Arbovirus infections in Sarawak, October 1968-February 1970: GETAH virus isolations from mosquitoes

A Systematic Review on the Viruses of Anopheles Mosquitoes: The Potential Importance for Public Health

Anopheles mosquitoes are the vectors of Plasmodium, the etiological agent of malaria. In addition, Anopheles funestus and Anopheles gambiae are the main vectors of the O'nyong-nyong virus. However, research on the viruses carried by Anopheles is scarce; thus, the possible transmission of viruses by Anopheles is still unexplored. This systematic review was carried out to identify studies that report viruses in natural populations of Anopheles or virus infection and transmission in laboratory-reared mosquitoes. The databases reviewed were EBSCO-Host, Google Scholar, Science Direct, Scopus and PubMed. After the identification and screening of candidate articles, a total of 203 original studies were included that reported on a variety of viruses detected in Anopheles natural populations. In total, 161 viruses in 54 species from 41 countries worldwide were registered. In laboratory studies, 28 viruses in 15 Anopheles species were evaluated for mosquito viral transmission capacity or viral infection. The viruses reported in Anopheles encompassed 25 viral families and included arboviruses, probable arboviruses and Insect-Specific Viruses (ISVs). Insights after performing this review include the need for (1) a better understanding of Anopheles-viral interactions, (2) characterizing the Anopheles virome-considering the public health importance of the viruses potentially transmitted by Anopheles and the significance of finding viruses with biological control activity-and (3) performing virological surveillance in natural populations of Anopheles, especially in the current context of environmental modifications that may potentiate the expansion of the Anopheles species distribution.

Molecular Detection and Genetic Characterization of Japanese Encephalitis Virus in Animals from 11 Provinces in China

Japanese encephalitis virus (JEV), which uses a mosquito primary vector and swine as a reservoir host, poses a significant risk to human and animal health. JEV can be detected in cattle, goats and dogs. A molecular epidemiological survey of JEV was conducted in 3105 mammals from five species, swine, fox, racoon dog, yak and goat, and 17,300 mosquitoes from 11 Chinese provinces. JEV was detected in pigs from Heilongjiang (12/328, 3.66%), Jilin (17/642, 2.65%), Shandong (14/832, 1.68%), Guangxi (8/278, 2.88%) and Inner Mongolia (9/952, 0.94%); in goats (1/51, 1.96%) from Tibet; and mosquitoes (6/131, 4.58%) from Yunnan. A total of 13 JEV envelope (E) gene sequences were amplified in pigs from Heilongjiang (5/13), Jilin (2/13) and Guangxi (6/13). Swine had the highest JEV infection rate of any animal species, and the highest infection rates were found in Heilongjiang. Phylogenetic analysis indicated that the predominant strain in Northern China was genotype I. Mutations were found at residues 76, 95, 123, 138, 244, 474 and 475 of E protein but all sequences had predicted glycosylation sites at ′N154. Three strains lacked the threonine 76 phosphorylation site from non-specific (unsp) and protein kinase G (PKG) site predictions; one lacked the threonine 186 phosphorylation site from protein kinase II (CKII) prediction; and one lacked the tyrosine 90 phosphorylation site from epidermal growth factor receptor (EGFR) prediction. The aim of the current study was to contribute to JEV prevention and control through the characterization of its molecular epidemiology and prediction of functional changes due to E-protein mutations.

Getah Virus (Alphavirus): An Emerging, Spreading Zoonotic Virus

Getah virus (GETV) is a zoonotic virus transmitted by mosquitoes, belonging to the Togaviridae family, Alphavirus genus. It was first isolated from mosquitoes in Malaysia in 1955, being widespread in island countries in the South Pacific region. Since the beginning of the 21st century, GETV expanded its range and geographical distribution from low-latitude tropical regions to 60° north latitude, being isolated from 17 different species of mosquitoes belonging to five genera of Culicidae (Culex, Anopheles, Armigeres, Aedes and Mansonia), as well as from midges in Eurasia. Molecular genetic evolution analysis revealed large molecular differences between the mosquitoes currently circulating Eurasia and those in the South Pacific in 1950s. The number of disease outbreaks caused by GETV in animals is increasing alongside the types of animals infected, from horses and pigs to cattle, blue foxes and red pandas. The disease burden is severely underestimated, and the economic cost to livestock production remains unknown. Herein, we review GETV temporal and spatial distribution, molecular genetic evolution, transmission and data on disease outbreaks. This work provides a reference for public health workers engaged in GETV research and zoonotic disease prevention and control.

