01).

CONCLUSIONS

The present results indicate that DCs may be functionally impaired in SFTS. A decreased level of circulating mDCs was closely correlated with SFTS progression.

Identification of habitat suitability for the dominant zoonotic tick species Haemaphysalis flava on Chongming Island, China

Haemaphysalis ticks are pathogenic vectors that threaten human and animal health and were identified in Chongming, the third largest island in China. To understand the distribution of these ticks and determine their potential invasion risk, this study aimed to identify the habitat suitability of the dominant tick H. flava based on natural environmental factors. Geographic information system (GIS) images were combined with sample points from tick investigations to map the spatial distribution of H. flava. Data on 19 bioclimatic variables, environmental variables, and satellite-based landscapes of Chongming Island were retrieved to create a landcover map related to natural environmental determinants of H. flava. These data included 38 sites associated with the vectors to construct species distribution models with MaxEnt, a model based on the maximum entropy principle, and to predict habitat suitability for H. flava on Chongming Island in 2050 and 2070 under different climate scenarios. The model performed well in predicting the H. flava distribution, with a training area under the curve of 0.84 and a test area under the curve of 0.73. A habitat suitability map of the whole study area was created for H. flava. The resulting map and natural environment analysis highlighted the importance of the normalized difference vegetation index and precipitation in the driest month for the bioecology of H. flava, with 141.61 km2 (11.77%), 282.94 km2 (23.35%), and 405.30 km2 (33.69%) of highly, moderately, and poorly suitable habitats, respectively. The distribution decreased by 135.55 km2 and 138.82 km2 in 2050 and 2070, respectively, under the shared socioeconomic pathway (SSP) 1.2.6 climate change scenario. However, under SSP 5.8.5, the total area will decrease by 128.5 km2 in 2050 and increase by 151.64 km2 in 2070. From a One Health perspective, this study provides good knowledge that will guide tick control efforts to prevent the spread of Haemaphysalis ticks or transmission risk of Haemaphysalis-borne infections at the human-animal-environment interface on the island.

Molecular evidence for potential transovarial transmission of Dabieshan tick virus in Haemaphysalis longicornis from Shandong Province, China

Dabieshan tick virus (DBTV) is a newly identified arbovirus, first detected in Haemaphysalis longicornis collected from Hubei Province in 2015. It has been confirmed that DBTV is widely distributed in Shandong Province, China. However, its entomological and epidemiological features remain to be further explored, particularly the feasibility of transovarial transmission. Our research tries to explain the possibility of transovarial transmission of DBTV from engorged female ticks to their offspring. All engorged female adult ticks were sampled from domestic sheep and allowed to lay eggs and hatch in appropriate laboratory conditions. All engorged ticks, larvae and unhatched eggs were classified into pools for nucleic acid extraction and DBTV RNA detection. According to the results of qRT-PCR, the positive rate of DBTV was 6.25% (8/128) in engorged female ticks, 3.57% (1/28) in eggs and 5% (3/60) in larvae pools, respectively. Phylogenetic analysis indicated that DBTV isolates from larvae were similar to those from maternal ticks with more than 99.5% homology, and DBTV was relatively conservative in evolution. Our findings are the first to provide molecular evidence of potential transovarial transmission of DBTV among H. longicornis. Nonetheless, the transovarial transmission of DBTV in frequency and proportion occurring in nature deserves further investigation.

Humoral immunity to phlebovirus infection

Phleboviruses are zoonotic pathogens found in parts of Africa, Asia, Europe, and North America and cause disease symptoms ranging from self-limiting febrile illness to severe disease, including hemorrhagic diathesis, encephalitis, and ocular pathologies. There are currently no approved preventative vaccines against phlebovirus infection or antivirals for the treatment of the disease. Here, we discuss the roles of neutralizing antibodies in phlebovirus infection, the antigenic targets present on the mature polyproteins Gn and Gc, progress in vaccine development, and the prospects of identifying conserved neutralizing epitopes across multiple phleboviruses. Further research in this area will pave the way for the rational design of pan-phlebovirus vaccines that will protect against both known phleboviruses but also newly emerging phleboviruses that may have pandemic potential.

Molecular Identification and Genetic Characterization of Public Health Threatening Ticks - Chongming Island, China, 2021-2022

What is already known about this topic?

Although ticks and tick-borne diseases are prevalent throughout China, there remains a knowledge gap regarding their biology and potential risk of distribution to human and animal populations on Chongming Island. The island, being China's third largest and a crucial component in the ecological preservation of the Yangtze Delta region, has yet to be comprehensively studied in this context.

What is added by this report?

In this study, employing molecular methodologies, a significant prevalence of Haemaphysalis (H.) longicornis and H. flava ticks - widely recognized for their high pathogenicity - is reported from Chongming Island. Additionally, the identification of two previously unreported species on the island, namely, H. doenitzi and H. japonica, expands our understanding of both the range and evolution of tick species.

What are the implications for public health practice?

The populations of humans and animals in nearly all 18 towns on Chongming Island are potentially at risk for transmission of tick-borne infectious agents. As a result, there is a pressing necessity for public health alerts, proactive tick surveillance, and effective screening of suspected clinical cases of tick-borne diseases within the Chongming population.

