Isolation of Karelian fever agent from Aedes communis mosquitoes

Genomic Analysis of Sindbis Virus Reveals Uncharacterized Diversity within the Australasian Region, and Support for Revised SINV Taxonomy

Sindbis virus (SINV) is a widely dispersed mosquito-borne alphavirus. Reports of Sindbis disease are largely restricted to northern Europe and South Africa. SINV is frequently sampled in Australian mosquito-based arbovirus surveillance programs, but human disease has rarely been reported. Molecular epidemiological studies have characterized six SINV genotypes (G1-G6) based on E2 gene phylogenies, mostly comprising viruses derived from the African-European zoogeographical region and with limited representation of Australasian SINV. In this study, we conducted whole genome sequencing of 66 SINV isolates sampled between 1960 and 2014 from countries of the Australasian region: Australia, Malaysia, and Papua New Guinea. G2 viruses were the most frequently and widely sampled, with three distinct sub-lineages defined. No new G6 SINV were identified, confirming geographic restriction of these viruses to south-western Australia. Comparison with global SINV characterized large-scale nucleotide and amino acid sequence divergence between African-European G1 viruses and viruses that circulate in Australasia (G2 and G3) of up to 26.83% and 14.55%, respectively, divergence that is sufficient for G2/G3 species demarcation. We propose G2 and G3 are collectively a single distinct alphavirus species that we name Argyle virus, supported by the inapparent or mild disease phenotype and the higher evolutionary rate compared with G1. Similarly, we propose G6, with 24.7% and 12.61% nucleotide and amino acid sequence divergence, is a distinct alphavirus species that we name Thomson's Lake virus.

Incidence of Sindbis Virus in Hospitalized Patients With Acute Fevers of Unknown Cause in South Africa, 2019-2020

BACKGROUND

Sindbis virus (SINV) is a mosquito-borne alphavirus that is widely distributed worldwide. Little is known about the febrile and neurological disease burden due to SINV in South Africa.

PATIENTS AND METHODS

Clinical samples of patients with acute febrile disease of unknown cause (AFDUC) were collected through the African Network for Improved Diagnostics, Epidemiology and Management of Common Infectious Agents at three sentinel hospital surveillance sites in South Africa. In total, 639 patients were screened using a PCR-based macroarray that can simultaneously detect nucleic acids of 30 pathogens, including SINV, from January 2019 to December 2020. Serum samples were randomly selected from the arbovirus season (January-June) and also screened with a commercial indirect immunofluorescence assay for anti-SINV IgM. In addition, 31 paired cerebrospinal fluid (CSF) specimens from the same patients were screened for IgM. Micro-neutralization assays were performed on all IgM-positive samples.

RESULTS

None of the specimens tested positive for SINV by molecular screening; however, 38/197 (19.0%) samples were positive for SINV-specific IgM. A total of 25/38 (65.8%) IgM-positive samples tested positive for SINV-neutralizing antibodies, giving an overall incidence of 12.7%. Furthermore, 2/31 (6.5%) CSF specimens tested positive for IgM but were negative for neutralizing antibodies. There was a higher incidence of SINV-positive cases in Mpumalanga (26.0%) than Gauteng province (15.0%). The most significant months for IgM-positive cases were April 2019 (OR = 2.9, p < 0.05), and May 2020 (OR = 7.7, p < 0.05).

CONCLUSION

SINV or a closely related virus contributed to 12.7% of AFDUC cases in hospitalized patients during the late summer and autumn months in South Africa and was significantly associated with arthralgia, meningitis, and headaches.

Sindbis Virus Strains of Divergent Origin Isolated from Humans and Mosquitoes During a Recent Outbreak in Finland

Sindbis virus (SINV) is a mosquito-borne avian hosted virus that is widely distributed in Europe, Africa, Asia, and Oceania. Disease in humans is documented mainly from Northern Europe and South Africa and associated with genotype I. In 2018 under extremely warm climatic conditions, a small outbreak of 71 diagnosed SINV infections was recorded in Finland. We screened 52 mosquito pools (570 mosquitoes) and 223 human sera for SINV with real-time RT-PCR and the positive samples with virus isolation. One SINV strain was isolated from a pool (n = 13) of genus Ochlerotatus mosquitoes and three strains from patient serum samples. Complete genome analysis suggested all the isolates to be divergent from one another and related to previous Finnish, Swedish, and German strains. The study provides evidence of SINV strain transfer within Europe across regions with different epidemiological characteristics. Whether these are influenced by different mosquito genera involved in the transmission remains to be studied.