Genomic and In Vitro Phenotypic Comparisons of Epidemic and Non-Epidemic Getah Virus Strains

Getah virus is an emerging mosquito-borne animal pathogen. Four phylogenetic groups of GETV, Group I (GI), GII, GIII and GIV, were identified. However, only the GETV GIII was associated with disease epidemics suggesting possible virulence difference in this virus group. Here, we compared the genetic and in vitro phenotypic characteristics between the epidemic and non-epidemic GETV. Our complete coding genome sequence analyses revealed several amino acid substitutions unique to the GETV GIII and GIV groups, which were found mainly in the hypervariable domain of nsP3 and E2 proteins. Replication kinetics of the epidemic (GIII MI-110 and GIII 14-I-605) and non-epidemic GETV strains (prototype GI MM2021 and GIV B254) were compared in mammalian Vero cells and mosquito C6/36 and U4.4 cells. In all cells used, both epidemic GETV GIII MI-110 and GIII 14-I-605 strains showed replication rates and mean maximum titers at least 2.7-fold and 2.3-fold higher than those of GIV B254, respectively (Bonferroni posttest, p < 0.01). In Vero cells, the epidemic GETV strains caused more pronounced cytopathic effects in comparison to the GIV B254. Our findings suggest that higher virus replication competency that produces higher virus titers during infection may be the main determinant of virulence and epidemic potential of GETV.

Group IV Getah Virus in Culex Mosquitoes, Malaysia

A new Getah virus (GETV) strain, B254, was isolated from Culex fuscocephalus mosquitoes captured at Mount Ophir, Malaysia, in 2012. Phylogenetic analyses revealed that GETV B254 is distinct from the old Malaysia GETV MM2021 strain but closely related to group IV GETV from Russia (LEIV16275Mag), China (YN12031), and Thailand (GETV/SW/Thailand/2017).

Sequencing of Historical Isolates, K-mer Mining and High Serological Cross-Reactivity with Ross River Virus Argue against the Presence of Getah Virus in Australia

Getah virus (GETV) is a mosquito-transmitted alphavirus primarily associated with disease in horses and pigs in Asia. GETV was also reported to have been isolated from mosquitoes in Australia in 1961; however, retrieval and sequencing of the original isolates (N544 and N554), illustrated that these viruses were virtually identical to the 1955 GETV_MM2021 isolate from Malaysia. K-mer mining of the >40,000 terabases of sequence data in the Sequence Read Archive followed by BLASTn confirmation identified multiple GETV sequences in biosamples from Asia (often as contaminants), but not in biosamples from Australia. In contrast, sequence reads aligning to the Australian Ross River virus (RRV) were readily identified in Australian biosamples. To explore the serological relationship between GETV and other alphaviruses, an adult wild-type mouse model of GETV was established. High levels of cross-reactivity and cross-protection were evident for convalescent sera from mice infected with GETV or RRV, highlighting the difficulties associated with the interpretation of early serosurveys reporting GETV antibodies in Australian cattle and pigs. The evidence that GETV circulates in Australia is thus not compelling.

Determinants of duck Tembusu virus NS2A/2B polyprotein procession attenuated viral replication and proliferation in vitro