The Tick-Borne Pathogens: An Overview of China's Situation

BACKGROUND

Ticks are important medical arthropods that can transmit hundreds of pathogens, such as parasites, bacteria, and viruses, leading to serious public health burdens worldwide. Unexplained fever is the most common clinical manifestation of tick-borne diseases. Since the emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the surge of coronavirus disease 2019 (COVID-19) cases led to the hospital overload and fewer laboratory tests for tick-borne diseases. Therefore, it is essential to review the tick-borne pathogens and further understand tick-borne diseases.

PURPOSE

The geographic distribution and population of ticks in the Northern hemisphere have expanded while emerging tick-borne pathogens have been introduced to China continuously. This paper focused on the tick-borne pathogens that are threatening public health in the world. Their medical significant tick vectors, as well as the epidemiology, clinical manifestations, diagnosis, treatment, prevention, and control measures, are emphasized in this document.

METHODS

In this study, all required data were collected from articles indexed in English databases, including Scopus, PubMed, Web of Science, Science Direct, and Google Scholar.

RESULTS

Ticks presented a great threat to the economy and public health. Although both infections by tick-borne pathogens and SARS-CoV-2 have fever symptoms, the history of tick bite and its associated symptoms such as encephalitis or eschar could be helpful for the differential diagnosis. Additionally, as a carrier of vector ticks, migratory birds may play a potential role in the geographical expansion of ticks and tick-borne pathogens during seasonal migration.

CONCLUSION

China should assess the risk score of vector ticks and clarify the potential role of migratory birds in transmitting ticks. Additionally, the individual and collective protection, vector control, comprehensive surveillance, accurate diagnosis, and symptomatic treatment should be carried out, to meet the challenge.

Molecular evidence for potential transovarial transmission of Jingmen tick virus in Haemaphysalis longicornis fed on cattle from Yunnan Province, China

Jingmen tick virus (JMTV) is a novel tick-borne virus first identified from Jingmen city, Hubei Province of China in 2010. It has been proved that JMTV can cause human diseases and is widely distributed both inside and outside of China. However, the survival mode and transmission characteristics of JMTV still need further research, particularly in terms of transovarial transmission. In this study, an investigation was conducted to explore the presence of JMTV from engorged female ticks to their offspring. All engorged female adult ticks were collected from domestic cattle and allowed to lay eggs in appropriate humidity and temperature conditions. Maternal ticks, eggs and larvae were screened for JMTV RNA through real-time polymerase chain reaction (RT-PCR) and nested PCR methods. The results revealed the positive rate of 10.53% (10/95) in engorged ticks, 9.09% (2/22) in eggs and 8% (4/50) in larvae pools, respectively. Phylogenetic analysis confirmed that sequences from eggs and larvae had closer relationship with those isolates from maternal engorged ticks with more than 99.7% homology and JMTV manifested with evolutional conservatism. Our study has identified for the first time that JMTV could be transmitted from mother generation to offspring of Haemaphysalis Longicornis. Nonetheless, the efficiency of transovarial transmission in JMTV and the significance of ticks as amplification hosts still need to be further illustrated.

Identification of Jingmen tick virus (JMTV) in Amblyomma testudinarium from Fujian Province, southeastern China

Background

Jingmen tick virus (JMTV) is a newly discovered tick-borne virus that can cause disease in humans. This virus has been authenticated as being extremely widespread worldwide and as posing a significant threat to public health and safety.

Methods

We collected 35 ticks belonging to two tick species from wild boars in Nanping, Fujian Province, China. JMTV-specific genes were amplified by qRT-PCR and nested PCR to confirm the presence of this pathogen.

Results

More than one third of of all ticks collected (11/35) were positive for JMTV. Viral sequences were obtained from three of the JMTV-positive ticks, including the complete genomic sequence from one tick. This was the first time that JMTV was identified in the hard-bodied tick Amblyomma testudinarium. Phylogenetic analysis revealed that JMTV from Fujian Province shared > 90% identity with other isolates derived from China, but was distinct from those reported in France and Cambodia.

Conclusions

JMTV is characterized by relatively low mutations and has its own local adaptive characteristics in different regions. Our findings provide molecular evidence of the presence of JMTV in an overlooked tick species from an area not unrecognized as being endemic. They also suggest that JMTV occupies a wider geographical distribution than currently believed and is a potential disease vector.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05478-2.

Epidemiological characteristics of severe fever with thrombocytopenia syndrome and its relationship with meteorological factors in Liaoning Province, China

Background

Severe fever with thrombocytopenia syndrome (SFTS), one kind of tick-borne acute infectious disease, is caused by a novel bunyavirus. The relationship between meteorological factors and infectious diseases is a hot topic of current research. Liaoning Province has reported a high incidence of SFTS in recent years. However, the epidemiological characteristics of SFTS and its relationship with meteorological factors in the province remain largely unexplored.

Methods

Data on reported SFTS cases were collected from 2011 to 2019. Epidemiological characteristics of SFTS were analyzed. Spearman’s correlation test and generalized linear models (GLM) were used to identify the relationship between meteorological factors and the number of SFTS cases.