Epidemic Alphaviruses: Ecology, Emergence and Outbreaks

Over the past century, the emergence/reemergence of arthropod-borne zoonotic agents has been a growing public health concern. In particular, agents from the genus Alphavirus pose a significant risk to both animal and human health. Human alphaviral disease presents with either arthritogenic or encephalitic manifestations and is associated with significant morbidity and/or mortality. Unfortunately, there are presently no vaccines or antiviral measures approved for human use. The present review examines the ecology, epidemiology, disease, past outbreaks, and potential to cause contemporary outbreaks for several alphavirus pathogens.

Ecological characterization and molecular differentiation of Culex pipiens complex taxa and Culex torrentium in eastern Austria

BACKGROUND

Culex pipiens complex taxa differ in behaviour, ecophysiology and epidemiologic importance. Despite their epidemiologic significance, information on genetic diversity, occurrence and seasonal and spatial distribution patterns of the Cx. pipiens complex is still insufficient. Assessment of seasonal and spatial distribution patterns of Culex pipiens forms and their congener Cx. torrentium is crucial for the understanding of their vector-pathogen dynamics.

METHODS

Female mosquitoes were trapped from April-October 2014 twice a month for a 24-h time period with BG-sentinel traps at 24 sampling sites in eastern Austria, using carbon dioxide as attractant. Ecological forms of Cx. pipiens s.l. and their hybrids were differentiated using the CQ11 locus, and Cx. pipiens forms and their congener Cx. torrentium using the ACE-2 gene. Differential exploitation of ecological niches by Cx. pipiens forms and Cx. torrentium was analysed using likelihood ratio tests. Possible effects of environmental parameters on these taxa were tested using PERMANOVA based on distance matrices and, if significant, were modelled in nMDS ordination space to estimate non-linear relationships.

RESULTS

For this study, 1476 Culex spp. were sampled. Culex pipiens f. pipiens representing 87.33 % of the total catch was most abundant, followed by hybrids of both forms (5.62 %), Cx. torrentium (3.79 %) and Cx. pipiens f. molestus (3.25 %). Differences in proportional abundances were found between land cover classes. Ecological parameters affecting seasonal and spatial distribution of these taxa in eastern Austria are precipitation duration, air temperature, sunlight and the interaction term of precipitation amount and the Danube water level, which can be interpreted as a proxy for breeding habitat availability.

CONCLUSIONS

The Cx. pipiens complex of eastern Austria comprises both ecologically different forms, the mainly ornithophilic form pipiens and the mainly mammalophilic and anthropophilic form molestus. Heterogeneous agricultural areas as areas of coexistence may serve as hybridization zones, resulting in potential bridge vectors between birds and humans. Occurrence, seasonal and spatial distribution patterns of the Cx. pipiens complex and Cx. torrentium and the presence of hybrids between both forms were quantified for the first time in Austria. These findings will improve the knowledge of their vector-pathogen dynamics in this country.

Arboviruses in southern Africa: are we missing something?

ABSTRACT 

The occurrence of the tick-borne zoonosis Crimean-Congo hemorrhagic fever is well established in South Africa. Similarly, mosquito-borne viruses Rift Valley fever, West Nile, Wesselsbron and Sindbis cause sporadic outbreaks. There is serological and/or virological evidence supporting the presence of lesser known arboviruses: the flaviviruses Usutu, Banzi and Spondweni, an Old World alphavirus Middelburg, orthobunyaviruses Germiston and Shuni and a tick-borne nairovirus, Dugbe. The medical significance of these viruses has not been established and lack of awareness and diagnostic capacity may lead to misdiagnosis. Historically, there have been outbreaks of chikungunya virus and dengue fever. This review focuses on arboviruses known to cause disease in South Africa or that have historically been shown to occur with potential for re-emergence.