Duck Tembusu virus (DTMUV), a mosquito-borne Flavivirus, has caused serious economic losses for the Chinese poultry industry. The genome is translated into a polyprotein that is cleaved to mature protein by host and viral proteases in the host cell, and this proteolytic process is important for the viral life cycle. However, the cleavage mechanism of DTMUV polyprotein is still unclear. In this study, we identified that several amino acids (P1-R, P1′-G, P2-R, P3-T, and P4-V) were vital for NS2A/2B cleavage. Meanwhile, both NS2A and NS2B were essential in cis for polyprotein NS2A/2B intramolecular cleavage. Subsequently, a DTMUV replicon and an infectious clone showed that the P1 site is essential to viral replication, while a mutation in P1′ could boost viral RNA replication. Furthermore, a recombinant virus with P1 and P1′ site mutations named rDTMUV-NS2A/2B-P1P1′(AA) was rescued from transfected BHK21 cells. The maximum viral titers and viral genome copies of rDTMUV-NS2A/2B-P1P1′(AA) were much lower than those of rDTMUV-WT both in the intracellular and extracellular samples of transfected and infected BHK21 cells. Taken together, the NS2A/2B cleavage sites processed by the NS2B3 protease are vital for DTMUV proliferation and virulence.

First isolation and characterization of Getah virus from cattle in northeastern China

Background

Getah virus (GETV) is a neglected mosquito-borne Alphavirus that causes pyrexia, body rash, and leg oedema in horses and foetal death and reproductive disorders in pigs. Infected animals may play a critical role in the amplification and circulation of the virus. The present study aimed to investigate GETV infection in clinically infected cattle and vector mosquito species in northeastern China.

Results

Serum samples were collected from beef cattle that presented sudden onset of fever in forest grazing areas, and metagenomic sequencing was conducted, revealing 29 contigs from ten serum samples matching the GETV genome. Quantitative RT-PCR (RT-qPCR) was performed with GETV RNA from 48 beef cattle serum samples, showing that the overall prevalence of GETV in the beef cattle samples was 6.25% (3/48). Serological investigation indicated that GETV neutralizing antibodies were detected in 83.3% (40/48, 95% CI 67–100) of samples from the study region. The GETV JL1808 strain was isolated from clinically infected cattle showing fever. Sequence comparisons showed high identity with the HuN1 strain, a highly pathogenic swine epidemic isolate obtained in Hunan province in 2017, at the nucleotide level (99.5%) and at the deduced amino acid level (99.7–99.9%). The phylogenetic analysis of JL1808 clustered in Group III, and also revealed a close genetic relationship with the HuN1 strain. Additionally, about 12,000 mosquitoes were trapped in this region. The presence of GETV infection was detected in mosquitoes, suggesting that the minimum infection rate (MIR) was 1.50‰, with MIRs of 1.67‰ in Culex pseudovishnui, 1.60‰ in Culex tritaeniorhynchus, and 1.21‰ in Anopheles sinensis.

Conclusions

To the best of our knowledge, this is the first report of GETV infection in cattle. These results demonstrated that a highly pathogenic, mosquito-borne swine GETV can infect and circulate in cattle, implying that it is necessary to conduct surveillance of GETV infection in animals in northeastern China.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2061-z) contains supplementary material, which is available to authorized users.

A quantitative reverse transcription-polymerase chain reaction for detection of Getah virus

Getah virus (GETV), a mosquito-borne alphavirus, is an emerging animal pathogen causing outbreaks among racehorses and pigs. Early detection of the GETV infection is essential for timely implementation of disease prevention and control interventions. Thus, a rapid and accurate nucleic acid detection method for GETV is highly needed. Here, two TaqMan minor groove binding (MGB) probe-based quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays were developed. The qRT-PCR primers and TaqMan MGB probe were designed based on the conserved region of nsP1 and nsP2 genes of 23 GETV genome sequences retrieved from GenBank. Only the qRT-PCR assay using nsP2-specific primers and probe detected all two Malaysia GETV strains (MM2021 and B254) without cross-reacting with other closely related arboviruses. The qRT-PCR assay detected as few as 10 copies of GETV RNA, but its detection limit at the 95% probability level was 63.25 GETV genome copies (probit analysis, P ≤ 0.05). Further validation of the qRT-PCR assay using 16 spiked simulated clinical specimens showed 100% for both sensitivity and specificity. In conclusion, the qRT-PCR assay developed in this study is useful for rapid, sensitive and specific detection and quantification of GETV.