Results

From 2011 to 2019, the incidence showed an overall upward trend in Liaoning Province, with the highest incidence in 2019 (0.35/100,000). The incidence was slightly higher in males (55.9%, 438/783), and there were more SFTS patients in the 60–69 age group (31.29%, 245/783). Dalian City and Dandong City had the largest number of cases of SFTS (87.99%, 689/783). The median duration from the date of illness onset to the date of diagnosis was 8 days [interquartile range (IQR): 4–13 days]. Spearman correlation analysis and GLM showed that the number of SFTS cases was positively correlated with monthly average rainfall (r_s = 0.750, P < 0.001; β = 0.285, P < 0.001), monthly average relative humidity (r_s = 0.683, P < 0.001; β = 0.096, P < 0.001), monthly average temperature (r_s = 0.822, P < 0.001; β = 0.154, P < 0.001), and monthly average ground temperature (r_s = 0.810, P < 0.001; β = 0.134, P < 0.001), while negatively correlated with monthly average air pressure (r_s = −0.728, P < 0.001; β = −0.145, P < 0.001), and monthly average wind speed (r_s = −0.272, P < 0.05; β = −1.048, P < 0.001). By comparing both correlation coefficients and regression coefficients between the number of SFTS cases (dependent variable) and meteorological factors (independent variables), no significant differences were observed when considering immediate cases and cases with lags of 1 to 5 weeks for dependent variables. Based on the forward and backward stepwise GLM regression, the monthly average air pressure, monthly average temperature, monthly average wind speed, and time sequence were selected as relevant influences on the number of SFTS cases.

Conclusion

The annual incidence of SFTS increased year on year in Liaoning Province. Incidence of SFTS was affected by several meteorological factors, including monthly average air pressure, monthly average temperature, and monthly average wind speed.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05395-4.

Rapid Spread of Severe Fever with Thrombocytopenia Syndrome Virus by Parthenogenetic Asian Longhorned Ticks

Severe fever with thrombocytopenia syndrome virus (SFTSV) is spreading rapidly in Asia. This virus is transmitted by the Asian longhorned tick (Haemaphysalis longicornis), which has parthenogenetically and sexually reproducing populations. Parthenogenetic populations were found in ≥15 provinces in China and strongly correlated with the distribution of severe fever with thrombocytopenia syndrome cases. However, distribution of these cases was poorly correlated with the distribution of populations of bisexual ticks. Phylogeographic analysis suggested that the parthenogenetic population spread much faster than bisexual population because colonization is independent of sexual reproduction. A higher proportion of parthenogenetic ticks was collected from migratory birds captured at an SFTSV-endemic area, implicating the contribution to the long-range movement of these ticks in China. The SFTSV susceptibility of parthenogenetic females was similar to that of bisexual females under laboratory conditions. These results suggest that parthenogenetic Asian longhorned ticks, probably transported by migratory birds, play a major role in the rapid spread of SFTSV.

Novel viruses in hard ticks collected in the Republic of Korea unveiled by metagenomic high-throughput sequencing analysis

Ticks are vectors of a wide range of zoonotic viruses of medical and veterinary importance. Recently, metagenomics studies demonstrated that they are also the source of potentially pathogenic novel viruses. During the period from 2015 to 2017, questing ticks were collected by dragging the vegetation from geographically distant locations in the Republic of Korea (ROK) and a target-independent high-throughput sequencing method was utilized to study their virome. A total of seven viruses, including six putative novel viral entities, were identified. Genomic analysis showed that the novel viruses were most closely related to members in the orders Jingchuvirales and Bunyavirales. Phylogenetic reconstruction showed that the Bunyavirales-like viruses grouped in the same clade with other viruses within the Nairovirus and Phlebovirus genera, while the novel Jingchuvirales-like virus grouped together with other viruses within the family Chuviridae. Real-time RT-PCR was used to determine the geographic distribution and prevalence of these viruses in adult ticks. These novel viruses have a wide geographic distribution in the ROK with prevalences ranging from 2% to 18%. Our study expands the knowledge about the composition of the tick virome and highlights the wide diversity of viruses they harbor in the ROK. The discovery of novel viruses associated with ticks in the ROK highlights the need for an active tick-borne disease surveillance program to identify possible reservoirs of putative novel human pathogens.

Detection and Phylogenetic Analysis of a Novel Tick-Borne Virus in Yunnan and Guizhou Provinces, Southwestern China

Dabieshan tick virus (DTV) is a novel tick-borne virus with the potential to infect both animals and humans. It has been confirmed that DTV is widely distributed in Shandong and Zhejiang Provinces. In this study, a total of 389 ticks were sampled from Honghe city of Yunnan Province and Bijie city of Guizhou Province, and then divided into 148 pools according to the location and species. QRT-PCR and nested PCR were performed to confirm the presence of DTV. The results showed a minimum infection rate of 2.43% (5/206) in Yunnan Province and 3.28% (6/183) in Guizhou Province, respectively. Interestingly, DTV was identified in Rhipicephalusmicroplus for the first time besides Haemaphysalis longicornis. Phylogenetic analysis showed that DTV from Yunnan and Guizhou Provinces shared over 94% identity with isolates derived from Hubei and Shandong Provinces, and DTV was relatively conservative in evolutionary dynamics. These findings provide molecular evidence of Dabieshan tick virus in different species of ticks from unrecognized endemic regions and suggest that DTV may be widely prevalent in southwestern China.

Comparison of RT-PCR, RT-nested PCRs, and real-time PCR for diagnosis of severe fever with thrombocytopenia syndrome: a prospective study

We designed a highly sensitive reverse transcription nested polymerase chain reaction targeting the M-segment (NPCR-M) of severe fever with thrombocytopenia syndrome (SFTS) virus. NPCR-M was performed in parallel with three other referenced PCR assays QPCR-S, PCR-M, and NPCR-S to assess their clinical usefulness as routine diagnostic techniques for SFTS. In this multi-centered prospective study, 122 blood samples from 38 laboratory-confirmed SFTS patients and 85 control samples were used. The results demonstrated that QPCR-S and NPCR-S had better sensitivity rate up to 21 days after symptom onset however, the PCR-M showed poor sensitivity after 7 days of symptom onset. Our designed NPCR-M had a higher detection rate up to 40 days from symptom onset and revealed the persistence of SFTSV RNA in the early convalescent phase. No false-positive results were seen for the control samples. Additionally, NPCR-M showed positive results for a sample that initially showed negative results from other PCRs and for many other samples collected in the convalescent phase of SFTS. Our designed nested PCR is suitable for SFTSV detection in patients’ blood collected in the acute and early convalescent phase of SFTS, and shows better sensitivity and high specificity even up to 40 days after symptom onset.