Climatic, ecological and socioeconomic factors as predictors of Sindbis virus infections in Finland

Mosquito-borne Sindbis virus (SINV) causes rash-arthritis syndrome in Finland. Major outbreaks with approximately 7-year cycles have caused substantial burden of illness. Forest dwelling grouse are suspected to be amplifying hosts, with the infection transmitted to humans by mosquito bites. SINV infection surveillance data for 1984–2010 were used to create a negative binomial hurdle model, with seasonality, long-term cycles, climatic, ecological and socioeconomic variables. Climatic factors during early summer and amount of snow in April described the occurrence and incidence of SINV infections. Regulated water shore and hatch-year black grouse density described the occurrence, while population working in agriculture, agricultural land (negative) and income (negative) described the incidence of the disease. The prediction for 2009 was 85 cases (95% prediction interval 2-1187), while the actual occurrence was 106. We identified novel and known risk factors. The prevention of SINV infections in regulated water areas by infected mosquito populations should be targeted.

Phenotypic and molecular characteristics of plaque-purified MX10 virus, an Oriental-Australian genotype of Sindbis virus from Yunnan, China

A previous investigation showed that MX10 virus, recently isolated in China, belongs to the Oriental-Australian (O/A) genotype of Sindbis virus (SINV) (Wang Jinglin, 2011, ATMH). Similar to the MRE16 isolate, the prototype O/A genotype of SINV, two derivate viruses with obviously different plaque morphologies were derived from MX10 virus, which were accordingly denoted as MX10-LP and MX10-SP. MX10-LP virus exhibited higher neurovirulence in neonatal mice than MX10-SP virus. Analysis of the complete genome revealed seven nucleotide differences between MX10-LP and MX10-SP. Compared with MRE16 virus, MRE16SP virus has a deletion of 30 aa in the E2 gene (200-229), which has been shown to be the molecular basis for the different plaque morphology. However, the MX10-SP virus did not have the 30-amino-acid deletion in the E2 gene. These results demonstrate that the molecular basis for the different plaque morphology of MX10 virus, the first strain of the O/A genotype of SINV isolated from China, is different from that of the prototype MRE16 virus.

Isolation and phylogenetic analysis of Sindbis viruses from mosquitoes in Germany

A molecular survey of 16,057 mosquitoes captured in Southwest Germany during the summer of 2009 demonstrated the presence of Sindbis virus (SINV) in Culex spp. and Anopheles maculipennis sensu lato. Phylogenetic analysis of the German SINV strains linked them with Swedish SINV strains, the causative agent of Ockelbo disease in humans.

Mosquito-borne viruses in Europe

The number of mosquito-borne viruses ('moboviruses') occurring in Europe since the twentieth century now stands at ten; they belong to three families-Togaviridae (Sindbis, Chikungunya), Flaviviridae (West Nile, Usutu, Dengue), and Bunyaviridae (Batai, Tahyna, Snowshoe hare, Inkoo, Lednice). Several of them play a definite role in human or animal pathology (Sindbis, Chikungunya, Dengue, West Nile, Tahyna). Mobovirus outbreaks are strictly determined by the presence and/or import of particular competent vectors of the disease. Ecological variables affect moboviruses considerably; the main factors are population density of mosquito vectors and their vertebrate hosts, intense summer precipitations or floods, summer temperatures and drought, and presence of appropriate habitats, e.g., wetlands, small water pools, or intravillan sewage systems. A surveillance for moboviruses and the diseases they cause in Europe is recommendable, because the cases may often pass unnoticed or misdiagnosed not only in free-living vertebrates but also in domestic animals and even in humans.

Possible ecology and epidemiology of medically important mosquito-borne arboviruses in Great Britain

Nine different arboviruses are known to be transmitted by, or associated with, mosquitoes in Europe, and several (West Nile, Sindbis and Tahyna viruses) are reported to cause outbreaks of human disease. Although there have been no reported human cases in Great Britain (GB), there have been no published in-depth serological surveys for evidence of human infection. This paper investigates the ecological and entomological factors that could influence or restrict transmission of these viruses in GB, suggesting that in addition to West Nile virus, Sindbis and Tahyna viruses could exist in enzootic cycles, and that certain ecological factors could facilitate transmission to humans. However, the level of transmission is likely to be lower than in endemic foci elsewhere in Europe due to key ecological differences related to spatial and temporal dynamics of putative mosquito vectors and presence of key reservoir hosts. Knowledge of the potential GB-specific disease ecology can aid assessments of risk from mosquito-borne arboviruses.