Significant inhibition of Tembusu virus envelope and NS5 gene using an adenovirus-mediated short hairpin RNA delivery system

Tembusu virus (TMUV) is a mosquito-borne flavivirus, which was first isolated in the tropics during the 1970s. Recently, a disease characterized by ovarian haemorrhage and neurological symptoms was observed in ducks in China, which threatens poultry production. However, there is no suitable vaccination strategy or effective antiviral drugs to combat TMUV infections. Consequently, there is an urgent need to develop a new anti-TMUV therapy. In this study, we report an efficient short hairpin RNA (shRNA) delivery strategy for the inhibition of TMUV production using an adenovirus vector system. Using specifically designed shRNAs based on the E and NS5 protein genes of TMUV, the vector-expressed viral genes, TMUV RNA replication and infectious virus production were downregulated at different levels in Vero cells, where the shRNA (NS52) was highly effective in inhibiting TMUV. Using the human adenovirus type 5 shRNA delivery system, the recombinant adenovirus (rAd-NS52) inhibited TMUV multiplication with high efficiency. Furthermore, the significant dose-dependent inhibition of viral RNA copies induced by rAd-NS52 was found in TMUV-infected cells, which could last for at least 96h post infection. Our results indicated that the adenovirus-mediated delivery of shRNAs could play an active role in future TMUV antiviral therapeutics.

Complete Genome Sequencing and Phylogenetic Analysis of a Getah Virus Strain (Genus Alphavirus, Family Togaviridae) Isolated from Culex tritaeniorhynchus Mosquitoes in Nagasaki, Japan in 2012

Getah virus (GETV; genus Alphavirus, family Togaviridae) is a mosquito-borne virus known to cause disease in horses and pigs. In 2014, for the first time in ∼30 years, a sudden GETV outbreak occurred among racehorses in Ibaraki, Japan. Two years before this outbreak, we obtained multiple GETV isolates from Culex tritaeniorhynchus mosquitoes collected in Nagasaki, Japan and determined the whole genome sequence of GETV isolate 12IH26. Our phylogenetic analysis of GETV strains revealed that the isolate 12IH26 forms a robust clade with the epidemic strains 14-I-605-C1 and 14-I-605-C2 isolated from horses in the 2014 outbreak in Ibaraki. Furthermore, the complete genomic sequence of the isolate 12IH26 was 99.9% identical to those of the 2014 epidemic strains in Ibaraki. Phylogenetic analysis also showed that the recent Japanese GETV strains, including the isolate 12IH26, are closely related to the Chinese and South Korean strains rather than the previous Japanese strains, suggesting that GETV strains may be transported from overseas into Japan through long-distance migration of the infected mosquitoes or migratory birds.

Advanced uracil DNA glycosylase-supplemented real-time reverse transcription loop-mediated isothermal amplification (UDG-rRT-LAMP) method for universal and specific detection of Tembusu virus

Tembusu virus (TMUV) is a mosquito-borne flavivirus which threatens both poultry production and public health. In this study we developed a complete open reading frame alignment-based rRT-LAMP method for the universal detection of TUMV. To prevent false-positive results, the reaction was supplemented with uracil DNA glycosylase (UDG) to eliminate carryover contamination. The detection limit of the newly developed UDG-rRT-LAMP for TMUV was as low as 100 copies/reaction of viral RNA and 1 × 10^0.89 − 1 × 10^1.55 tissue culture infectious dose/100 μL of viruses. There were no cross-reactions with other viruses, and the reproducibility of the assay was confirmed by intra- and inter-assay tests with variability ranging from 0.22–3.33%. The new UDG-rRT-LAMP method for TMUV produced the same results as viral isolation combined with RT-PCR as the “gold standard” in 96.88% of cases for 81 clinical samples from subjects with suspected TMUV infection. The addition of UDG can eliminate as much as 1 × 10⁻¹⁶ g/reaction of contaminants, which can significantly reduce the likelihood of false-positive results during the rRT-LAMP reaction. Our result indicated that our UDG-rRT-LAMP is a rapid, sensitive, specific, and reliable method that can effectively prevent carryover contamination in the detection of TMUV.