Development and evaluation of two different double-antibody sandwich ELISAs for detecting severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly emerging tick-borne virus with a case fatality rate between 12% and 50%. Currently, effective vaccines or antiviral drugs are not available, and a diagnostic method for detecting SFTSV is urgently needed. The monoclonal (MAb) and polyclonal antibodies (PAb) against SFTSV were prepared by immunizing animals with SFTSV nucleocapsid protein (NP), and using both monoclonal and polyclonal antibodies as capture antibodies against NP, we developed two different double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) for detecting the NP of SFTSV. Both methods were applicable for the diagnosis of SFTSV-infected patients, as confirmed by quantitative polymerase chain reaction. Furthermore, the sensitivity and specificity of two assays for diagnosing SFTS were both 100%, and had no reaction to recombinant Dabieshan NP or recombinant Dengue virus NS1 subtype 1 and 2 proteins. In addition, two standard curves were established for quantitative detection of the NP, and the monoclonal antibody-based ELISA (MAb-based ELISA) test had a lower limit of detection than the polyclonal-based ELISA (PAb-based ELISA) test. Therefore, the MAb-based ELISA could be employed for detecting SFTSV in a convenient and effective way.

Preparation of a polyclonal antibody against the non-structural protein, NSs of SFTSV

Severe fever with thrombocytopenia syndrome virus (SFTSV) is newly discovered virus which is the member of the order Bunyavirales, family phenuiviridae, phlebovirus genus. Its genome is composed of 3 segments of negative-sense RNA L, M and S. NSs is a non structure protein encoded by S segment which is important for viral replication and virulence. NSs protein of SFTSV is only involved in the regulation of host innate immune responses and suppression of IFN-promoter activities. So, the exact functions of this protein need to be studied deeply. To understand the exact role of NSs from SFTSV in viral replication and host immune response, a qualified antibody against this protein is required. In this study, NSs gene of SFTSV, was cloned into a bacterial expression vector (pGEX-6P-1) and the recombinant plasmid was transformed into Escherichia coli BL21 (DE3) cells. The SFTSV NSs fusion protein was purified using Glutathione Sepharose 4B and utilized as an antigen to immunize rabbits and obtain an anti-SFTSV NSs polyclonal antibody. Proper expression of the fusion protein and polyclonal antibody specificity were confirmed by western blotting and immunofluorescence analyses. The polyclonal antibody recognized NSs from SFTSV specifically. This is the first report that NSs can form viroplasm-like structures not only in infected cells but also in transfected cells with NSs plasmids. This polyclonal antibody will be useful for future studies of NSs functions.

How accurately can we assess zoonotic risk?

Identifying the animal reservoirs from which zoonotic viruses will likely emerge is central to understanding the determinants of disease emergence. Accordingly, there has been an increase in studies attempting zoonotic “risk assessment.” Herein, we demonstrate that the virological data on which these analyses are conducted are incomplete, biased, and rapidly changing with ongoing virus discovery. Together, these shortcomings suggest that attempts to assess zoonotic risk using available virological data are likely to be inaccurate and largely only identify those host taxa that have been studied most extensively. We suggest that virus surveillance at the human–animal interface may be more productive.

Determining which organisms harbour viruses that could potentially infect humans is of great topical interest. This Essay demonstrates that the data on which such zoonotic risk assessments are conducted are incomplete, biased, and rapidly changing with ongoing virus discovery.

Baseline mapping of severe fever with thrombocytopenia syndrome virology, epidemiology and vaccine research and development

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly emergent tick-borne bunyavirus first discovered in 2009 in China. SFTSV is a growing public health problem that may become more prominent owing to multiple competent tick-vectors and the expansion of human populations in areas where the vectors are found. Although tick-vectors of SFTSV are found in a wide geographic area, SFTS cases have only been reported from China, South Korea, Vietnam, and Japan. Patients with SFTS often present with high fever, leukopenia, and thrombocytopenia, and in some cases, symptoms can progress to severe outcomes, including hemorrhagic disease. Reported SFTSV case fatality rates range from ~5 to >30% depending on the region surveyed, with more severe disease reported in older individuals. Currently, treatment options for this viral infection remain mostly supportive as there are no licensed vaccines available and research is in the discovery stage. Animal models for SFTSV appear to recapitulate many facets of human disease, although none of the models mirror all clinical manifestations. There are insufficient data available on basic immunologic responses, the immune correlate(s) of protection, and the determinants of severe disease by SFTSV and related viruses. Many aspects of SFTSV virology and epidemiology are not fully understood, including a detailed understanding of the annual numbers of cases and the vertebrate host of the virus, so additional research on this disease is essential towards the development of vaccines and therapeutics.