Viral zoonoses in Europe

A number of new virus infections have emerged or re-emerged during the past 15 years. Some viruses are spreading to new areas along with climate and environmental changes. The majority of these infections are transmitted from animals to humans, and thus called zoonoses. Zoonotic viruses are, as compared to human-only viruses, much more difficult to eradicate. Infections by several of these viruses may lead to high mortality and also attract attention because they are potential bio-weapons. This review will focus on zoonotic virus infections occurring in Europe.

Sindbis viruses and other alphaviruses as cause of human arthritic disease

Amongst the arthritis-causing arboviruses, i.e. those spread by insects, the alphavirus group is of special interest. These viruses occasionally cause vast outbreaks, such as O'nyong-nyong in Africa in 1959. In Fennoscandia, Sindbis-related Ockelbo, Pogosta, or Karelian fever viruses have been found to cause significant morbidity. The major symptoms in addition to joint inflammation are fever, fatigue, headache and rash. The joint symptoms may persist for weeks, even months. The diagnosis is based on the clinical picture and serology. The causative viruses are closely related but not identical. It appears that at least in Finland the Pogosta disease is more common than thought, and the symptoms may often be overlooked. Several factors related to the viruses, their hosts, and global environmental changes may affect the spread of these viruses. All over the world arbovirus-caused diseases have increased, because of global changes.

Causative agent of Pogosta disease isolated from blood and skin lesions

Pogosta disease is a mosquito-borne viral disease in Finland, which is clinically manifested by rash and arthritis; larger outbreaks occur in 7-year intervals. The causative agent of the disease has been suspected of being closely related to Sindbis virus (SINV). We isolated SINV from five patients with acute Pogosta disease during an outbreak in fall 2002 in Finland. One virus strain was recovered from a whole blood sample and four other strains from skin lesions. The etiology of Pogosta disease was confirmed by these first Finnish SINV strains, which also represent the first human SINV isolates from Europe. Phylogenetic analysis indicates that the Finnish SINV strains are closely related to the viral agents isolated from mosquitoes and that cause clinically similar diseases in nearby geographic areas.

Complete genomic sequence of the Australian south-west genotype of Sindbis virus: comparisons with other Sindbis strains and identification of a unique deletion in the 3'-untranslated region

Our previous studies have shown that two distinct genotypes of Sindbis (SIN) virus occur in Australia. One of these, the Oriental/Australian type, circulates throughout most of the Australian continent, whereas the recently identified south-west (SW) genetic type appears to be restricted to a distinct geographic region located in the temperate south-west of Australia. We have now determined the complete nucleotide and translated amino acid sequences of a SW isolate of SIN virus (SW6562) and performed comparative analyses with other SIN viruses at the genomic level. The genome of SW6562 is 11,569 nucleotides in length, excluding the cap nucleotide and poly (A) tail. Overall this virus differs from the prototype SIN virus (strain AR339) by 23% in nucleotide sequence and 12.5% in amino acid sequence. Partial sequences of four regions of the genome of four SW isolates were determined and compared with the corresponding sequences from a number of SIN isolates from different regions of the World. These regions are the non-structural protein (nsP3), the E2 gene, the capsid gene, and the repeated sequence elements (RSE) of the 3'UTR. These comparisons revealed that the SW SIN viruses were more closely related to South African and European strains than to other Australian isolates of SIN virus. Thus the SW genotype of SIN virus may have been introduced into this region of Australia by viremic humans or migratory birds and subsequently evolved independently in the region. The sequence data also revealed that the SW genotype contains a unique deletion in the RSE of the 3'UTR region of the genome. Previous studies have shown that deletions in this region of the SIN genome can have significant effects on virus replication in mosquito and avian cells, which may explain the restricted distribution of this genotype of SIN virus.