Liposomes containing recombinant E protein vaccine against duck Tembusu virus in ducks

To obtain an effective vaccine candidate against duck Tembusu viral (DTMUV) disease which causes egg-drop and great economical loss in the Chinese duck industry, liposome vaccines containing recombinant E protein were prepared and assessed in this study. The recombinant plasmid (PET28a-E) was constructed and transformed into BL21 (DE3) cells to produce E proteins. The recombinant E proteins were purified and entrapped by liposomes through reverse-phase evaporation. Eighty-four cherry valley ducks were randomly divided into seven groups and inoculated intramuscularly at one- or seven-day-old with liposomes-E protein or Freund's adjuvant-E protein vaccine. Blood samples were collected from the first week to the tenth week for serum antibody, plasma for viremia, as well as oropharyngeal and cloacal swabs for virus shedding analyses after being challenged with a 10(2.4) 50% tissue culture infective dose (TCID50) of duck Tembusu virus. Results showed that serum antibody level of the liposomes vaccine was higher than the Freund's adjuvant vaccine, and inoculating twice was superior to once; furthermore, the viremia and virus shedding tests also proved that the liposomes vaccine can provide complete protection against DTMUV challenge. These results demonstrated that the liposomes-E protein vaccine could be used as a potential candidate vaccine to prevent DTMUV infection in ducks.

Airborne Transmission of a Novel Tembusu Virus in Ducks

The routes of transmission of a newly emerged Tembusu virus (TMUV, Flavivirus) in ducks in China remain unclear. Our epidemiological data show that TMUV is spread in winter, when mosquitos are inactive, which suggests that nonvector transmission routes are involved in the spread of TMUV. Furthermore, in vivo studies indicate that TMUV can be transmitted efficiently among ducks by both direct contact and aerosol transmission. This finding has important implications for the control of infection with this novel TMUV in the field.

Getah virus as an equine pathogen

Getah virus is a member of the genus Alphavirus in the family Togaviridae and has been frequently isolated from mosquitoes. Seroepizootiologic studies indicate that the virus is mosquito-borne and widespread, ranging from Eurasia to southeast and far eastern Asia, the Pacific islands, and Australasia. The natural host animal of the virus was not known until the first recognized occurrence of Getah virus infection among racehorses in two training centers in Japan in 1978. Outbreaks of clinical disease due to Getah virus infection occur infrequently, and only one outbreak has been reported outside Japan; this was in India in 1990. Clinical signs of the disease are mild and nonlife-threatening and are characterized by pyrexia, edema of the hind limbs, swelling of the submandibular lymph nodes, and urticarial rash, as reported in the 1978 epizootic. The morbidity was 37.9% (722 of 1903 horses) in one training center, with 96% of 722 affected horses making a full clinical recovery within a week without any significant sequelae. Antibodies against Getah virus were detected in 61.2% (172 of 281) and 55.8% (254 of 455) of horses at two training centers, respectively. Virus isolation can be attempted in VERO, RK-13, BHK-21, and many other cell lines as well as in suckling mouse brain. Blood plasma collected from suspect cases of infection at the onset of pyrexia is the specimen of choice. A diagnosis of Getah virus infection can also be confirmed serologically based on testing acute and convalescent phase sera by using SN, CF, HI, and ELISA tests. An inactivated vaccine is available for the prevention and control of Getah virus infection in horses in Japan.

Clinical and virological observations on swine experimentally infected with Getah virus

The pathogenicity of Getah virus for swine was examined. All 8 pigs (4 adults and 4 piglets) inoculated with Strains MIP-99 and MI-110 developed pyrexia ranging from 39.4 to 40.7 degrees C and anorexia. Mild depression and diarrhea were observed in 2 of the 4 piglets. These clinical signs were transient. Viremia occurred 1-2 days post-inoculation (p.i.) and the maximum titer was 10(3.0) TCID50 0.1 ml-1. The virus was recovered from a piglet autopsied on Day 3 p.i. from spleen and various lymph nodes. The maximum titer of virus (10(3.75) TCID50 0.1 g-1) was detected in the inguinal lymph node. Seroconversion was demonstrated in all the pigs on Day 6 p.i. These results suggest that Getah virus is mildly pathogenic for swine, which may play a role as an amplifying host in nature.