Viral Hemorrhagic Fevers Other than Ebola and Lassa

Viral hemorrhagic fevers represent a group of diseases caused by enveloped RNA viruses. The epidemiology is broadly variable, ranging from geographically localized to more diffuse infections. Viral hemorrhagic fevers are classified as category A bioweapon agents by the Centers for Disease Control and Prevention. Viral hemorrhagic fevers are severe febrile illnesses with hemorrhagic phenomena. Laboratory diagnosis takes place in highly specialized reference laboratories. Treatment is essentially supportive. In this article, we focus the attention on yellow fever and viral hemorrhagic fevers other than Ebola and Lassa virus diseases that have been described elsewhere in this issue.

Molecular genetic analysis and clinical characterization of Rickettsia species isolated from the Republic of Korea in 2017

Rickettsia sp. CNH17-7 was isolated from patients' blood and identified by gene analysis as a species distinct from Rickettsia japonica. In addition, similar rickettsial infection was confirmed in two species (Haemaphysalis longicornis and Ixodes nipponensis) of ticks and rodents in northeastern and southwestern provinces, Republic of Korea. Subsequently, the analysis of 16S rRNA, ompA, ompB and sca4 genes of isolate CNH17-7 revealed 100%, 99.68%, 99.57% and 99.44% sequence similarity with Rickettsia sp. HlR/D91 and Candidatus R. longicornii ROK-HL727. In this study, we report the isolation of a new Rickettsia sp. CNH17-7 and infection of different types of ticks with the same rickettsial agents.

Ticks (Acari: Ixodoidea) in China: Geographical distribution, host diversity, and specificity

Ticks are obligate blood-sucking ectoparasites, which not only directly damage through bites but also transmit many pathogens. China has a high diversity of tick species, 125 species have been reported, including 111 hard tick and 14 soft tick species. Many of the ticks are important vectors of pathogens, resulting in zoonoses. The dynamics of ticks are affected by both the host and habitat environment. However, systematic studies on the geographical distribution, host diversity, and specificity of ticks are limited in China. To achieve this goal, the relevant available data were summarized and analyzed in this study. Ticks are distributed in all parts of China and Xinjiang has the most records of ticks. The distribution of ticks in adjacent areas is similar, indicating that the habitat environment affects their distribution. Most ticks are widely distributed, whereas some species are endemic to their distributed regions. Ticks are parasitic on mammals, birds, and reptiles, of which mammals are the main host species. Overall, most ticks parasitize different hosts, only a few ticks have strict host specificity, such as ticks that are specifically parasitic on reptiles and bats. In addition, environmental changes and control efforts also influence the dynamics of ticks. These results can better reveal tick biological traits and are valuable for tick control.

Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Phlebovirus in Domesticated Deer in South Korea

Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV) has a wide host range. Not only has it been found in humans, but also in many wild and domesticated animals. The infection of breeding deer on farms is a particularly worrisome public health concern due to the large amount of human contact and the diverse use of deer products, including raw blood. To investigate the prevalence of breeding domesticated deer, we examined the SFTSV infection rate on deer farms in South Korea from 2015 to 2017. Of the 215 collected blood samples, 0.9% (2/215) were found to be positive for viral RNA by PCR, and sequence analysis showed the highest homology with the KADGH human isolate. Both SFTSV-specific recombinant N and Gn protein-based ELISAs revealed that 14.0% (30/215) and 7.9% (17/215) of collected blood specimens were positive for SFTSV antibody. These results demonstrate that the breeding farm deer are exposed to SFTSV and could be a potential infection source for humans through direct contact or consumption of byproducts.

An anti-Gn glycoprotein antibody from a convalescent patient potently inhibits the infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease localized to China, Japan, and Korea that is characterized by severe hemorrhage and a high fatality rate. Currently, no specific vaccine or treatment has been approved for this disease. To develop a therapeutic agent for SFTS, we isolated antibodies from a phage-displayed antibody library that was constructed from a patient who recovered from SFTS virus (SFTSV) infection. One antibody, designated as Ab10, was reactive to the Gn envelope glycoprotein of SFTSV and protected host cells and A129 mice from infection in both in vitro and in vivo experiments. Notably, Ab10 protected 80% of mice, even when injected 5 days after inoculation with a lethal dose of SFTSV. Using cross-linker assisted mass spectrometry and alanine scanning, we located the non-linear epitope of Ab10 on the Gn glycoprotein domain II and an unstructured stem region, suggesting that Ab10 may inhibit a conformational alteration that is critical for cell membrane fusion between the virus and host cell. Ab10 reacted to recombinant Gn glycoprotein in Gangwon/Korea/2012, HB28, and SD4 strains. Additionally, based on its epitope, we predict that Ab10 binds the Gn glycoprotein in 247 of 272 SFTSV isolates previously reported. Together, these data suggest that Ab10 has potential to be developed into a therapeutic agent that could protect against more than 90% of reported SFTSV isolates.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease localized to China, Japan, and Korea. The tick-borne virus that causes SFTS has infected more than 5,000 humans, with a 6.4% to 20.9% fatality rate. Currently, there are no prophylactic or therapeutic measures against this virus. Historically, antibodies from patients who recovered from viral infection have been used to treat new patients, and commercially available antiviral monoclonal antibodies have been developed. Palivizumab was approved for the prophylaxis of respiratory syncytial virus (RSV) infection, and ibalizumab-uiyk was recently approved for the treatment of human immunodeficiency virus (HIV)-infected patients. To develop an antiviral monoclonal antibody for SFTS patients, we selected 10 antibodies from a patient who recovered from SFTS and found that one antibody potently inhibited SFTS viral infection both in vitro and in animal studies. We mapped the binding site of this antibody on the SFTS virus, which allowed us to predict that this antibody could bind 247 out of the 272 SFTS virus isolates reported to date. We anticipate that this antibody could be developed into a therapeutic treatment against SFTS.