Vector-borne viral diseases in Sweden--a short review

Ockelbo disease, caused by a Sindbis-related virus transmitted to man by mosquitoes, was first described in the central part of Sweden in the 1960s as clusters of patients with fever, arthralgia and rash. An average annual rate of 30 cases was recorded in the 1980s but no cases have been diagnosed during the last few years. Nephropathia epidemica (NE) characterized by fever, abdominal pain and renal dysfunction has been known to cause considerable morbidity in Sweden during the last 60 years but the etiologic agent (Puumala virus) was not isolated until 1983. This virus's main reservoir is the bank vole (Clethrionomys glareolus). NE is endemic in the northern two thirds of Sweden where more than a hundred cases are diagnosed each year. Tick-borne encephalitis transmitted by Ixodes ricinus ticks is restricted to the archipelago and Lake M-alaren on the east coast close to Stockholm. Between 30 and 110 cases are diagnosed every year. Inkoo virus, a California encephalitis group virus, has been isolated from mosquitoes in Sweden. The antibody prevalence to Inkoo virus is very high in a normal population, but no disease has as yet been associated with this virus in Sweden. Among the vector-borne virus diseases imported to Sweden, dengue is the most important, with approximately 50 cases recorded every year.

Detection of Ockelbo virus RNA in skin biopsies by polymerase chain reaction

A sensitive assay based on the polymerase chain reaction for the detection of Ockelbo virus RNA was developed. Two primer pairs from the gene coding for the E2 glycoprotein were chosen. By use of a nested strategy for the primers, as few as 1 to 10 PFU could be detected. The amplified products were visualized as bands of appropriate size on ethidium bromide-stained agarose gels. The primer pairs allowed amplification of several Ockelbo and Sindbis virus isolates but discriminated between these and other alphaviruses. Ockelbo virus RNA was detected in 4 of 10 skin biopsy specimens collected during the acute stage of the disease. The identities of the amplified products were confirmed by restriction endonuclease cleavage. Acute- and convalescent-phase sera as well as lymphocytes collected during the convalescent phase were negative by the polymerase chain reaction. No infectious virus could be recovered from any of the specimens.

Structure of the Ockelbo virus genome and its relationship to other Sindbis viruses

Ockelbo virus was first isolated in 1982 in Sweden. It is the causal agent of disease in humans characterized by arthritis, rash, and fever and is antigenically very closely related to Sindbis virus. We have determined the nucleotide and translated amino acid sequences of the prototype Ockelbo virus isolate (82-5) to determine the relatedness of Ockelbo virus to Sindbis virus at the genomic level and clarify the taxonomic position of Ockelbo virus within the alphavirus genus. The numbers of nucleotides and of translated amino acids in each region of the Ockelbo virus genome were exactly the same as those for the prototype AR339 strain of Sindbis virus except for three small deletions and insertions in the C-terminal half of nsP3 and for three single nucleotide insertions and deletions in the 3' untranslated region. Overall there were 672 nucleotide differences (5.7% divergence), resulting in 97 amino acid changes (2.6% divergence), between the two viruses: more than 85% of the nucleotide changes were silent. Only the C-terminal domain of nsP3 and the E2 glycoprotein showed a higher degree of amino acid substitution than the overall average. The former domain is not conserved among alphaviruses, and the latter is primarily responsible for antigenic variation. Sequence analysis of 420 nucleotides at the 3' end of a number of other Sindbis-like alphaviruses, including Karelian fever virus and South African, Indian, and Australian isolates of Sindbis virus, demonstrated that Ockelbo virus is more closely related to South African strains of Sindbis virus than it is to the prototypic Egyptian AR339 strain. Thus the South African strains, which have caused epidemic disease in humans, may have been introduced into Northern Europe by man or by migratory birds to establish Ockelbo disease there. The Indian and Australian strains form a distinct branch of the evolutionary tree and differ from prototypic AR339 Sindbis virus in 17% of the nucleotides sequenced.

Sensitive enzyme immunoassay for detecting immunoglobulin M antibodies to Sindbis virus and further evidence that Pogosta disease is caused by a western equine encephalitis complex virus

An antibody capture enzyme immunoassay (EIA) was adapted for the detection of immunoglobulin M (IgM) antibody to Sindbis (SIN) virus. Sera from humans with a febrile illness characterized by rash and arthralgia in eastern Finland (Pogosta [POG] disease) and Sweden (Ockelbo disease) and from humans with western equine encephalitis (WEE) virus infection in the United States were tested for IgM antibodies by EIA. Seroconversions were documented in patients with POG disease and with WEE virus infections by using SIN virus as antigen and rabbit anti-SIN virus immunoglobulin; this confirms previous observations that POG disease is caused by a virus closely related to SIN virus and that IgM antibodies to WEE complex alphaviruses are not type specific. This IgM EIA provided a sensitive diagnostic and research tool applicable to epidemiologic problems posed by POG disease.