Getah virus in several species of mosquitoes

Vector competence of Aedes (Ae.) vexans nipponii (nip.) and Culex (Cx) tritaeniorhynchus for Getah virus was compared after incubation at 28 degrees C and 20 degrees C. Marked differences existed between Ae. vexans nip. strains Sapporo and Cx tritaeniorhynchus strain Kyoto in infection and transmission rates following ingestion of blood meals containing several concentrations of Getah virus. Simultaneous comparison of infectivity also revealed that infection rates of Ae. vexans nip. strains Sapporo (74%) and Shizunai (68%) were higher than those of Cx tritaeniorhynchus strain Kyoto (44%). No significant differences were seen in infection rates between three strains of Cx tritaeniorhynchus or between two strains of Ae. vexans nip. Getah virus propagated and was transmitted in Ae. vexans nip. as rapidly at 20 degrees C as at 28 degrees C. Following seven days' incubation both at 20 degrees C and 28 degrees C, Ae. vexans nip. was capable of transmitting the virus. 14 days' incubation at 20 degrees C were needed for Cx tritaeniorhynchus to acquire the same capability. Ae. japonicus, Ae. aegypti, Ae. albopictus, Cx pipens pallens, Armigeres subalbatus and Tripteroides bambusa were also susceptible to Getah virus infection.

Getah virus in Aedes vexans nipponii and Culex tritaeniorhynchus: vector susceptibility and ability to transmit

Vector competences of Aedes (Ae.) vexans nipponii (nip.) and Culex (Cx.) tritaeniorhynchus to Getah virus were assessed by using a membrane feeding technique. The Getah virus was present at high titer in both species of mosquitoes after 21 days of extrinsic incubation at 28 degrees C. Infection rates on 21 post-feeding were 100 per cent (4/4) for Ae. vexans nip. at a virus dosage of 10(5.3) PFU/ml and 60 per cent (3/5) for Cx. tritaeniorhynchus at similar virus dosage. More than 10(3.5) PFU of virus was detected in salivary glands of both species of mosquitoes on day 21 of extrinsic incubation. Forty percent (2/5) of Ae. vexans nip. transmitted the virus into serum-agar after ingesting 10(4.3) PFU/ml of virus blood mixture. In experiments with Cx. tritaeniorhynchus ingesting 10(7.5) PFU/ml of virus blood mixture, 57 per cent (4/7) were able to transmit the virus to suckling mice and 59 per cent (10/17) transmitted the virus into serum-agar.

Arbovirus infections in Sarawak: the role of the domestic pig

The possible role of pigs as arbovirus maintenance hosts and their importance as amplifier hosts was studied. Blood samples from 464 pigs of all ages collected in 1962 and 1964 were tested against 10 arboviruses. Antibodies to Japanese encephalitis and Getah viruses were particularly prevalent and their calculated monthly infection rates were 19-5% and 13-3% respectively. In 1969, 447 pigs were bled monthly throughout the year and the infection rates for Japanese encephalitis virus were calculated in pigs during the first year of life. Infection rates were not uniform throughout the year; the rate increases as the pig grew older and there was a marked seasonal increase in the infection rate in the period from November to January. This coincided with the seasonal major population peak of Culex tritaeniorhynchus following intense breeding of this mosquito prior to rice planting. It is suggested that, in Sarawak, the pig acts as a maintenance host of Japanese encephalitis in a cycle involving C. gelidus mosquitoes and also acts as an important amplifier host towards the end of the year in a cycle involving C. tritaeniorhynchus. It is further suggested that Getah virus is maintained in a similar cycle between C. tritaeniorhynchus and pigs.

Arbovirus infections in Sarawak, October 1968-February 1970: human serological studies in a land Dyak village

449 human sera collected in a Land Dyak village were tested for antibodies to 11 arboviruses. Japanese encephalitis and dengue virus antibodies were particularly prevalent. The rates of infection with these viruses were estimated to be 5-2% per annum for Japanese encephalitis, 8-8% for dengue 1 and 4-3% for dengue 2. Chikungunya virus antibodies were quite common with an annual infection rate of the order of 5% per annum. Infections with other Group A and B and Bunyamwera group viruses were generally at a low level.