Virome analysis of tick-borne viruses in Heilongjiang Province, China

Ticks are implicated in the transmission of various human and livestock pathogens worldwide. This study aimed to understand the geographical distribution of tick species, along with tick-associated viruses, in Heilongjiang Province, northeast China. Molecular methods were used to classify tick species, with next-generation sequencing and polymerase chain reaction-based analyses used to assess the viromes of ticks from four representative sampling locations in the Greater Khingan Mountains. Five species of ixodid ticks were identified, including Ixodes persulcatus, Dermacentor nuttalli, Dermacentor silvarum, Haemaphysalis longicornis, and Haemaphysalis concinna. From the 1102 ticks, 3,568,561 high-quality reads were obtained by next-generation sequencing. Following trimming, 302,540 reads were obtained, of which 6577 (2.16%) reads were annotated to viruses. Phylogenetic analysis revealed that the viral sequences shared a close relationship with Orthonairovirus, Phlebovirus, deer tick Mononegavirales-like virus, and Jingmen tick virus sequences, but the significance of these newly-identified tick-borne viruses to human and animal health requires further investigation. The results of this study provide a basis not only for further studies on the relationship between ticks and tick-borne viruses, but also for preventing future tick-borne epidemic outbreaks by means of vector control.

Laboratory detection and molecular phylogenetic analysis of severe fever with thrombocytopenia syndrome virus in Hubei Province, central China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus (SFTSV). Hubei Province is a major epidemic area for SFTS in China. In this study, quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and serological testing (IgM) were used simultaneously for laboratory detection of SFTS; however, testing results showed poor consistency between these two methods. Further analysis revealed that time post-onset was the main factor leading to inconsistent results. Thus, qRT-PCR is unable to detect all SFTS cases, and serological testing is essential. Here, 15 strains of SFTSV were successfully isolated from serum samples of acute SFTSV infection and their complete genomes were sequenced and submitted to GenBank. Phylogenetic analysis showed that the 15 SFTS virus strains clustered into four independent genotypes (A, B, D, and E), demonstrating that at least four genotypes of SFTSV have been co-circulating in Hubei Province. Furthermore, four strains of our isolates (HB2014-31, HB2014-35, HB2014-36, and HB2014-37) clustered in genotype E, which was the predominant genotype in Japan and South Korea. In this study, we identified multiple co-prevalent genotypes and confirmed the existence of genotype E viruses circulating in the Dabie Mountains of Hubei, central China. We concluded that SFTSV strains from Hubei exhibit most of the genetic diversity found in China.

Laboratory evaluation of the efficacy of lotilaner (Credelio™) against Haemaphysalis longicornis infestations of dogs

Background

Throughout Japan, Korea and China, Haemaphysalis longicornis ticks are vectors of Babesia gibsoni, which causes severe and progressive anemia in dogs. This study evaluated the efficacy of a single administration of lotilaner flavored chewable tablets (Credelio^TM) against experimental canine H. longicornis infestations.

Methods

Twenty-two healthy Beagles were ranked in descending order of counts of H. longicornis completed 48 h after challenge on Day -7. The 16 dogs with the highest live tick counts were blocked into pairs and within pairs randomized to either lotilaner-treatment at a minimum dose rate of 20 mg/kg or sham-treated controls. Treatment was administered within 30 ± 5 min following feeding on Day 0. Infestations with 50 unfed adult H. longicornis were completed on Days -2, 7, 14, 21, 28 and 35. Elizabethan collars were placed for 48 (± 2) h after each infestation and a T-shirt was placed on each dog to facilitate attachment. Ticks were counted in situ 12 and 24 h post-treatment and counted and removed after an additional 24 h (48 h after treatment) and 48 h after each post-treatment infestation. Dogs were sedated for tick challenges and counts. Live attached ticks on each dog were counted for efficacy assessments. Lotilaner was considered effective if the average tick attachment rate in the control group was at least 20%, if there was a statistically significant difference (P < 0.05) in mean tick counts between treated and control groups, and if the lotilaner-treated group had a calculated efficacy of at least 90%.

Results

Average control group retention of the H. longicornis challenge exceeded 20% at each assessment. Lotilaner started killing H. longicornis ticks quickly, achieving 57.4% efficacy within 12 h. At 48 h post-treatment, and following each subsequent infestation, between-group differences in mean H. longicornis counts were significant (P < 0.0001). From 48 h post-treatment, through the final assessment on Day 37, lotilaner efficacy remained greater than 95%, including on Day 37 when efficacy was 98.4%.

Conclusion

Lotilaner, administered to dogs orally at a minimum dose rate of 20 mg/kg is well tolerated, provides rapid reduction of existing H. longicornis tick infestations, and provides sustained residual protection for at least 35 days.

Nonstructural protein of severe fever with thrombocytopenia syndrome phlebovirus targets STAT2 and not STAT1 to inhibit type I interferon-stimulated JAK-STAT signaling

The nonstructural protein NSs of severe fever with thrombocytopenia syndrome phlebovirus blocks type I interferon (IFN)-stimulated JAK-STAT signaling. However, there is continuing controversy as to whether NSs targets STAT1 or STAT2 or both for this blockade. The present study was designed to gain a further understanding of the blockade mechanism. Immunoprecipitation experiments revealed a stronger interaction of NSs with STAT2 than with any other component constituting the JAK-STAT pathway. Expression of NSs resulted in the formation of cytoplasmic inclusion bodies (IBs), and affected cytoplasmic distribution of STAT2. STAT2 was relocated to NSs-induced IBs. Consequently, NSs inhibited IFN-α-stimulated tyrosine phosphorylation and nuclear translocation of STAT2. These inhibitory effects as well as the signaling blockade activity were not observed in NSs mutant proteins lacking the STAT2-binding ability. In contrast, NSs affected neither subcellular distribution nor phosphorylation of STAT1 in response to IFN-α and IFN-γ, demonstrating that NSs has little physical and functional interactions with STAT1. Taken together, these results suggest that NSs sequesters STAT2 into NSs-induced IBs, thereby blocking type I IFN JAK-STAT signaling.

Climate Change and the Neglected Tropical Diseases

Climate change is expected to impact across every domain of society, including health. The majority of the world's population is susceptible to pathological, infectious disease whose life cycles are sensitive to environmental factors across different physical phases including air, water and soil. Nearly all so-called neglected tropical diseases (NTDs) fall into this category, meaning that future geographic patterns of transmission of dozens of infections are likely to be affected by climate change over the short (seasonal), medium (annual) and long (decadal) term. This review offers an introduction into the terms and processes deployed in modelling climate change and reviews the state of the art in terms of research into how climate change may affect future transmission of NTDs. The 34 infections included in this chapter are drawn from the WHO NTD list and the WHO blueprint list of priority diseases. For the majority of infections, some evidence is available of which environmental factors contribute to the population biology of parasites, vectors and zoonotic hosts. There is a general paucity of published research on the potential effects of decadal climate change, with some exceptions, mainly in vector-borne diseases.

Evaluation of two different enzyme-linked immunosorbent assay for severe fever with thrombocytopenia syndrome virus diagnosis

To develop the large scale serological assay for severe fever with thrombocytopenia syndrome virus (SFTSV) infection, we evaluated two different enzyme-linked immunosorbent assay (ELISA) methods using nucleocapsid protein (NP) and Gn proteins of CB1 (genotype B) SFTSV strains. The NP-based ELISA tests showed more sensitive with broad cross-reactivity between two different genotype A and B strains compared with those of Gn-based ELISA tests. However, Gn-based ELISA showed more genotype specificity and specificity. These result suggested that NP-based ELISA test could be applicable for general sero-prevalence studies of SFTSV infections, while Gn-based ELISA could be applicable for a certain specific genotype sero-prevalence study.

Landscape of emerging and re-emerging infectious diseases in China: impact of ecology, climate, and behavior

For the past several decades, the infectious disease profile in China has been shifting with rapid developments in social and economic aspects, environment, quality of food, water, housing, and public health infrastructure. Notably, 5 notifiable infectious diseases have been almost eradicated, and the incidence of 18 additional notifiable infectious diseases has been significantly reduced. Unexpectedly, the incidence of over 10 notifiable infectious diseases, including HIV, brucellosis, syphilis, and dengue fever, has been increasing. Nevertheless, frequent infectious disease outbreaks/events have been reported almost every year, and imported infectious diseases have increased since 2015. New pathogens and over 100 new genotypes or serotypes of known pathogens have been identified. Some infectious diseases seem to be exacerbated by various factors, including rapid urbanization, large numbers of migrant workers, changes in climate, ecology, and policies, such as returning farmland to forests. This review summarizes the current experiences and lessons from China in managing emerging and re-emerging infectious diseases, especially the effects of ecology, climate, and behavior, which should have merits in helping other countries to control and prevent infectious diseases.

Characterizing the virome of Ixodes ricinus ticks from northern Europe

RNA viruses are abundant infectious agents and present in all domains of life. Arthropods, including ticks, are well known as vectors of many viruses of concern for human and animal health. Despite their obvious importance, the extent and structure of viral diversity in ticks is still poorly understood, particularly in Europe. Using a bulk RNA-sequencing approach that captures the complete transcriptome, we analysed the virome of the most common tick in Europe - Ixodes ricinus. In total, RNA sequencing was performed on six libraries consisting of 33 I. ricinus nymphs and adults sampled in Norway. Despite the small number of animals surveyed, our virus identification pipeline revealed nine diverse and novel viral species, phylogenetically positioned within four different viral groups - bunyaviruses, luteoviruses, mononegavirales and partitiviruses - and sometimes characterized by extensive genetic diversity including a potentially novel genus of bunyaviruses. This work sheds new light on the virus diversity in I. ricinus, expands our knowledge of potential host/vector-associations and tick-transmitted viruses within several viral groups, and pushes the latitudinal limit where it is likely to find tick-associated viruses. Notably, our phylogenetic analysis revealed the presence of tick-specific virus clades that span multiple continents, highlighting the role of ticks as important virus reservoirs.

The Emergence of Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome (SFTS) is a newly recognized hemorrhagic fever disease found throughout Asia with a case fatality rate between 12% and 30%. Since 2009, SFTS has been reported in China throughout 14 Chinese Provinces. In addition, SFTS has been recognized in South Korea and Japan with the first confirmed cases reported in 2012. A similar disease, caused by the closely related Heartland virus, was also reported in the United States in 2009. SFTS is caused by SFTS virus, a novel tick-borne virus in the family Bunyaviridae, genus Phlebovirus. Unlike other mosquito- and sandfly-borne bunyaviruses, SFTS virus has not been extensively studied due to its recent emergence and many unknowns regarding its pathogenesis, life cycle, transmission, and options for therapeutics remains. In this review, we report the most current findings in SFTS virus research.

Discovery of a Highly Divergent Coronavirus in the Asian House Shrew from China Illuminates the Origin of the Alphacoronaviruses

Although shrews are one of the largest groups of mammals, little is known about their role in the evolution and transmission of viral pathogens, including coronaviruses (CoVs). We captured 266 Asian house shrews (Suncus murinus) in Jiangxi and Zhejiang Provinces, China, during 2013 to 2015. CoV RNA was detected in 24 Asian house shrews, with an overall prevalence of 9.02%. Complete viral genome sequences were successfully recovered from the RNA-positive samples. The newly discovered shrew CoV fell into four lineages reflecting their geographic origins, indicative of largely allopatric evolution. Notably, these viruses were most closely related to alphacoronaviruses but sufficiently divergent that they should be considered a novel member of the genus Alphacoronavirus, which we denote Wénchéng shrew virus (WESV). Phylogenetic analysis revealed that WESV was a highly divergent member of the alphacoronaviruses and, more dramatically, that the S gene of WESV fell in a cluster that was genetically distinct from that of known coronaviruses. The divergent position of WESV suggests that coronaviruses have a long association with Asian house shrews. In addition, the genome of WESV contains a distinct NS7 gene that exhibits no sequence similarity to genes of any known viruses. Together, these data suggest that shrews are natural reservoirs for coronaviruses and may have played an important and long-term role in CoV evolution.IMPORTANCE The subfamily Coronavirinae contains several notorious human and animal pathogens, including severe acute respiratory syndrome coronavirus, Middle East respiratory syndrome coronavirus, and porcine epidemic diarrhea virus. Because of their genetic diversity and phylogenetic relationships, it has been proposed that the alphacoronaviruses likely have their ultimate ancestry in the viruses residing in bats. Here, we describe a novel alphacoronavirus (Wénchéng shrew virus [WESV]) that was sampled from Asian house shrews in China. Notably, WESV is a highly divergent member of the alphacoronaviruses and possesses an S gene that is genetically distinct from those of all known coronaviruses. In addition, the genome of WESV contains a distinct NS7 gene that exhibits no sequence similarity to those of any known viruses. Together, these data suggest that shrews are important and longstanding hosts for coronaviruses that merit additional research and surveillance.

Emerging Tick-Borne Viruses in the Twenty-First Century

Ticks, as a group, are second only to mosquitoes as vectors of pathogens to humans and are the primary vector for pathogens of livestock, companion animals, and wildlife. The role of ticks in the transmission of viruses has been known for over 100 years and yet new pathogenic viruses are still being detected and known viruses are continually spreading to new geographic locations. Partly as a result of their novelty, tick-virus interactions are at an early stage in understanding. For some viruses, even the principal tick-vector is not known. It is likely that tick-borne viruses will continue to emerge and challenge public and veterinary health long into the twenty-first century. However, studies focusing on tick saliva, a critical component of tick feeding, virus transmission, and a target for control of ticks and tick-borne diseases, point toward solutions to emerging viruses. The aim of this review is to describe some currently emerging tick-borne diseases, their causative viruses, and to discuss research on virus-tick interactions. Through focus on this area, future protein targets for intervention and vaccine development may be identified.

Metagenomic assessment of adventitious viruses in commercial bovine sera

Animal serum is an essential supplement for cell culture media. Contamination of animal serum with adventitious viruses has led to major regulatory action and product recalls. We used metagenomic methods to detect and characterize viral contaminants in 26 bovine serum samples from 12 manufacturers. Across samples, we detected sequences with homology to 20 viruses at depths of up to 50,000 viral reads per million. The viruses detected represented nine viral families plus four taxonomically unassigned viruses and had both RNA genomes and DNA genomes. Sequences ranged from 28% to 96% similar at the amino acid level to viruses in the GenBank database. The number of viruses varied from zero to 11 among samples and from one to 11 among suppliers, with only one product from one supplier being entirely "clean." For one common adventitious virus, bovine viral diarrhea virus (BVDV), abundance estimates calculated from metagenomic data (viral reads per million) closely corresponded to Ct values from quantitative real-time reverse transcription polymerase chain reaction (rtq-PCR), with metagenomics being approximately as sensitive as rtq-PCR. Metagenomics is useful for detecting taxonomically and genetically diverse adventitious viruses in commercial serum products, and it provides sensitive and quantitative information.

Current status of severe fever with thrombocytopenia syndrome in China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV). SFTSV is associated with a high mortality rate and has been reported in China, South Korea and Japan. SFTSV undergoes rapid changes owing to evolution, gene mutations, and reassortment between different strains of SFTSV. In this review, we summarize the recent cases and general properties of SFTS, focusing on the epidemiology, genetic diversity, clinical features, and diagnostics of SFTSV in China. From 2010 to October 2016, SFTS cases were reported in 23 provinces of China, with increased numbers yearly. Infection and death cases are mainly found in central China, where the Haemaphysalis longicornis ticks are spread. The national average mortality rate of SFTS infection was 5.3%, with higher risk to elder people. The main epidemic period was from May to July, with a peak in May. Thus, SFTS reminds a significant public health problem, and development of prophylactic vaccines and effective antiviral drugs will be highly needed.